JPH088373A - Heat dissipation device - Google Patents

Abstract

(57) [Summary] [Objective] An object of the present invention is to provide a heat dissipation device which is excellent in heat dissipation and does not cause a defect during a thermal shock test. [Structure] A circuit pattern 12 is fixed on a wiring board 11, and a high power semiconductor element 13 such as an FET transistor is formed.
Are connected by leads 14. A back surface pattern 15 of a copper foil having a larger area than that of the wiring board 11 is formed on the back surface of the wiring board 11. The end portion of the wiring board 11 is bent by press working, and then the wiring board 11 is formed so that the concave side becomes the wiring board side. Stick to it. The bent portion 16 is bent from the joint surface between the back surface pattern 15 and the heat sink base 17 to the end surface of the wiring board 11. The wiring board 11 is connected to the heat sink base 17 by using the solder 18. The heat sink base 17 is attached to the heat sink 20 using screws 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat dissipation device for dissipating heat generated by a heat generating component mounted on a wiring board.

[0002]

2. Description of the Related Art A high power semiconductor element such as an FET has a very high temperature during its operation. Therefore, how to efficiently dissipate heat is an important issue. In recent years, a structure has been adopted in which a semiconductor element is directly mounted on a wiring board having good thermal conductivity such as aluminum nitride and the wiring board is mounted on a heat sink.

FIG. 11 is a structural sectional view of a conventional heat dissipation device. In the figure, 51 is a wiring board made of aluminum nitride or the like, and a circuit pattern 52 is formed on the wiring board 51 with copper foil. On the circuit pattern 52, a high power semiconductor element 53 such as an FET transistor is electrically connected to the circuit pattern 52 by a lead 54 using a TAB mounting method or the like. On the back surface of the wiring board 51, a back surface pattern 55 of copper foil having almost the same area as that of the wiring board is formed.
By using 6, the insulating substrate 51 is fixed on the heat sink base 57. Then heat sink base 55
Are screwed to the heat sink 59 by screws 58.

With such a structure, the heat of the semiconductor element 53, which has generated heat during operation, is generated by the insulating substrate 51,
Back surface pattern 55, solder 56, heat sink base 5
7. Radiated through the heat sink 59. Therefore, a heat dissipation device having excellent heat dissipation can be obtained.

However, in the above-mentioned structure, since the thermal expansion coefficient of the wiring board 51 and the heat sink base 57 is different, stress is applied to the solder 56 used for connection between them when a thermal shock test or the like is performed. At this time, the back surface pattern 55
Since the solder fillet portion 60 on the end face is farther from the center of the substrate, a particularly large stress is applied and a crack is generated. If the solder fillet portion is made large and thick, the stress can be relieved. In conventional reflow soldering with screen printing solder paste, no matter how much the screen thickness is increased to form a thicker solder paste, problems such as solder flowing out during reflow soldering occur Was not obtained.

[0006]

In the conventional heat dissipation device described above, the solder fillet cannot be made large and thick in the solder connection between the wiring board and the heat sink base. In addition, defects such as cracks occurred in the solder fillet portion.

It is an object of the present invention to provide a heat dissipation device which is excellent in heat dissipation and does not cause a defect during a thermal shock test.

[0008]

In order to solve the above-mentioned problems, a heat dissipation device of the present invention is a heat dissipation device which radiates heat of a wiring board on which a heat-generating electronic component is mounted by a heat sink, wherein the wiring board is soldered. At least a part of the pattern portion provided to perform thermal coupling with the heat sink via the wiring board is larger than the outer periphery of the wiring board, and the protruding portion of the pattern from the wiring board is bent toward the wiring board side. Characteristic heat dissipation device. The pattern bending portion is provided at least at an edge of the wiring board farthest from the center of the wiring board.

In a heat dissipation device for dissipating heat of a wiring board on which a heat-generating electronic component is mounted by a heat sink, the wiring board on the pattern side is provided for thermally coupling the wiring board to the heat sink via solder. A heat dissipation device, characterized in that at least a part of the end portion is provided with an inclination.
The inclined portion of the wiring board is provided at least at an edge of the wiring board farthest from the center of the wiring board.

In a heat dissipation device for dissipating heat of a wiring board on which a heat-generating electronic component is mounted by a heat sink, at least a part of the end portion of the wiring board is bent together with a pattern portion which is thermally coupled to the heat sink via solder. A heat dissipation device characterized by: The bent portion of the wiring board is provided at least at the edge of the wiring board farthest from the center of the wiring board.

Further, in the heat dissipation device for dissipating the heat of the wiring board on which the heat-generating electronic component is mounted by the heat sink, the wiring board is provided with the convex portion at the joint portion of the heat sink for thermally coupling through the solder. The heat dissipation device is characterized in that the convex portion is smaller than the outer shape of the wiring board. It is characterized in that the convex portion of the heat sink is not provided at least below the edge of the wiring board farthest from the center of the wiring board.

[0012]

By the above means, the solder fillet at the end portion of the back surface pattern of the wiring board can be increased and the stress can be relieved during the thermal shock test, so that the back surface pattern area is resistant to solder cracks. Therefore, a heat dissipation device having excellent heat dissipation can be obtained.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a structural cross-sectional view of a heat dissipation device for explaining an embodiment of the present invention. In the figure,
Reference numeral 11 denotes a wiring board such as aluminum nitride.
The circuit pattern 12 is fixed to the upper part by copper foil. On the circuit pattern 12, a high power semiconductor element 13 such as an FET transistor is electrically connected to the circuit pattern 12 by a lead 14 using a TAB mounting method or the like. Wiring board 1
A back surface pattern 15 is formed on the back surface of No. 1 using copper foil.
The back surface pattern 15 has a larger area than the wiring board 11,
After bending the end portion by press working, the end portion is fixed to the wiring board 11 so that the concave side becomes the wiring board side. At this time, the bent portion 16 is bent from the joint surface between the back surface pattern 15 and the heat sink base 17 to the end surface of the wiring board. By using the solder 18, the wiring board 1
1 is connected to the heat sink base 17. The heat sink base 17 is then attached to the heat sink 2 using the screws 19.
Attach to 0.

At this time, the solder 18 enters the lower surface of the bent portion 16 formed on the back surface pattern 15, so that the solder fillet 21 larger than the conventional one can be formed. Usually, the fatigue life Nf of a solder joint is given by the following equation called the Coffin-Manson equation.

Nf = CΔε ⁿ where Δε is the inelastic strain range and C and n are material constants.

The inelastic strain range Δε is proportional to 1 / t, where t is the solder thickness at the back side soldering portion of the wiring board 11 and 1 is the distance from the center of the board. In general, the smaller Δε is, the longer the life Nf can be extended. Therefore, if 1 is made small and t is made large, the fatigue life can be extended. However, making l smaller means making the wiring board smaller, and this is limited to circuits and the like formed on the wiring board.
Significant reduction is difficult. It suffices to increase t, but even if the thickness of the solder formed is simply increased, the solder will flow during reflow soldering, making it difficult to effectively increase the thickness.

Therefore, a protruding portion due to the back surface pattern is provided at the edge portion of the wiring board to which a large stress is applied, and by bending the protruding portion, a solder pool is provided at the protruding portion and the solder thickness of the stress concentration portion is effectively increased. I can do it. Even when the stress-concentrated portion having the solder thickness receives a thermal shock, the solder portion can effectively absorb the stress.

In the conventional structure, the solder thickness is about 150 μm, and when a thermal shock test is performed on such a heat dissipation device, solder cracks occur in about 100 cycles. However, in the heat dissipation device with a solder thickness of 300 μm, it was confirmed by experiments that cracks did not occur even after 300 cycles, and it was found that sufficient reliability was ensured. Therefore, a sufficient effect can be obtained by providing a bend of about several hundred μm even in this bent portion.

Further, since the back surface pattern area is also increased by such a structure, the heat dissipation can be further improved,
Further, it is possible to obtain a heat dissipation device which is strong against stress and has high reliability.

FIG. 2 is a perspective view for explaining another embodiment of the present invention. In this embodiment, the circuit pattern 12 is fixed to the upper surface of the wiring board 11 with copper foil. Although the back surface pattern 15 is formed of copper foil on the back surface of the wiring board 11, the protruding portion from the wiring board 11 is bent toward the upper surface of the wiring board 11 to form a bent portion 16a. The bent portion 16a can increase the solder thickness of the soldering portion, and can absorb the stress at the time of thermal shock.

FIG. 3 is a perspective view of a first other embodiment of the present invention. In this embodiment, since the wiring board 11 has a rectangular shape, the stress is particularly concentrated on the short side portion having a large distance from the central portion of the board. Therefore, in order to prevent cracks on the short sides, the bent portions 16b of the back surface pattern 15 may be provided only on the short sides and the two sides. As a result, the same effect as the first embodiment can be obtained.

FIG. 4 is a perspective view of the wiring board 11 according to the second embodiment of the present invention. The corners in the wiring board are the points farthest from the board center in the board, and there are four points in the rectangular board. Therefore, at this point, the largest stress is applied to the substrate, and solder cracks occur. Therefore, solder cracks can be prevented by increasing the solder thickness at the corners and absorbing the stress. Therefore, the back surface pattern 15 is projected to this corner portion, and the bent portion 16c is provided at this portion. With such a structure, it is possible to increase the solder thickness at the corners, absorb the stress, and prevent cracks.

FIG. 5 is a sectional view of a wiring board 11 according to a third embodiment of the present invention. The bent portion 16d of the back surface pattern 15 may be bent to the end surface of the wiring board 11. As a result, the solder wets to the height near the surface of the wiring board 11, and a large solder fillet can be formed. As a result, the same effect as when the solder thickness is increased is obtained, and the stress at the edge of the wiring board 11 can be absorbed by the fillet portion. Therefore, it is possible to prevent solder cracks generated at the time of thermal shock.

FIG. 6 is a sectional view of a wiring board 11 according to a fourth embodiment of the present invention. In this way, it is also possible to form the bent portion 16e in which the protruding portion of the back surface pattern 15 has an arc shape. Even in the case of this structure, the stress concentration in the soldering portion between the wiring board and the heat sink base can be alleviated by increasing the solder thickness. Further, in the case of such an arc-shaped bent portion 16e, a corner is not formed unlike when bent at one point, so that stress is not concentrated at the corner of the bent portion, and more solder cracks are generated. Effective in prevention.

Further, as in the fifth embodiment of the present invention shown in FIG. 7, even if the bending portion 16f is bent in two steps or several steps, the stress concentration at the corners of the bending portion is dispersed. The same effect can be obtained.

FIG. 8 is a sectional view of a wiring board 11 in a sixth embodiment of the present invention. In this way, the inclined portion 11a is provided at the end portion of the back surface of the wiring board 11 and the back surface pattern 15a is formed up to this inclined portion, so that the solder at the stress concentration portion at the edge portion of the wiring board is formed as in the previous embodiments. The thickness can be increased to relieve stress and prevent solder cracks.

FIG. 9 is a sectional view of a wiring board 11 according to a seventh embodiment of the present invention. In this way, in the area where there is no problem in the arrangement of electronic components, the end portion 11b of the wiring board 11 is bent, and the circuit pattern 12 and the back surface pattern 1 are formed.
5 also bends, respectively. Similar to the above-described embodiments, the solder thickness at the stress concentration portion at the edge of the wiring board can be increased to relieve the stress and prevent solder cracks. This embodiment is particularly effective for a substrate having excellent workability such as a metal printed wiring board.

FIG. 10 is a structural sectional view of a heat dissipation device in the eighth other embodiment of the present invention. In the figure, 31 is a wiring board made of aluminum nitride or the like, and a circuit pattern 32 is fixed on the wiring board 31 with copper foil or the like. On the circuit pattern 32, a high power semiconductor element 33 such as an FET transistor is electrically connected to the circuit pattern 32 by a lead 34 by a TAB mounting method or the like. A back surface pattern 35 is formed of copper foil on the back surface of the wiring board 31. Then, by using the solder 36, the wiring board 31 is connected to the heat sink base 37. A protrusion 38 is formed below the heat sink base on the wiring board so as to be smaller than the outer shape of the wiring board 31. Then, the heat sink base 37 is attached to the heat sink 40 using the screws 39.

Also with this embodiment having such a structure, it is possible to increase the thickness and size of the solder fillet, which is the stress concentration portion at the edge portion of the wiring board 11, to relieve the stress, and to prevent the solder crack. Can be prevented.

Table 1 compares the test results with respect to thermal shock in the conventional example and each of Examples 1 to 9.

[0031]

[Table 1] The test conditions are 30 ° C. to 85 ° C. and a 30-minute cycle. In addition, the wiring board has 12.7 mm × 25.
A 4 mm × 0.635 mm aluminum nitride substrate is used.

As is clear from Table 1, in the conventional case, it is 1
It was confirmed that solder cracks were generated at about 00 cycles, whereas solder cracks were not generated at all even after 300 cycles in each of Examples 1 to 9 and it was confirmed that sufficient reliability could be secured. It was

[0033]

As described above, according to the heat dissipation device of the present invention, good heat dissipation can be obtained, and also when the thermal shock is applied, stress is relieved to prevent solder cracks and improve reliability. Can be achieved.

[Brief description of drawings]

FIG. 1 is a structural sectional view for explaining an embodiment of the present invention.

FIG. 2 is a perspective view of the insulating substrate of FIG.

FIG. 3 is a perspective view for explaining another embodiment of the present invention.

FIG. 4 is a perspective view for explaining a second other embodiment of the present invention.

FIG. 5 is a sectional view for explaining a third other embodiment of the present invention.

FIG. 6 is a sectional view for explaining a fourth another embodiment of the present invention.

FIG. 7 is a sectional view for explaining a fifth other embodiment of the present invention.

FIG. 8 is a sectional view for explaining a sixth embodiment of the present invention.

FIG. 9 is a sectional view for explaining a seventh other embodiment of the present invention.

FIG. 10 is a structural sectional view for explaining an eighth embodiment of the present invention.

FIG. 11 is a structural cross-sectional view for explaining a conventional heat dissipation device.

[Explanation of symbols]

11, 31 ... Insulating substrate, 12, 32 ... Circuit pattern, 1
3, 33 ... Semiconductor element, 14, 34 ... Lead, 15, 3
5 ... Back surface pattern, 16 ... Bent portion, 17, 37 ... Heat sink base, 18, 36 ... Solder, 19, 39 ... Screw,
20, 40 ... Heat sink, 21 ... Solder fillet, 3
8 ... Convex part.

Claims (8)

[Claims] 1. A heat dissipation device for dissipating heat of a wiring board on which a heat-generating electronic component is mounted by means of a heat sink, wherein the wiring board is provided with a pattern portion provided for thermal coupling with the heat sink via solder. At least a part is made larger than the outer circumference of the wiring board, and a protruding portion of the pattern from the wiring board is bent toward the wiring board. 2. The heat dissipation device according to claim 1, wherein the pattern bent portion is provided at least at a wiring board edge portion farthest from the center of the wiring board. 3. A heat dissipation device for dissipating heat of a wiring board on which a heat-generating electronic component is mounted by a heat sink, wherein the wiring board is provided on a pattern side provided for thermal coupling with the heat sink via solder. At the end of the wiring board,
A heat dissipation device characterized in that at least a part thereof is provided with an inclination. 4. The heat dissipation device according to claim 3, wherein the inclined portion of the wiring board is provided at least at an edge of the wiring board farthest from the center of the wiring board. 5. A heat dissipation device for dissipating heat of a wiring board on which a heat-generating electronic component is mounted by a heat sink,
A heat dissipation device characterized in that at least a part of the end portion of the wiring board is bent together with a pattern portion that is thermally coupled to a heat sink via solder. 6. The heat dissipation device according to claim 5, wherein the bent portion of the wiring board is provided at least at an edge of the wiring board farthest from the center of the wiring board. 7. A heat dissipation device for dissipating heat of a wiring board on which a heat-generating electronic component is mounted by means of a heat sink, wherein the wiring board is provided with a convex portion at a joint portion of the heat sink for performing thermal coupling through solder. The heat dissipation device is characterized in that the convex portion is smaller than the outer shape of the wiring board. 8. The heat dissipation device according to claim 7, wherein the convex portion of the heat sink is not provided at least below the edge of the wiring board farthest from the center of the wiring board.