Heat dissipation structure of semiconductor device

The present invention relates to a heat dissipation structure (also referred to as a cooling structure) of a surface mount semiconductor device (semiconductor device), and particularly relates to a heat dissipation structure with heat dissipation and insulation reliability, which can suitably be applied to a thin package semiconductor device.

FIG. 7( a ) is a schematic perspective view exemplarily showing a conventional lead type discrete component 1 . FIG. 7( b ) is a schematic perspective view exemplarily showing a surface mount semiconductor device 10 that has recently been developed.

In association with increasing an operational speed of a semiconductor switching device, it is necessary to reduce parasitic inductance of the device itself. Unlike the conventional discrete component 1 (for example, a lead type IGBT) as shown in FIG. 7( a ) , the semiconductor device 10 as shown in FIG. 7( b ) , for example, has a very high switching speed. Thus, thinning of its device package has progressed so as to realize the smallest possible parasitic inductance.

As shown in FIG. 7( b ) , such a semiconductor device 10 is housed in an ultra-thin package 11 , and has, for example, an electrical bonding surface 11 a and a heat dissipation surface 11 b on the opposite side. On the electrical bonding surface 11 a , at least one electrode (terminal) 12 that is electrically connected to a substrate is disposed. On the heat dissipation surface 11 b , a large electrode 13 that also serves to dissipate heat is disposed. When the semiconductor device 10 is mounted, it is necessary to have an excellent heat dissipation as well as an excellent insulation reliability. For this purpose, techniques have been proposed as disclosed in, for example, Patent Documents 1 to 3.

Patent Documents

[Patent Document 1] JP 2006-147862 A

[Patent Document 2] JP 2014-241340 A

[Patent Document 3] JP 2000-311971 A

Problem to be Solved by the Invention

FIG. 8( a ) is a cross-sectional view exemplarily and schematically showing a conventional heat dissipation structure 202 . FIG. 8( b ) is a cross-sectional view exemplarily and schematically showing a heat dissipation structure 202 A, which is a variation of the heat dissipation structure 202 .

In order to reduce device costs, each device is required to have the maximum possible capacity, which needs a structure that can efficiently dissipate generated heat. As an example, it is possible to consider that a heat sink 30 is directly connected to the semiconductor device 10 .

Alternatively, as shown in the heat dissipation structure 202 in FIG. 8( a ) , the semiconductor device 10 may be connected to the heat sink 30 via a conductive TIM 33 (for example, 50 W/deg·m), which is an example of conductive thermal interface materials (TIM).

However, due to thinning of the package 11 of the semiconductor device 10 , the distance between the electrodes 12 having different voltages is reduced, and the insulation distance may not be maintained depending on conditions of a conductive material such as solder, which may result in generation of electrical breakdown that damages the semiconductor device 10 .

In order to avoid the above disadvantages, it is possible to interpose an insulating TIM 43 (for example, −10 W/deg·m) between the semiconductor device 10 and the heat sink 30 in place of the conductive TIM 33 , as shown, for example, in the heat dissipation structure 202 A in FIG. 8( b ) . With such a configuration, although generation of electrical breakdown can be avoided, the device cannot have a large capacity due to a low coefficient of thermal conductivity. For this reason, there needs to be increase in size and capacity of the semiconductor device 10 , and/or parallel use of multiple semiconductor devices 10 , which may increase overall cost.

In consideration of the above problems in the conventional art, an object of the present invention is to provide a heat dissipation structure of a semiconductor device with an excellent heat dissipation as well as an excellent insulation reliability that can be suitably applied to a thin type surface mount semiconductor device.

Means for Solving the Problem

In order to achieve the above object, in the present invention, a heat dissipation structure of a semiconductor device is provided. The semiconductor device includes: an electrical bonding surface electrically connected to a substrate; and a heat dissipation surface as an opposite side of the electrical bonding surface. The heat dissipation surface makes contact with a high-heat-transferring conductive member via a non-insulating member, and the high-heat-transferring conductive member makes contact with a heat dissipation component via an insulating member. A surface of the high-heat-transferring conductive member facing the semiconductor device includes a recess part formed in at least a part in a vicinity of an outer periphery of the semiconductor device.

With the above-described heat dissipation structure of a semiconductor device, heat generated by the semiconductor device is transmitted from the heat dissipation surface to the high-heat-transferring conductive member via the non-insulating member so as to be diffused, and further is transmitted to the heat dissipation component via the insulating member. Thus, the heat dissipation structure has an excellent heat dissipation. In addition, it is possible to avoid generation of electrical breakdown thanks to the recess part in a surface of the high-heat-transferring conductive member facing the semiconductor device, which is formed in the vicinity of the outer periphery of the semiconductor device.

In the heat dissipation structure of the semiconductor device of the present invention, the substrate may be fixed to the high-heat-transferring conductive member by a conductive fixing material (such as a screw) so that at least a part of a pattern on the substrate is conducted to the high-heat-transferring conductive member. Also, the substrate may be further fixed to the high-heat-transferring conductive member by an insulating fixing material (such as a screw).

With the above-described heat dissipation structure of the semiconductor device, it is possible to more reliably avoid generation of electrical breakdown, as well as to accurately position the components. When the substrate is fixed using also the insulating fixing material, the above positioning and fixing can be performed more accurately and reliably.

Effect of the Invention

With a heat dissipation structure of a semiconductor device of the present invention, heat generated by the semiconductor device is transmitted from a heat dissipation surface to a high-heat-transferring conductive member via a non-insulating member so as to be diffused, and further is transmitted to a heat dissipation component via an insulating member. Thus, the heat dissipation structure has an excellent heat dissipation. In addition, it is possible to avoid generation of electrical breakdown thanks to the recess part in a surface of the high-heat-transferring conductive member facing the semiconductor device, which is formed in the vicinity of the outer periphery of the semiconductor device.

FIG. 1 is a cross-sectional view schematically showing a heat dissipation structure 103 according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a heat dissipation structure 103 A according to a variation of the first embodiment of the present invention.

FIG. 3( a ) is a perspective view schematically showing a heat dissipation structure 202 B in which a conventional heat dissipation structure 202 A is further mounted on a heat sink 30 via a conductive TIM 33 . FIG. 3( b ) is a cross-sectional view thereof.

FIG. 4 is a table indicating detailed conditions of a thermal simulation performed in the heat dissipation structure 202 B shown in FIGS. 3( a ) and 3( b ) .

FIG. 5( a ) is a cross-sectional view schematically showing a heat dissipation structure 103 B largely similar to the heat dissipation structure 103 according to the first embodiment of the present invention. FIG. 5( b ) is a partially enlarged perspective view thereof, and FIG. 5( c ) is a cross-sectional view thereof.

FIG. 6 is a table indicating detailed conditions of a thermal simulation performed in the heat dissipation structure 103 B shown in FIGS. 5( a ) to 5( c ) .

FIG. 7( a ) is a schematic perspective view exemplarily showing a conventional lead type discrete component 1 . FIG. 7( b ) is a schematic perspective view exemplarily showing a surface mount semiconductor device 10 that has recently been developed.

FIG. 8( a ) is a cross-sectional view exemplarily and schematically showing another conventional heat dissipation structure 202 . FIG. 8( b ) is a cross-sectional view exemplarily and schematically showing the heat dissipation structure 202 A, which is a variation of the heat dissipation structure 202 .

Hereinafter, several embodiments of the present invention will be described with reference to the drawings.

First Embodiment

FIG. 1 is a cross-sectional view schematically showing a heat dissipation structure 103 according to a first embodiment of the present invention.

As shown in FIG. 1 , in this heat dissipation structure 103 , a heat spreader 31 as one example of non-insulating heat spreading elements is mounted on the heat sink 30 via an insulating TIM 43 . On the heat spreader 31 , a semiconductor device 10 is mounted via a conductive TIM 33 , with a heat dissipation surface 11 b of the semiconductor device 10 being a lower side. Electrodes 12 on an electrical bonding surface 11 a of the semiconductor device 10 are electrically connected to a lower surface pattern 22 of a substrate 20 by soldering and the like.

Furthermore, in an upper surface of the heat spreader 31 , a recess part 31 a is formed near the outer periphery of the semiconductor device 10 , and more specifically, in the vicinity of the electrodes 12 and the like that are electrically connected to the substrate 20 by soldering and the like (especially the electrodes 12 to which are applied potentials different from that is applied to the heat dissipation surface 11 b ). The recess part 31 a has, for example, a groove shape along the outer periphery of the semiconductor device 10 , and the internal surface of the groove is preferably formed as a shape substantially having an equal distance from any of the soldering positions.

With the above-described heat dissipation structure 103 , it is possible to realize a high thermal conductivity by interposing the conductive TIM 33 between the semiconductor device 10 and the heat spreader 31 . It is also possible to ensure a sufficient insulation distance between the soldering positions of the electrodes 12 and the like of the semiconductor device 10 and the upper surface of the heat spreader 31 that may have a voltage highly different from the soldering positions. Thus, both the high heat dissipation and the insulation reliability can be obtained by the low-cost structure, which results in overall cost reduction in a power converter and the like.

The resistance value of the conductive TIM 33 is not zero, but changes according to the temperature and/or the adhesion state. Thus, it is assumed that the resistance value changes during driving of the semiconductor device 10 . As a result, the potential of the heat spreader 31 may become instable, which may lead to malfunction of or damage to the semiconductor device 10 due to generation of voltage noise or surge voltage.

Thus, a screw hole 31 b may be formed in the heat spreader 31 so as to fix the substrate 20 to the heat spreader 31 by screwing a conductive screw 51 from the surface of the substrate 20 .

In this way, the heat spreader 31 is electrically connected to the pattern on the substrate 20 (for example, the lower surface pattern 22 ) that should have the same potential as the heat spreader 31 , so that the electrical stability is improved. Thus, it is possible to more reliably avoid electrical breakdown of the semiconductor device 10 . Also, it is possible to accurately position the semiconductor device 10 bonded to the substrate 20 by soldering and the like and the recess part 31 a in the heat spreader 31 . Such a positioning is important to ensure a sufficient insulation distance.

Variation of First Embodiment

FIG. 2 is a cross-sectional view schematically showing a heat dissipation structure 103 A of the semiconductor device 10 according to a variation of the first embodiment of the present invention. The common elements with the first embodiment are indicated by the same reference numerals, and hereinafter, a description will be given mainly on the configuration that differs from the configuration of the first embodiment.

In order to accurately position the semiconductor device 10 bonded to the substrate 20 by soldering and the like and the recess part 31 a in the heat spreader 31 , or to fix the substrate 20 to the heat spreader 31 , there may be a case in which a part on the substrate 20 that should not be conducted to the heat spreader 31 (for example, an upper surface pattern 21 conducted to the electrode 12 of the semiconductor device 10 via a via hole 23 ) is required to be fixed to the heat spreader 31 by the screw.

In this case, as shown in FIG. 2 , another screw hole 31 c may be formed in the heat spreader 31 so as to fix the substrate 20 to the heat spreader 31 by screwing an insulating screw 52 .

With the above-described heat dissipation structure 103 A, it is possible to more reliably perform the positioning of the semiconductor device 10 and the recess part 31 a , and the fixing of the substrate 20 to the heat spreader 31 .

FIG. 3( a ) is a perspective view schematically showing a heat dissipation structure 202 B in which the conventional heat dissipation structure 202 A is further mounted on the heat sink 30 via the conductive TIM 33 . FIG. 3( b ) is a cross-sectional view thereof. FIG. 4 is a table indicating detailed conditions of a thermal simulation performed in the heat dissipation structure 202 B shown in FIGS. 3( a ) and 3( b ) .

First, for the sake of comparison, the thermal simulation was performed in the heat dissipation structure 202 B under conditions indicated in FIG. 4 . In order to avoid electrical breakdown, the insulating TIM 43 (0.3 mmt) was interposed between the semiconductor device 10 and the heat spreader 31 , and the conductive TIM 33 (0.3 mmt) was interposed between the heat spreader 31 and the heat sink 30 .

By the cross-sectional temperature distribution in the steady state obtained by the thermal simulation, it was confirmed that the temperature increased up to 58° C. at a maximum due to heat generation from the semiconductor device 10 in the heat dissipation structure 202 B.

FIG. 5( a ) is a cross-sectional view schematically showing a heat dissipation structure 103 B largely similar to the heat dissipation structure 103 according to the first embodiment of the present invention. FIG. 5( b ) is a partially enlarged perspective view thereof, and FIG. 5( c ) is a cross-sectional view thereof. FIG. 6 is a table indicating detailed conditions of a thermal simulation performed in the heat dissipation structure 103 B shown in FIGS. 5( a ) to 5( c ) .

Second, as an example of the present invention, the thermal simulation was performed in the heat dissipation structure 103 B under conditions indicated in FIG. 6 . In the heat dissipation structure 103 B, the recess part 31 a is formed in a part of the heat spreader 31 that is close to one side of the semiconductor device 10 . The semiconductor device 10 is connected to the heat spreader 31 via the conductive TIM 33 while the heat spreader 31 is connected to the heat sink 30 via the insulating TIM 43 .

By the cross-sectional temperature distribution in the steady state obtained by the thermal simulation, it was confirmed that the temperature increased up to only 46° C. at a maximum due to heat generation from the semiconductor device 10 in the heat dissipation structure 103 B. Thus, a large reduction in temperature (approximately 36% reduction in temperature increase) was confirmed.

Also, it was found that the recess part 31 a formed in the heat spreader 31 exerts little or no adverse effect on thermal diffusion. Thus, it is possible to realize both heat dissipation and insulation reliability at low cost, by forming the recess part 31 a in the heat spreader 31 so as to ensure insulation reliability and by interposing the conductive TIM 33 between the heat spreader 31 and the semiconductor device 10 .

The respective configurations in the above-described embodiments and their variations may be combined with each other, provided that there is not any particular obstructive factor.

The present invention may be embodied in other forms without departing from the gist or essential characteristics thereof. Therefore, the embodiments described herein are to be considered in all respects as illustrative and not limiting. The technical scope of the present invention is indicated by the appended claims rather than by the foregoing embodiments, and all modifications and changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

This application claims priority on Patent Application No. 2016-081963 filed in Japan on Apr. 15, 2016. The entire contents thereof are hereby incorporated in this application by reference. Also, the entire contents of the documents cited herein are hereby incorporated in this application by reference.

10 Semiconductor device

11 Package

12 Electrode

13 Electrode

20 Substrate

30 Heat sink

31 Heat spreader

33 Conductive TIM

43 Insulating TIM

51 Conductive screw

52 Insulating screw