Semiconductor-module external terminal

A semiconductor-module external terminal includes a bottom portion to be soldered and a terminal body vertically bent from the bottom portion, and the terminal body includes a first groove on a left end side and a second groove on a right end side of a bending portion which is bent immediately above the bottom portion, and the first groove and the second groove are asymmetrical with respect to a center line passing the terminal body in a vertical direction.

TECHNICAL FIELD

The present invention relates to an external terminal to be used for a semiconductor module, and more particularly to an external terminal suitable for a high-power semiconductor module.

BACKGROUND ART

In the high-power semiconductor module, thermal stress (bending stress and shear stress) causes a problem such as solder peeling and cracking when stress is applied to a substrate due to the temperature rise of the substrate. In particular, in a case in which an external terminal is soldered in a longer direction of a rectangular-shaped substrate, bending in the longer direction of the substrate is more likely to occur, which may easily cause a solder crack at a bottom portion to which the external terminal is soldered. In addition, the terminal body of the external terminal is fixed with a sealing material such as an epoxy resin with a small thermal expansion coefficient, so that a soldered portion located at the bottom portion of the external terminal is subjected to uneven stress due to a difference in thermal expansion of the sealing material and is also susceptible to thermal stress.

In other words, in order to ensure the reliability of the high-power semiconductor module, the distribution of the thermal stress that occurs in the soldered portion of the external terminal is a problem.

In order to solve the problem, conventionally, a structure in which a slit is provided in a terminal is proposed (Patent Literature 1). In this terminal, when thermal stress is applied from the substrate to the soldered portion, the slit bends to relieve stress.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. H6-021603

SUMMARY OF INVENTION

Technical Problem

However, the terminal shown in Patent Literature 1 does not provide sufficient stress relief when the distribution of the thermal stress from the substrate3changes in a complex manner. The reason for this is that the bending strength and the shear strength on left and right of the terminal body are the same, and thus the stress diffused from the bottom portion to be soldered to the substrate, to the terminal body, is unable to be effectively absorbed, thereby preventing the terminal body from deforming.

Solution to Problem

It is an object of the present invention to provide a semiconductor-module external terminal that causes a terminal body to easily deform by changing bending strength and shear strength on the left and right of the terminal body.

A semiconductor-module external terminal of the present invention includes a bottom portion to be soldered and a plate-shaped terminal body vertically bent from the bottom portion.

The terminal body includes a first groove on a left end side and a second groove on a right end side of a bending portion which is bent immediately above the bottom portion, and the first groove and the second groove are asymmetrical with respect to a center line passing the terminal body in a vertical direction.

In an embodiment of the present invention, the first groove and the second groove each have different lengths in a horizontal direction.

Other embodiments of the present invention include a third groove and a fourth groove. The third groove and the fourth groove are also asymmetrical with respect to the center line passing the terminal body in the vertical direction.

Advantageous Effects of Invention

In the present invention, the first groove and the second groove are provided on the bending portion bent immediately above the bottom portion to be soldered, so that stress concentrated on the bottom portion is affected by the first groove and the second groove, which causing the terminal body to easily deform. In addition, the first groove and the second groove are asymmetrical with respect to the center line passing through the terminal body in the vertical direction, which causes the terminal body to even more easily deform in response to stress. As a result, the stress concentrated on the bottom portion is absorbed by the deformation of the terminal body, which can prevent a solder fracture and a crack at the bottom portion from occurring.

DESCRIPTION OF EMBODIMENTS

FIG.1is a perspective view of a semiconductor module according to an embodiment of the present invention.FIG.2is a top view of the semiconductor module.

This semiconductor module includes a base plate1of a metal conductor, a case2made of a resin that is attached on the base plate1, and a ceramic substrate (hereinafter referred to as a substrate)3stored in the case2.

A plurality of semiconductor elements, circuit components, and the like that are not shown, are mounted to the substrate3, and seven external terminals4(4ato4g) for external connection are solder-connected to the upper and lower ends and the right side end of the substrate3. Actually, the substrate3is configured by a DCB (Direct Copper Bond) substrate in which a plurality of ceramic substrates are directly bonded to a copper plate, and the three external terminals4cto4elocated on the right side ofFIG.2are disposed in a line in the longer direction of the rectangular DCB substrate30. The other external terminals4a,4b,4f, and4gare disposed in a shorter direction of other not-shown DCB substrates.

All the seven external terminals4(4ato4g) have the same shape and are each provided by punching a plate-shaped metal conductor into a predetermined shape and then performing bending. InFIG.1andFIG.2, the upper end portions of the seven external terminals4(4ato4g), although being not bent, are bent after the bottom portion is soldered and the inside of the case is sealed with a resin. Hereinafter, the external terminal4(4ato4g) is referred to as an external terminal4, and will be described as a single external terminal4.

FIG.3is a left perspective view of the external terminal4.

The external terminal4is configured by a bottom portion40that is soldered to the substrate3, a first vertical piece41bent from the bottom portion40in a vertical direction, a horizontal piece42bent from the vertical piece41in a horizontal direction, and a second vertical piece43bent from the horizontal piece42in the vertical direction. The first vertical piece41, the horizontal piece42, and the second vertical piece43configure a terminal body44.

A first groove45on a left end side and a second groove on a right end side of a bending portion which is bent immediately above the bottom portion40, are provided at the first vertical piece41of the terminal body44. In addition, a third groove47on the left end side and a fourth groove48on the right end side at a lower end of the second vertical piece43, above the first groove45and the second groove46, are provided.

A bending part49is provided in a substantially central position of the second vertical piece43of the terminal body44. A connection hole50for screwing a terminal to a cable or bus bar is provided in an upper portion of the terminal body44. Positioning protrusions51and52are provided on the opposite ends of the second vertical piece43, slightly below the bending part49of the second vertical piece43. A fixing anchor hole53is provided in a center portion of the second vertical piece43, slightly below the positioning protrusions51and52of the second vertical piece43. These positioning protrusions51and52are hooked on the case2, and positioned in predetermined points of the case2. Then, the external terminal4is soldered to the substrate3. When the sealing material is injected into the case2, the sealing material also enters the anchor hole53, and the terminal body44is fixed in the sealing material.

FIG.4AtoFIG.4Dare a top view (FIG.4A), a front view (FIG.4B), a bottom view (FIG.4C), and a right side view (FIG.4D) of the external terminal4.

The first groove45provided on a left end side and the second groove46provided on a right end side of the bending portion which is bent immediately above the bottom portion40, are asymmetrical with respect to a center line X passing through the terminal body in the vertical direction. In other words,FIG.4AtoFIG.4Dshow a length L1of the first groove45<a length L2of the second groove46.

The first groove45and the second groove46are provided immediately above the bottom portion40, that is, in contact with the bottom portion40, and L1<L2, so that the external terminal4absorbs stress in an unbalanced state to the left and right in response to thermal stress generated at the bottom portion40. As a result, in response to the thermal stress at the bottom portion40, the first vertical piece41of the external terminal4easily deforms to the left and right, and behaves to absorb more stress. According to an experiment, setting L1<L2rather than setting L1=L2caused an unbalanced state in response to the thermal stress, resulting in greater stress absorption and less solder cracks at the bottom portion40. Further, the first groove45and the second groove46were provided immediately above the bottom portion40, so that this effect was observed more significantly.

In the present embodiment, in order to form a further unbalanced state to the left and right to the thermal stress, the third groove47and the fourth groove48are provided. The third groove47and the fourth groove48are provided on a lower end of the second vertical piece43, and the position is above the first groove45and the second groove46. The third groove47is provided on a left end side of the second vertical piece43, and the fourth groove48is provided on a right end side of the vertical piece43. A length L4of the third groove47is the same as the length L1of the first groove L1. In addition, the third groove47and the fourth groove48are asymmetrical with respect to the center line X in the horizontal direction. In other words,FIG.4AtoFIG.4Dshow the length L4(=L1) of the third groove47>a length L3of the fourth groove48.

The third groove47and the fourth groove48as well as the first groove45and the second groove46also form an unbalanced state in response to the thermal stress to be generated at the bottom portion40. Therefore, the terminal body44of the external terminal more easily deforms to the left and right in response to the thermal stress at the bottom portion40. Herein, even when only one pair of either a pair of the first groove45and the second groove46or a pair of the third groove47and the fourth groove48is formed, an unbalanced state in response to thermal stress is able to be formed. In addition, in a case in which both of the pair of the first groove45and the second groove46, and the pair of the third groove47and the fourth groove48are provided, the length of each of those grooves is able to be set to any length that allows an unbalanced state to be formed. For example, the combination of L1>L2and L3>L4and the combination of L1>L2and L3<L4are possible. In addition, in these combinations, it is possible to set the relationship between L1and L4to L1>L4or L1<L4. In these combinations, a longer groove Lx of L1or L2and a longer groove Ly of L3or L4may be disposed on the left side with respect to the center line X or may be disposed on the right side with respect to the center line X. As another example, Lx can be disposed on the left side with respect to the center line X, and Ly can also be disposed on the right side with respect to the center line X. In either case, an unbalanced state in response to thermal stress can be formed.

In addition, the second vertical piece43is fixed by the sealing material, so that the third groove47and the fourth groove48behave in such a way that the terminal body44may deform more easily to the left and right.

According to the above configuration, even when a large thermal stress is generated at the bottom portion40of the external terminal4due to continued high temperature of the substrate3or repeated thermal cycling, this thermal stress is absorbed by deformation of the terminal body44, in this example, both or one of the first vertical piece41and the second vertical piece43. As a result, a crack can be prevented from being generated at a soldering portion that fixes the bottom portion40.

The above effect can be obtained by making at least the first groove45and the second groove46asymmetrical with respect to the center line X. In addition, the same effect is significant in the external terminals4cto4e. The reason for this is that the external terminals4cto4eare disposed in a line on a side in the longer direction of the rectangular-shaped DCB substrate30. The rectangular-shaped DCB substrate30tends to bend in the longer direction due to heat, and thereby the external terminals4cto4eare presumed to be relatively more susceptible to thermal stress than the other external terminals.

Subsequently, other embodiments will be described.

FIG.5is a front view of an external terminal according to a second embodiment.

The third groove47and the fourth groove48are each located at different positions in the vertical direction. Others are the same as inFIG.4AtoFIG.4D. The lengths of the third groove47and the fourth groove48may be the same or may be different.

As a result, the first groove45and the second groove46are asymmetrical with respect to the center line X, and the third groove47and the fourth groove48are also asymmetrical with respect to the center line X.

It is to be noted that the external terminal4is positioned at a predetermined spot inside the substrate3by hooking the positioning protrusions51and52on the case2, and then the bottom portion40of the external terminal4is soldered on the substrate3. Subsequently, the inside of the case2is sealed so that a soldered area may be covered with a gel-like sealing material, and then the inside of the case2is further sealed with an epoxy sealing material over again. At this time, the epoxy sealing material enters also into the anchor hole53and solidifies, and the terminal body44is fixed in the sealing material.

REFERENCE SIGNS LIST