Circuit board and electronic component-attached circuit board

Abstract

A circuit board (1) has a substrate (11) having one surface on which a pad (21) is disposed. The pad (21) includes a rectangular heat dissipation part (31) and a plurality of terminal parts (32). An exposed pad (7) on the bottom surface of an electronic component (5) is soldered to the heat dissipation part (31). The terminal parts (32) are arranged outside the heat dissipation part (31) along the rectangle of the heat dissipation part (31), and have terminal pads (6) of the electronic component (5) soldered thereto. First recessed sections (41) and second recessed sections (42) are formed in the heat dissipation part (31). The first recessed sections (41) and the second recessed sections (42) are disposed so as to correspond to a first segmentation line (51) and a second segmentation line (52) that are each parallel to a respective edge of two adjacent edges of the heat dissipation part (31). The portions of the heat dissipation part (31) that are adjacent to each other across the first segmentation line (51) are integrally connected to each other, and the portions thereof that are adjacent to each other across the second segmentation line (52) are integrally connected to each other.

Description

Circuit boards and circuit boards with electronic components

[0001] The present invention relates to a circuit board.

[0002] 2. Description of the Related Art Conventionally, circuit boards provided with pads or lands for electrically connecting to electronic components have been known. Patent Document 1 discloses such a circuit board.

[0003] The circuit board of Patent Document 1 includes a substrate having multiple layers made of conductive materials. Lands are provided on a first layer, which is the layer arranged on one side of the substrate. Electronic components are soldered to the lands. A heat dissipation section is provided on the layer arranged on the substrate. The heat dissipation section is provided on a layer different from the first layer. A via hole is provided extending from a portion of the land to a portion of the heat dissipation section. The via hole is electrically connected to the land and the heat dissipation section. In the circuit board, an insulating resist is provided on the land. The insulating resist is configured to surround the entire periphery of the via hole. Furthermore, the embodiments of Patent Document 1 describe that the land is composed of multiple partition lands partitioned by the resist.

[0004] Japanese Patent Application Laid-Open No. 2022-120923

[0005] Consider a case where the circuit board of Patent Document 1 is installed near an automobile engine, for example. The circuit board and electronic components, which are soldered together, deform as the ambient temperature changes. Typically, the circuit board and electronic components have different thermal expansion coefficients. Therefore, a large load is applied to the solder due to thermal deformation, reducing the reliability of the electrical connection.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a circuit board that reduces the load on the solder. Means to solve the problem and effects

[0007] The problem to be solved by the present invention is as described above. Next, the means for solving this problem and the effects thereof will be explained.

[0008] According to an aspect of the present invention, there is provided a circuit board having the following configuration. That is, this circuit board is for mounting electronic components. The circuit board has a plate-shaped base material and pads arranged on one surface of the base material. The pads have a rectangular heat dissipation portion and a plurality of terminal portions. The bottom surface of the electronic component is soldered to the rectangular heat dissipation portion. The terminal portions are arranged outside the heat dissipation portion along the rectangle of the heat dissipation portion, and the terminal pads of the electronic component are soldered to the terminal portions. The heat dissipation portion is formed with a first recess and a second recess. The first recess is arranged corresponding to a first partition line parallel to one of two adjacent sides of the heat dissipation portion. The second recess is arranged corresponding to a second partition line parallel to the other of the two sides. Adjacent portions of the heat dissipation portion across the first partition line are connected together via a periphery of the first recess. Adjacent portions of the heat dissipation portion across the second partition line are connected together via a periphery of the second recess.

[0009] In this way, neither the first recess nor the second recess completely separates the heat dissipation section, forming a single, continuous heat dissipation section. Therefore, even if the circuit board and electronic components deform due to temperature changes, the four areas deform independently to some extent, allowing the deformation to be accommodated without significantly reducing the rigidity of the heat dissipation section itself, thereby preventing excessive deformation of the circuit board and electronic components. Furthermore, because the heat dissipation section extends to the four corners of the rectangle where the terminals are arranged, deformation of the circuit board near the four corners can be effectively suppressed. Therefore, the load on the solder of the terminals near the four corners is reduced, resulting in excellent reliability of the electrical connection at the terminals.

[0010] In the circuit board, it is preferable that the first recess and the second recess are each formed so as to open an outer edge of the heat dissipation portion.

[0011] As a result, the outer edge and its vicinity of the heat dissipation section are divided by the first recess and the second recess, which increases the degree of freedom of deformation of each area of ​​the heat dissipation section, particularly in the four corners, and thus makes it possible to flexibly suppress deformation of the four corners.

[0012] In the circuit board, it is preferable that a through-hole be formed in at least one of the first recess and the second recess.

[0013] This allows heat from the exposed pad to escape to the opposite surface of the circuit board through the via hole facing the exposed pad, thereby improving the heat dissipation effect of the electronic component.

[0014] In the circuit board, it is preferable that a cutout be formed in the center of the heat dissipation portion.

[0015] This allows the four areas to move with greater freedom through the combination of the first recess, the second recess, and the cutout, thereby flexibly suppressing deformation of the circuit board.

[0016] In the circuit board, it is preferable that a through-hole be formed in the cutout portion.

[0017] This allows heat from the exposed pad to escape to the opposite surface of the circuit board through the via hole facing the exposed pad, thereby improving the heat dissipation effect of the electronic component.

[0018] According to another aspect of the present invention, there is provided a circuit board with an electronic component, comprising the circuit board described above and the electronic component, the electronic component being soldered to the heat dissipation portion and the terminal portion.

[0019] 1 is a plan view of a circuit board according to an embodiment of the present invention; FIG. 2 is a perspective view showing a circuit board and an electronic component; FIG. 3 is a cross-sectional view taken along line B-B in FIG. 2 , showing an enlarged view of a portion where a terminal pad of an electronic component and a terminal portion of the circuit board are soldered; FIG. 4 is a cross-sectional view taken along line A-A in FIG. 1 , showing a schematic view of deformation when heat is applied to a circuit board of the present embodiment with an electronic component mounted thereon; FIG. 5 is a cross-sectional view showing a schematic view of deformation when heat is applied to a circuit board of a comparative example with an electronic board mounted thereon; FIG. 6 is a plan view of a circuit board of a control example; FIG. 7 is a plan view of a first modified example of the circuit board; FIG. 8 is a plan view of a second modified example of the circuit board.

[0020]

[0023] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is an overall view of a circuit board 1 according to an embodiment of the present invention. Fig. 2 is a perspective view showing the circuit board 1 and an electronic component 5.

[0021] The circuit board 1 is configured as a printed circuit board and includes a substrate 11 and a conductor pattern 12 .

[0022] In this embodiment, the circuit board 1 constitutes a battery state detection device (not shown) installed in an automobile. The battery state detection device includes a shunt resistor for detecting the output current of the automobile battery. The principle of detecting the output current of the battery using a shunt resistor is well known, so a description thereof will be omitted.

[0023] The base material 11 is an electrically insulating plate material. The base material 11 is made of, for example, a glass epoxy plate material, but the material is not particularly limited.

[0024] The conductor pattern 12 is made of, for example, copper foil and is fixed to the base material 11 by an appropriate method such as adhesive. In this embodiment, the conductor pattern 12 is disposed on both surfaces of the base material 11 in the thickness direction, but may be disposed on only one surface.

[0025] The conductive pattern 12 includes a pad 21 disposed on one surface in the thickness direction of the substrate 11. The electronic component 5 shown in FIG.

[0026] In this embodiment, the electronic component 5 is a surface-mount integrated circuit having an exterior conforming to a standard called QFN, which stands for Quad Flat Non-leaded package.

[0027] To briefly explain QFN, it is one of the package standards for integrated circuits. QFN is characterized by a rectangular package made of synthetic resin, with multiple terminal pads 6 arranged in a row on each side. The terminal pads 6 may be exposed on the four sides and the bottom of the package, or only on the bottom. An electronic component 5 conforming to the QFN standard may have a metal pad exposed in the center of the bottom of the package. This metal pad exposed on the bottom is called an exposed pad 7. The terminal pads 6 are arranged in a row surrounding the exposed pad 7.

[0028] Pad 21 on the circuit board 1 side has one heat dissipation portion 31 and multiple terminal portions 32. Exposed pad 7 of electronic component 5 is soldered to heat dissipation portion 31. Terminal pad 6 of electronic component 5 is soldered to terminal portion 32. Soldering is performed by a known method including printing cream solder on circuit board 1 and heating in a reflow furnace.

[0029] The heat dissipation portion 31 is formed in a rectangular shape corresponding to the exposed pad 7 which is rectangular.

[0030] The terminal portions 32 are arranged in a row along the four sides of the rectangular shape of the heat dissipation portion 31. Each of the terminal portions 32 has an elongated rectangular shape.

[0031] Next, the shape of the heat dissipation portion 31 will be described in detail.

[0032] The outer contour of the heat dissipation portion 31 has a pair of first recesses 41 and a pair of second recesses 42. The first recesses 41 and the second recesses 42 are each formed to penetrate the heat dissipation portion 31 in the thickness direction.

[0033] Consider a first dividing line 51 that extends parallel to one of two adjacent sides of the heat dissipation section 31 and is arranged to divide the heat dissipation section 31 into two equal parts. A pair of first recesses 41 are formed elongated along this imaginary first dividing line 51. The pair of first recesses 41 are arranged to face each other in the direction of the first dividing line 51, with the center position of the heat dissipation section 31 in between.

[0034] Similarly to the above, consider a second partition line 52 that extends parallel to the other of the two adjacent sides of the heat dissipation section 31 (in other words, perpendicular to the first partition line 51) and is arranged so as to divide the heat dissipation section 31 in half. The first partition line 51 and the second partition line 52 intersect in a crisscross pattern at the center of the heat dissipation section 31. A pair of second recesses 42 are formed elongated along this imaginary second partition line 52. The pair of second recesses 42 are arranged so as to face each other in the direction of the second partition line 52, with the center position of the heat dissipation section 31 in between.

[0035] In other words, the pair of first recesses 41 and the pair of second recesses 42 are arranged radially from the center position of the heat dissipation portion 31. As shown in FIG. 1 , the pair of first recesses 41 and the pair of second recesses 42 are formed so as not to completely divide the heat dissipation portion 31. Therefore, adjacent portions of the heat dissipation portion 31 on either side of the first partition line 51 are integrally connected via the periphery of the first recess 41 (specifically, the portion toward the center of the rectangular heat dissipation portion 31). Furthermore, adjacent portions of the heat dissipation portion 31 on either side of the second partition line 52 are integrally connected via the periphery of the second recess 42 (specifically, the portion toward the center of the rectangular heat dissipation portion 31).

[0036] A circular cutout 43 is formed in the center of the heat dissipation section 31. The cutout 43 is formed so as to penetrate the heat dissipation section 31 in the thickness direction. The center of the cutout 43 coincides with the point where the first partition line 51 and the second partition line 52 intersect. The pair of first recesses 41 are arranged to face each other with the cutout 43 in between, and the pair of second recesses 42 are arranged to face each other with the cutout 43 in between.

[0037] In this way, although the rigidity of the heat dissipation section 31 in this embodiment is slightly weakened by the first recess 41, the second recess 42, and the cut-out section 43, the overall integrity of the four areas separated by the first dividing line 51 and the second dividing line 52 is maintained.

[0038] Consider a case where the heat dissipation portion 31p is provided in four completely separated areas, as shown in the comparative example of FIG. 5 . In FIGS. 5 and 6 , components identical or similar to those in the above embodiment are denoted by the same reference numerals, and their description will be omitted. The heat dissipation portion 31p is fixed to the exposed pad 7 via solder 8 in each of the four areas. Because FIG. 5 is a cross-sectional view, only two of the four areas are shown. In the comparative example of FIG. 5 , the four areas have too much freedom to deform / move due to thermal deformation of the substrate 11 or electronic component 5, resulting in significant relative displacement between the substrate 11 and the electronic component 5, particularly near the four corners of the heat dissipation portion 31. Therefore, at the terminal portions 32 located near the four corners of the heat dissipation portion 31, a heavy load is likely to be applied to the solder 8 that secures the terminal portions 32 to the terminal pads 6, increasing the risk of solder cracks and the like.

[0039] 4 , in this embodiment, the four areas included in the heat dissipation section 31 are fixed to the exposed pad 7 via solder 8 in a state where they are partially but integrally connected. Therefore, according to the configuration of this embodiment, the portion corresponding to the heat dissipation section 31 can be constrained with a certain degree of gradualness so as to suppress thermal deformation of the substrate 11 or the electronic component 5. As a result, relative displacement between the substrate 11 and the electronic component 5 is suppressed particularly in the portions near the four corners of the heat dissipation section 31, and therefore the load applied to the solder 8 that fixes the terminal portion 32 to the terminal pad 6 can be reduced in the terminal portion 32 located near the four corners of the heat dissipation section 31.

[0040] Next, the effect of the heat dissipation portion 31 being formed in this embodiment so as to extend to the vicinity of the four corners of the rectangle in which the terminal portions 32 are arranged will be described.

[0041] Consider a configuration in which the heat dissipation portion 31q does not extend to the four corners, as shown in the comparative example of FIG. 6 . In the comparative example of FIG. 6 , the four corners of the heat dissipation portion 31q are notched, so the four corners of the rectangular exposed pad 7 are not solder-bonded to the heat dissipation portion 31q. Therefore, it is difficult to suppress deformation of the circuit board 1 corresponding to the portion surrounded by the dashed line in FIG. 6 . As a result, a large load is likely to be applied to the solder 8 that secures the terminal portion 32 to the terminal pad 6 at the terminal portion 32 located near the four corners. Furthermore, since a large bonding area cannot be secured between the exposed pad 7 and the heat dissipation portion 31q, the heat dissipation effect of the electronic component 5 is reduced.

[0042] 1, in this embodiment, the four corners of the heat dissipation portion 31 are located near the four corners of the rectangle in which the terminal portions 32 are arranged. Therefore, relative displacement between the substrate 11 and the electronic component 5 near the four corners of the exposed pad 7 can be effectively suppressed, and the load on the solder 8 that secures the terminal portions 32 to the terminal pads 6 can be reduced in the terminal portions 32 located near the four corners. Furthermore, because the exposed pad 7 and the heat dissipation portion 31 are joined over a wide area, the heat dissipation effect of the electronic component 5 can be effectively exhibited.

[0043] As described above, the heat dissipation portion 31 is formed in a substantially rectangular shape, but small arc-shaped fillets 44 are formed at the four corners thereof, which can prevent peeling of the heat dissipation portion 31. Although not shown in the drawings, it is preferable to also form fillets at the four corners of each terminal portion 32.

[0044] Through-holes 45 are formed in the circuit board 1 in the portions where the pair of first recesses 41 are formed and in the portions where the cutouts 43 are formed. As shown in Fig. 2, the via holes 45 are arranged so as to face the exposed pads 7 of the electronic components 5. This allows heat from the exposed pads 7 to escape to the opposite surface of the circuit board 1, thereby improving the heat dissipation efficiency of the electronic components 5.

[0045] Each of the pair of first recesses 41 is formed so that the vicinity of the open end is wider. In this way, the first recesses 41 are provided with wider portions, so that it is easy to ensure space for arranging the via holes 45.

[0046] Resist (not shown) is disposed on the surface of the substrate 11 in the first recess 41, the second recess 42, and the cutout 43. This prevents cream solder from entering the first recess 41, the second recess 42, and the cutout 43 when the electronic component 5 is mounted. This prevents the solder from leaking out through, for example, the via hole 45.

[0047] 1, appropriate gaps L1 and L2 are formed between the heat dissipation portion 31 and the terminal portion 32. In this embodiment, the gaps L1 and L2 between the heat dissipation portion 31 and the terminal portion 32 are wider than the gap between adjacent terminal portions 32. Setting the gaps L1 and L2 to 0.25 millimeters or more is preferable because it is possible to prevent an electrical short circuit between the heat dissipation portion 31 and the terminal portion 32.

[0048] It is preferable that the width L3 of the first recess 41 and the width L4 of the second recess 42 are both 0.3 millimeters or more, since this effectively reduces the load on the solder 8 due to the thermal deformation described above.

[0049] The circuit board 1 of this embodiment is assumed to have an electronic component 5 with a length of 6 mm and a width of 6 mm, but is not limited to this. When a larger electronic component 5 is mounted, the above-mentioned intervals L1 and L2 can be made larger than 0.25 mm, and the widths L3 and L4 can be made larger than 0.3 mm.

[0050] As described above, the circuit board 1 of this embodiment is used to mount electronic components 5. The circuit board 1 has a plate-shaped base material 11 and pads 21. The pads 21 are arranged on one surface of the base material 11. The pads 21 have rectangular heat dissipation sections 31 and multiple terminal sections 32. Exposed pads 7 on the bottom surfaces of electronic components 5 are soldered to the rectangular heat dissipation sections 31. The terminal sections 32 are arranged outside the heat dissipation sections 31 along the rectangular shape of the heat dissipation sections 31, and electrodes of the electronic components 5 are soldered to the terminal sections 32. A first recess 41 and a second recess 42 are formed in the heat dissipation sections 31. The first recess 41 is arranged to correspond to a first partition line 51 parallel to one of two adjacent sides of the heat dissipation sections 31. The second recess 42 is arranged to correspond to a second partition line 52 parallel to the other of the two sides. Adjacent portions of the heat dissipation section 31 across the first partition line 51 are connected together via the periphery of the first recess 41. Adjacent portions of the heat dissipation section 31 across the second partition line 52 are connected together via the periphery of the second recess 42.

[0051] In this configuration, when considering four adjacent areas of the heat dissipation portion 31 sandwiched between the first and second partition lines 51 and 52, these four areas are partially separated and partially connected by the first and second recesses 41 and 42. Therefore, even if the circuit board 1 and electronic components 5 attempt to deform due to temperature changes, the four areas deform somewhat independently to accommodate, and the rigidity of the heat dissipation portion 31 itself does not decrease significantly, thereby preventing excessive deformation of the circuit board 1 and electronic components 5. Because the heat dissipation portion 31 extends to the four corners of the rectangle in which the terminal portions 32 are arranged, deformation of the circuit board 1 near the four corners can be effectively suppressed. Therefore, the load on the solder of the terminal portions 32 near the four corners is reduced, resulting in excellent reliability of the electrical connection at the terminal portions 32.

[0052] In the circuit board 1 of this embodiment, the first recess 41 and the second recess 42 are each formed so as to open the outer edge of the heat dissipation portion 31 .

[0053] As a result, the outer edge and its vicinity of the heat dissipation section 31 among the four areas are divided by the first recess 41 and the second recess 42. Therefore, the degree of freedom of deformation of each area of ​​the heat dissipation section 31, particularly in the four corner portions, is increased, and deformation of the four corner portions can be flexibly suppressed.

[0054] In the circuit board 1 of this embodiment, a through-hole 45 is formed in at least one of the first recess 41 and the second recess 42 .

[0055] This allows heat from exposed pad 7 to escape to the opposite surface of circuit board 1 through via hole 45 facing exposed pad 7. This improves the heat dissipation effect of electronic component 5.

[0056] In the circuit board 1 of this embodiment, a cutout 43 is formed in the center of the heat dissipation portion 31 .

[0057] The combination of the first recess 41, the second recess 42, and the cutout 43 can increase the degree of freedom for movement of the four areas, thereby flexibly suppressing deformation of the circuit board 1.

[0058] In the circuit board 1 of this embodiment, a through-hole 45 is formed in the cutout portion 43 .

[0059] This allows heat from exposed pad 7 to escape to the opposite surface of circuit board 1 through via hole 45 facing exposed pad 7. This improves the heat dissipation effect of electronic component 5.

[0060] Next, modifications of the above embodiment will be described. In the description of the modifications from FIG. 7 onward, the same reference numerals will be used to designate the same or similar components as those in the above embodiment, and the description thereof may be omitted.

[0061] 7, the via holes 45 are omitted from the first recess 41. Accordingly, the width of the first recess 41 is constant, unlike the embodiment of FIG.

[0062] 8, the circuit board 1 of the second modification has a first recess 41 and a second recess 42 that are linear and are arranged so as to intersect with each other at the center of the heat dissipation portion 31. Neither the first recess 41 nor the second recess 42 reaches the outer edge of the heat dissipation portion 31.

[0063] 8, a cutout 43 may be formed at the intersection of the first recess 41 and the second recess 42. In this case, it can be considered that the pair of first recesses 41 and the pair of second recesses 42 are formed so as to be open on the cutout 43 side formed in the center of the heat dissipation portion 31.

[0064] The preferred embodiment and modifications of the present invention have been described above, but the above configurations can be modified, for example, as follows. Each modification may be made alone, or multiple modifications may be made in any combination.

[0065] The first recess 41 is not limited to being formed elongated along the first partition line 51, and may have any shape. The same applies to the second recess 42. For example, the first recess 41 and the second recess 42 may be formed in a semicircular shape.

[0066] 1, at least one of the punched portion 43, the fillet 44, and the via hole 45 may be omitted. The via hole 45 may be disposed in both the first recess 41 and the second recess 42.

[0067] The electronic component 5 may be of the QFP type instead of the QFN type. QFP is an abbreviation for Quad Flat Package.

[0068] The circuit board 1 can be applied to an automobile device other than the battery state detection device, and can also be applied to a device other than an automobile device.

Claims

1. A circuit board for mounting electronic components, comprising: a plate-shaped base material; and a pad arranged on one surface of the base material, wherein the pad has: a rectangular heat dissipation section to which the bottom surface of the electronic component is soldered; and a plurality of terminal sections arranged outside the heat dissipation section along the rectangle of the heat dissipation section, and to which terminal pads of the electronic component are soldered; wherein the heat dissipation section is formed with a first recess arranged to correspond to a first dividing line parallel to one of two adjacent sides of the heat dissipation section, and a second recess arranged to correspond to a second dividing line parallel to the other of the two sides, wherein adjacent portions of the heat dissipation section on either side of the first dividing line are connected together via the periphery of the first recess, and adjacent portions of the heat dissipation section on either side of the second dividing line are connected together via the periphery of the second recess.

2. A circuit board according to claim 1, wherein each of the first recess and the second recess is formed so as to open the outer edge of the heat dissipation portion.

3. A circuit board according to claim 1, characterized in that a through-hole is formed in at least one of the first recess and the second recess.

4. A circuit board according to any one of claims 1 to 3, characterized in that a cutout is formed in the center of the heat dissipation section.

5. The circuit board according to claim 4, wherein a through-hole is formed in the cutout portion.

6. A circuit board with electronic components comprising: the circuit board according to claim 1; and the electronic components soldered to the heat dissipation portion and the terminal portion.

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