POWER MODULE, POWER SEMICONDUCTOR UNIT AND METHOD FOR MANUFACTURING A POWER MODULE

Abstract

Power module (20) comprising: a power element (4), a metal base (3) for dissipating heat from the power element (4), a lead frame (1) electrically connected to electrodes of the power element (4), and a resin encapsulation (7) encapsulating the power element (4) such that one surface of the metal base (3) and a part of the lead frame (1) are exposed from the encapsulation, wherein the resin encapsulation (7) comprises: - a body portion (10) in which the power element (4) and a part of the lead frame (1) are arranged and on the lower surface (10b) of which one surface of the metal base (3) is exposed; and - a rib portion (11) disposed on the lower surface (10b) of the body portion (10) so as to surround an outer periphery of the metal base (3) and formed to protrude from the lower surface (10b) of the body portion (10) in a direction perpendicular to the lower surface (10b); wherein the rib portion (11) has a recess (101) at its end protruding from the lower surface (10b), and wherein the recess (101) has a depth which is greater than the width (ws1, ws2) in a transverse direction of the end of the rib portion (11).

Description

TECHNICAL FIELD

[0001] The present invention relates to a power module and a power semiconductor unit provided with the power module and a heat sink. STATE OF THE ART

[0002] Power modules are used in a wide variety of devices, from industrial equipment to consumer or household electronics and information terminals, to control a power supply (for power control). Some examples of power modules include inverters for converting DC power to AC power, and the like. Because such power modules operate at high current and high voltage, it is considered important that they ensure high electrical insulation and allow heat generated during operation to escape efficiently to the exterior of the power modules.

[0003] For example, Patent Document 1 discloses a power semiconductor unit (a power module) in which a plurality of power semiconductor elements (power elements) are bonded to a heat dissipation plate using solder and encapsulated by a molded resin package. The power semiconductor unit according to Patent Document 1 is sandwiched between: a holding plate disposed on an upper surface of the molded resin package; and a heat dissipation fin (a heat sink) in contact with the lower surface where the heat dissipation plate (the metal base) is exposed through a thermally conductive grease; and the power semiconductor unit is fixed to the heat dissipation fin by means of a screw inserted into a through-hole formed in the holding plate, the molded resin package, and the heat dissipation plate.

[0004] Furthermore, in the power semiconductor device according to Patent Document 1, respective ends of a plate-like wiring element (a lead frame) connected to electrodes of the plurality of semiconductor elements protrude as external electrodes from lateral surfaces of the molded resin package. The electrodes on the front surface of the semiconductor elements are connected to the wiring element via wires, and the electrodes on the back surface of the semiconductor elements are connected to the wiring element via the heat dissipation plate.

[0005] Meanwhile, in each of a semiconductor module (a power module) in Patent Document 2 and a power module in Patent Document 3, respective end portions of an exposed material member exposed on the surface disposed toward the heat dissipation plate are each covered with an encapsulating resin to form a fin.

[0006] Patent Document 4 discloses a power module comprising: a heat radiation layer having a first main surface and an opposite second main surface; an insulating layer disposed on the first main surface of the heat radiation layer; a wiring portion for a power circuit disposed on the insulating layer; a plurality of switching elements disposed on the insulating layer and electrically connected to the wiring portion; a plurality of external terminals electrically connected to the wiring portion; and a resin sealing the insulating layer, the wiring portion, the switching elements, and the first main surface of the heat radiation layer, as well as a portion of the second main surface of the heat radiation layer.

[0007] From Patent Document 5, a semiconductor package is known which comprises: an inner terminal having at least one electronic component mounted on a surface thereof; a heat sink disposed below the inner terminal; a molded portion sealing the at least one electronic component, the inner terminal, and the heat sink; an outer terminal extending from the inner terminal and projecting outward from the molded portion in the radial direction; a heat radiating member mounted on the heat sink and a surface of the molded portion; and an insulating coating layer formed on a surface of the outer terminal.

[0008] Patent Document 6 discloses a semiconductor device comprising: a semiconductor element; a mounting portion for securely mounting the semiconductor element; inner leads electrically connected to the semiconductor element; connecting means for electrically connecting the semiconductor element to the inner leads; a heat radiation plate disposed facing the semiconductor element with the mounting portion therebetween and separated from the mounting portion by a predetermined distance; a sealing material for sealing the semiconductor element, the mounting portion, the inner leads, the connecting means, and the heat radiation plate; and outer leads extending from the inner leads to the outside of the sealing material. The heat radiation plate has an outer peripheral adjacent portion sealed in a frame configuration with the sealing material.Furthermore, a rear surface of the heat radiation plate facing away from the mounting region has a central region which is not part of the outer edge adjacent region and is not covered with the sealing material, wherein the central region of the rear surface is exposed as the outer side of the semiconductor device.

[0009] Patent Document 7 discloses a chip carrier comprising: a first side; a second side opposite to the first side and last removed from an engagement surface of a mold in a demolding process; and at least one grounding means formed on the second side and corresponding in position to an ejector pin of the mold. LITERATURE LISTPatent documents Patent Document 1: Japanese Patent Application Laid-Open No. JP 2004-165406 A (paragraphs

[0010] to

[0016] and Fig. 7) Patent Document 2: International Patent Application Publication WO 2015 / 145 752 A1 ( Fig. 3, Fig. 8 and Fig. 13) Patent Document 3: Japanese Patent Application Laid-Open No. JP 2003-31765 A ( Fig. 1) Patent document 4: US 2008 / 0 106 160 A1 Patent document 5: US 2014 / 0 001 613 A1 Patent document 6: DE 197 00 056 A1 Patent document 7: US 2004 / 0 072 389 A1 SUMMARY OF THE INVENTION Problems to be solved by the invention

[0010] For such a power module in which power elements connected to a metal base are encapsulated with a resin as in the power module according to Patent Document 1, it is necessary to insulate its outer electrode, which is arranged as one end of the lead frame connected to the electrodes on the front surface of the power elements, from the metal base connected to the electrode on the rear surface of the power element.

[0011] The insulation distance between the lead frame protruding from the resin and the metal base exposed from the resin is determined by the resin creepage distance between the lead frame and the metal base. To ensure the necessary insulation distance, the distance between the outer periphery of the metal base and the outer periphery of the resin must be sufficiently maintained.

[0012] The higher the electrical power of the power module, the larger the insulation distance required according to the power involved. Therefore, to ensure a larger insulation distance, it is necessary to increase the distance between the lead frame and the metal base, specifically, by widening the power module laterally. Consequently, there is a problem in that the area of ​​the power module is increased, thus increasing the size of the power module.

[0013] A case may occur where the power module warps or buckles at its end portions relative to the plane of the power module's metal base, forming an indented shape. It is known that in this case, when the size of the power module is large, the thermal contraction of the encapsulating resin is significant, and thus the extent of warping or buckle tends to be significant. As the extent of warping or buckle of the power module increases, its area in contact with the heat sink relative to the power module's metal base becomes smaller, causing a problem in that the heat generated by the power element cannot be efficiently transferred to the heat sink, and the chip temperature of the power element thus increases.

[0014] Accordingly, a large-sized power module requires special measures for heat dissipation. One example of special measures for heat dissipation in a power module is to limit warping or buckling of the power module by applying pressure to increase the contact area between the metal base of the power module and the heat sink.

[0015] In order to allow the metal base of the power module to make contact with the heat sink over a large contact area, in order to limit the warping or distortion of the power module, a holding member such as the holding plate in Patent Document 1 is required, and thus there is a problem that the step of fixing the power module to the heat sink requires more time and becomes complicated.

[0016] Meanwhile, as shown in Patent Document 2, it is possible to increase the amount of encapsulating resin at the end portion of the power module by forming a rib or the like. However, there is a problem that the power module is enlarged when the width of the rib is increased. On the other hand, the power module warps or distorts with respect to the plane of the metal base. This becomes particularly significant when the module size becomes large, since the module is affected by the resin contraction ratio.

[0017] At a bottom surface portion located at the end portion of a power module, as shown in Patent Document 3, it is difficult to control the amount of warping or buckling. Thus, it is necessary to precisely control a linear expansion difference between the encapsulating resin and the frame member, resulting in reduced manufacturing margin.

[0018] This invention has been conceived to solve the problems as described above, and its object is to provide a power module with a small size, wherein the electrical insulation between the lead frame and the metal base is improved. Means to solve the problems

[0019] The problem is solved by a power module having the features of claim 1. Advantageous further developments of the power module arise from subclaims 2 to 11. Furthermore, the problem is solved by a power semiconductor unit having the features of claim 12. Advantageous further developments of the power semiconductor unit arise from subclaims 13 to 15. Furthermore, the problem is solved by a power module manufacturing method having the features of claim 16. An advantageous further development of the power module manufacturing method arises from subclaim 17. Effect of the invention

[0020] In the power module according to the invention, the body portion has a shape that is upwardly convex with respect to the exposed one surface of the metal base as a vertical reference, and is provided with the rib portion disposed on the lower surface of the body portion in the resin encapsulation so as to surround the outer periphery of the metal base, and formed to protrude from the lower surface of the body portion in a direction perpendicular to the lower surface. Thus, it is possible to downsize the lead module while improving the insulation between the lead frame and the metal base. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The figures show: Fig. 1 is a cross-sectional view of a power module according to Embodiment 1 of the invention; Fig. 2 a perspective view of the power module according to Fig. 1 when viewed from a side where a metal base is visible; Fig. 3 a view from below of the line module according to Fig. 1 when viewed from a side where the metal base is located; Fig. 4 an enlarged view of a rib region in the power module according to Fig. 1; Fig. 5 is a diagram showing an insulation distance of a power module of a comparative example; Fig. 6 is a cross-sectional view of a power module according to Embodiment 2 of the invention (not claimed); Fig. 7 is a cross-sectional view of a power module according to Embodiment 3 of the invention; Fig. 8 is a perspective view of a power module according to Embodiment 4 of the invention; Fig. 9 a view from below of the power module according to Fig. 8 when viewed from a side on which a metal base is arranged; Fig. 10 is a cross-sectional view of a power semiconductor device according to Embodiment 5 of the invention; Fig. 11 is a diagram showing an essential part of the power semiconductor unit according to Fig. 10 shows; Fig. 12 a perspective view of the power semiconductor unit according to Fig. 10; Fig. 13 is a perspective view of a power semiconductor unit according to Embodiment 7 of the invention; Fig. 14 is a perspective view of another power semiconductor unit according to Embodiment 7 of the invention; Fig. 15 is a cross-sectional view of another power module according to Embodiment 1 of the invention; Fig. 16 a perspective view of the power module according to Fig. 15 when viewed from a side where a metal base is visible; Fig. 17 is a diagram showing an intermediate product structure according to Embodiment 1 of the invention; Fig. 18 is a diagram illustrating a method of manufacturing a power module according to Embodiment 1 of the invention; Fig. 19 is a cross-sectional view of a molded article according to Embodiment 1 of the invention; Fig. 20 is a cross-sectional view of another molded article according to Embodiment 1 of the invention; Fig. 21 a cross-sectional view of the body of a molded article and the cover of a molded article in Fig. 20; Fig. 22 is a diagram illustrating the extent of warping or buckling of a power module; Fig. 23 is a diagram illustrating the extent of warping or warping of a power module in a plus direction; Fig. 24 is a diagram illustrating the extent of warping or distortion of the power module in a minus direction; Fig. 25 is a cross-sectional view of a power semiconductor unit according to Embodiment 6 of the invention; Fig. 26 is a bottom view of a power module according to Embodiment 8 of the invention when viewed from a side on which a metal base is arranged; Fig. 27 is a bottom view of a power module according to Embodiment 9 of the invention when viewed from a side on which a metal base is arranged. EMBODIMENTS OF THE INVENTION Embodiment 1

[0022] Fig. 1 is a cross-sectional view of a power module according to Embodiment 1 of the invention. Fig. 2 is a perspective view of the power module according to Fig. 1 when viewed from a side where a metal base is visible, and Fig. 3 is a bottom view of the power module according to Fig. 1 when viewed from a side where the metal base is located. Fig. 4 is an enlarged view of a fin portion in the power module according to Fig. 1.

[0023] Fig. 5 is a diagram illustrating an insulation distance of a power module of a comparative example, which is an enlarged view of a portion Fig. 4 corresponds. Fig. 1 is a cross-sectional view of a cut surface shown in Fig. 2 is marked with a broken line, when viewed from a direction A which has a vertically inverted relation to Fig. 2. It should be noted that a connection area 22 of a lead frame 1 in Fig. 3 is omitted from the illustration. A power module 20 includes the following: the lead frame 1, a metal base 3, power elements 4, an insulating sheet 5, and a resin encapsulation 7.

[0024] Examples of the power module 4 include: a diode to be used in a converter unit for converting input AC power into DC power; and a bipolar transistor, an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), a GTO (Gate Turn-Off Thyristor), and the like to be used in an inverter unit for converting DC power into AC power.

[0025] The insulating sheet 5 is an insulating layer with high heat dissipation performance that insulates a wiring portion 21 of the lead frame 1 from the metal base 3 and dissipates heat generated by the power elements 4 to the metal base 3. An epoxy or similar thermosetting resin containing a highly conductive filler of silicon dioxide, boron nitride (BN), or the like is used as the insulating sheet 5.

[0026] The metal base 3 dissipates heat from the power elements 4. A highly thermally conductive element, such as a copper plate, an aluminum plate, a copper foil, or the like, is used as the metal base 3. The lead frame 1 is formed into a structure by press-molding from a copper plate or an aluminum plate.

[0027] The lead frame 1 includes the wiring portion 21 and the terminal portion 22. The power elements 4 are mounted on the wiring portion 21, and electrodes on the rear surface of the power elements 4 are connected to that portion using solder or the like. Furthermore, wires 6 establish the connections between the plurality of power elements 4 and the connections between the electrodes on the front surface of the power elements 4 and the wiring portion 21. The lead frame 1 is electrically connected to these electrodes of the power elements 4.

[0028] The terminal portion 22 has a plurality of terminals 23a, 23b, 23c to be connected to an external device or the like. The respective terminals of the terminal portion 22 are bent in the shape of an L and are exposed from a body portion 10 of the resin encapsulation 7. Fig. 2 shows such an example in which five terminals 23a, five terminals 23b and five terminals 23c protrude in three directions around the power module 20.

[0029] In a central portion of the power module 20, a hole 18 is formed to penetrate the metal base 3 from an upper surface 10a of the resin encapsulant 7 to fix the power module 20 to a heat sink 16 (see FIG. 10) described later using a screw. Fig. 10). The terminals are collectively designated by reference numeral 23, and reference numerals 23a, 23b, 23c, 23d (see Fig. 8) are used when these are to be described in a different way.

[0030] The resin encapsulant 7 is formed from an epoxy or similar thermosetting resin, which is delivered as a product through a high-temperature molding process and ensures insulation between elements disposed within the resin encapsulant 7. A highly conductive filler of silicon dioxide, aluminum oxide, boron nitride, or the like is contained in the resin. Examples of how to achieve encapsulation using the resin include an injection molding process and a transfer molding process.

[0031] For power modules, a transfer molding process is generally used. The resin encapsulant 7 encapsulates the power elements 4 such that one surface of the metal base 3 (the exposed surface) and a part (in the terminal area 22) of the lead frame 1 are exposed from the encapsulant. The resin encapsulant 7 includes the body area 10 and a fin area 11. The power elements 4 and a part (in the terminal area 22) of the lead frame 1 are arranged in the body area 10, and one surface (the exposed surface) of the metal base 3 is exposed on the lower surface 10b thereof.

[0032] Exposing the metal base 3 makes it possible to reduce the surface area of ​​the resin, which has a hygroscopic property, thus preventing electrical malfunctions such as ion migration or the like due to moisture absorption. The rib portion 11 is arranged on the lower surface 10b of the body portion 10 so as to surround the outer periphery of the metal base 3 and is formed to protrude from the lower surface 10b of the body portion 10 in a direction perpendicular to the lower surface 10b.

[0033] The rib portion 11 has four ribs 2a, 2b, 2c, 2d near the outer periphery of the lower surface 10b of the body portion 10. The ribs are collectively designated by the reference numeral 2, and the reference numerals 2a, 2b, 2c, 2d are used when they are to be described distinctively.

[0034] The ribs 2 are respectively arranged on the lower surface 10b of the resin encapsulant 7 and outside the lateral surface of the metal base 3, and are formed to protrude with respect to the lower surface (the exposed surface) of the metal base 3 as a reference plane in a direction opposite to the direction in which the terminals 23 of the lead frame 1 are bent.

[0035] Furthermore, the cross-section of the Fig. 1 by a transverse cross section in a direction perpendicular to the direction in which it extends, that is, in a direction parallel to the lateral surface of the body portion 10. The transverse cross sections of the ribs 2 each have a tapered shape that becomes narrower toward the end thereof, so that the mold releasability of a molded article used for molding the resin encapsulant 7 is improved. Furthermore, the ribs 2 are arranged with the same height so as to surround (encapsulate) the lower surface (the exposed surface) of the metal base 3 in which the adjacent ribs are connected to each other.

[0036] Since the adjacent ribs are connected to each other, the rigidity of their edge portions in the rib portion 11 is improved, so that the bending rigidity of the power module 20 is improved in the directions toward the opposite edges (in the directions toward the three opposite edges). Note that it is desirable to apply an R-shape or a tapered shape to the edges of the rib 2 in order to improve the mold releasability of the molded article used at the time of molding the resin encapsulant 7.

[0037] Another power module that is Fig. 15 and Fig. 16 is shown as an example in which the rib 2 has a recess 101 having a circular shape on the top. Fig. 15 is a cross-sectional view of the further power module according to Embodiment 1 of the invention, and Fig. 16 is a perspective view of the power module according to Fig. 15 when viewed from a side where the metal base is visible. The recess 101 is positioned between the terminal 23 of the lead frame 1 and the metal base 3, thereby increasing the insulation distance between the terminal 23 of the lead frame 1 and the metal base 3. Accordingly, it is possible to reduce the width of the rib 2 by increasing the insulation distance by an amount corresponding to the recess.

[0038] This allows for a significant reduction in the module area. For example, the recess 101 is shown to have a circular shape; however, it may also have a polygonal shape, such as a triangular shape, a square shape, a pentagonal shape, a hexagonal shape, an octagonal shape, or the like.

[0039] The power elements 4 are mounted on the wiring portion 21 of the lead frame 1. The insulating sheet 5 and the metal base 3 are arranged on a surface of the lead frame 1 opposite to the surface on which the power elements 4 are mounted. The power elements 4, the lead frame 1, the wires 6, the insulating sheet 5, and the metal base 3 are covered by the resin encapsulant 7 in a state where the terminal portion 22 of the lead frame 1 and the lower surface of the metal base 3 are exposed. The heat generated by the power elements 4 is dissipated to the lead frame 1, the insulating sheet 5, and the metal base 3.

[0040] In the power module 20 according to Embodiment 1, at the time of molding the resin encapsulant 7, the lead frame 1 is disposed on a copper foil arranged as the metal base 3, on which a partially cured insulating sheet 5 is mounted. At this time, positioning of the copper foil relative to the molding body for molding the resin encapsulant 7 is performed in such a manner that movable pins are sequentially arranged in a longitudinal direction and in a transverse direction near an edge portion of the copper foil, and one set of these movable pins is arranged for each of the four edges of the copper foil.

[0041] This limits the occurrence of foil displacement due to resin pressure during resin injection. If the copper foil is thin, it easily warps or distorts, making transportation in a device difficult, while if it is thick, it increases costs. Thus, a copper foil thickness between 0.03 mm and 0.1 mm is desirable. The base plate 3, which is the copper foil exposed from the bottom surface 10b of the resin encapsulant 7 in the power module 20, is coplanar with the bottom surface 10b of the resin encapsulant 7.

[0042] In the step of molding the resin encapsulant 7, the resin for the resin encapsulant 7 is cured using a resin application pressure and a resin temperature in the molded body, and at the same time, the insulating sheet 5 is cured from a partially cured state while being pressed against the copper foil (the metal base 3) by the lead frame 1. This ensures high heat dissipation performance and high electrical insulation performance of the insulating sheet 5.

[0043] Furthermore, when the thickness of the copper foil is between 0.03 mm and 0.1 mm, the power module is likely to warp or deform, so that the power module 20 assumes a convex shape as shown in Fig. 15. Furthermore, the power module 20 according to Embodiment 1 does not absorb moisture through the copper foil surface of the module, so that electrical malfunction such as ion migration or the like due to moisture absorption is suppressed.

[0044] When, in the step of forming the resin encapsulation 7 of the power module 20, the focus is on applying resin for the power module 20, the resin having a high viscosity (stickiness) is first applied to an area above the lead frame 1, where the resin thickness will be large, and the resin having a high viscosity (stickiness) is applied last to an area for the fins 2, where the flow resistance is high. Specifically, an intermediate assembly 60, in which the insulating sheet 5 and the metal base 3 are arranged on the lead frame 1, on which the power elements 4 are mounted, is arranged in a mold 62 such that the fin region 11 is directed downward, as shown in FIG. Fig. 1 shown (see Fig. 18), and then the resin corresponding to the resin of the lead frame 1 is injected through one surface (lateral side of the body portion 10).

[0045] At this time, the insulating sheet 5 and the metal base 3 are arranged first in the mold body 62 in terms of the arrangement order, and then the lead frame 1 on which the power elements 4 are mounted is arranged. Accordingly, the positioning accuracy of the respective elements is improved in such a way that positioning of the lead frame 1 is performed independently after performing the positioning of the metal base 3. Fig. 17 is a diagram showing the intermediate product structure according to Embodiment 1 of the invention. Fig. 18 is a diagram illustrating a method of manufacturing a power module according to Embodiment 1 of the invention, and Fig. 19 is a cross-sectional view of the molded article according to Embodiment 1 of the invention.

[0046] The molded body 62 includes a molded body 63 in which terminal openings 65a, 65b are formed, through which the terminal portion 22 of the lead frame 1 is to be exposed to the outside; and a molded body cover 64. A portion in the molded body 63 located below a broken line 73 is a fin end forming portion 69 for forming each end of the fins 2 of the fin portion 11 in the power module 20.

[0047] With a rib height hm1, a body area height hm2, a resin encapsulation height hm3, a body area height hm8 on the upper side and a body area height hm9 on the rib side, which are Fig. 19 are heights corresponding respectively to a rib height h1, a body portion height h2, a resin encapsulation height h3, a resin thickness h8 and a resin thickness h9 in the Fig. 15, and these heights are given with dimensions taking into account a contraction of the resin encapsulation 7 due to curing.

[0048] At the time of arranging the intermediate assembly 60 in the mold body 62, the intermediate assembly 60 is arranged in the mold body 62 such that the metal base 3 is in contact with a metal base arranging part 66 and a part of the lead frame 1 is exposed from the mold body 62. In an area which is Fig. 17 on the left side of a broken line 61a and an area shown there on the right side of a broken line 61b are each an area to be exposed from the resin encapsulation 7.

[0049] When the intermediate assembly 60 is arranged in the mold body 62 so that the metal base 3 is in contact with the metal base arranging part 66, it is possible to manufacture the power module 20 with one surface of the metal base 3 exposed. Note that, after the resin encapsulation molding step for forming the resin encapsulation 7, the terminal portion 22 exposed from the resin encapsulant 7 is bent into an L-shape, so that the plurality of terminals 23a, 23b are formed oriented in a direction specified for the finished product (the power module as the product).

[0050] Fig. 20 is a cross-sectional view of another molded article according to Embodiment 1 of the invention, and Fig. 21 is a cross-sectional view of the body of a molded article and the cover of a molded article in Fig. 20. In the step of forming the resin encapsulation 7 in the Fig. 15 shown power module 20 is the one in Fig. 20 is used. The molded body 62 shown in Fig. The molded body 62 shown in Fig. 20 comprises the molded body body 63 having the terminal openings 65a, 65b and the pin openings 67a, 67b; the molded body cover 64; and the ejection pins 71 for improving the molded body detachability, which are movably inserted into the pin openings 67a, 67b.

[0051] The ejection pins 71 are actuated by a spring (not shown). In a state where the mold body 62 is closed, namely closed, the ejection pins 71 are not actuated, and at the same time when the mold body 62 is opened, the ejection pins 71 are actuated by the spring. The pin opening 67a is a through hole into which the pin is inserted at the time when the rib 2a of the power module 20 is in Fig. 15 is pressed out. Similarly, the pin hole 67b is a through hole into which the pin is inserted at the time when the rib 2b of the power module 20 is in Fig. 15 is pushed out.

[0052] At the time of carrying out the resin encapsulation molding step by using the Fig. In the mold body 62 shown in FIG. 20, which is a step for molding the resin encapsulant 7, the pin holes 67a, 67b are closed with the pins 71. The resin encapsulant molding step is carried out in a state where the pin holes 67a, 67b are closed, and then, after the resin for molding the resin encapsulant 7 (the transfer molding resin) is cured and at the same time as the mold body 62 is opened, the ejection pins 71 exit the pin holes 67a, 67b toward the resin encapsulant 7 side, thereby pushing out the rib portion 11 of the resin encapsulant 7, so that the resin encapsulant 7 is ejected from the mold body 62 (resin encapsulant ejection step).

[0053] At the time of ejecting the resin encapsulant 7 from the molded body 62, the recesses 101 are formed in the rib portion 11. Accordingly, the resin encapsulant ejection step is also a step for forming the recesses 101 in the rib portion 11 (a rib portion recess formation step). The depth of the recess 101 in the rib portion 11 is set greater than a width ws1 of the bottom surface of the rib portion 11 (see Fig. 3), namely a furthest end in the rib 2 protruding from the body portion 10, so that the resin is prevented from penetrating into and adhering to the molded body, and thus cleaning of the molded body 62 is facilitated.

[0054] It should be noted that it is possible to create a notch on the mold body for forming the resin encapsulant 7 and then arrange the copper foil on the notch. By using the notch, positioning of the metal base 3 as the copper foil relative to the mold body for forming the resin encapsulant 7 can be performed. In this case, the surface of the copper foil protrudes from the lower surface 10b of the resin encapsulant 7 in the power module 20; however, this geometry is not important.

[0055] On the other hand, in a conventional power module, only one body portion is disposed, so there are concerns about the following problems in a resin encapsulation molding step for forming its resin encapsulation. When the power elements 4 mounted on the lead frame 1 are arranged facing upward in the molded body in the resin encapsulation molding step, since the resin is injected from the lateral surface side of the body portion, there is a concern that air remains on a side where the power element mounting surface of the lead frame 1 is disposed, or remains on a lateral side of that surface, forming a void.

[0056] In particular, when the wire 6 is provided around the cavity, there are concerns about a problem that the resin encapsulant 7 covering the wire 6 becomes thin, or a problem that the wire 6 is exposed outside the resin encapsulant 7. When such a state is produced, there are concerns that the spatial insulation distance between the wire 6 and a component arranged outside the power module 20 is reduced, making it impossible to ensure insulation between them.

[0057] Since the fins 2 in the power module 20 are the final target for resin deposition, in the power module 20 according to Embodiment 1, there is no case where air remains on the side where the mounting surface of the lead frame 1 for power elements is disposed, or remains on the lateral side of that surface and forms a void, during the resin encapsulation molding step. Consequently, it becomes possible to ensure the spatial insulation distance from a component disposed outside the power module 20 without causing wire exposure or the like.

[0058] Furthermore, in the power module 20 according to Embodiment 1, the fin height h1, that is, the height of each of the fins 2a, 2b, 2c, 2d in the fin portion 11, is set smaller than the body portion height h2, that is, the height of the body portion 10 that encapsulates the lead frame 1. Namely, a relationship h1 < h2 holds. Since the resin encapsulation height h3 is equal to the sum of the fin height h1 and the body portion height h2, a relationship h1 < 0.5 × h3 also holds.

[0059] In manufacturing the power module 20, it is necessary to adjust the curing time of the resin for the resin encapsulation 7 so that it is equal to the curing time of the insulating sheet 5. If the curing time of the resin for the resin encapsulation 7 becomes longer, the insulating sheet is cured earlier, so that adhesion between the lead frame 1 and the insulating sheet 5 becomes poor, making it impossible to ensure heat dissipation and insulation performance.

[0060] For this reason, the fin height h1 in the power module 20 is set smaller than the body portion height h2 to thereby reduce the amount of resin applied to the fin portion 11 and thus shorten the resin application time to the fin portion 11. In the rib structure of the fin portion 11, the cross sections of the fins 2 each have a tapered shape as described above, and a taper is formed in the fin 2 to improve the resin application capability.

[0061] The width (joint width) of a joint portion where the rib 2 of the rib portion 11 and the body portion 10 are connected is a rib base width wb1, and a width of an end of the rib 2 that protrudes and is located farthest from the body portion 10 is an end width ws1. Since the taper is formed in the rib 2 of the rib portion 11, the end width ws1 is smaller than the rib base width wb1, and a relationship of ws1 < wb1 holds.

[0062] A groove for forming the rib portion 11 of the power module 20 in the molded body 62 is narrow, so that in some cases, there is a concern that the resin remains in the molded body 62 when the power module 20 is ejected from the molded body 62, namely that the rib portion loses its shape. In the case where there is a concern that the rib portion loses its shape, the molded body releasability can be improved in such a way that the resin encapsulation 7 is Fig. 20 and the power module 20 is then pressed out of the molded body from the rib side by pressing using the pins.

[0063] In this case, the recesses 101 are formed on the ribs 2 in the power module 20. By maintaining the recesses 101, it is possible to increase the insulation distances between the terminals 23 of the lead frame 1 and the metal base 3. In view of mold releasability, it is preferable that the cross section of the pin has a circular shape. Accordingly, it is preferable that the shape of the recess 101 be circular, as this is adapted to both the manufacturing process and the aspect of ensuring the insulation distance.

[0064] In the power module 20 according to Embodiment 1, it is possible to cause the insulating sheet 5 to harden within the time for applying resin for the resin encapsulation 7, thereby ensuring the heat dissipation performance and the insulation performance of the insulating sheet 5.

[0065] In the power module 20 according to Embodiment 1, the fin 2 of the fin portion 11 can increase a length Li of a lower peripheral portion, which is a creepage distance between the lead frame 1 and the metal base 3. The length Li of a lower peripheral portion as a creepage distance between the lead frame 1 and the metal base 3 corresponds to the insulation distance (creepage distance) between the lead frame 1 and the metal base 3.

[0066] Thus, in the power module 20 according to Embodiment 1, it is possible to increase the insulation distance (creepage distance) between the lead frame 1 and the metal base 3. The length Li of a lower peripheral portion of the power module 20 according to Embodiment 1 is determined using Fig. 4 and Fig. 5. It should be noted that the fin 2 of the power module 20 according to Embodiment 1 in a power module 100 according to Fig. 5 as a comparative example is marked as a broken line.

[0067] The length Li of a lower peripheral region as a creepage distance between the lead frame 1 and the metal base 3 in the power module 20 according to Embodiment 1 is equal to the sum of: a resin lower surface length L1, that is, a length from the periphery of the metal base 3 to the rib 2 of the rib portion 11; an outer periphery length L2, that is, a length of the outer periphery of the rib 2; and a body lower region length L3, that is, a length in the body portion 10 from its boundary with the rib portion 10 to the terminal portion 22 of the lead frame 1.

[0068] Regarding the power module (the comparative example) that does not have the fin 2, an insulation distance (a creepage distance) Lex between the lead frame 1 and the metal base 3 is described using the lengths and widths described for the power module 20 according to Embodiment 1. In the power module 100 of the comparative example, the insulation distance (the creepage distance) Lex between the lead frame 1 and the metal base 3 is equal to the sum of the length L1 of a bottom surface of the resin, the fin base width wb1, and the length L3 of a bottom portion of the body.

[0069] Since the fin base width wb1 of the fin 2 is smaller than the outer periphery length L2 of the fin 2, the insulation distance (the length Li of a lower peripheral portion) of the power module 20 according to Embodiment 1 can be larger than the insulation distance Lex of the power module of the comparative example. Furthermore, the larger the fin height h1 of the fin 2, the larger the outer periphery length L2 can be made as the outer periphery length of the fin 2 in the power module 20 according to Embodiment 1.

[0070] Assume the case where the length Li of the lower peripheral portion of the power module 20 according to Embodiment 1 is set equal to the insulation distance Lex of the power module 100 of the comparative example. In this case, in the power module 20 according to Embodiment 1, it is possible to set a length L4 from end to end (see Fig. 3) between the lateral surface (end) of the body portion 10 in the resin encapsulant 7, from which the lead frame 1 is exposed, and the periphery (end) of the metal base 3, smaller than that of the power module 100 of the comparative example.

[0071] The end-to-end length L4 is equal to the sum of the length L1 of a bottom surface of the resin and the fin base width wb1 of the fin 2. Accordingly, the power module area of ​​the power module 20 according to Embodiment 1 can be made smaller than that of the power module 100 of the comparative example with the same insulation length, and thus it can be downsized.

[0072] Furthermore, the fin height h1 of the power module 20 is larger than the fin base width wb1, and if the insulation distance is extended in the direction of the fin height, it is possible to greatly reduce the area of ​​the power module 20. Furthermore, as shown in Fig. 15, a thickness h10 of the resin in the power module 20, which is a thickness determined by subtracting the thickness of the lead frame 1 from a thickness h8 of the resin above a lower-side surface disposed in the lead frame 1 and protruding from the resin encapsulant 7, is larger than a thickness h9 of the resin below the lower-side surface of the lead frame 1, the resin below the lower-side surface is likely to cause thermal shrinkage.

[0073] This becomes particularly significant when the resin encapsulation 7 expands less linearly than the lead frame 1. The resin thickness h10 is a maximum thickness between: an upper side 51a of a frame contact region, which is arranged in a frame contact region 51 in which the lead frame 1 protrudes from the resin encapsulation 7 and on a side toward the upper surface 10a; and the upper surface 10a. The resin thickness h9 is a minimum thickness between: a lower side 51b of a frame contact region, which is arranged in the frame contact region 51 and on its side toward the lower surface 10b; and the exposed surface of the metal base 3.

[0074] The shape of the frame contact portion 51 is the same as the cross section of the lead frame 1 protruding from the resin encapsulant 7. Furthermore, the inclusion of the ribs 2 at the end portions of the power module 20 increases the amount of resin, so that the power module 20 is likely to warp or curl into an upwardly convex shape with respect to the exposed surface of the metal base 3 as a vertical reference when a portion located below the surface on the lower side causes thermal contraction.

[0075] It is possible to make the resin thickness h10, which is the thickness determined by subtracting the thickness of the lead frame 1 from the thickness h8 of the resin, larger than the resin thickness h9 by performing the resin encapsulation molding step using the mold body 62 in which the body portion height hm8 on the upper side is larger than the body portion height hm9 on the fin side.

[0076] Furthermore, in the power module 20 according to Embodiment 1, the rib also serves as a support, so that the bending rigidity of the power module is improved. In the power module 20 according to Embodiment 1, due to the improvement in the bending rigidity of the power module, it is possible to reduce: the thermal shrinkage of the resin that occurs when the power module with the resin encapsulant 7 molded at a high temperature is cooled to ambient temperature; and the amount of warping or distortion of the power module due to a difference in linear expansion that occurs during this cooling step among the members of the lead frame 1, the metal base 3, the resin encapsulant 7, and the like.

[0077] Therefore, in the power module 20 according to Embodiment 1, it is not necessary to use the holding member as in Patent Document 1, so that the step of attaching the power module to the heat sink can be shortened compared to the power module of Patent Document 1. Furthermore, the cost of this holding member is not incurred in the power module 20 according to Embodiment 1 because it is not necessary to use the holding member as in Patent Document 1, thus enabling cost reduction.

[0078] The power module 20 according to Embodiment 1 includes the rib portion 11 disposed on the lower surface 10b of the body portion 10 in the resin package 7 so as to surround the outer periphery of the metal base 3 and formed to protrude from the lower surface 10b of the body portion 10 in a direction perpendicular to the lower surface 10b, namely, it includes the ribs 2 each disposed on the lower surface 10b of the resin package 7 and outside the lateral surface of the metal base 3 and formed to protrude from the lower surface 10b.

[0079] Thus, it can be downsized while improving the insulation between the lead frame 1 and the metal base 3. Furthermore, in the power module 20 according to Embodiment 1, the insulating sheet 5 is disposed within the lower surface 10b of the body portion 10, so that the insulating sheet 5, which is costly, is minimized in size.

[0080] It should be noted that in Fig. 1 shows such an example, in which a step is formed in the lead frame 1 within an end surface in contact with the insulating sheet 5, thereby providing the wiring portion 21. Due to the step between the wiring portion 21 and the terminal portion 22, the terminal portion 22 is arranged at a height from the metal base 3 that is greater than that of the wiring portion 21, so that the insulation distance between the lead frame 1 and the metal base 3 is extended to the extent of a thickness of the resin encapsulant 7 corresponding to that step.

[0081] In this embodiment, the step is formed so that its height is equal to or less than half the thickness of the lead frame 1, for example, equal to 0.3 mm relative to the thickness of the lead frame 1 of 0.6 mm. This is because, when the step of the lead frame 1 is formed by a step-forming process such as a pressing process or the like, there is a concern about breakage or the like when the step height of the lead frame 1 is large, and thus, it is required that the step be arranged as one that cannot be broken.

[0082] As the thickness of the lead frame 1 increases, the amount of warping or buckling of the power module 20 due to a difference in linear expansion between the lead frame member and the resin increases, so it is desired that the thickness of the lead frame 1 falls within a range of 0.3 mm to 1.0 mm.

[0083] In the power module 20 according to Embodiment 1, applying the step-forming process to the lead frame 1 enables the resin to encapsulate the lead frame 1 in a thin state, so that the module thickness can be reduced and made uniform. In the case of reducing the module thickness, it is desirable that the module thickness of the power module 20, namely the body portion height h2, falls within a range of 5 mm to 15 mm.

[0084] Furthermore, if the amount of warping or distortion in the convex shape of the power module 20 exceeds 0.1 mm, it becomes difficult to make the power module 20 flat using a screw fastening force, so the amount of warping or distortion is desired to be 0.1 mm or less. Meanwhile, in the power module 20 according to Embodiment 1, the fin height h1 is set larger than the fin base width wb1, and this serves to both ensure the insulation performance of the module and downsize the module.

[0085] The extent of warping or warping of a power module is described below. Fig. 22 is a figure illustrating the extent of warping or buckling of the power module. Fig. 23 is a diagram illustrating the amount of warping or warping of the power module in a plus direction, and Fig. Figure 24 is a diagram illustrating the extent of warping or distortion of the power module in a minus direction. In each figure of Fig. 22 to Fig. 24 shows a state of a power module 55 before fastening with a screw.

[0086] The power module 55 in Fig. 22 to Fig. 24 is simplified so that the rib portion 11, the metal base 3 and the like are omitted. On the upper side in Fig. 22, a power module lateral surface 55c is shown, which is a lateral surface of the power module 55, and on the lower side, a power module upper surface 55a is shown, which is the upper surface of the power module 55.

[0087] The metal base 3, which is not shown, is arranged on a lower surface 55b of the power module, which is the lower surface of the power module 55. The extent of warping or warping of this power module can also be applied to the power module 20 of this application.

[0088] The signs “+” (“plus”) and “-” (“minus”), which indicate the directions of the amount of warping or distortion of the power module 55, are respectively drawn with respect to the exposed surface of the metal base 3 (the lower surface 55b of the power module in Fig. 22) as a vertical reference, and assume that "+" corresponds to warping or buckling with an upward protruding shape, and "-" corresponds to warping or buckling with a downward protruding shape. However, the amount of warping or buckling is measured from the upper surface of the power module 55 (from the upper surface 55a of the power module).

[0089] Thus, in the Fig. 22 to 24, a broken line 56a on the upper surface 55a of the power module is used as a reference for the actual measurement. Before screwing the power module 55, as shown in Fig. As shown in Figure 22, the extent is represented by a difference between: a measurement point p1 in the center on the resin side of the power module 55, namely on the upper surface 55a of the power module; and a middle point of the measurement points p2, p3, p4, and p5 at the four corners. In Fig. 22, the measuring point p1 is located at a position furthest up, and the measuring points p2, p3, p4 and p5 at the four corners are located at positions which are further down with respect to the measuring point p1.

[0090] A broken line 56b passes through the measurement point at which the absolute value of the amount of warping or distortion becomes maximum, and it runs parallel to the broken line 56a. It should be noted that the broken line 56a used as the reference is set, for example, perpendicular to the hole 18 through which the screw 13 passes for screwing. Accordingly, the amount of warping or distortion in the power module 55 according to Fig. 22 by “-”, so that the warping or warping has a downward protruding shape.

[0091] In every figure of Fig. 23 and Fig. 24 shows a state in which the module is screwed to the heat sink 16 (not shown here) using the screw 13 at the measuring point p1 located in the center of the upper surface 55a of the power module. In each figure of Fig. 23 and Fig. 24 shows a cross-section 55d of the power module, which is a cross-section of the power module 55. Note that diagonal lines indicative of a cross-section are omitted here. The amount of warping or distortion of the power module 55 in a state during bolting is determined with reference to the center measurement point p1, namely the dashed line 56a, so that it represents a difference between: a measurement point that is a point farthest in height from the center measurement point p1; and the measurement point p1.

[0092] For the power module 55 according to Fig. 23, the extent of warping or distortion is determined to represent a difference between: a measuring point p6, which is a point farthest in height from the central measuring point p1; and the measuring point p1. A broken line 56c passes through the measuring point p6 and is parallel to the broken line 56a. In the power module 55 according to Fig. 23, the degree of warping or distortion is equal to "+", so that the warping or distortion has an upwardly projecting shape. In the power module 55 according to Fig. 24, the degree of warping or distortion is determined to represent a difference between: a measuring point p7, which is a point farthest in height from the central measuring point p1; and the measuring point p1. A broken line 56d passes through the measuring point p7 and is parallel to the broken line 56a.

[0093] For the power module 55 according to Fig. 24, the degree of warpage is "-", so that the warpage has a downward protruding shape. It should be noted that the power module 55 according to Fig. 24 an initial state during screwing of the power module 55 according to Fig. 22 and that the power module 55 according to Fig. 23 a final state during the screwing of the power module 55 according to Fig. 22 shows.

[0094] In this embodiment, however, a unit in which the single insulating sheet 5 and the metal base 3 are combined is used. However, this is not a limitation, and the fin structure of this embodiment can be applied to a power module using a conventional ceramic plate or metal plate. Furthermore, the fin structure of this embodiment can be applied to a module in which the insulating sheet 5 is not used and the power elements 4 are bonded to the thick metal base 3.

[0095] As described above, the power module 20 according to Embodiment 1 includes the power elements 4; the metal base 3 for dissipating heat from the power elements 4; the lead frame 1 electrically connected to the electrodes of the power elements 4; and the resin encapsulant 7 that encapsulates the power elements 4 such that one surface of the metal base 3 and a part of the lead frame 1 are exposed from the encapsulant.

[0096] The resin encapsulation 7 of the power module 20 is characterized by including: the body portion 10 in which the power elements 4 and a part of the lead frame 1 are arranged, and on the lower surface 10b of which one surface of the metal base 3 is exposed; and the rib portion 11 arranged on the lower surface 10b of the body portion 10 so as to surround the outer periphery of the metal base 3 and formed to protrude from the lower surface of the body portion 10 in a direction perpendicular to the lower surface 10b.

[0097] By including the rib portion 11, which is disposed on the lower surface 10b of the body portion 10 of the resin encapsulant 7 so as to surround the outer periphery of the metal base 3 and is formed to protrude from the lower surface 10b of the body portion 10 in a direction perpendicular to the lower surface 10b, the power module 20 according to Embodiment 1 can be downsized while improving the insulation between the lead frame 1 and the metal base 3. Furthermore, in the power module 20 according to Embodiment 1, the rigidity of the power module 20 can be increased due to the action of the rib 2 as a support, so that the amount of warping or buckling is effectively controlled.

[0098] The power module manufacturing method for manufacturing the power module 20 according to Embodiment 1 is characterized by including: a step of arranging the intermediate assembly 60 including the power elements 4, the metal base 3, and the lead frame 1 in the mold body 62 such that the metal base 3 is in contact with the metal base arranging part 66 and a part of the lead frame 1 is exposed from the mold body 62; and a step of molding the resin encapsulant 7 by injecting an injection-molding resin into the mold body 62.

[0099] In the method for manufacturing a power module according to Embodiment 1, it is possible to manufacture the power module 20 having the rib portion 11 disposed on the lower surface 10b of the body portion 10 of the resin encapsulant 7 so as to surround the outer periphery of the metal base 3 and formed to protrude from the lower surface 10b of the body portion 10 in a direction perpendicular to the lower surface 10b.

[0100] Furthermore, according to the method for manufacturing a power module according to Embodiment 1, it is possible to manufacture the power module 20 having an upwardly convex shape with respect to the exposed one surface of the metal base 3 as a vertical reference by using such a molded body 62 in which a length in a direction perpendicular to the lower surface 10b of the resin encapsulant 7 (a body portion height hm9 on the rib side) located between the metal base arranging part 66 with which the metal base 3 is in contact and one side of an opening located on a side toward the metal base in an opening of the molded body (terminal openings 65a, 65b) through which the lead frame 1 is to be exposed is smaller than a length in a direction perpendicular to the lower surface 10b of the resin encapsulant 7 (the body portion height hm8 on the upper side).which is located between an inner surface of the molded body, on which the upper surface 10a of the power module 20 is to be formed, which is opposite the lower surface 10b, and one side of the opening.

[0101] In another aspect, the method for manufacturing a power module according to Embodiment 1 is characterized in that: such a molded body 62 is used in which, in its rib end forming part 69, at which the end of the rib portion 11 is to be formed, which protrudes from the lower surface 10b of the resin encapsulant 7, the plurality of pin holes 67a, 67b are formed, into which pins for ejecting the resin encapsulant 7 are to be inserted; the step of molding the resin encapsulant 7 is carried out in a state in which the pin holes 67a, 67b are closed;and the method for manufacturing a power module further includes a step of forming recesses 101 in the rib portion 11 in such a manner that, at the time of ejecting the resin encapsulant 7 from the molded body 62, the pins are inserted beyond the pin holes 67a, 67b to push out the rib portion 11 of the resin encapsulant 7. In the method for manufacturing a power module according to Embodiment 1, it is possible to manufacture the power module 20 provided with the rib portion 11 having the recesses 101 at its end protruding from the bottom surface 10b by using the molded body 62 in which the plurality of pin holes 67a, 67b are formed. Embodiment 2 (not according to the claims)

[0102] Fig. 5 is a cross-sectional view of a power module according to Embodiment 2 of the invention. A power module 20 according to Embodiment 2 differs from that according to Embodiment 1 in the shape of the rib 2 of the rib portion 11. The rib 2 includes a rib base part 26 and a protruding part 27. Similar to Embodiment 1, the power module 20 according to Embodiment 2 includes the ribs 2 each disposed on the lower surface 10b of the resin encapsulant 7 and outside the lateral surface of the metal base 3, and formed to protrude from the lower surface 10b, so that it can be downsized while improving the insulation between the lead frame 1 and the metal base 3.

[0103] In Fig. 6, the ribs 2a, 2b are shown. The protruding part 27 has the shape of a small rib arranged on the rib base part 26. The rib base part 26 is connected to the lower surface 10b of the body portion 10, and the protruding part 27 is arranged at an end of the rib base part 26 protruding from the lower surface 10b of the body portion 10, and is formed to protrude in a direction perpendicular to the lower surface 10b of the body portion 10. Since the small rib shape of the protruding part 27 provides a narrow upper end, it is desirable to take a measure to prevent peeling of the upper end portion, for example, to provide an R-shape to that portion.

[0104] Similar to Fig. 1 is the Fig. 6 shown cross-section of the rib 2 by a transverse cross-section perpendicular to the direction in which it extends, which is parallel to the lateral surface of the body portion 10.In the rib base part 26, the shape thereof in a transverse cross section, which is a cross section perpendicular to the lower surface 10b of the body portion 10, is a tapered shape in which a connecting width at which the rib base part is connected to the lower surface 10b of the body portion 10 is larger than a width of an end of the rib base part, which is an end protruding from the lower surface 10b; and in the protruding part 27, the shape thereof in a transverse cross section, which is a cross section perpendicular to the lower surface 10b of the body portion 10, is a tapered shape in which a connecting width at which the protruding part is connected to the rib base part 26 is larger than a width of an end of the protruding part, which is an end protruding from the end of the rib base part.

[0105] The rib 2 in Embodiment 2 has a two-stage shape in which the taper slope of the protruding part 27 is steeper than the taper slope of the rib base part 26, so that the length L2 of the outer circumference of the rib 2 is longer than that of a rib having a single-stage shape as shown in Embodiment 1, even if these ribs have the same height.

[0106] Thus, in the power module 20 according to Embodiment 2, it is possible to increase the length Li of a lower peripheral part between the lead frame 1 and the metal base 3 compared to the case of a fin 2 of the same height having a single-stage shape, and specifically, it is possible to increase the insulation distance between the lead frame 1 and the metal base 3. Further, in the power module 20 according to Embodiment 2, when the required insulation distance is to be established, it is possible to reduce a fin height h4 compared to the case of the power module 20 according to Embodiment 1.

[0107] In the power module 20 according to Embodiment 2, the height of the body portion 10 in the resin package 7 is the body portion height h2, the height of the fin portion 11 is the fin height h4, and the height of the resin package 7 is a resin package height h5.

[0108] Since the fin height h4 is smaller than the fin height h1 in Embodiment 1, the power module 20 can reduce the height of the resin encapsulant 7 while sufficiently ensuring the insulation distance between the lead frame 1 and the metal base 3, and thus the resin encapsulant 7 can be downsized more than in the case of the power module 20 according to Embodiment 1. Furthermore, in the power module 20 according to Embodiment 2, it is possible to reduce the amount of resin for the fins 2 and thereby reduce the cost of the resin of the resin encapsulant 7. Embodiment 3

[0109] Fig. Figure 7 is a cross-sectional view of a power module according to Embodiment 3 of the invention. A power module 20 according to Embodiment 3 differs from that according to Embodiment 1 in that the heights of the fins 2 in the fin region 11 are divided into two types. Fig. 7 shows such an example, in which the height of a rib 2a is equal to a rib height h1 and the height of a rib 2b is equal to a rib height h6.

[0110] The insulation distance between the lead frame 1 and the metal base 3 depends on a voltage required for each of the terminals 23. For example, a high voltage is applied to the terminal 23a, which is an output terminal on the lead frame 1, on which a power element 4, such as an IGBT, a FWD (freewheeling diode), a CVD (converter diode), or the like, is mounted.

[0111] In contrast, a low voltage is present at terminal 23b, which is a control terminal on the lead frame 1 for controlling the gate of an IGBT or a control terminal on the lead frame 1 for detecting a current for a current sensor. Fig. The ribs 2a and 2b shown in Fig. 7 may also be referred to as a high voltage side rib and a low voltage side rib, respectively.

[0112] Accordingly, it is permissible to set the height of the rib 2a located between the terminal 23a as the output terminal on the lead frame 1, to which a high voltage is applied, and the metal base 3 to be larger, while setting the height of the rib 2b located between the terminal 23b as the control terminal on the lead frame 1, to which a low voltage is applied, and the metal base 3 to be smaller. Namely, it is permissible to set the height of the rib 2a on the high voltage side to be larger, while setting the height of the rib 2b on the low voltage side to be smaller.

[0113] In this embodiment, the terminals 23 of the lead frame 1 protrude similarly to the Fig. 2 in the three directions, so that with respect to the direction in which no terminal of the lead frame 1 protrudes, with respect to the rib 2d, since it is associated with a low voltage, the rib is applied on the side of a lower voltage whose height is equal to the rib height h6.

[0114] With respect to the rib 2c, when the terminal 23c is a terminal to which a high voltage is given, the rib is applied on the high voltage side, and when the terminal 23c is a terminal to which a low voltage is given, the rib is applied on the low voltage side.

[0115] Similar to Embodiment 1, the power module 20 according to Embodiment 3 includes the fins 2 disposed on the bottom surface 10b of the resin encapsulant 7 and outside the lateral surface of the metal base 3, and formed to protrude from the bottom surface 10b, so that the size of the bottom surface 10b can be reduced while improving the insulation between the lead frame 1 and the metal base 3. In the power module 20 according to Embodiment 3, in at least one of the plurality of fins 2 of the fin portion 11 (the fins 2b, 2d), the fin height h6, that is, a height from the bottom surface 10b of the body portion 10 to an end of the fin (the fins 2b, 2d) located farthest from the bottom surface 10b of the body portion 10, is smaller than the fin height h1 of the other fin (the fin 2a).

[0116] In the power module 20 according to Embodiment 3, since it has the fins 2 with different heights conforming to the stresses at the terminals of the lead frame 1, it is possible to reduce the amount of resin for the resin encapsulation 7 while obtaining an effect of reducing warpage or distortion of the power module, thereby reducing the cost of the resin of the resin encapsulation 7. Note that the description was made using an example in which the heights of the fins 2 in the fin region 11 are divided into two types; however, they may be divided into three types. Embodiment 4

[0117] Fig. Fig. 8 is a perspective view of a power module according to Embodiment 4 of the invention, and Fig. 9 is a bottom view of the power module according to Fig. 8 when viewed from a side where the metal base is arranged. It should be noted that the terminal area 22 of the lead frame 1 in Fig. 9 is omitted from the illustration. A power module 20 according to Embodiment 4 differs from that according to Embodiment 1 in that its external shape is an elongated shape when viewed from the side of the upper surface 10a or the lower surface 10b of the resin encapsulant 7.

[0118] Note that the external shape, viewed from the side of the upper surface 10a or the lower surface 10b of the resin encapsulant 7, is not limited to an elongated shape and may be a quadrangular shape with long sides and short sides. In terms of external appearance, the power module 20 has a configuration in which the terminals 23 of the lead frame 1 protrude in four directions, and holes 18 for fixing the power module 20 are formed at two locations.

[0119] The thickness of the ribs 2c, 2d arranged peripherally on the respective long sides and in the longitudinal direction of the power module 20 is greater than that of the ribs 2a, 2b arranged peripherally on the respective short sides and in the transverse direction. Furthermore, in this embodiment, the terminals 23 of the lead frame 1 are assumed to protrude from the lateral surfaces of the power module 20 in four directions; however, the number of directions in which the terminals 23 protrude is not limited to these.

[0120] In Fig. 8 shows such an example, in which the respective sets of five terminals 23a, 23b protrude from the lateral surfaces of the resin encapsulant 7, along which the respective ribs 2a, 2b are formed to be peripherally arranged on the short sides; and the respective sets of six terminals 23c, 23d protrude from the lateral surfaces of the resin encapsulant 7, along which the respective ribs 2c, 2d are formed to be peripherally arranged on the long sides. Generally, the amount of warping or buckling of a power module is greater in its longitudinal direction than in its transverse direction. Since the warping or buckling of the power module in the transverse direction of the power module is smaller in the power module 20 according to Embodiment 3, which is provided with the ribs 2, it is permissible to make the thickness of the ribs 2a, 2b arranged in the transverse direction smaller than that of the ribs 2c, 2d arranged in the longitudinal direction.

[0121] It should be noted that the rib arranged in the transverse direction is referred to as a transverse rib or a short side rib, as appropriate, and the rib arranged in the longitudinal direction is referred to as a longitudinal rib or a long side rib, as appropriate.

[0122] Similar to Embodiment 1, the cross sections of the fins 2 in the fin structure of the fin portion 11 in the power module 20 according to Embodiment 4 each have a tapered shape.

[0123] The width of a connecting portion where each of the ribs 2a, 2b of the rib portion 11 is connected to the body portion 10 in the transverse direction is the rib base width wb1, and the width of the end of each of the ribs 2a, 2b that protrudes and is farthest from the body portion 10 is the end width ws1. The width of a connecting portion where each of the ribs 2c, 2d of the rib portion 11 is connected to the body portion 10 in the longitudinal direction is the rib base width wb2, and the width of the end of each of the ribs 2c, 2d that protrudes and is farthest from the body portion 10 is the end width ws2. Since the taper is formed in each of the ribs 2a, 2b, 2c, 2d of the rib region 11, the end widths ws1, ws2 are each smaller than the rib base widths wb1, wb2, namely the relations ws1 < wb1 and ws2 < wb2 apply.

[0124] In the power module 20 according to Embodiment 4, the thickness of the ribs 2a, 2b in the transverse direction is set smaller than that of the ribs 2c, 2d in the longitudinal direction, namely, the rib base width wb1 of the rib in the transverse direction is smaller than the rib base width wb2 of the rib in the longitudinal direction, and the end width ws1 of the rib in the transverse direction is smaller than the end width ws2 of the rib in the longitudinal direction. Specifically, the relationships wb1 < wb2 and ws1 < ws2 hold.

[0125] Similar to Embodiment 1, the power module 20 according to Embodiment 4 has the ribs 2 each disposed on the lower surface 10b of the resin encapsulant 7 and outside the lateral surface of the metal base 3, and formed to protrude from the lower surface 10b so that it can be downsized while improving the insulation between the lead frame 1 and the metal base 3.

[0126] In the power module 20 according to Embodiment 4, since the thickness of the ribs 2a, 2b in the transverse direction is smaller than that of the ribs 2c, 2d in the longitudinal direction, it becomes possible to reduce the amount of resin for the resin encapsulation 7 while obtaining an effect of reducing the warpage or distortion of the power module, thereby reducing the cost of the resin of the resin encapsulation 7. Embodiment 5

[0127] Fig. 10 is a cross-sectional view of a power semiconductor unit according to Embodiment 5 of the invention. Fig. 11 is a diagram showing an essential part of the power semiconductor unit according to Fig. 10 shows, and Fig. 12 is a perspective view of the power semiconductor unit according to Fig. 10. Fig. 10 is a cross-sectional view of a Fig. 12 is a sectional view indicated by a broken line when viewed from a direction B. In Embodiment 5, an example is described that is a power semiconductor device 40 including a power module 20 and a heat sink 16. A case is described in which the configuration of the power module 20 is the same as in Embodiment 1.

[0128] The heat sink 16 includes a heat sink base portion 31, a base stepped portion 32, and fins 33. A grease 14 is applied to a flat upper surface 32a of the base stepped portion 32 disposed within the heat sink 16, so that the lower surface of the metal base 3 in the power module 20 is coupled to the heat sink 16 through the grease 14 using a screw 13.

[0129] The heat generated by the power elements 4 in the power module 20 is transferred through the grease 14 from the metal base 3 to the base stepped part 32 in the heat sink 16 and then dissipated to the heat sink base part 31 and the fins 33 in the heat sink 16.

[0130] The flat upper surface 32a of the base stepped part 32 is wider than the flat lower surface of the metal base 3. The purpose is to make a heat dissipation area on the base stepped part 32 larger than the heat dissipation area of ​​the metal base 3, from which the heat generated by the power elements 4 is dissipated, thereby improving the heat dissipation performance for the heat generated by the power elements 4.

[0131] The base stepped portion 32 is integrally structured with the heat sink base portion 31 and the fins 33, and a highly conductive member made of copper, aluminum, or the like is used therefor. Note that this is not a limitation, and the base stepped portion 32 may be connected to the heat sink base portion 31 as a separate part.

[0132] Meanwhile, the fin portion 11 of the power module 20 is fixed to the heat sink 16 so as to surround the outer periphery of the base stepped portion 32, so that a grease accumulation 17 is formed in the grease 14 by means of the base stepped portion 32 and the fin 2.

[0133] Due to the arrangement of the grease accumulation 17, at the time of screwing the power module 20 and the heat sink 16 together, the grease 14 spread out from the contact area between the metal base 3 and the base stepped part 32 in the power semiconductor unit 40 according to Embodiment 5 migrates to a lateral surface 32b of the base stepped part 32. Thus, the contact area between the grease 14 and the base stepped part 32 in the power semiconductor unit 40 according to Embodiment 5 is increased, so that the thermal conduction to the grease 14 is improved, and thus the heat dissipation performance is improved.

[0134] Furthermore, in the power semiconductor unit 40 according to Embodiment 5, the height of the base stepped portion 32 is set large so as to prevent the fin 2 in the power module 20 from coming into contact with the heat sink base portion 31 in the heat sink 16. Namely, the height of the base stepped portion 32 is greater than the fin height h1 of the fin 2. Note that when the fins 2 are provided with a plurality of fin heights as in Embodiment 3, the height of the base stepped portion 32 is greater than the height of the highest fin among them.

[0135] In the case where the power module 20, which is a Fig. 15 is bolted to the heat sink 16 at a location around its center, the power module 20 acts as if it tightens a spring by using a bolting force across the center gap formed by the power module 20 from the state where end portions of the power module 20 are in contact with the upper surface 32a of the base stepped part 32 in the heat sink 16.

[0136] Accordingly, in the case of the power module 20 having the convex shape, the power module 20 is deformed from the convex shape to a flat shape while the metal base 3 is further pressed against the grease 14 attached to the upper surface 32a of the base stepped part 32 in the heat sink 16, so that the grease 14 is formed thin. As the grease 14 becomes thinner, the thermal conductivity becomes higher, and thus the heat dissipation performance of the power module 20 is improved.

[0137] Generally, a power module is bolted to a heat sink through a grease seal. If the power module is continuously used in this state in a hot-cold environment, repeated expansion and contraction will occur due to a difference in linear expansion between elements within the power module. Thus, the power module changes from a flat state to a warped or distorted state, and from a warped or distorted state to a flat state, causing repeated warping or distortion and flattening movements at the end face of the module.

[0138] For this reason, it is known that a pump-out phenomenon occurs in which the grease flows out from the end face of the power module, thereby impairing the heat dissipation performance. Regarding the power semiconductor unit 40 according to Embodiment 5, which is equipped with the power module 20 having the convex shape, the power module 20 is tightened by means of the screw 13 by utilizing the spring force of the power module 20, so that a state is maintained in which the module is pressed against the heat sink 16, thereby restricting the flow of the grease 14. When the power module 20 is convex upward, as shown in Fig. As shown in Figure 15, the amount of warpage of the power module 20 in the bolted state is -50 to +50 µm. This amount of warpage is determined for each of the cases including a case where the grease 14 remains in the center of the power module 20, a case where it remains at both ends of the module, and the like. Furthermore, the amount depends on the diameter of the filler in the grease 14 and is generally 50 µm or less.

[0139] It is assumed that, just like Fig. 22 to Fig. 24, the direction of the amount of warping or distortion at the time of screwing with respect to a top surface of the module in the screwing area is "+" ("plus") when the direction is upward, and "-" ("minus") when the direction is downward. "0 µm" means flat. When warping or distortion occurs in the plus direction, the shape of the power module 20 is an M-like shape as shown in Fig. 23, that is, a shape having an upper portion (a portion having the measuring point p6) that is further upward than the surface of the module in the screwing portion (the upper surface 10a).

[0140] In contrast, the shape of the power module 20 will be upwardly convex if there is warping or distortion in the minus direction. This is because a shape that is originally upwardly convex will be subjected to screwing. A shape with a warping or distortion amount of -50 to 0 µm has higher reliability than others and is therefore more preferable.

[0141] In the power semiconductor unit 40 according to the embodiment 5 shown in Fig. 10 to Fig. 12, the base stepped part 32 of the heat sink 16 is inserted toward the lower surface 10b of the resin encapsulant 7 located at a lower position than that of the fin portion 11 of the power module 20, and is inserted toward the lower surface of the metal base 3 (when appropriate, this is referred to as a lower surface inside the module), and is then fixed at a point such that the screw 13 is inserted into the hole 18 formed in the central portion.

[0142] Screwing is performed such that the end of the fin 2 in the fin 2 of the power module 20 is positioned lower than the upper surface 32a of the base stepped portion 32 in the heat sink 16, but does not come into contact with the heat sink base portion 31 in the heat sink 16. Thus, in the power semiconductor device 40 according to Embodiment 5, the grease accumulation 17 is formed between the base stepped portion 32 and the fin 2, so that concerns about dripping of the grease 14 are alleviated even when the product is used for a long period of time in an installed state.

[0143] Furthermore, in the power semiconductor unit 40 according to Embodiment 5, since the fin 2 of the power module 20 is disposed at a position not in contact with the heat sink 16, the power module 20 can be screwed in a non-floating state even if it includes the fin 2. The heat sink 16 is the one formed integrally with the base stepped part 32; however, the same effect is achieved when it is formed with the base stepped part 32 as a separate part.

[0144] When such a single-point fastening is applied to the power module 100 of the comparative example, which does not have the rib portion 11, the power module 100 is screwed while being immobilized, so that it does not rotate. If the power module 100 is loosely immobilized at this time, the power module 100 rotates, so that the upper end of the terminal in the lead frame 1 also rotates, and thus, a rotation-preventing clamping device is required to prevent the rotation of the power module 100.

[0145] Unlike this comparative example, in the power semiconductor unit 40 according to Embodiment 5, the rotation of the power module 20 is prevented in such a manner that the end face (lateral surface 32b) of the base stepped portion 32 in the heat sink 16 comes into contact with the end face of the fin 2 opposite the base stepped portion 32, so that a rotation-preventing jig is not required. In the power semiconductor unit 40 according to Embodiment 5, it is possible to smoothly perform the assembly steps for the power semiconductor unit because no rotation-preventing jig is required.

[0146] Furthermore, in the power semiconductor unit 40 according to Embodiment 5, since the fin 2 of the power module 20 serves as a support, it is possible to restrict the warping or buckling of the module, and since it is not necessary to use the holding member as in Patent Document 1, it is possible to shorten the step of fixing the power module 20 to the heat sink 16 compared with the power module in Patent Document 1.

[0147] Furthermore, in the power semiconductor unit 40 according to Embodiment 5, the power module 20 can be fixed to the heat sink 16 using the screw 13 at a location in the central region of the power module 20. Consequently, the number of screws for fixing the power module 20 to the heat sink 16 in the power semiconductor unit 40 according to Embodiment 5 can be reduced, and a smaller power module 20 can be mounted, thus miniaturizing the power semiconductor unit.

[0148] In the power semiconductor unit 40 according to Embodiment 5, since the power module 20 is fixed to the heat sink 16 such that the fin portion 11 thereof surrounds the outer periphery of the base stepped portion 32, the grease 14 once accumulates between the fin 2 and the base stepped portion 32. Then, after flowing out of the base stepped portion 32 in an outflow direction, the grease 14 migrates along the fin 2 in a direction perpendicular to the outflow direction.

[0149] Since the grease 14 is subjected to conduction resistance or conduction bending resistance by the fin 2 and the base stepped portion 32, it does not easily migrate. Accordingly, the power semiconductor device 40 according to Embodiment 5 can reduce the leakage of the grease 14 in a hot-cold environment, thereby limiting a reduction in the heat dissipation performance of the power module 20. Embodiment 6

[0150] Fig. 25 is a cross-sectional view of a power semiconductor unit according to Embodiment 6 of the invention. A power semiconductor unit 40 according to Embodiment 6 is shown as an example in which a heat sink groove 16a is formed in the heat sink 16, into which the fin portion 11 in the power module 20 is to be inserted. In the heat sink 16 in Fig. 25, a part arranged on the inner side of the heat sink groove 16a and on the upper side of a broken line 34 is the base stepped part 32, and that arranged on the lower side of a broken line 35 is the ribs 33.

[0151] In comparison with the heat sink base part 31 of the heat sink 16 in Fig. 10 it can be said that the heat sink base part 31 of the heat sink 16 in Fig. 25 has a structure provided with an outer peripheral frame 36 on the side closer to the outer periphery thereof. The outer peripheral frame 36 is arranged on the outer side of the heat sink groove 16a and on the upper side of the broken line 34.

[0152] Since the power semiconductor unit 40 according to Embodiment 6 uses the heat sink groove 16a, the grease 14 can migrate into the heat sink groove 16a and accumulate there. Thus, in the power semiconductor unit 40 according to Embodiment 6, it is possible to prevent leakage of the grease 14 that occurs when the power module 20 is placed vertically. This is particularly effective for the grease 14 with a low viscosity. Embodiment 7

[0153] In Embodiments 5 and 6 described above, examples of the power semiconductor unit 40 are described in which the power module 20 is fixed to the heat sink 16 using the screw 13 at a location in the central region of the power module 20; however, the number of fixing locations for the power module 20 may be increased.

[0154] When a plurality of screws 13 are provided, it is desirable that the fastening positions (the screwing areas) for the screws 13 be arranged in such a state that the positions of the screws are line-symmetrical to each other, within an area around the center of the power module 20 that is equal to two-thirds of the entire area of ​​the power module. This makes the exposed surface of the metal base 3 in the power module 20 flat, so that the thickness of the grease can be made uniform.

[0155] Fig. 13 is a perspective view of a power semiconductor unit according to Embodiment 7 of the invention, and Fig. 14 is a perspective view of another power semiconductor unit according to Embodiment 7 of the invention. Fig. 13 is an example of the power semiconductor unit 40 in which the power module 20 is screwed to the heat sink 16 at two locations (two points). Fig. 14 is an example of the power semiconductor unit 40 in which the power module 20 is screwed to the heat sink 16 at four locations (four points).

[0156] When the power module 20 is bolted to the heat sink 16 at two points, the fastening force for securing the flat lower surface of the metal base 3 in the power module 20 and the flat upper surface 32a of the base stepped portion 32 in the heat sink 16 to each other is increased. Thus, it is possible to more effectively restrict the pump-out phenomenon of the power module 20, thereby reducing the leakage of the grease 14 in a hot-cold environment, and thus limiting a reduction in the heat dissipation performance of the power module 20.

[0157] Furthermore, if the grease 14 has a high viscosity and is thus solid, the grease does not easily migrate between the screw connection area and the end face of the power module 20 (the end face of the module), thus stagnating. This may cause the power module 20 to expand at the screw connection area and the end face of the module.

[0158] At the Fig. In the power semiconductor unit 40 shown in Figure 13, the power module 20 and the heat sink 16 are bolted together at two points, so that the thickness of the grease can be made uniform. It should be noted that the thickness of the grease can be made uniform if the power module 20 and the heat sink 16 are bolted together at two or more points.

[0159] Furthermore, the power module 20 can be configured as in the power semiconductor unit 40 according to Fig. 14 may be screwed to the heat sink 16 at four points. It is known that the width of the terminal is made larger, as shown by the terminal 23c of the lead frame 1, as the current flowing in the power module 20 increases. Similar to Embodiment 1, the power module 20 arranged with the lead frame 1 having the terminals 23c with a large width also includes the ribs 2 each disposed on the lower surface 10b of the resin encapsulant 7 and outside the lateral surface of the metal base 3, and formed to protrude from the lower surface 10b, so that it can be downsized while improving the insulation between the lead frame 1 and the metal base 3.

[0160] In the power semiconductor devices 40 according to Embodiments 5 and 7, when the power module 20 and the heat sink 16 are bolted together at four points, it is possible to restrict the pump-out phenomenon of the power module 20 in a similar manner and more strongly, thereby reducing the leakage of the grease 14.

[0161] Since the fin 2 of the power module 20 serves as a support, it is possible to restrict the warping or buckling of the module in the power semiconductor devices 40 according to Embodiments 5 and 7. Furthermore, in the power semiconductor devices 40 according to Embodiments 5 to 7, the power module 20 is attached to the heat sink 16 such that its fin portion 11 surrounds the outer periphery of the base stepped portion 32.

[0162] Thus, the pump-out phenomenon of the power module 20 occurring in a hot-cold environment is restricted, so that it is possible to reduce the leakage of the grease 14 to thereby restrict a reduction in the heat dissipation performance of the power module 20.

[0163] As described above, the power semiconductor units 40 according to Embodiments 5 to 7 each include the power module 20 and the heat sink 16 bonded to the metal base 3 of the power module 20 through the grease 14. The power module 20 includes the power elements 4; the metal base 3 for dissipating heat from the power elements 4; the lead frame 1 electrically connected to the electrodes of the power elements 4; and the resin encapsulant 7 that encapsulates the power elements 4 such that one surface of the metal base 3 and a part of the lead frame 1 are exposed from the encapsulant.

[0164] The resin encapsulation 7 of the power module 20 includes: the body portion 10 in which the power elements 4 and a part of the lead frame 1 are arranged, and on the lower surface 10b of which one surface of the metal base 3 is exposed; and the rib portion 11 arranged on the lower surface 10b of the body portion 10 so as to surround the outer periphery of the metal base 3 and formed to protrude from the lower surface of the body portion 10 in a direction perpendicular to the lower surface 10b.

[0165] The heat sink 16 of the power semiconductor unit 40 is characterized in that it has the heat sink base part 31 and the base stepped part 32 which is connected to the metal base 3 by the grease 14, and that the power module 20 is fixed to the heat sink 16 such that the fin portion 11 surrounds the outer periphery of the base stepped part 32. In the power semiconductor devices 40 according to Embodiments 5 to 7, since the power module 20 is fixed to the heat sink 16 such that the fin portion 11 surrounds the outer periphery of the base stepped part, the pump-out phenomenon of the power module 20 occurring in a hot-cold environment is restricted, so that it is possible to reduce the leakage of the grease 14 to thereby restrict a reduction in the heat dissipation performance of the power module 20. Embodiment 8

[0166] Fig. Fig. 26 is a bottom view of a power module according to Embodiment 8 of the invention, viewed from a side where a metal base is arranged. A power module 20 according to Fig. 26 includes resin parts 50 formed by partially covering the terminals 23a, 23b of the lead frame 1, each exposed from an edge of the resin encapsulant 7, with a resin. Due to this structure, in the power module 20 according to Embodiment 8, it is possible to increase the insulation distance between the lead frame 1 and the metal base 3, thus enabling downsizing of the power module 20.

[0167] In the power semiconductor unit 40 according to Embodiment 8, which includes the power module 20 and the heat sink 16 connected to the metal base 3 of the power module 20 through the grease 14, the pump-out phenomenon of the power module 20 occurring in a hot-cold environment can be restrained because the power module 20 is fixed to the heat sink 16 such that the fin portion 11 surrounds the outer periphery of the base stepped part 32, so that it is possible to reduce the leakage of the grease 14 to thereby restrain a reduction in the heat dissipation performance of the power module 20. Embodiment 9

[0168] Fig. Fig. 27 is a bottom view of a power module according to Embodiment 9 of the invention, viewed from a side where a metal base is arranged. A power module 20 according to Fig. 27 has a structure in which no rib 2 is arranged in a region where no terminal 23 of the lead frame is exposed from the edge of the resin encapsulant 7.

[0169] In Fig. 27 shows such an example, in which three ribs 2a, 2b, 2c are formed, and the respective terminals 23a, 23b, 23c are exposed at the edges of the resin encapsulant 7 where these ribs 2a, 2b, 2c are formed. Due to this structure, in the power module 20 according to Embodiment 9, it is possible to reduce the amount of resin for a part that does not require an insulation gap, thereby achieving cost reduction.

[0170] In the power semiconductor unit 40 according to Embodiment 9, which includes the power module 20 and the heat sink 16 connected to the metal base 3 of the power module 20 through the grease 14, since the power module 20 is fixed to the heat sink 16 such that the fin portion 11 surrounds the outer periphery of the base stepped part 32, the pump-out phenomenon of the power module 20 occurring in a hot-cold environment is restricted, so that it is possible to reduce the leakage of the grease 14 to thereby restrict a reduction in the heat dissipation performance of the power module 20.

[0171] It should be noted that, in the above respective embodiments, the power element 4 mounted in the power module 20, which serves as a switching element such as an IGBT, a MOSFET, or the like, or as a rectifying element such as an SBD (Schottky Barrier Diode), a FwD, or the like, may be a conventional element whose base element is a silicon wafer; however, a so-called wide band gap semiconductor material having a wider band gap than silicon, represented by silicon carbide (SiC), a gallium nitride (GaN), or diamond, may also be used.

[0172] For example, when silicon carbide (SiC), a gallium nitride (GaN)-based material, or diamond is used for the power element 4 serving as a switching element or the power element 4 serving as a rectifying element, the efficiency of the power module 20 can be improved because the power loss is lower than that of a conventional element formed of silicon (Si). Furthermore, since the withstand voltage is high and the allowable current density is also high, the power module 20 can be downsized.

[0173] Furthermore, since semiconductor elements with a wide band gap exhibit high heat resistance, they can operate at high temperatures. This allows for a downsizing of the heat sink 16 and the substitution of the water cooling unit with an air cooling unit, thus further miniaturizing the power semiconductor unit 40 provided with the heat sink 16. DESCRIPTION OF REFERENCE SIGNS AND SYMBOLS 1 ladder frame 2, 2a, 2b, 2c, 2d rib 3 metal base 4 Performance element 7 Resin encapsulation 10 Body area 10b lower surface 11 Rib area 13 Screw 14 Fat 16 heat sinks 16a Heatsink groove 18 holes 20 power module 26 Rib base part 27 protruding part 31 Heatsink base part 32 part stepped at the base 40 power semiconductor units 50 resin parts 51 Frame contact area 51a upper side of the frame contact area 51b lower side of the frame contact area 60 Intermediate product structure 62 molded bodies 65a, 65b connection opening 66 Metal base assembly part 67a, 67b pin opening 69 part forming a rib end 71 Ejection pin 101 Deepening h1, h4, h6 rib height wb1, wb2 Width of the rib base hm8 Body area height on the upper side hm9 Body area height on the rib side

Claims

[1] Power module (20) comprising: a power element (4), a metal base (3) for dissipating heat from the power element (4), a lead frame (1) electrically connected to electrodes of the power element (4), and a resin encapsulation (7) encapsulating the power element (4) such that one surface of the metal base (3) and a part of the lead frame (1) are exposed from the encapsulation, wherein the resin encapsulation (7) comprises: - a body portion (10) in which the power element (4) and a part of the lead frame (1) are arranged and on the lower surface (10b) of which one surface of the metal base (3) is exposed; and - a rib portion (11) disposed on the lower surface (10b) of the body portion (10) so as to surround an outer periphery of the metal base (3) and formed to protrude from the lower surface (10b) of the body portion (10) in a direction perpendicular to the lower surface (10b); wherein the rib portion (11) has a recess (101) at its end protruding from the lower surface (10b), and wherein the recess (101) has a depth which is greater than the width (ws1, ws2) in a transverse direction of the end of the rib portion (11). [2] The power module (20) according to claim 1, wherein in the rib portion (11), the height (h1, h4) of the rib portion, that is, the height from the lower surface (10b) of the body portion (10) to an end farthest from the lower surface (10b) of the body portion (10), is greater than the connection width (wb1) in a transverse cross section with which the rib portion (11) is connected to the lower surface (10b) of the body portion (10). [3] The power module (20) according to claim 1 or 2, wherein the body portion (10) is warped or distorted into an upwardly convex shape with respect to the exposed one surface of the metal base (3) as a vertical reference. [4] The power module (20) according to any one of claims 1 to 3, wherein in the rib portion (11), the shape thereof in a transverse cross section, that is, a cross section perpendicular to the lower surface (10b) of the body portion (10), is a tapered shape in which the connecting width (wb1) with which the rib portion (11) is connected to the lower surface (10b) of the body portion (10) is larger than the end width (ws1) of an end protruding from the lower surface (10b). [5] Power module (20) according to one of claims 1 to 4, wherein the rib portion (11) has a plurality of ribs and wherein, with respect to at least one of the ribs (2), the rib height (h6), that is, the height from the lower surface (10b) of the body portion (10) to an end of that rib (2) which is farthest from the lower surface (10b) of the body portion (10), is smaller than the rib height (h1, h4) with respect to the other of the ribs (2). [6] Power module (20) according to one of claims 1 to 5, wherein the lower surface (10b) of the body portion (10) in the resin encapsulation (7) forms a quadrilateral shape having long sides and short sides; wherein the rib portion (11) comprises a plurality of ribs (2); wherein two of the plurality of ribs (2) are long-side ribs (2c, 2d) arranged peripherally on the lower surface (10b) on the respective long sides; wherein the other two of the plurality of ribs (2) are short-side ribs (2a, 2b) arranged peripherally on the lower surface (10b) on the respective short sides; and wherein the connecting width (wb2) in a transverse cross section of the rib (2c, 2d) on the long side, with which the rib (2c, 2d) on the long side is connected to the lower surface (10b) of the body portion (10), is greater than the connecting width (wb1) in a transverse cross section of the rib (2a, 2b) on the short side, with which the rib (2a, 2b) on the short side is connected to the lower surface (10b) of the body portion (10). [7] The power module (20) according to any one of claims 1 to 6, wherein terminals arranged as the part of the lead frame (1) exposed from the resin encapsulation (7) are each partially covered with a resin part (50). [8] The power module (20) according to any one of claims 1 to 7, wherein the resin encapsulant (7) has the rib portion (11) on the lower surface (10b) corresponding to a portion where the part of the lead frame (1) is exposed. [9] The power module (20) according to any one of claims 1 to 8, wherein in the resin encapsulant (7), the length (h9) in a direction perpendicular to the lower surface (10b) of the resin encapsulant (7) located between a lower side (51b) of a frame contact portion located in a frame contact portion (51) from which the lead frame (1) is exposed and on a side toward the lower surface (10b) and the exposed surface of the metal base (3) is smaller than the length (h10) in a direction perpendicular to the lower surface (10b) of the resin encapsulant (7) located between an upper side (51a) of a frame contact portion located in the frame contact portion (51) on a side toward an upper surface (10a) of the resin encapsulant (7) located opposite the lower surface (10b) and the upper surface (10a). [10] Power module (20) according to one of claims 1 to 9, wherein the power element (4) is formed from a semiconductor material with a wide band gap. [11] The power module (20) of claim 10, wherein the wide band gap semiconductor material is silicon carbide, a gallium nitride based material, or diamond. [12] Power semiconductor unit (40) comprising the power module (20) according to one of claims 1 to 11 and a heat sink (16) connected to the metal base (3) of the power module (20) by a grease (14), - wherein the heat sink (16) has a heat sink base part (31) and a stepped part (32) on the base, which is connected to the metal base (3) by the grease (14), and - wherein the power module (20) is attached to the heat sink (16) such that the fin portion (11) surrounds an outer periphery of the base stepped portion (32). [13] The power semiconductor unit (40) according to claim 12, wherein the power module (20) has a through-hole (18) penetrating the metal base (3) from an upper surface opposite to the lower surface (10b), and wherein the power module (20) is fixed to the base stepped part (32) of the heat sink (16) by means of a screw (13) inserted into the through-hole (18). [14] Power semiconductor unit (40) according to claim 12, wherein the power module (20) has a through-hole (18) penetrating the metal base (3) from an upper surface opposite to the lower surface (10b), wherein the heat sink (16) has a groove (16a) into which the fin region (11) of the power module (20) is to be inserted, and wherein the fin region (11) of the power module (20) is inserted into the groove (16a) of the heat sink (16) and the power module (20) is fastened to the heat sink (16) by means of a screw (13) inserted into the through-hole (18). [15] Power semiconductor unit (40) according to claim 13 or 14, wherein the through hole (18) in the power module (20) is formed singularly in the center thereof. [16] A power module manufacturing method for manufacturing a power module (20) according to any one of claims 1 to 8, wherein, in a fin-end forming part (69) of the molded body (62) at which the end of the fin portion (11) is to be formed, which protrudes from the lower surface (10b) of the resin encapsulant (7), a plurality of pin holes (67a, 67b) are formed, into which pins (71) for ejecting the resin encapsulant (7) are to be inserted; the method for manufacturing a power module comprising: - a step of arranging an intermediate product assembly (60) comprising the power element (4), the metal base (3) and the lead frame (1) in a mold body (62) such that the metal base (3) is in contact with the metal base arranging part (66) and a part of the lead frame (7) is exposed from the mold body (62); - a step in which the resin encapsulation (7) is formed by injecting an injection-molding resin into the molded body (62) in a state in which the pin openings (67a, 67b) are closed with the pins (71); and - a step of forming recesses (101) in the rib portion (11) in such a manner that the pins (71) are inserted beyond the pin openings (67a, 67b) to a depth greater than the width (ws1, ws2) in a transverse direction of the end of the rib portion (11) at the time of ejecting the resin encapsulant (7) from the molded body (62), so that the pins (71) push out the rib portion (11) of the resin encapsulant (7). [17] A method for manufacturing a power module according to claim 16, wherein in the molded body (62), the length (hm9) in a direction perpendicular to the lower surface (10b) of the resin encapsulant (7) arranged between the metal base disposing part (66) with which the metal base (3) is to be in contact and one side of an opening arranged on a side toward the metal base (3) in an opening (65a, 65b) of the molded body (62) through which the lead frame (1) is to be exposed is smaller than the length (hm8) in a direction perpendicular to the lower surface (10b) of the resin encapsulant (7) arranged between an inner surface of the molded body (62) on which an upper surface of the power module (20) is to be formed, which is located opposite to the lower surface (10b), and one side of the opening.

Images