Electronic device

Abstract

An electronic device (10) comprises: a printed circuit board (30); a surface-mounted semiconductor package (41); and a case (21) which is a fixed structure. The case (21) has a section facing the one surface (301) of the printed circuit board (30). The printed circuit board (30) has a plurality of fixing holes (31) for fixing the printed circuit board to the case (21). When there is a temperature fluctuation, the direction in which the printed circuit board (30) warps and the direction in which the semiconductor package (41) warps are opposite to each other. The printed circuit board (30) has a stress relief part (32) that reduces stress acting on a mounting part of the semiconductor package (41), the stress being caused due to the difference in the warping directions.

Description

electronic equipment CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2024-8245 filed in Japan on January 23, 2024, the contents of which are incorporated by reference in their entirety.

[0002] TECHNICAL FIELD The disclosure herein relates to electronic devices.

[0003] Patent Document 1 discloses an electronic device including a printed circuit board, a semiconductor package mounted on the printed circuit board, and a fixed structure. The printed circuit board has through holes for screw fastening, and is fixed to the fixed structure by screw fastening. The contents of the prior art document are incorporated by reference as an explanation of the technical elements in this specification.

[0004] JP 2014-212240 A

[0005] In Patent Document 1, a slit is provided between the through hole and the semiconductor package to suppress distortion caused around the through hole by screw fastening, thereby ensuring connection reliability for the semiconductor package located near the through hole. However, even if the printed circuit board and the semiconductor package have a common configuration, connection reliability may be ensured without providing a slit depending on the mounting position of the semiconductor package. Furthermore, even if the semiconductor package is mounted at a position away from the through hole, connection reliability may decrease. Further improvements are required for electronic devices in terms of the above and other aspects not mentioned.

[0006] An object of the present disclosure is to provide an electronic device that can improve the connection reliability of a semiconductor package.

[0007] One disclosed embodiment of an electronic device comprises a printed circuit board having one side and a back side that is the side opposite the one side in the thickness direction of the board, a surface-mounted semiconductor package mounted on the printed circuit board, and a fixing structure having a portion facing the one side, wherein the printed circuit board has a plurality of fixing holes for fixing the printed circuit board to the fixing structure, the warping direction of the printed circuit board and the warping direction of the semiconductor package during temperature fluctuations are opposite directions along the thickness direction of the board, and the printed circuit board has a stress relief portion that relieves stress acting on the mounting portion of the semiconductor package due to the different warping directions.

[0008] It has been discovered that if the warpage direction of a semiconductor package during temperature fluctuations is opposite to the warpage direction of the printed circuit board, stress concentrates on the mounting portion of the semiconductor package, reducing connection reliability. The disclosed electronic device has a stress relief portion, which can relieve the stress acting on the mounting portion of the semiconductor package due to the different warpage directions. This can improve the connection reliability of the semiconductor package.

[0009] The various aspects disclosed in this specification employ different technical means to achieve their respective objectives. The claims and the reference symbols in parentheses in this section are intended to exemplify the correspondence with the embodiments described below and are not intended to limit the technical scope. The objectives, features, and advantages disclosed in this specification will become more apparent by referring to the following detailed description and the accompanying drawings.

[0010] 1 is a cross-sectional view showing an electronic device according to a first embodiment. FIG. 2 is a plan view showing an example of a printed circuit board. FIG. 3 is a plan view showing another example of a printed circuit board. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2. FIG. 5 is a cross-sectional view showing an example of a semiconductor package. FIG. 6 is a view showing warpage of a semiconductor package. FIG. 7 is a view showing a reference example. FIG. 8 is a view showing a reference example. FIG. 9 is a view showing a reference example. FIG. 10 is a view showing a reference example. FIG. 11 is a view showing a reference example. FIG. 12 is a view showing a reference example. FIG. 13 is a view showing a reference example. FIG. 14 is a view showing a reference example. FIG. 15 is a view showing a reference example. FIG. 16 is a view showing a reference example. FIG. 17 is a cross-sectional view showing a semiconductor package in an electronic device according to a second embodiment. FIG. 18 is a view showing a reference example. FIG. 19 is a view showing a reference example. FIG. 20 is a cross-sectional view showing an example of an electronic device. FIG. 21 is a cross-sectional view showing a modified example. FIG. 22 is a cross-sectional view showing a semiconductor package in an electronic device according to a third embodiment. FIG. 23 is a cross-sectional view showing an example of an electronic device. FIG. 24 is a cross-sectional view showing another example of an electronic device. FIG. 25 is a cross-sectional view showing an electronic device according to a fourth embodiment. FIG. 26 is a cross-sectional view showing a part of a printed circuit board in an electronic device according to a fifth embodiment. 13 is a plan view showing a printed circuit board in an electronic device according to a sixth embodiment. FIG.

[0011] Hereinafter, several embodiments will be described with reference to the drawings. Note that in each embodiment, corresponding components are designated by the same reference numerals, and redundant description may be omitted. When only a portion of the configuration is described in each embodiment, the configuration of another embodiment previously described may be applied to the remaining portion of the configuration. Furthermore, in addition to the combinations of configurations explicitly stated in the description of each embodiment, configurations of several embodiments may be partially combined together even if not explicitly stated, provided that there is no particular problem with the combination.

[0012] First Embodiment First, a schematic configuration of an electronic device will be described. The electronic device may be mounted on, for example, a moving object. The moving object may be, for example, a vehicle, an aircraft, a ship, a construction machine, an agricultural machine, etc. As an example, the electronic device of this embodiment is mounted on a vehicle.

[0013] <Electronic Device> Fig. 1 is a cross-sectional view showing an example of an electronic device. Fig. 1 is a cross-sectional view of the electronic device taken along line II shown in Fig. 2. Hereinafter, the thickness direction of a printed circuit board is referred to as the Z direction. Furthermore, one direction perpendicular to the Z direction is referred to as the X direction, and a direction perpendicular to both the Z direction and the X direction is referred to as the Y direction. Unless otherwise specified, the shape viewed from the Z direction, in other words, the shape along the XY plane defined by the X direction and the Y direction, is referred to as the planar shape. The planar view from the Z direction may sometimes be simply referred to as the planar view.

[0014] 1 , the electronic device 10 includes a housing 20, a printed circuit board 30, and electronic components 40. As an example, the electronic device 10 of this embodiment further includes screws 50 and heat dissipation gel 60. The electronic device 10 may further include a connector (not shown). The connector is mounted on the printed circuit board 30 to electrically connect a circuit formed by the printed circuit board 30 and the electronic components 40 to the outside of the electronic device 10 (external equipment).

[0015] The housing 20 forms the outer periphery of the electronic device 10. The housing 20 houses other elements that make up the electronic device 10. The housing 20 may be formed using a metal material such as Al or Fe, or a resin material such as PPS or PBT. It may also be formed using ceramic. For example, a portion of the housing 20 may be formed using a metal material and another portion may be formed using a resin material. The planar shape of the housing 20 is, for example, approximately rectangular.

[0016] As an example, the housing 20 of this embodiment includes a case 21 and a cover 22. The case 21 and the cover 22 are made of aluminum. The case 21 is box-shaped with one side open in the Z direction. The case 21 has an opposing wall 211, a side wall 212, a plurality of pedestals 213, and screw holes 214. The opposing wall 211 faces one surface 301 of the printed circuit board 30. The side wall 212 is continuous with the opposing wall 211. The side wall 212 extends from the opposing wall 211 in the Z direction.

[0017] The pedestal 213 protrudes from the opposing wall 211 and supports the printed circuit board 30. The pedestal 213 may be provided apart from the side wall 212, or may be provided in a manner that is continuous with the side wall 212. The case 21 has four pedestals 213 to support the four corners of the printed circuit board 30. A screw hole 214 is provided in each of the pedestals 213. The case 21 corresponds to a fixed structure.

[0018] The cover 22 is attached to the case 21. In the attached state, the cover 22 provides a storage space together with the case 21. The cover 22 is provided so as to close the opening of the case 21, for example. The cover 22 is fixed to the case 21 by screw fastening or the like.

[0019] The printed circuit board 30 may be referred to as a board, a wiring board, a printed wiring board, etc. The printed circuit board 30 has one surface 301 and a back surface 302. The back surface 302 is the surface opposite to the one surface 301 in the Z direction, which is the thickness direction of the printed circuit board 30. The planar shape of the printed circuit board 30 is not particularly limited. As an example, the printed circuit board 30 of this embodiment has a substantially rectangular planar shape.

[0020] The printed circuit board 30 includes an insulating substrate and a conductor. The insulating substrate is formed using an electrically insulating material such as resin. The insulating substrate may contain only resin, or may be a combination of resin and glass cloth, nonwoven fabric, or the like. The conductor is formed using a metal material with good conductivity, such as Cu. The conductor includes a wiring layer. The wiring layer may be referred to as wiring, a wiring pattern, a conductor pattern, or the like. The wiring layer may be formed, for example, by patterning metal foil or by printing. At least a portion of the conductor, together with the electronic components 40, constitutes a circuit. For this reason, the printed circuit board 30 on which the electronic components 40 are mounted is sometimes referred to as a circuit board.

[0021] The wiring includes at least surface wiring arranged on the surface layer on the first surface 301 side of the substrate. The wiring may include surface wiring arranged on the surface layer on the back surface 302 side, or may include inner layer wiring arranged inside the substrate. In other words, the printed circuit board 30 may be a single-layer board, a double-sided board, or a multilayer board. As an example, the printed circuit board 30 of this embodiment is a glass epoxy board in which multiple wiring layers are arranged. The printed circuit board 30 has lands, which are electrode portions of the wiring layers, on the surface layers of the first surface 301 and the back surface 302.

[0022] The conductors may include via conductors or through-hole lands in addition to wiring layers. Via conductors are formed by disposing conductors such as plating in through holes (vias) formed in an insulating layer that constitutes an insulating substrate. The via conductors electrically connect, for example, wiring layers arranged on different layers. The through-hole lands are formed on the wall surfaces of through-holes that penetrate the printed circuit board 30 in the Z direction. The conductors may also include conductors that do not provide a wiring function, for example, conductors for heat dissipation.

[0023] The printed circuit board 30 has fixing holes 31. The fixing holes 31 penetrate the printed circuit board 30 in the Z direction. The fixing holes 31 are holes for fixing the printed circuit board 30 to the case 21. The fixing holes 31 are provided at the four corners of the printed circuit board 30. The fixing holes 31 are provided so as to overlap with the screw holes 214 in a plan view. The fixing holes 31 are sometimes referred to as mounting holes, etc. Screws 50 are inserted into the fixing holes 31. The screws 50 are inserted through the fixing holes 31 and threadedly engage with the screw holes 214 of the base 213. The printed circuit board 30 is fixed to the case 21 (housing 20) by fastening the screws.

[0024] The electronic component 40 is mounted on the printed circuit board 30. The electronic component 40, together with the conductors of the printed circuit board 30, provides a circuit. The electronic component 40 is solder-bonded to a corresponding land. The electronic component 40 includes at least a surface-mount semiconductor package 41. The semiconductor package 41 is sometimes referred to as an IC package. The electronic component 40 may include only the semiconductor package 41, or may include the semiconductor package 41 and other components in addition to the semiconductor package 41. The electronic component 40 may be arranged only on the first surface 301, or only on the back surface 302. The electronic component 40 may be arranged on both the first surface 301 and the back surface 302.

[0025] As an example, the electronic device 10 of this embodiment includes a plurality of electronic components 40. The electronic components 40 are arranged on each of the first surface 301 and the back surface 302. The semiconductor package 41 is arranged on the first surface 301. A heat dissipation gel 60 is in close contact with the semiconductor package 41. The heat dissipation gel 60 is interposed between the semiconductor package 41 and the inner surface of the opposing wall 211 of the case 21. This allows heat generated by the semiconductor package 41 to be released to the case 21 (housing 20) via the heat dissipation gel 60. Note that the arrangement of the semiconductor package 41 is not limited to the example shown in FIG. 1 . The semiconductor package 41 may be arranged on the back surface 302, or on both the first surface 301 and the back surface 302.

[0026] <Printed Circuit Board> Next, the structure of the printed circuit board will be described in more detail with reference to Figures 2 to 4. Figure 2 is a plan view showing an example of a printed circuit board. Figure 3 is a plan view showing another example of a printed circuit board. Figures 2 and 3 also show a semiconductor package mounted on the printed circuit board. Figure 4 is a cross-sectional view taken along line IV-IV in Figure 2. For convenience, Figure 4 shows only the case, which is the fixed structure of the housing. The case is also shown in a simplified form. Only the semiconductor package is shown as the electronic component. The P direction shown in Figure 4 is a predetermined direction taken along line IV-IV.

[0027] 2 and 3 , the printed circuit board 30 has a generally rectangular planar shape with the X direction as the longitudinal direction and the Y direction as the lateral direction. The printed circuit board 30 has side surfaces 303, 304, 305, and 306 connecting one surface 301 and a back surface 302. The side surface 304 is opposite the side surface 303 in the X direction. The side surface 306 is opposite the side surface 305 in the Y direction.

[0028] As described above, the printed circuit board 30 has a plurality of fixing holes 31. The fixing holes 31 are provided around the four corners of the printed circuit board 30, which has a substantially rectangular shape in plan view. The printed circuit board 30 has four fixing holes 311, 312, 313, and 314 as fixing holes 31. The fixing hole 311 is provided in a corner defined by two side surfaces 303 and 304. The fixing hole 312 is provided in a corner defined by two side surfaces 304 and 305. The fixing hole 313 is provided in a corner defined by two side surfaces 305 and 306. The fixing hole 314 is provided in a corner defined by two side surfaces 306 and 303.

[0029] Hereinafter, the portion of the printed circuit board 30 that is fixed to the case 21 by the screws 50, i.e., the fixing holes 31 and their surroundings, may be referred to as a fixing portion 315. The fixing portion 315 is the portion that overlaps with the heads of the screws 50 in a plan view. For convenience, FIG. 4 omits the screw holes 214, fixing holes 31, and screws 50 to show the fixing portion 315. One of the fixing portions 315 shown in FIG. 4 corresponds to the fixing hole 311, and the other corresponds to the fixing hole 313.

[0030] The printed circuit board 30 further includes a stress relief portion 32. As will be described later, the stress relief portion 32 relieves stress acting on the mounting portion (solder joint portion) of the semiconductor package 41 when the warpage direction of the semiconductor package 41 and the warpage direction of the printed circuit board 30 are different (opposite directions). As an example, the stress relief portion 32 of this embodiment includes a slit 321 and a partition portion 322.

[0031] The slits 321 penetrate the printed circuit board 30 in the Z direction and extend in a predetermined direction within the XY plane. The slits 321 block the transmission of stress originating from the fixing holes 31 (fixing portions 315). The slits 321 define a portion of the printed circuit board 30 that includes the fixing holes 31 (fixing portions 315). The slits 321 are provided corresponding to the fixing holes 31. The slits 321 are provided individually for the fixing holes 31. The slits 321 are provided near the four corners of the printed circuit board 30. The slits 321 are arranged so as to cross at least one of multiple imaginary straight lines L1, L2, L3, L4, L5, and L6 that virtually connect different fixing holes 31 in a plan view, for example, the centers of the fixing holes 31. In FIGS. 2 and 3 , the imaginary straight lines are indicated by two-dot chain lines.

[0032] Imaginary line L1 is a line that virtually connects fixing holes 311 and 312. Imaginary line L2 is a line that virtually connects fixing holes 311 and 314. Imaginary line L3 is a line that virtually connects fixing holes 311 and 313. Imaginary line L4 is a line that virtually connects fixing holes 312 and 313. Imaginary line L5 is a line that virtually connects fixing holes 312 and 314. Imaginary line L6 is a line that virtually connects fixing holes 313 and 314.

[0033] As an example, in this embodiment, at least one slit 321 is arranged to cross all of the imaginary straight lines L1, L2, L3, L4, L5, and L6. Each slit 321 is arranged to cross two imaginary straight lines. The slits 321 open to the side surfaces of the printed circuit board 30. The slits 321 open to a first side surface of the printed circuit board 30, which has a substantially rectangular shape in plan view, and extend from the first side surface to a second side surface located opposite the first side surface. All of the slits 321 have a common shape in plan view.

[0034] Specifically, slit 321 corresponding to fixing hole 311 opens in side surface 303, extends toward side surface 305, and crosses imaginary lines L2 and L3. Slit 321 corresponding to fixing hole 312 opens in side surface 304, extends toward side surface 306, and crosses imaginary lines L1 and L5. Slit 321 corresponding to fixing hole 312 is positioned at a position rotated 90° clockwise around an axis substantially parallel to the Z direction relative to slit 321 corresponding to fixing hole 311. Slit 321 corresponding to fixing hole 313 opens in side surface 305, extends toward side surface 303, and crosses imaginary lines L3 and L4. Slit 321 corresponding to fixing hole 313 is positioned at a position rotated 90° clockwise around an axis substantially parallel to the Z direction relative to slit 321 corresponding to fixing hole 312. The slits 321 corresponding to the fixing holes 314 open in the side surface 306, extend toward the side surface 304, and cross the imaginary lines L5 and L6. The slits 321 corresponding to the fixing holes 314 are arranged rotated 90° clockwise around an axis substantially parallel to the Z direction relative to the slits 321 corresponding to the fixing holes 313. The multiple slits 321 have rotational symmetry.

[0035] The shape and extension length of the slits 321 are not particularly limited. In the examples shown in FIGS. 2 and 3 , each slit 321 crosses two imaginary straight lines. The stress relief portion 32 may employ any of the slits 321 shown in FIGS. 2 and 3 . The slit 321 shown in FIG. 2 has a first slit portion 3211 and a second slit portion 3212. One end of the first slit portion 3211 opens to the side surface and extends perpendicular to the side surface. The second slit portion 3212 is connected to the end opposite the open end of the first slit portion 3211 and extends obliquely to narrow the width of the partition portion 322. For example, the first slit portion 3211 of the slit 321 corresponding to the fixing hole 311 extends in the X direction, and the second slit portion 3212 extends obliquely to approach the side surface 304.

[0036] The slit 321 shown in Fig. 3 is longer than the slit 321 shown in Fig. 2. The slit 321 shown in Fig. 3 has a third slit portion 3213 in addition to a first slit portion 3211 and a second slit portion 3212. The first slit portion 3211 and the second slit portion 3212 have the same configuration as shown in Fig. 2. The third slit portion 3213 is continuous with the end of the second slit portion 3212 on the opposite side to the first slit portion 3211, and extends approximately parallel to the first slit portion 3211. For example, the third slit portion 3213 of the slit 321 corresponding to the fixing hole 311 extends in the X direction.

[0037] The partition section 322 is a portion of the printed circuit board 30 defined by the slit 321, and includes the fixing hole 31 (fixing section 315). The partition section 322 is an area located more inward than the slit 321. The ends of the partition section 322 are defined by the slit 321. The dashed lines shown in FIGS. 2 and 3 indicate the ends of the partition section 322. The partition section 322 extends generally in the X direction or Y direction. The partition section 322 is configured to be capable of elastic deformation (spring deformation). The partition section 322 relieves stress originating from the fixing hole 31 (fixing section 315) through deformation.

[0038] The partition section 322 including the fixing hole 311 extends in the X direction from the fixing hole 311 (fixing section 315). The partition section 322 including the fixing hole 312 extends in the Y direction from the fixing hole 312. The partition section 322 including the fixing hole 313 extends in the X direction from the fixing hole 313. The partition section 322 including the fixing hole 314 extends in the Y direction from the fixing hole 314.

[0039] <Semiconductor Package> Next, the structure of the semiconductor package will be described in more detail with reference to Figures 2 to 5. Figure 5 is a cross-sectional view showing an example of a semiconductor package. Figure 5 is a cross-sectional view corresponding to Figure 4.

[0040] The semiconductor package 41 may be a package in which leads protrude from the main body, or may be a non-leaded package in which leads do not protrude. As an example, the semiconductor package 41 of this embodiment is a non-leaded package as shown in FIG. 5. As the non-leaded package, QFN, SON, BGA, etc. can be used. QFN is an abbreviation for Quad Flat Non-leaded package. SON is an abbreviation for Small Outline Non-leaded package. BGA is an abbreviation for Ball Grid Array. The semiconductor package 41 of this embodiment is a QFN.

[0041] The semiconductor package 41 has a lower surface 411, an upper surface 412, and a side surface 413 as surfaces forming its outer shell. The lower surface 411 is the surface facing the printed circuit board 30. The lower surface 411 may also be referred to as the bottom surface, the facing surface, or the like. The upper surface 412 is the surface opposite the lower surface 411 in the Z direction. The side surface 413 is a surface connecting the lower surface 411 and the upper surface 412. In the example shown in FIG. 4 , the heat dissipation gel 60 is interposed between the upper surface 412 of the semiconductor package 41 and the inner surface of the facing wall 211 of the case 21.

[0042] The semiconductor package 41 includes a lead frame 42, a semiconductor chip 43, and a sealing resin body 44. The lead frame 42 is a metal plate formed using a metal material with good conductivity, such as Cu. As an example, the lead frame 42 in this embodiment is formed using Cu. The lead frame 42 may be referred to as a conductor, a metal plate, or the like. The lead frame 42 has an island 421 and multiple terminals 422. The semiconductor chip 43 is disposed on the island 421. The island 421 may also be referred to as a heat sink, heat diffusion plate, heat sink, or heat dissipation pad. The island 421 is substantially flush with the lower surface 411 and exposed from the lower surface 411. The island 421 is solder-bonded to a corresponding land on the printed circuit board 30. The land may provide a circuit, or may not provide a circuit function but may provide a heat dissipation function.

[0043] The terminals 422 are soldered to corresponding lands on the printed circuit board 30. The terminals 422 may also be referred to as electrodes, electrode pads, etc. The terminals 422 are arranged to surround the island 421 in a plan view. The multiple terminals 422 are arranged along each of the four sides of the lower surface 411, which has a generally rectangular shape in plan view. The terminals 422 are exposed from the lower surface 411, being generally flush with the lower surface 411. Each of the multiple terminals 422 is exposed from the side surface 413, being generally flush with the side surface 413. The terminals 422 are exposed from the four side surfaces 413.

[0044] The semiconductor chip 43 is formed by forming elements and integrated circuits on a semiconductor substrate. As an example, the semiconductor chip 43 of this embodiment is formed by forming integrated circuits on a semiconductor substrate made of Si. The semiconductor chip 43 is disposed on one surface of the island 421 and bonded to the island 421. The one surface is the surface opposite to the exposed surface. The semiconductor chip 43 has pads (not shown) on the surface opposite to the island 421. The pads of the semiconductor chip 43 are electrically connected to the terminals 422 via conductive members (not shown), such as bonding wires.

[0045] The sealing resin body 44 seals the semiconductor chip 43. The sealing resin body 44 is in contact with the top and side surfaces of the semiconductor chip 43. The sealing resin body 44 forms the outer periphery of the semiconductor package 41. A portion of each of the island 421 and the terminals 422 is sealed by the sealing resin body 44. The sealing resin body 44 may be referred to as a mold resin, a sealing body, or the like.

[0046] <Warpage of Semiconductor Package> Next, warpage of a semiconductor package will be described with reference to FIG. 6. FIG. 6 shows the relationship between the amount of shrinkage and warpage when the temperature drops. The solid line with inward-pointing arrows at both ends indicates the magnitude of shrinkage (amount of shrinkage). The two-dot chain line indicates the shape of the warpage of the semiconductor package when the temperature drops. FIG. 6 corresponds to FIG. 5.

[0047] The semiconductor package 41 warps during temperature changes due to differences in the linear expansion coefficients of its components. In the semiconductor package 41 illustrated in FIG. 5, the linear expansion coefficient of Cu constituting the lead frame 42 is approximately 16 ppm / °C, while the linear expansion coefficient of Si constituting the semiconductor chip 43 is approximately 3 ppm / °C. Therefore, when the temperature drops, the lead frame 42 shrinks significantly in a direction perpendicular to the Z direction. On the other hand, the semiconductor chip 43 shrinks less. As a result, the outer periphery of the semiconductor package 41 warps downward, as shown by the two-dot chain line in FIG. 6, resulting in so-called cry warpage.

[0048] The strength of the encapsulating resin body 44 is weaker than that of Cu or Si. The linear expansion coefficient of the encapsulating resin body 44 is selected to be approximately 8 to 14 ppm / °C, which is an intermediate value between Cu and Si, so that it approaches the linear expansion coefficient of the printed circuit board 30. For this reason, the encapsulating resin body 44 cannot eliminate Cry warpage. When the temperature drops, Cry warpage occurs in the semiconductor package 41.

[0049] Although the example given here is one in which the temperature decreases, the same applies to a temperature increase. Due to the difference in the linear expansion coefficients described above, the lead frame 42 expands significantly when the temperature increases. On the other hand, the semiconductor chip 43 expands less. This results in an upward convex warp at the outer periphery, known as a smile warp.

[0050] <Warpage of Printed Circuit Boards and Their Impact on Semiconductor Package Mounting Portions> Next, warpage of printed circuit boards will be described with reference to FIGS. 7 to 10. Furthermore, the impact of the relationship between warpage of printed circuit boards and warpage of semiconductor packages on mounting portions of semiconductor packages will be described. FIGS. 7 to 10 show a reference example. The reference example differs from this embodiment in that stress relief portions such as slits are not provided in the printed circuit board. In the reference example, the reference symbols of elements related to this embodiment have an r added to the end. FIGS. 7 to 10 correspond to FIG. 4. However, for convenience, the heat dissipation gel has been omitted. As in FIG. 6, the solid line with inward-pointing arrows at both ends indicates the magnitude (amount) of shrinkage. The two-dot chain line indicates the warpage shape of the printed circuit board when the temperature drops. The dashed line indicates the warpage shape of the semiconductor package when the temperature drops.

[0051] In the reference example shown in FIG. 7 , the case 21r, which is the fixed structure, is made of aluminum. The aluminum that makes up the case 21r has a linear expansion coefficient of 21 to 23 ppm / °C, while the printed circuit board 30r has a linear expansion coefficient of approximately 14 ppm / °C. Therefore, when the temperature drops while the printed circuit board 30r is fixed to the case 21r, the case 21r (opposing wall 211r) shrinks significantly in a direction perpendicular to the Z direction. On the other hand, the amount of shrinkage of the printed circuit board 30r is small. As a result, the outer periphery of the printed circuit board 30r warps upward, resulting in a so-called smile warp.

[0052] The semiconductor package 41r is disposed on one surface 301r of the printed circuit board 30r. The semiconductor package 41r has a configuration similar to that of the semiconductor package 41 shown in FIG. 5. Therefore, when the temperature drops, the semiconductor package 41r develops a Cry warp, with the outer peripheral edge convex downward as shown by the dashed line. Therefore, the warp of the printed circuit board 30r is forced to change shape to a Cry warp when it reaches the portion where the semiconductor package 41r is mounted.

[0053] In this way, when the warpage direction of the printed circuit board 30r due to the difference in linear expansion coefficients between the case 21r and the printed circuit board 30r and the warpage direction of the semiconductor package 41r are opposite to each other in the Z direction, a sudden deformation stress is applied to the mounting portion (solder joint) of the semiconductor package 41r. Specifically, the contraction of the case 21r due to a temperature drop causes a displacement between the fixing portions 315r (fixing holes) of the printed circuit board 30r, resulting in deformation in a direction that shortens the distance between the fixing portions 315r. The stress caused by this deformation acts on the semiconductor package 41r from the fixing portions 315r (fixing holes). Particularly in environments with large temperature changes and frequent thermal cycles, such as in automotive products, the connection reliability of the mounting portion is likely to decrease. In other words, the solder life is likely to decrease.

[0054] Furthermore, when the temperature rises, the case 21r expands more than the printed circuit board 30r, causing cry warpage in the printed circuit board 30r. The semiconductor package 41r also experiences smile warpage, as described above. The semiconductor package 41r is mounted on one surface 301r, and the direction of warpage is reversed. This can easily reduce the connection reliability of the mounting portion of the semiconductor package 41r.

[0055] In the reference example shown in Fig. 8, a semiconductor package 41r is disposed on a rear surface 302r of a printed circuit board 30r. The other configurations are the same as those of the reference example shown in Fig. 7. When the temperature drops, a smile warp occurs in the printed circuit board 30r due to the difference in the linear expansion coefficients between the case 21r and the printed circuit board 30r.

[0056] When the temperature drops, the semiconductor package 41r develops a Cry warp, with the outer peripheral edge convex downward as shown by the dashed line. However, the semiconductor package 41r is disposed on the rear surface 302r. Therefore, the warp direction of the printed circuit board 30r and the warp direction of the semiconductor package 41r are the same (common direction). This makes it possible to prevent sudden deformation stress from being applied to the mounting portion (solder joint) of the semiconductor package 41r.

[0057] When the temperature rises, cry warpage occurs in the printed circuit board 30r. Smile warpage occurs in the semiconductor package 41r. The semiconductor package 41r is disposed on the back surface 302r, and the direction of the warpage is the same. Therefore, it is possible to prevent sudden deformation stress from being applied to the mounting portion of the semiconductor package 41r.

[0058] In the reference example shown in FIG. 9 , the case 21r, which is the fixed structure, is made of Fe. The linear expansion coefficient of Fe constituting the case 21r is 10 to 12 ppm / °C, which is smaller than the linear expansion coefficient of the printed circuit board 30r (approximately 14 ppm / °C). When the temperature drops, the printed circuit board 30r shrinks significantly in a direction perpendicular to the Z direction. On the other hand, the amount of shrinkage of the case 21r (opposing wall 211r) is small. As a result, the outer periphery of the printed circuit board 30r warps downward, a phenomenon known as Cry warpage.

[0059] When the temperature drops, the semiconductor package 41r develops a Cry warp, with the outer peripheral edge convex downward as shown by the dashed line. As shown in FIG. 7 , the semiconductor package 41r is mounted on one surface 301r of the printed circuit board 30r. Therefore, the warp direction of the printed circuit board 30r and the warp direction of the semiconductor package 41r are the same. This prevents sudden deformation stress from being applied to the mounting portion (solder joint) of the semiconductor package 41r.

[0060] When the temperature rises, smile warpage occurs in the printed circuit board 30r. Smile warpage also occurs in the semiconductor package 41r. The semiconductor package 41r is arranged on one surface 301r, and the direction of the warpage is the same. Therefore, it is possible to prevent sudden deformation stress from being applied to the mounting portion of the semiconductor package 41r.

[0061] In the reference example shown in FIG. 10 , a semiconductor package 41r is disposed on the back surface 302r of a printed circuit board 30r. The remaining configuration is similar to that of the reference example shown in FIG. 9 . When the temperature drops, the difference in the linear expansion coefficient between the case 21r and the printed circuit board 30r causes Cry warpage in the printed circuit board 30r. When the temperature drops, the semiconductor package 41r experiences Cry warpage with the outer peripheral edge convex downward, as shown by the dashed line. However, the semiconductor package 41r is disposed on the back surface 302r. Therefore, the warpage direction of the printed circuit board 30r and the warpage direction of the semiconductor package 41r are opposite to each other. This easily reduces the connection reliability of the mounting portion of the semiconductor package 41r.

[0062] Furthermore, when the temperature rises, the case 21r expands less than the printed circuit board 30r, causing a smile warp in the printed circuit board 30r. The semiconductor package 41r also undergoes a smile warp. The semiconductor package 41r is disposed on the back surface 302r, and the direction of the warp is opposite to that of the case 21r. This can easily reduce the connection reliability of the mounting portion of the semiconductor package 41r.

[0063] As described above, it has been found that the relationship between the warpage of the printed circuit board 30r due to the difference in the linear expansion coefficient between it and the fixed structure and the direction of the warpage of the semiconductor package 41r due to the difference in the linear expansion coefficient between the components is important for the connection reliability of the mounting portion of the semiconductor package 41r. For example, it has been found that when the warpage direction is reversed, stress is concentrated on the mounting portion of the semiconductor package 41r, reducing the connection reliability.

[0064] <Effect of Stress Relief Portion> Next, the effect of the stress relief portion will be described with reference to Fig. 11 and Fig. 12. Both Fig. 11 and Fig. 12 show simulation results. Fig. 11 shows the warpage characteristics of a printed circuit board when the temperature is reduced from 20°C to -40°C in a case where the warpage direction of the printed circuit board and the warpage direction of the semiconductor package are different.

[0065] As a configuration with a different warpage direction, a configuration was used in which a printed circuit board was fixed to a case (housing) made of aluminum and a semiconductor package was placed on one side of the printed circuit board, i.e., a configuration similar to that shown in Figure 7. The amount of warpage (variation in depth dimension) of the printed circuit board was sampled along the diagonal line of the printed circuit board. In Figure 11, no slit (stress relief portion) is indicated by a solid line, a small slit by a dashed line, and a large slit by a two-dot chain line. Note that the size of the slit indicates the length of the slit. The small slit corresponds to the configuration shown in Figure 2. The large slit corresponds to the configuration shown in Figure 3.

[0066] Because the case, which is the fixing structure, is made of aluminum, smile warpage occurs in the printed circuit board when the temperature drops due to the difference in linear expansion coefficient between the case and the printed circuit board. Cry warpage also occurs in the semiconductor package. Because the semiconductor package is mounted on one side of the printed circuit board, the warpage direction of the printed circuit board and the warpage direction of the semiconductor package are opposite. When no slits (stress relief portions) are provided, the results shown by the solid line in Figure 11 clearly show that smile warpage from the fixing holes (fixing portions) suddenly deforms into Cry warpage. In other words, it is clear that a sudden deformation stress is applied to the mounting portion (solder joint) of the semiconductor package, which is the boundary between smile warpage and Cry warpage.

[0067] When small slits are provided, the results shown by the dashed line in Figure 11 clearly show that the printed circuit board bends sharply around the fixing holes, reducing the amount of warping, i.e., alleviating stress. It is also clear that the printed circuit board becomes almost flat in the area closer to the center of the board than the slits. When large slits are provided, the effect of the slits becomes even more pronounced. The results shown by the two-dot chain line in Figure 11 clearly show that the effect of stress alleviation and the effect of flattening the central area are enhanced.

[0068] Figure 12 shows the warpage characteristics of printed circuit boards with the same warpage direction when the temperature is reduced from 20°C to -40°C. A configuration with the same warpage direction was used, in which the printed circuit board was fixed to a case (housing) made of Al and a semiconductor package was placed on the backside of the printed circuit board, i.e., a configuration similar to that shown in Figure 8. The warpage of the printed circuit board was then sampled along the diagonal line. In Figure 12, the solid line indicates no slit (stress relief portion), the dashed line indicates a small slit, and the chain double-dashed line indicates a large slit. For comparison, the results for the case without a slit shown in Figure 11 are shown with a chain double-dashed line.

[0069] When the temperature drops, smile warpage occurs in the printed circuit board due to the difference in the linear expansion coefficient between the case and the printed circuit board. Cry warpage also occurs in the semiconductor package. Because the semiconductor package is located on the back surface of the printed circuit board, the warpage of the printed circuit board and the warpage of the semiconductor package are in the same direction. When no slits (stress relief portions) are provided, the results shown by the solid line in Figure 12 clearly show that the mounting area of ​​the semiconductor package does not deform into Cry warpage, and smile warpage occurs throughout the entire area. In other words, it is clear that no sudden deformation stress is applied to the mounting area (solder joint) of the semiconductor package. This point is also clear from the comparison of the solid line and the dashed line in Figure 12.

[0070] When small slits are provided, the results shown by the dashed line in Figure 12 clearly show that the printed circuit board bends sharply around the fixing holes, reducing the amount of warpage. It is also clear that the area closer to the center of the board than the slits becomes almost flat. When large slits are provided, the results shown by the two-dot chain line in Figure 12 clearly show that the effect of flattening the central area is even greater. The results for small and large slits are almost the same in Figures 11 and 12.

[0071] Summary of First Embodiment According to this embodiment, as shown in FIGS. 1 and 4 , the linear expansion coefficient of the case 21, which is a fixed structure, is greater than the linear expansion coefficient of the printed circuit board 30. For example, when the temperature drops, the printed circuit board 30 experiences a smile warp, with the outer periphery convex upward, similar to the configuration shown in FIG. 7 . The semiconductor package 41 includes a lead frame 42, a semiconductor chip 43 disposed on the lead frame 42, and an encapsulating resin body 44. Therefore, when the temperature drops, the semiconductor package 41 experiences a cry warp, with the outer periphery convex downward, as shown in FIG. 6 . The semiconductor package 41 is disposed on one surface 301 of the printed circuit board 30, and when the temperature drops, the warp direction of the printed circuit board 30 and the warp direction of the semiconductor package 41 are opposite to each other.

[0072] For example, when the temperature rises, cry warpage occurs in the printed circuit board 30. Smile warpage occurs in the semiconductor package 41. The semiconductor package 41 is arranged on one surface 301, and the direction of warpage is reversed.

[0073] In this configuration in which the warping direction reverses during temperature fluctuations, the printed circuit board 30 is provided with a stress relief portion 32. The stress relief portion 32 relieves the stress acting on the mounting portion (solder joint) of the semiconductor package 41 due to the different warping directions, thereby improving the connection reliability of the semiconductor package 41.

[0074] As illustrated, a non-lead package may be used as the semiconductor package 41. In the case of a non-lead package, since there are no leads protruding from the encapsulating resin body 44, stress relief due to elastic deformation of the leads is not possible. Compared to packages with leads, connection reliability is more likely to decrease due to the application of stress. In other words, solder life is more likely to decrease. Connection reliability is particularly likely to decrease in environments with large temperature changes and frequent thermal cycles, such as in automotive products. By employing a non-lead type semiconductor package 41 and providing a stress relief portion 32 in a configuration in which the warpage direction is reversed, the connection reliability of the non-lead type semiconductor package 41 can be improved. Furthermore, using a non-lead package allows the printed circuit board 30, and ultimately the electronic device 10, to be made smaller.

[0075] The semiconductor package 41 may be a package having leads protruding from the sealing resin body 44. Due to the effect of the stress relief portion 32, a part of the stress acting on the mounting portion of the semiconductor package 41 can be relieved by changing the direction of warpage. The other part of the stress can be relieved by elastic deformation of the leads.

[0076] As illustrated, the stress relief portion 32 may be provided around the fixing hole 31 (fixing portion 315). By providing the stress relief portion 32 around the fixing hole 31 (fixing portion 315), which is the starting point of the stress, it becomes easier to reduce the stress.

[0077] As shown in the example, the stress relief portion 32 may be configured to include a portion that relieves stress by elastic deformation. By elastically deforming (spring deformation), it is possible to effectively relieve stress acting on the mounting portion of the semiconductor package 41.

[0078] As illustrated, the stress relief portion 32 may include slits 321 provided individually for the fixing holes 31, and partition portions 322. The slits 321 penetrate the printed circuit board 30, and therefore can block the transmission of stress. In other words, the range of stress transmission can be limited. The partition portions 322 defined by the slits 321 elastically deform when stress is applied. The elastic deformation of the partition portions 322 can relieve stress.

[0079] As shown in the example, the slits 321 may be arranged to cross at least one of a plurality of imaginary straight lines L1, L2, L3, L4, L5, and L6 that virtually connect different fixing holes 31. Displacement occurs between the fixing holes 31 due to temperature fluctuations, and deformation stress acts with the fixing holes 31 as the origin. Therefore, by arranging the slits 321 to cross the imaginary straight lines, it is possible to suppress displacement between the fixing holes 31 and alleviate stress acting on the mounting portion of the semiconductor package 41.

[0080] Preferably, at least one slit 321 should be arranged to cross all of the imaginary straight lines L1, L2, L3, L4, L5, and L6. Since the slit 321 is always located between the fixing holes 31, stress acting on the mounting portion of the semiconductor package 41 can be effectively alleviated.

[0081] As shown in the example, the slit 321 may be provided so as to open to the side surface of the printed circuit board 30. Providing the slit 321 to the end of the printed circuit board 30 in this way makes it easier to limit the stress transmission range. Also, the partition section 322 and the mounting area are connected at a single point, making it easier for the partition section 322 to elastically deform.

[0082] As shown in the example, the slit 321 may be formed in the printed circuit board 30, which has a generally rectangular planar shape, so as to open on a first side surface and extend from the first side surface to a second side surface opposite the first side surface. This narrows and lengthens the width of the partition 322, making it easier for the partition 322 to elastically deform. This effectively relieves stress acting on the mounting portion of the semiconductor package 41.

[0083] <Modifications> The arrangement of the semiconductor package 41 is not limited to the one surface 301. For example, as shown in FIG. 13 , in a configuration in which the semiconductor package 41 is provided on the back surface 302, a stress relief portion 32 may be provided on the printed circuit board 30. In FIG. 13 , the case 21 is formed using Fe. As a result, for example, Cry warpage occurs in the printed circuit board 30 when the temperature drops. Although Cry warpage occurs in the semiconductor package 41, because the semiconductor package 41 is provided on the back surface 302, the warpage direction of the printed circuit board 30 and the warpage direction of the semiconductor package 41 when the temperature fluctuates are opposite to each other. By providing the stress relief portion 32, it is possible to relieve stress acting on the mounting portion (solder joint portion) of the semiconductor package 41, thereby improving connection reliability.

[0084] In the configuration shown in Figure 13, when the temperature rises, a smile warp occurs in the printed circuit board 30. A smile warp occurs in the semiconductor package 41. The semiconductor package 41 is disposed on the back surface 302, and the direction of the warp is reversed. By providing the stress relief portion 32, the stress acting on the mounting portion (solder joint portion) of the semiconductor package 41 can be relieved, thereby improving connection reliability. In the configuration shown in Figure 13, a heat dissipation gel 60 may be disposed between the semiconductor package 41 and the cover 22 (not shown).

[0085] Although Al has been used as an example of the material of the case 21 having a linear expansion coefficient greater than that of the printed circuit board 30, the material is not limited to this. For example, resin materials such as PPS and PBT may also be used. Although Fe has been used as an example of the material of the case 21 having a linear expansion coefficient smaller than that of the printed circuit board 30, the material is not limited to this. For example, ceramic may also be used.

[0086] As shown in FIG. 14 , fixing holes 33 may be provided in the printed circuit board 30 to reinforce the fixation of the printed circuit board 30 to the case 21 (fixed structure). Fixing holes 31 correspond to the first fixing hole, and fixing holes 33 correspond to the second fixing hole. Providing fixing holes 33 increases the attachment strength to the case 21. Fixing holes 33 are provided in region 34 surrounded by all slits 321. Region 34 is an area where slits 321 block the transmission of stress originating from fixing holes 31. Fixing holes 33 are arranged between slits 321. In the example shown in FIG. 14 , fixing holes 33 are provided in the central region of the board. Stress originating from fixing holes 31 is not transmitted to fixing holes 33 provided in region 34. Therefore, slits 321 are not required for fixing holes 33, and fixing holes 33 function as holes that improve the attachment strength between the printed circuit board 30 and the case 21.

[0087] The shape and arrangement of the slits 321 are not limited to the above example. For example, as shown in Fig. 15, discontinuous slits 321 may be used. The slits 321 are divided into multiple parts in the extension direction. Also, as shown in Fig. 16, the slits 321 may be arranged in multiple parts. The slits 321 are arranged in multiple parts in the radial direction from the fixing hole 31.

[0088] Second Embodiment This embodiment is a modification of the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, the top surface of the semiconductor chip in the semiconductor package is covered with an encapsulating resin body. Instead, a semiconductor package having a metal plate disposed on the semiconductor chip may be used.

[0089] <Semiconductor Package and Warpage> Fig. 17 is a cross-sectional view showing an example of a semiconductor package in an electronic device according to this embodiment. Fig. 17 corresponds to Fig. 5. Like Fig. 6, Fig. 17 shows the relationship between the amount of shrinkage and warpage when the temperature drops. The solid line with inward-pointing arrows at both ends indicates the magnitude of shrinkage (amount of shrinkage). The two-dot chain line shows the shape of the warpage of the semiconductor package when the temperature drops.

[0090] The semiconductor package 41 is a QFN-type non-leaded package, as in the previous embodiment. Similar to the configuration shown in the previous embodiment (see FIG. 5 ), the semiconductor package 41 includes a lead frame 42, a semiconductor chip 43, and an encapsulating resin body 44. The semiconductor package 41 of this embodiment further includes a clip 45, which is a metal plate. The encapsulating resin body 44 encapsulates the clip 45 together with the semiconductor chip 43.

[0091] The clip 45 is made of a metal material with good conductivity, such as Cu. The clip 45 is mounted on the semiconductor chip 43. This type of structure is used in power semiconductors that pass large currents, such as power MOS. The semiconductor chip 43 of this embodiment has a MOSFET formed on a semiconductor substrate. MOSFET is an abbreviation for Metal Oxide Semiconductor Field Effect Transistor. The semiconductor chip 43 has a drain electrode formed on its lower surface facing the lead frame 42 and a source electrode formed on its upper surface. The clip 45 is soldered to the source electrode.

[0092] If the clip 45 is thicker than the lead frame 42 and / or larger than the island 421, the effect of the clip 45 on the semiconductor chip 43 during expansion and contraction will be stronger than the effect of the lead frame 42. For example, when the temperature drops, even if both the lead frame 42 and the clip 45 are made of Cu, the contraction strength of the clip 45 will be stronger. Therefore, the semiconductor package 41 will develop a smile warp, with the periphery convex upward as shown by the two-dot chain line. When the temperature rises, the semiconductor package 41 will develop a cry warp, with the periphery convex downward.

[0093] In the above package structure, Si is sandwiched between Cu, which can offset the influence of the semiconductor chip 43. In particular, if the thickness of the clip 45 is increased, the strength becomes stronger on the clip 45 side than on the lead frame 42, resulting in deformation due to tension toward the clip 45 side. The strength is proportional to the cube of the thickness.

[0094] <Warpage of Printed Circuit Boards and Their Impact on Mounting Portions of Semiconductor Packages> Next, warpage of printed circuit boards will be described with reference to FIGS. 18 to 21. Furthermore, the impact of the relationship between warpage of printed circuit boards and warpage of semiconductor packages on mounting portions of semiconductor packages will be described. FIGS. 18 to 21 show a reference example. FIGS. 18 to 21 correspond to FIGS. 7 to 10. The reference example differs from this embodiment in that a stress relief portion such as a slit is not provided in the printed circuit board. In the reference example, the suffix "r" is added to the reference symbols of elements related to this embodiment. The solid line with inward-pointing arrows at both ends indicates the magnitude of shrinkage (amount of shrinkage). The two-dot chain line indicates the warpage shape of the printed circuit board when the temperature drops. The dashed line indicates the warpage shape of the semiconductor package when the temperature drops.

[0095] In the reference example shown in Fig. 18, the case 21r, which is a fixed structure, is made of aluminum. When the temperature drops, the case 21r (opposing wall 211r) shrinks significantly in a direction perpendicular to the Z direction. On the other hand, the amount of shrinkage of the printed circuit board 30r is small. The printed circuit board 30r develops a smile warp with an upward convex outer periphery.

[0096] The semiconductor package 41r has a configuration similar to that of the semiconductor package 41 shown in FIG. 17. When the temperature drops, the semiconductor package 41r develops a smile warp, with the outer peripheral edge convex upward, as indicated by the dashed line. The semiconductor package 41r is disposed on one surface 301r. Therefore, the warp direction of the printed circuit board 30r and the warp direction of the semiconductor package 41r are the same. This makes it possible to prevent sudden deformation stress from being applied to the mounting portion (solder joint) of the semiconductor package 41r.

[0097] When the temperature rises, Cry warpage occurs in the printed circuit board 30r. Cry warpage also occurs in the semiconductor package 41r. The semiconductor package 41r is arranged on one surface 301r, and the direction of warpage is the same. Therefore, it is possible to prevent sudden deformation stress from being applied to the mounting portion of the semiconductor package 41r.

[0098] In the reference example shown in Fig. 19, a semiconductor package 41r is disposed on a rear surface 302r of a printed circuit board 30r. The other configurations are the same as those of the reference example shown in Fig. 18. When the temperature drops, a smile warp occurs in the printed circuit board 30r due to the difference in the linear expansion coefficients between the case 21r and the printed circuit board 30r.

[0099] When the temperature drops, the semiconductor package 41r develops a smile warp, with the outer periphery convex upward, as indicated by the dashed line. The semiconductor package 41r is mounted on the back surface 302r. As a result, the warp direction of the printed circuit board 30r and the warp direction of the semiconductor package 41r are opposite to each other. This causes a sudden deformation stress to be applied to the mounting portion (solder joint) of the semiconductor package 41r, which can easily reduce the connection reliability of the mounting portion of the semiconductor package 41r.

[0100] When the temperature rises, Cry warpage occurs in the printed circuit board 30r. Cry warpage also occurs in the semiconductor package 41r. The semiconductor package 41r is disposed on the rear surface 302r, and the direction of warpage is reversed. Therefore, the connection reliability of the mounting portion of the semiconductor package 41r is likely to decrease.

[0101] In the reference example shown in Fig. 20, the case 21r, which is the fixed structure, is made of Fe. When the temperature drops, the printed circuit board 30r shrinks significantly in a direction perpendicular to the Z direction. On the other hand, the case 21r (opposing wall 211r) shrinks less. The printed circuit board 30r develops a Cry warp, with the outer periphery convex downward.

[0102] When the temperature drops, the semiconductor package 41r develops a smile warp, with the outer periphery convex upward, as shown by the dashed line. The semiconductor package 41r is mounted on one surface 301r of the printed circuit board 30r. As a result, the warp direction of the printed circuit board 30r and the warp direction of the semiconductor package 41r are opposite to each other. This easily reduces the connection reliability of the mounting portion of the semiconductor package 41r.

[0103] Furthermore, when the temperature rises, smile warpage occurs in the printed circuit board 30r. Cry warpage occurs in the semiconductor package 41r. The semiconductor package 41r is mounted on one surface 301r, and the direction of warpage is reversed. Therefore, the connection reliability of the mounting portion of the semiconductor package 41r is likely to decrease.

[0104] In the reference example shown in FIG. 21 , a semiconductor package 41r is disposed on the back surface 302r of a printed circuit board 30r. Other configurations are similar to those of the reference example shown in FIG. 20 . When the temperature drops, the difference in the linear expansion coefficients between the case 21r and the printed circuit board 30r causes cry warpage in the printed circuit board 30r. When the temperature drops, the semiconductor package 41r causes smile warpage, with the outer peripheral edge convex upward, as shown by the dashed line. Because the semiconductor package 41r is disposed on the back surface 302r, the warpage direction of the printed circuit board 30r and the warpage direction of the semiconductor package 41r are the same. Therefore, it is possible to prevent sudden deformation stress from being applied to the mounting portion (solder joint) of the semiconductor package 41r.

[0105] As the temperature rises, smile warpage occurs in the printed circuit board 30r. Cry warpage occurs in the semiconductor package 41r. The semiconductor package 41r is disposed on the rear surface 302r, and the warpage occurs in the same direction. This prevents sudden deformation stress from being applied to the mounting portion (solder joint) of the semiconductor package 41r.

[0106] Figures 22 to 26 show simulation results of deformation due to temperature fluctuations. Figures 22, 23, and 24 show simulation results when the temperature changes to a low temperature using a structural model similar to the reference example shown in Figure 18. Figure 22 is a side view of the electronic device as seen from the Y direction. Figure 23 shows warpage of a printed circuit board. Figure 24 shows warpage of a semiconductor package.

[0107] In the electronic device 10r, a semiconductor package 41r is disposed on one surface 301r of a printed circuit board 30r. The case 21r is formed using aluminum, and as shown in Figures 22 and 23, a smile warp occurs in the printed circuit board 30r during low-temperature fluctuations. As shown in Figures 23 and 24, a smile warp occurs in the semiconductor package 41r. It is clear that the warp direction is the same.

[0108] Figures 25 and 26 show simulation results when the temperature is changed to a low temperature using a structural model in which slits (stress relief portions) are added to the structural models shown in Figures 22 to 24. Figure 25 is a side view of the electronic device as seen from the Y direction. Figure 25 corresponds to Figure 22. Figure 26 shows warpage of the printed circuit board.

[0109] As shown in Fig. 26, slits 321r and partitions 322r are provided at the four corners of the printed circuit board 30r. As shown in Fig. 25 and Fig. 6, by providing the slits 321r and partitions 322r, it is clear that even if displacement is applied to the fixing holes of the printed circuit board 30r, deformation can be absorbed.

[0110] 17, a simulation was also performed on the warpage characteristics of the printed circuit board when the temperature was decreased from 20°C to -40°C. The simulation was performed for three levels: no slit (stress relaxation portion), a small slit, and a large slit, for cases where the warpage direction of the printed circuit board and the warpage direction of the semiconductor package were different and where the warpage directions were the same. Although not shown, the results were similar to those of the preceding embodiment (see FIGS. 11 and 12).

[0111] <Electronic Device> Fig. 27 shows an example of an electronic device according to this embodiment. Fig. 27 corresponds to Fig. 4. For convenience, Fig. 27 shows only the case, which is the fixed structure of the housing. The case is also shown in a simplified form. Only a semiconductor package is shown as the electronic component. Screw holes, fixing holes, and screws are also omitted.

[0112] As shown in FIG. 27 , the electronic device 10 includes a semiconductor package 41 having the structure shown in FIG. 17 . The semiconductor package 41 is disposed on the rear surface 302 of the printed circuit board 30. The case 21, which is a fixed structure, is formed using aluminum. The printed circuit board 30 has a stress relief portion 32. As shown in the preceding embodiment, the stress relief portion 32 includes a slit 321 and a partition portion 322. The stress relief portion 32 has a configuration similar to that shown in the preceding embodiment (see FIGS. 2 and 3 ). The stress relief portion 32 is provided individually for each fixing portion 315 (fixing hole). In the configuration shown in FIG. 27 , a heat dissipation gel 60 may be disposed between the semiconductor package 41 and the cover 22 (not shown). The other configurations are similar to those shown in the preceding embodiment.

[0113] Summary of the Second Embodiment The electronic device 10 of this embodiment can achieve the same effects as the electronic device 10 described in the preceding embodiment. For example, in the configuration shown in FIG. 27 , the linear expansion coefficient of the case 21, which is a fixed structure, is greater than the linear expansion coefficient of the printed circuit board 30. For example, when the temperature drops, the printed circuit board 30 experiences a smile warp with the outer periphery convex upward, similar to the configuration shown in FIG. 19 . The semiconductor package 41 includes a clip 45 (metal plate material) disposed on the semiconductor chip 43, and when the temperature drops, the semiconductor package 41 experiences a smile warp as shown in FIG. 17 . The semiconductor package 41 is disposed on the back surface 302 of the printed circuit board 30, and when the temperature drops, the direction of warp of the printed circuit board 30 and the direction of warp of the semiconductor package 41 are opposite to each other.

[0114] For example, when the temperature rises, Cry warpage occurs in the printed circuit board 30. Cry warpage occurs in the semiconductor package 41. The semiconductor package 41 is disposed on the back surface 302, and the direction of warpage is reversed.

[0115] In this configuration in which the warping direction reverses during temperature fluctuations, the printed circuit board 30 is provided with a stress relief portion 32. The stress relief portion 32 relieves the stress acting on the mounting portion (solder joint) of the semiconductor package 41 due to the different warping directions, thereby improving the connection reliability of the semiconductor package 41.

[0116] The external appearance of the semiconductor package of the previous embodiment (see FIG. 5 ) and the external appearance of the semiconductor package of this embodiment (see FIG. 17 ) appear to be substantially the same. However, due to differences in internal structure, the warping direction when the temperature changes is opposite. As such, even semiconductor packages 41 that appear the same in appearance may warp in different directions when the temperature changes. However, based on the knowledge gained, a stress relief portion 32 is provided on the printed circuit board 30 in a configuration in which the warping direction when the temperature changes is opposite. The connection reliability of the semiconductor package 41 can be improved without blindly providing stress relief portions.

[0117] <Modification> The arrangement of the semiconductor package 41 is not limited to the back surface 302. For example, as shown in FIG. 28 , in a configuration in which the semiconductor package 41 is provided on one surface 301, a stress relief portion 32 may be provided on the printed circuit board 30. In FIG. 28 , the case 21 is formed using Fe. As a result, for example, cry warpage occurs in the printed circuit board 30 when the temperature drops. Smile warpage occurs in the semiconductor package 41. Because the semiconductor package 41 is provided on one surface 301, the warpage direction of the printed circuit board 30 and the warpage direction of the semiconductor package 41 when the temperature fluctuates are opposite to each other. By providing the stress relief portion 32, it is possible to relieve stress acting on the mounting portion (solder joint) of the semiconductor package 41 and improve connection reliability.

[0118] In the configuration shown in Figure 28, smile warpage occurs in the printed circuit board 30 when the temperature rises. Cry warpage occurs in the semiconductor package 41. The semiconductor package 41 is arranged on one surface 301, and the direction of warpage is reversed. By providing the stress relief portion 32, it is possible to relieve stress acting on the mounting portion (solder joint portion) of the semiconductor package 41 and improve connection reliability. In the configuration shown in Figure 28, a heat dissipation gel 60 may be placed between the semiconductor package 41 and the case 21.

[0119] Third Embodiment This embodiment is a modification of the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, the semiconductor package includes only one semiconductor chip. Alternatively, a multi-chip package may be used as the semiconductor package.

[0120] <Semiconductor Package> Fig. 29 is a cross-sectional view showing an example of a semiconductor package in an electronic device according to this embodiment. Fig. 29 corresponds to Fig. 17. Like Fig. 17, Fig. 29 shows the relationship between the amount of shrinkage and warpage when the temperature drops. The solid line with inward-pointing arrows at both ends indicates the magnitude of shrinkage (amount of shrinkage). The two-dot chain line shows the shape of the warpage of the semiconductor package when the temperature drops.

[0121] The semiconductor package 41 shown in Figure 29 is a QFN-type non-leaded package, similar to the preceding embodiment. The semiconductor package 41 has a structure in which the configuration shown in Figure 5 and the configuration shown in Figure 17 are arranged side by side within a common (single) package. The semiconductor package 41 includes a lead frame 42, semiconductor chips 43A and 43B, a sealing resin body 44, and a clip 45. A power MOSFET that drives a large current is formed on the semiconductor chip 43B. A control IC that controls the driving of the MOSFET of the semiconductor chip 43B is formed on the semiconductor chip 43A. Such a semiconductor package 41 is sometimes referred to as an IPD.

[0122] The semiconductor chip 43A corresponds to the semiconductor chip 43 shown in FIG. 5. The semiconductor chip 43A is arranged on one of the islands 421 of the lead frame 42. Pads (not shown) are formed on the upper surface of the semiconductor chip 43A, and the pads are electrically connected to terminals 422 via bonding wires. The upper surface of the semiconductor chip 43A is covered with a sealing resin body 44. The semiconductor chip 43B corresponds to the semiconductor chip 43 shown in FIG. 17. A clip 45 is bonded to the upper surface of the semiconductor chip 43B. In the example shown in FIG. 32, the semiconductor chip 43B is arranged on a different island 421 from the semiconductor chip 43A. Alternatively, the semiconductor chips 43A and 43B may be arranged on a common (single) island 421.

[0123] In the stacked portion including the semiconductor chip 43A, the linear expansion coefficient of Cu constituting the lead frame 42 is greater than the linear expansion coefficient of Si constituting the semiconductor chip 43. Therefore, when the temperature drops, the lead frame 42 shrinks significantly, resulting in Cry warpage, with the outer periphery convex downward. In the stacked portion including the semiconductor chip 43B, the clip 45 is thicker than the lead frame 42 and / or larger than the island 421. Therefore, when the temperature drops, even though both the lead frame 42 and the clip 45 are made of Cu, the contraction strength of the clip 45 increases. Therefore, a smile warpage, with the outer periphery convex upward, occurs. Both Cry warpage and smile warpage appear in a single semiconductor package 41.

[0124] The same applies when the temperature rises. When the temperature rises, smile warpage occurs in the stacked portion of the semiconductor chip 43A, and cry warpage occurs in the stacked portion of the semiconductor chip 43B. Cry warpage and smile warpage appear in the single semiconductor package 41.

[0125] <Electronic Device> Fig. 30 shows an example of an electronic device according to this embodiment. Fig. 30 corresponds to Fig. 4. For convenience, Fig. 30 shows only the case, which is the fixed structure of the housing. The case is also shown in a simplified form. Only a semiconductor package is shown as the electronic component. Screw holes, fixing holes, screws, and heat dissipation gel are also omitted.

[0126] As shown in Fig. 30, the electronic device 10 includes a semiconductor package 41 having the structure shown in Fig. 29. The semiconductor package 41 is disposed on one surface 301 of a printed circuit board 30. The case 21, which is a fixed structure, is formed using Al. The printed circuit board 30 has a stress relief portion 32. The stress relief portion 32 includes, for example, a slit 321 and a partition portion 322. The stress relief portion 32 has a configuration similar to that shown in the preceding embodiment (see Figs. 2 and 3). The stress relief portion 32 is provided individually for each fixing portion 315 (fixing hole).

[0127] Fig. 31 shows another example of an electronic device. In Fig. 31, a semiconductor package 41 is disposed on a rear surface 302 of a printed circuit board 30. The other configuration is the same as the example shown in Fig. 30.

[0128] Summary of the Third Embodiment As shown in this embodiment, a multi-chip package may be used as the semiconductor package 41. The multi-chip package includes a semiconductor chip 43A without a clip 45 on its upper surface and a semiconductor chip 43B with a clip 45 (metal plate) on its upper surface. In this configuration, as shown in FIG. 29 , cry warpage and smile warpage occur in the single semiconductor package 41 during temperature fluctuations. Therefore, as shown in FIGS. 30 and 31 , whether the semiconductor package 41 is mounted on the first surface 301 or the back surface 302, the semiconductor package 41 has a warped portion that is opposite to the warp of the printed circuit board 30. By providing a stress relief portion 32 regardless of the mounting surface, the stress acting on the mounting portion of the semiconductor package 41 due to the reverse warpage can be relieved.

[0129] Without the stress relief portion 32, the connection reliability of the mounting portion of the laminated portion including the semiconductor chip 43A and the laminated portion including the semiconductor chip 43B, which warp in the opposite direction to the warp of the printed circuit board 30, would be reduced. In other words, the solder life would be reduced. This would also reduce the product life. By providing the stress relief portion 32, the solder life of the warped portion in the opposite direction can be improved, and ultimately the product life can be improved.

[0130] 30 and 31 . The electronic device may be configured such that the linear expansion coefficient of the case 21 is smaller than that of the printed circuit board 30. In this case, whether the semiconductor package 41 is mounted on the first surface 301 or the back surface 302, the semiconductor package 41 will have a warped portion that is opposite to the warp of the printed circuit board 30. Therefore, by providing the stress relief portion 32 regardless of the mounting surface, it is possible to relieve the stress acting on the mounting portion of the semiconductor package 41 due to the warp in the opposite direction.

[0131] (Fourth Embodiment) This embodiment is a modification of the preceding embodiment as a basic form, and the description of the preceding embodiment can be used. In the preceding embodiment, a single semiconductor package is provided. Instead of this, a configuration in which multiple types of semiconductor packages are mounted on a common surface may be used.

[0132] Fig. 32 shows an example of an electronic device according to this embodiment. Fig. 32 corresponds to Fig. 4. For convenience, Fig. 32 shows only the case, which is the fixed structure of the housing. The case is also shown in a simplified form. Only the semiconductor package is shown as the electronic component. Screw holes, fixing holes, screws, and heat dissipation gel are also omitted. The dashed line in Fig. 32 indicates the warped shape of the semiconductor package when the temperature drops. The two-dot chain line indicates the warped shape of the printed circuit board when the temperature drops.

[0133] As shown in FIG. 32 , the electronic device 10 includes a semiconductor package 41A having a configuration similar to that shown in FIG. 5 and a semiconductor package 41B having a configuration similar to that shown in FIG. 17 . The semiconductor package 41A corresponds to the first semiconductor package, and the semiconductor package 41B corresponds to the second semiconductor package. The semiconductor package 41A includes a lead frame 42A, a semiconductor chip 43A, and a sealing resin body 44A. The lead frame 42A corresponds to the first lead frame, and the semiconductor chip 43A corresponds to the first semiconductor chip. The sealing resin body 44A corresponds to the first sealing resin body. The semiconductor package 41B includes a lead frame 42B, a semiconductor chip 43B, a sealing resin body 44A, and a clip 45. The lead frame 42B corresponds to the second lead frame, and the semiconductor chip 43B corresponds to the second semiconductor chip. The sealing resin body 44B corresponds to the second sealing resin body.

[0134] Two types of semiconductor packages 41A, 41B are arranged on a common surface of the printed circuit board 30. In the example shown in FIG. 32 , the semiconductor packages 41A, 41B are arranged on one surface 301. The semiconductor packages 41A, 41B are arranged on a back surface 302. The case 21, which is a fixed structure, is formed using, for example, Al. The printed circuit board 30 has a stress relief portion 32. The stress relief portion 32 includes, for example, a slit 321 and a partition portion 322. The stress relief portion 32 has a configuration similar to that shown in the preceding embodiment (see FIGS. 2 and 3 ). The stress relief portion 32 is provided individually for each fixing portion 315 (fixing hole).

[0135] Summary of the Fourth Embodiment As shown in this embodiment, a semiconductor package 41A (first semiconductor package) and a semiconductor package 41B (second semiconductor package) are arranged on a common surface of a printed circuit board 30. During temperature fluctuations, one of the semiconductor packages 41A and 41B exhibits cry warpage, while the other exhibits smile warpage. Whether the two types of semiconductor packages 41A and 41B are mounted on the first surface 301 or the back surface 302, the direction of warpage of one of the semiconductor packages 41A and 41B is opposite to the direction of warpage of the printed circuit board 30. Therefore, by providing a stress relief portion 32 regardless of the mounting surface, it is possible to relieve the stress acting on the mounting portion of the semiconductor package 41 due to the opposite warpage.

[0136] In the configuration shown in FIG. 32 , for example, a temperature drop causes smile warpage in the printed circuit board 30. Cry warpage occurs in the semiconductor package 41A, and smile warpage occurs in the semiconductor package 41B. Therefore, of the semiconductor packages 41A and 41B arranged on the first surface 301, the warpage direction of the semiconductor package 41A is opposite to that of the printed circuit board 30. Of the semiconductor packages 41A and 41B arranged on the back surface 302, the warpage direction of the semiconductor package 41B is opposite to that of the printed circuit board 30. Therefore, the semiconductor package 41A arranged on the first surface 301 and the semiconductor package 41B arranged on the back surface 302 correspond to semiconductor packages 41 in which stress acts on the mounting portion due to the different warpage directions. Providing the stress relief portion 32 can improve the connection reliability between the semiconductor package 41A arranged on the first surface 301 and the semiconductor package 41B arranged on the back surface 302. As with multi-chip packages, the product life can be improved.

[0137] The electronic device is not limited to the configuration shown in Fig. 32 . The two types of semiconductor packages 41A and 41B may be arranged on only one surface 301 or only the back surface 302. A configuration may be adopted in which the linear expansion coefficient of the case 21 is smaller than that of the printed circuit board 30. In this case, in the configuration shown in Fig. 32 , the semiconductor package 41B arranged on one surface 301 and the semiconductor package 41A arranged on the back surface 302 correspond to semiconductor packages 41 in which stress acts on the mounting portion due to warpage in different directions. By providing stress relief portions 32 regardless of the mounting surface, it is possible to relieve stress acting on the mounting portion of the semiconductor package 41 due to warpage in opposite directions.

[0138] Fifth Embodiment This embodiment is a modification of the preceding embodiment as a basic form, and the description of the preceding embodiment can be used. In the preceding embodiment, slits and partitions are provided as stress relief portions. Instead of this, grooves and thin-walled portions may be provided.

[0139] Fig. 33 is a cross-sectional view showing a portion of a printed circuit board of an electronic device according to this embodiment. Fig. 33 shows the periphery of fixing holes and stress relief portions. As in the preceding embodiment, the printed circuit board 30 shown in Fig. 33 has stress relief portions 32 provided corresponding to fixing holes 31. The stress relief portions 32 are provided individually for the multiple fixing holes 31. The stress relief portions 32 include grooves 323 and thin-walled portions 324.

[0140] The grooves 323 are blind holes extending in a predetermined direction. The grooves 323 may be open to one surface 301 or to the back surface 302. In the example shown in Fig. 33 , the grooves 323 opening to one surface 301 and the grooves 323 opening to the back surface 302 are provided so as to overlap along the extension direction.

[0141] The thin-walled portion 324 is a portion whose thickness is reduced by the groove 323 compared to the surrounding area of ​​the groove 323. The thin-walled portion 324 is adjacent to the groove 323 in the Z direction. In the example shown in FIG. 33 , the thin-walled portion 324 is sandwiched between a groove 323 opening on one surface 301 and a groove 323 opening on the back surface 302. The thin-walled portion 324 connects a portion closer to the fixing hole 31 than the groove 323 to a portion opposite the fixing hole 31 via the groove 323. When stress is applied, the thin-walled portion 324 undergoes elastic deformation (spring deformation). Because the groove 323 does not penetrate the printed circuit board 30, for example, the groove 323 corresponding to the fixing hole 311 may be provided so that one end opens to the side surface 303 and the other end opens to the side surface 304. The other configurations are similar to those shown in the preceding embodiment.

[0142] As shown in this embodiment, the stress relief portion 32 may include a portion that relieves stress by elastic deformation. By elastically deforming (spring deformation), it is possible to effectively relieve the stress acting on the mounting portion of the semiconductor package 41 due to reverse warpage.

[0143] As illustrated, the stress relief portion 32 may be configured to include a non-penetrating groove 323 and a thin-walled portion 324 adjacent to the groove 323 in the Z direction. The non-penetrating groove 323 can limit the range of stress transmission. The thin-walled portion 324 adjacent to the groove 323 elastically deforms when stress is applied. The elastic deformation of the thin-walled portion 324 can relieve stress.

[0144] The stress relaxation portion 32 including the slit 321 and the partition portion 322 shown in the previous embodiment may be replaced with the stress relaxation portion 32 including the groove 323 and the thin portion 324 shown in this embodiment.

[0145] Sixth Embodiment This embodiment is a modification of the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, an example was shown in which a slit or a groove was included as the stress relief portion. Instead of this, an extension portion extending from the main body portion may be provided.

[0146] Fig. 34 is a cross-sectional view showing a portion of a printed circuit board of an electronic device according to this embodiment. As in the preceding embodiment, the printed circuit board 30 shown in Fig. 34 has stress relief portions 32 provided corresponding to the fixing holes 31. The stress relief portions 32 are provided individually for the multiple fixing holes 31. The stress relief portions 32 include extension portions 325 that are continuous with the main body portion 35.

[0147] The main body 35 is the main part of the printed circuit board 30. Conductors such as wiring layers are arranged in the main body 35, and electronic components 40 including a semiconductor package 41 are mounted on the main body 35. The printed circuit board 30 has four extension portions 325. Fixing holes 31 are provided in the extension portions 325. The extension portions 325 extend from the main body 35 toward the fixing positions with the case 21. The extension portions 325 shown in FIG. 34 extend in one direction. The extension portions 325 extend in the X direction or the Y direction. The extension portions 325 undergo elastic deformation (spring deformation) when stress is applied. The other configurations are the same as those shown in the preceding embodiment.

[0148] As shown in this embodiment, the stress relief portion 32 may include a portion that relieves stress by elastic deformation. By elastically deforming (spring deformation), it is possible to effectively relieve the stress acting on the mounting portion of the semiconductor package 41 due to reverse warpage.

[0149] As illustrated, the stress relief portion 32 may include an extension portion 325 that extends from the main body portion 35 and is provided with a fixing hole 31. The extension portion 325 elastically deforms when stress is applied. The elastic deformation of the extension portion 325 can relieve stress.

[0150] <Modifications> The shape of the extension portion 325 is not limited to the above example. For example, as shown in FIG. 35 , the extension portion 325 may include a first extension portion 3251 and a second extension portion 3252. The first extension portion 3251 extends in a predetermined direction. The second extension portion 3252 is connected to the first extension portion 3251 and extends in a direction different from the predetermined direction. In the example shown in FIG. 35 , one end of the first extension portion 3251 is connected to the main body portion 35, and the other end is connected to the second extension portion 3252. For example, the first extension portion 3251 extends in the X direction, and the second extension portion 3252 extends in the Y direction. Furthermore, the first extension portion 3251 extends in the Y direction, and the second extension portion 3252 extends in the X direction. The first extension portion 3251 extends in a direction perpendicular to the side surface of the printed circuit board 30 (main body portion 35). The second extension portion 3252 extends along the side surface of the printed circuit board 30. The extension portion 325 has a generally L-shape in plan view. According to the configuration shown in Fig. 35, the length from the fixing hole 31 to the main body portion 35 is increased, making the extension portion 325 more susceptible to elastic deformation. In addition, an increase in the physical size can be suppressed.

[0151] The stress relaxation portion 32 including the slit 321 and the partition portion 322 shown in the previous embodiment may be replaced with the stress relaxation portion 32 including the extension portion 325 shown in this embodiment.

[0152] (Other Embodiments) The disclosure in this specification and drawings, etc. is not limited to the exemplified embodiments. The disclosure encompasses the exemplified embodiments and modifications thereto by those skilled in the art. For example, the disclosure is not limited to the combinations of parts and / or elements shown in the embodiments. The disclosure can be implemented in various combinations. The disclosure can have additional parts that can be added to the embodiments. The disclosure encompasses the omission of parts and / or elements from the embodiments. The disclosure encompasses the substitution or combination of parts and / or elements between one embodiment and another embodiment. The disclosed technical scope is not limited to the description of the embodiments. Some disclosed technical scopes are defined by the claims, and should be interpreted as including all modifications within the meaning and scope equivalent to the claims.

[0153] The disclosure in the specification, drawings, etc. is not limited by the claims. The disclosure in the specification, drawings, etc. encompasses the technical ideas described in the claims, and extends to more diverse and broader technical ideas than the technical ideas described in the claims. Therefore, various technical ideas can be extracted from the disclosure in the specification, drawings, etc. without being bound by the claims.

[0154] When an element or layer is referred to as being "on," "coupled," "connected," or "coupled," it may be directly on, coupled, connected, or coupled to another element or layer, and intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly coupled," "directly connected," or "directly coupled" to another element or layer, no intervening elements or layers are present. Other terms used to describe relationships between elements should be construed in a similar manner (e.g., "between" vs. "directly between," "adjacent" vs. "directly adjacent," etc.). As used in this specification, the term "and / or" includes any and all combinations of one or more of the associated listed items. That is, a reference to A and / or B means at least one of A and B.

[0155] Spatially relative terms such as "inside," "outside," "back," "below," "low," "top," "top," and the like are used herein to facilitate the description of one element or feature's relationship to other elements or features, as illustrated. Spatially relative terms may be intended to encompass different orientations of the device during use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures were turned over, elements described as "below" or "directly below" other elements or features would then be oriented "above" the other elements or features. Thus, the term "bottom" can encompass both an orientation of top and bottom. The device may also be oriented in other ways (rotated 90 degrees or at other orientations), and the spatially relative descriptors used in this specification would be interpreted accordingly.

[0156] (Disclosure of Technical Ideas) This specification discloses multiple technical ideas described in the following multiple clauses. Some clauses may be described in a multiple dependent form, with the subsequent clause alternatively referring to the preceding clause. Furthermore, some clauses may be described in a multiple dependent form, with the subsequent clause referring to another multiple dependent clause. These multiple dependent clauses define multiple technical ideas.

[0157] <Technical Idea 1> An electronic device comprising: a printed circuit board (30) having one surface (301) and a back surface (302) that is the surface opposite to the one surface in a plate thickness direction; a surface-mounted semiconductor package (41) mounted on the printed circuit board; and a fixing structure (21) having a portion facing the one surface, wherein the printed circuit board has a plurality of fixing holes (31) for fixing the printed circuit board to the fixing structure, the warping direction of the printed circuit board and the warping direction of the semiconductor package during temperature fluctuations are directions along the plate thickness direction and are opposite to each other, and the printed circuit board has a stress relaxation portion (32) that relieves stress acting on a mounting portion of the semiconductor package due to the different warping directions.

[0158] <Technical Concept 2> The electronic device according to Technical Concept 1, wherein the semiconductor package is a non-leaded package.

[0159] <Technical Concept 3> The electronic device according to Technical Concept 1 or 2, wherein the stress relaxation portion is provided around the fixing hole.

[0160] Technical Concept 4 The electronic device according to Technical Concept 3, wherein the stress relaxation portion includes a portion that relaxes the stress by elastic deformation.

[0161] <Technical Idea 5> The electronic device according to Technical Idea 4, wherein the stress relaxation portion includes a slit (321) that is provided individually for the fixing hole and penetrates the printed circuit board in the thickness direction, and a partition portion (322) that is partitioned by the slit and in which the fixing hole is provided.

[0162] <Technical Idea 6> The electronic device according to Technical Idea 5, wherein the slit is arranged to cross at least one of a plurality of imaginary straight lines virtually connecting different fixing holes with each other in a plan view in the plate thickness direction.

[0163] <Technical Concept 7> The electronic device according to Technical Concept 6, wherein at least one of the slits is disposed so as to cross all of the imaginary straight lines.

[0164] <Technical Concept 8> The electronic device according to any one of Technical Concepts 5 to 7, wherein the slit opens on a side surface of the printed circuit board.

[0165] <Technical Idea 9> The electronic device described in Technical Idea 8, wherein the printed circuit board has a rectangular shape when viewed in a plane in the plate thickness direction, and the slit opens to a first side surface of the printed circuit board and extends from the first side surface to a second side surface located opposite the first side surface.

[0166] <Technical Idea 10> The electronic device according to any one of Technical Ideas 5 to 9, wherein the printed circuit board has second fixing holes (33) that are provided separately from the first fixing holes, which are the fixing holes, and that reinforce the fixing of the printed circuit board to the fixing structure, and the second fixing holes are provided in an area surrounded by all of the slits.

[0167] <Technical Idea 11> The electronic device described in Technical Idea 4, wherein the stress relaxation portion includes a non-penetrating groove (323) and a thin-walled portion (324) adjacent to the groove in the plate thickness direction and connecting a portion on the fixing hole side of the groove to a portion on the opposite side of the fixing hole via the groove.

[0168] <Technical Idea 12> The electronic device according to Technical Idea 4, wherein the printed circuit board has a main body portion (35) and an extension portion (325) extending from the main body portion and having the fixing hole provided therein, and the stress relaxation portion includes the extension portion.

[0169] <Technical Idea 13> The electronic device according to Technical Idea 12, wherein the extension portion includes a first extension portion (3251) extending in a predetermined direction, and a second extension portion (3252) connected to the first extension portion and extending in a direction different from the predetermined direction.

[0170] <Technical Idea 14> The semiconductor package comprises a lead frame (42), a semiconductor chip (43) having a bottom surface and a top surface and arranged on the lead frame so that the bottom surface faces the lead frame, and an encapsulating resin body (44) that encapsulates the semiconductor chip so that it is in contact with the top surface, wherein the linear expansion coefficient of the fixed structure is greater than the linear expansion coefficient of the printed circuit board, and the semiconductor package is mounted on one surface, an electronic device described in any one of Technical Ideas 1 to 13.

[0171] <Technical Idea 15> The semiconductor package comprises a lead frame (42), a semiconductor chip (43) having a bottom surface and a top surface and arranged on the lead frame so that the bottom surface faces the lead frame, and an encapsulating resin body (44) that encapsulates the semiconductor chip so that it is in contact with the top surface, wherein the linear expansion coefficient of the fixed structure is smaller than the linear expansion coefficient of the printed circuit board, and the semiconductor package is mounted on the back surface, an electronic device described in any one of Technical Ideas 1 to 13.

[0172] <Technical Idea 16> The electronic device according to any one of Technical Ideas 1 to 13, wherein the semiconductor package has a lead frame (42), a semiconductor chip (43) arranged on the lead frame, a metal plate (45) arranged on the semiconductor chip, and an encapsulating resin body (44) that encapsulates the semiconductor chip and the metal plate, wherein the linear expansion coefficient of the fixed structure is greater than the linear expansion coefficient of the printed circuit board, and the semiconductor package is mounted on the back surface.

[0173] <Technical Idea 17> The electronic device according to any one of Technical Ideas 1 to 13, wherein the semiconductor package has a lead frame (42), a semiconductor chip (43) arranged on the lead frame, a metal plate (45) arranged on the semiconductor chip, and a sealing resin body (44) that seals the semiconductor chip and the metal plate, wherein the linear expansion coefficient of the fixed structure is smaller than the linear expansion coefficient of the printed circuit board, and the semiconductor package is mounted on one surface.

[0174] <Technical Idea 18> The electronic device described in any one of Technical Ideas 1 to 13, wherein the semiconductor package is a multi-chip package, and the semiconductor package has a lead frame (42), a first semiconductor chip (43A) arranged on the lead frame, a second semiconductor chip (43B) arranged on the lead frame, a metal plate (45) arranged on the second semiconductor chip, and an encapsulating resin body (44) that encapsulates the first semiconductor chip, the second semiconductor chip, and the metal plate.

[0175] <Technical Idea 19> An electronic device according to any one of Technical Ideas 1 to 13, comprising: a first semiconductor package (41A) having a first lead frame (42A), a first semiconductor chip (43A) having a bottom surface and a top surface and arranged on the first lead frame so that the bottom surface faces the first lead frame, and a first sealing resin body (44A) that seals the first semiconductor chip so as to be in contact with the top surface; and a second semiconductor package (41B) having a second lead frame (42B), a second semiconductor chip (43B) arranged on the second lead frame, a metal plate (45) arranged on the second semiconductor chip, and a second sealing resin body (44B) that seals the second semiconductor chip and the metal plate, wherein the first semiconductor package and the second semiconductor package are mounted on a common surface of the printed circuit board, and one of the first semiconductor package and the second semiconductor package is the semiconductor package that warps in a direction opposite to a direction of warping of the printed circuit board during temperature changes.

Claims

1. A printed circuit board (30) having a front surface (301) and a back surface (302) which is opposite to the front surface in the thickness direction, a surface-mounted semiconductor package (41) mounted on the printed circuit board, and a fixing structure (21) having a portion facing the front surface. The printed circuit board has a plurality of fixing holes (31) for fixing the printed circuit board to the fixing structure. When the temperature fluctuates, the warping direction of the printed circuit board and the warping direction of the semiconductor package are in directions along the thickness direction and are opposite to each other. The printed circuit board has a stress relaxation portion (32) for relaxing the stress acting on the mounting portion of the semiconductor package due to the different warping directions. An electronic device.

2. The electronic device according to claim 1, wherein the semiconductor package is a non-lead package.

3. The electronic device according to claim 2, wherein the stress relaxation portion is provided around the fixing hole.

4. The electronic device according to claim 3, wherein the stress relaxation portion includes a portion that relaxes the stress by elastic deformation.

5. The electronic device according to claim 4, wherein the stress relaxation portion is provided individually for the fixing holes and includes a slit (321) that penetrates the printed circuit board in the thickness direction and a partition portion (322) that is partitioned by the slit and in which the fixing hole is provided.

6. The electronic device according to claim 5, wherein the slit is arranged so as to cross at least one of a plurality of virtual straight lines that virtually connect different fixing holes in a plan view in the thickness direction.

7. The electronic device according to claim 6, wherein at least one slit is arranged so as to cross all the virtual straight lines.

8. The electronic device according to claim 5, wherein the slit opens to a side surface of the printed circuit board.

9. The printed circuit board has a rectangular shape in a plan view in the thickness direction. The slit opens to a first side surface of the printed circuit board and extends from the first side surface toward a second side surface located opposite to the first side surface. The electronic device according to claim 8.

10. The printed circuit board is provided separately from the first fixing hole which is the fixing hole, and has a second fixing hole (33) for reinforcing the fixing of the printed circuit board to the fixing structure. The second fixing hole is provided in a region surrounded by all the slits. The electronic device according to claim 5.

11. The stress relaxation portion includes an unpenetrated groove (323), and a thin portion (324) that is adjacent to the groove in the plate thickness direction and connects a portion on the fixing hole side of the groove and a portion on the side opposite to the fixing hole via the groove. The electronic device according to claim 4.

12. The printed circuit board has a main body portion (35) and an extended portion (325) that extends from the main body portion and in which the fixing hole is provided. The stress relaxation portion includes the extended portion. The electronic device according to claim 4.

13. The extended portion includes a first extended portion (3251) that extends in a predetermined direction and a second extended portion (3252) that is continuous with the first extended portion and extends in a direction different from the predetermined direction. The electronic device according to claim 12.

14. The semiconductor package has a lead frame (42), a semiconductor chip (43) disposed on the lead frame such that the lower surface and the upper surface thereof face the lead frame, and a sealing resin body (44) that seals the semiconductor chip so as to contact the upper surface. The linear expansion coefficient of the fixing structure is larger than the linear expansion coefficient of the printed circuit board. The semiconductor package is mounted on the one surface. The electronic device according to any one of claims 1 to 13.

15. The semiconductor package has a lead frame (42), a semiconductor chip (43) disposed on the lead frame such that the lower surface and the upper surface thereof face the lead frame, and a sealing resin body (44) that seals the semiconductor chip so as to contact the upper surface. The linear expansion coefficient of the fixing structure is smaller than the linear expansion coefficient of the printed circuit board. The semiconductor package is mounted on the back surface. The electronic device according to any one of claims 1 to 13.

16. The semiconductor package includes a lead frame (42), a semiconductor chip (43) disposed on the lead frame, a metal plate member (45) disposed on the semiconductor chip, and a sealing resin body (44) that seals the semiconductor chip and the metal plate member. The linear expansion coefficient of the fixing structure is greater than that of the printed circuit board. The semiconductor package is mounted on the back surface, and is the electronic device according to any one of claims 1 to 13.

17. The semiconductor package includes a lead frame (42), a semiconductor chip (43) disposed on the lead frame, a metal plate member (45) disposed on the semiconductor chip, and a sealing resin body (44) that seals the semiconductor chip and the metal plate member. The linear expansion coefficient of the fixing structure is smaller than that of the printed circuit board. The semiconductor package is mounted on the one surface, and is the electronic device according to any one of claims 1 to 13.

18. The semiconductor package is a multi-chip package. The semiconductor package includes a lead frame (42), a first semiconductor chip (43A) disposed on the lead frame, a second semiconductor chip (43B) disposed on the lead frame, a metal plate member (45) disposed on the second semiconductor chip, and a sealing resin body (44) that seals the first semiconductor chip, the second semiconductor chip, and the metal plate member, and is the electronic device according to any one of claims 1 to 13.

19. A first semiconductor package (41A) having a first lead frame (42A), a first semiconductor chip (43A) having a lower surface and an upper surface and disposed on the first lead frame such that the lower surface faces the first lead frame, and a first encapsulation resin body (44A) that encapsulates the first semiconductor chip so as to contact the upper surface; a second semiconductor package (41B) having a second lead frame (42B), a second semiconductor chip (43B) disposed on the second lead frame, a metal plate member (45) disposed on the second semiconductor chip, and a second encapsulation resin body (44B) that encapsulates the second semiconductor chip and the metal plate member; wherein the first semiconductor package and the second semiconductor package are mounted on a common surface of the printed circuit board, and one of the first semiconductor package and the second semiconductor package is the semiconductor package in which the direction of warping during temperature variation is opposite to the direction of warping of the printed circuit board. The electronic device according to any one of claims 1 to 13.

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