JP4760267B2 - Junction structure - Google Patents

Description

  The present invention relates to a joint structure that relieves stress when joining different materials to a metal plate.

Conventionally, as a joint structure in which different materials are joined to a metal plate, there is a mounting structure in which a semiconductor element is mounted on a metal plate as described in Patent Document 1, for example.
In this mounting structure, a metal plate made of aluminum is bonded to both surfaces of a ceramic plate, and a semiconductor element is bonded to the metal plate by brazing.
In this case, the metal plate and the semiconductor element are subjected to a temperature change in which the metal plate and the semiconductor element are heated to the brazing temperature and then cooled to room temperature.
Therefore, due to the difference in thermal expansion coefficient between the semiconductor element and the metal plate, a residual stress is generated at the joint between the semiconductor element and the metal plate, and a crack may occur at the joint depending on the design.
Similarly, even when the semiconductor device is repeatedly operated, repeated thermal stresses are generated due to temperature rise and temperature drop, and there is a possibility that cracks may occur in the joint due to metal fatigue.
Further, it is known that the magnitude of the thermal stress is affected by a difference in thermal expansion coefficient, a joining distance, a temperature difference, a Young's modulus, and the like.
In particular, these cracks are likely to occur at the corners of the semiconductor element, which may reduce the connection reliability of the semiconductor element.

Therefore, in Patent Document 1, instead of copper, which is generally used as a metal plate for mounting a semiconductor element, by using aluminum having a Young's modulus lower than copper, the joint portion between the semiconductor element and the metal plate Thermal stress is relieved.
Thereby, the occurrence of cracks in the semiconductor element, the brazing material, or the metal plate is prevented, thereby improving the reliability.
JP 2001-144224 A

  However, when the mounting structure described above is applied to a mounting structure of a semiconductor element (for example, SiC) that can use such a base substrate at a high temperature, when the semiconductor element is operated at a high temperature, Therefore, there is a problem that it becomes more difficult to prevent the occurrence of cracks in the semiconductor element, the brazing material, or the metal plate only by changing the material of the metal plate.

  Therefore, in view of such a problem, the present invention has an object to provide a joint structure in which thermal stress generated on a joint surface between different materials is further reduced, for example, when a semiconductor element is joined to a metal plate.

In the present invention, the second member is joined to the main surface of the first member, and at least one or more third members are embedded in the first member or the first member around the second member. together are joined to the main surface of the member, the third member has a higher thermal expansion coefficient than the first member, second member, configuration and having a lower thermal expansion coefficient than the first member did.

According to the present invention, around the second member, at least one third member is embedded in the first member or joined to the main surface of the first member, and the third member is has a higher thermal expansion coefficient than the first member, the second member, since the configuration has a lower thermal expansion coefficient than the first member, the first due to thermal stress of the third member Residual stress generated on the joint surface between the member and the second member can be relaxed, and cracks generated in the first member can be prevented.

Next, embodiments of the present invention will be described by way of examples.
First, the first embodiment will be described.
In this embodiment, a mounting structure in which a semiconductor chip is mounted on an aluminum plate will be described as a bonding structure in which different materials are bonded to each other.
FIG. 1A shows a planar shape of the mounting structure in the present embodiment, and FIG. 1B shows a cross section taken along the line AA in FIG.
The rectangular semiconductor chip 1 is bonded to the element mounting surface 2 a of the aluminum plate 2 by the bonding agent 3.
The semiconductor chip 1 is a power semiconductor chip that is a low thermal expansion body compared to the aluminum plate 2 and is composed of a wide band gap compound semiconductor made of, for example, SiC.
A rectangular column-shaped zinc body 4 is embedded in the aluminum plate 2 around the semiconductor chip 1 and in the vicinity of the four corners of the semiconductor chip 1.
The aluminum plate 2 serves as a current path for a current flowing through the bonded semiconductor chip 1 and has a heat dissipation function on the surface opposite to the element mounting surface 2a to which the semiconductor chip 1 is mounted.
On the other hand, the zinc body 4 has a higher thermal expansion coefficient than the aluminum plate 2 and has a high Young's modulus and a high yield stress.

A case where a temperature change occurs in the mounting structure in a state where the semiconductor chip 1 is mounted on the aluminum plate 2 will be described.
2A shows a planar shape of the mounting structure, and FIG. 2B shows a cross section taken along the line BB in FIG. 2A.
In particular, FIG. 2B shows an enlarged view of the periphery of the corner of the semiconductor chip 1, and the bonding agent 3 is not shown.
The semiconductor chip 1 is assumed to be a SiC chip configured with SiC as a base.
The Young's modulus of the aluminum plate 2 is 70 GPa, and the Young's modulus of the zinc body 4 is 90 GPa.
When the semiconductor chip 1 is brazed, the temperature of the semiconductor chip 1 or the aluminum plate 2 drops from high temperature to room temperature.
At this time, as indicated by an arrow in FIG. 2A, stress is generated in a direction in which the semiconductor chip 1, the aluminum plate 2, and the zinc body 4 contract.

In the aluminum plate 2 (Al plate), as shown in FIG. 2B, thermal stress TA1 is generated by thermal contraction just below the corner of the semiconductor chip 1 (SiC chip).
The direction of the thermal stress TA1 faces the center side of the aluminum plate 2, and the magnitude of the thermal stress TA1 is 24 ppm / K × ΔT.
Here, K is the Young's modulus, and ΔT is the temperature difference when the temperature drops from high temperature to room temperature.
The semiconductor chip 1 also generates thermal stress TS1 at the corners of the semiconductor chip 1 due to thermal contraction.
The direction of the thermal stress TS1 faces the center side of the semiconductor chip 1, that is, the same direction as the thermal stress TA1, and the magnitude of the thermal stress TS1 is 3 ppm / K × ΔT.

In the zinc body 4 (Zn plate), thermal stress TZ <b> 1 directed toward the center of the zinc body 4 is generated at the end of the semiconductor chip 1 on the corner side.
Since the zinc body 4 has a thermal expansion coefficient larger than that of the aluminum plate 2, the zinc body 4 is thermally contracted more than the aluminum plate 2.
The magnitude of the thermal stress TZ1 is 35 ppm / K × ΔT.
Note that the end of the zinc body 4 opposite to the end where the thermal stress TZ1 is generated is opposite in direction to the thermal stress TZ1 and the thermal stress TZ1 ′ having the same magnitude is also present. It has occurred.

As shown in FIG. 2 (b), since the directions of the thermal stress TA1 of the aluminum plate 2 and the thermal stress TZ1 of the zinc body 4 are opposite to each other, the region immediately below the corner of the semiconductor chip 1 in the aluminum plate 2 ( Hereinafter, in the region 2b), the displacement due to the thermal contraction of the aluminum plate 2 is canceled out.
Therefore, in the region 2b, the thermal stress due to the thermal contraction difference between the semiconductor chip 1 and the aluminum plate 2 is relieved.
Similarly, even when the temperature drops after the temperature of the semiconductor chip 1 rises (when the temperature rises due to the operation of the semiconductor chip), the thermal stress in the region 2b can be relaxed.
In this embodiment, the aluminum plate 2 constitutes the first member in the present invention, and the semiconductor chip 1 constitutes the second member in the present invention. The zinc body 4 constitutes the third member in the present invention.

In this embodiment, the semiconductor chip 1 is bonded to the aluminum plate 2 and the zinc bodies 4 are embedded in the vicinity of the four corners of the semiconductor chip 1 in the aluminum plate 2, so that the semiconductor chip 1 and the aluminum plate 2 are embedded. Even when a temperature change occurs, the residual stress generated on the joint surface between the semiconductor chip 1 and the aluminum plate 2 is relieved by the thermal stress of the zinc body 4, and the repeated fatigue of the aluminum plate 2 is reduced during repeated use. Can be extended.
Therefore, the occurrence of cracks can be suppressed in the corner portions of the semiconductor chip 1, the region 2b of the aluminum plate 2, and the bonding agent 3 on the region 2b.
Since the zinc body 4 having a higher Young's modulus than the aluminum plate 2 is used, stress due to thermal deformation of the zinc body 4 can be effectively transmitted to the aluminum plate 2 without the zinc body 4 being greatly bent. The effect of reducing the thermal stress in the region 2b can be enhanced by the zinc body 4.

Further, the shape of the zinc body 4 is not limited to the quadrangular prism shape, and may be other shapes such as a columnar shape, and as shown in the top view of FIG. Can be formed so as to be surrounded by a zinc body 4A having an L-shaped cross section.
Furthermore, besides embedding the zinc body 4 in the aluminum plate 2, for example, as shown in the sectional view of FIG. 3B, the zinc body 4A can be joined on the element mounting surface 2a.
FIG. 3B is a cross-sectional view taken along the line BB in FIG.
The zinc body 4 may be an alloy containing zinc as a main component.
In the first embodiment, the mounting structure in which the semiconductor chip 1 is bonded to the aluminum plate 2 as a bonding structure of different materials has been described. However, in addition to this, for example, in the bonding structure in which a ceramic plate is bonded to the aluminum plate 2, The same effect as the embodiment can be obtained.
When joining the semiconductor chip 1 on a copper plate or an alloy plate containing copper as a main component instead of the aluminum plate 2, aluminum or an alloy containing aluminum as a main component can be used instead of the zinc body 4. .

Next, a second embodiment will be described.
FIG. 4A shows a planar shape of the mounting structure in the second embodiment, and FIG. 4B shows a cross section taken along the line CC in FIG. 4A.
The mounting structure in the present embodiment is similar to the first embodiment in that the semiconductor chip 1 is bonded to the element mounting surface 2a of the aluminum plate 2 using the bonding agent 3, and zinc bodies are formed at the four corners of the semiconductor chip 1 in the aluminum plate 2. 4 is embedded, and the ceramic plate 5 is bonded to the side surface of the aluminum plate 2 opposite to the element mounting surface 2a.
The ceramic plate 5 is made of a material having good thermal conductivity and insulation, and for example, alumina, aluminum nitride, silicon nitride or the like can be used.
The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

A case where a temperature change occurs in the mounting structure will be described.
When the temperature drops, the thermal stress TA1 is generated in the aluminum plate 2 due to thermal contraction just below the corner of the semiconductor chip 1 as in the first embodiment.
Further, in the zinc body 4, thermal stress TZ <b> 1 is generated at the end of the semiconductor chip 1 on the corner portion side and directed toward the center of the zinc body 4.
Although not shown, the thermal stress TS1 is also generated in the semiconductor chip 1 as in the first embodiment.

Here, a force is applied to the zinc body 4 so that the position of the zinc body 4 itself is pulled closer to the side closer to the semiconductor chip 1 (the center side of the aluminum plate 2) as the aluminum plate 2 is thermally contracted.
This force acts in a direction to weaken the force that the zinc body 4 pulls the aluminum plate 2 by the thermal stress TZ1 in the region 2b.
Therefore, by fixing the aluminum plate 2 and the zinc body 4 to the ceramic plate 5, the force with which the zinc body 4 is drawn toward the center side of the aluminum plate 2 is suppressed, and the zinc body 4 is suppressed by the thermal stress TZ1. Can be transmitted to the aluminum plate 2 without weakening the pulling force.
Similarly, even when the temperature drops after the temperature of the semiconductor chip 1 rises, the thermal stress in the region 2b can be relaxed.
The ceramic plate 5 constitutes the fourth member in the present invention.

In this embodiment, the semiconductor chip 1 is bonded to the aluminum plate 2, the zinc bodies 4 are embedded in the vicinity of the four corners of the semiconductor chip 1 in the aluminum plate 2, and the ceramic plate 5 is bonded to the aluminum plate 2. Therefore, the zinc body 4 is restrained from being drawn into the center side of the aluminum plate 2, and the thermal stress TZ1 due to the zinc body 4 can be effectively transmitted to the aluminum plate 2, and in repeated use, the region 2b Repetitive fatigue can be reduced and the life can be extended.
Moreover, since the thermal stress TZ1 due to the zinc body 4 can be effectively transmitted to the aluminum plate 2, the thermal stress generated in the region 2b can be relaxed even if the zinc body 4 has a small size.

  The embodiments described above are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in each of the above embodiments is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

It is a figure which shows the mounting structure in a 1st Example. It is a figure which shows the detail of a thermal stress. It is a figure which shows the modification of a zinc body. It is a figure which shows the mounting structure in a 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor chip 2, 2A Aluminum plate 2a Element attachment surface 2b Area | region 3 Bonding agent 4, 4A Zinc body 5 Ceramic plate TZ1, TZ1 ', TA1, TS1 Thermal stress

Claims (6)

A joining structure in which the second member is joined to the main surface of the first member,
Comprising at least one or more third members around a joint portion between the first member and the second member, embedded in the first member, or joined to the main surface of the first member;
The third member has a higher coefficient of thermal expansion than the first member;
The joining structure, wherein the second member has a lower coefficient of thermal expansion than the first member. The first member is made of copper or an alloy containing copper as a main component,
The joining structure according to claim 1, wherein the third member is made of aluminum, an alloy containing aluminum as a main component, zinc, or an alloy containing zinc as a main component . The first member is made of aluminum or an alloy containing aluminum as a main component,
It said third member, the bonding structure of claim 1, characterized in that it is constituted by an alloy composed mainly of zinc or zinc. The second member is polygonal ;
Said third member is either of claims 1 to 3, wherein Rukoto arranged at least one outward side of the joint portion of the second member of the corner portion between the first member 1 The joint structure described in 1. On the opposite side with respect to the main surface in said first member has a low thermal expansion coefficient than the first member, and it is connected a fourth member having an equivalent or higher Young's modulus The joining structure according to any one of claims 1 to 4, wherein: The second member joint structure as claimed in any one of 5, wherein the Oh Rukoto in semiconductor devices.

Images