JP2004128264A - Semiconductor modules and plate leads - Google Patents

Abstract

Provided is a semiconductor module having excellent electrode wiring reliability of a semiconductor element.
A semiconductor module (100) of the present invention includes an electrode joint (31) joined to an electrode of a semiconductor element (20) mounted on a substrate (10), and a wiring outside the semiconductor element. A plate-like lead (30) having a wiring joint (32) joined to the part (43) and a connecting part (33) for connecting them, wherein the plate-like lead has a low electrode joint at least. It is characterized by being composed of a composite material in which an expanding material is included in a high thermal conductive material.
Not only is the heat of the semiconductor element efficiently guided to the outside by the high thermal conductive material at the electrode joint, but also the difference in thermal expansion between the electrode joint and the electrode is suppressed by the low expansion material.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor module having improved bonding reliability at an electrode of a semiconductor element and a plate-like lead used therein.
[0002]
[Prior art]
Conventionally, connection between an electrode of a semiconductor element and an external terminal has been often performed by wire bonding. This wire bonding is performed by applying ultrasonic waves while pressing an aluminum wire against an electrode or the like as a bonding partner. At this time, the oxide film between the two members to be joined is removed, the new surface is exposed, and the two members are welded.
However, since the wire bonding is performed by applying a load to the bonding surface and applying an ultrasonic wave, the semiconductor element is liable to be broken and the breakdown voltage is reduced. Further, since the bonding surface between the wire and the electrode or the like is small, there is a possibility that cracks or peeling may occur at the bonding portion with the temperature cycle. Furthermore, since the current-carrying capacity of each wire is small, a large number of wires are required for joining a high-power semiconductor element, and a long time is required for a wire bonding step, so that productivity cannot be improved.
Thus, many proposals have been made to use plate-like leads instead of linear wiring members (leads) such as wires. JP-A-6-268027, JP-A-2000-277558, and JP-A-2002-43508 can be cited as related publications.
[0003]
[Patent Document 1]
JP-A-6-268027 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2000-277558 [Patent Document 3]
JP 2002-43508 A [Patent Document 4]
JP-A-11-163045 [Patent Document 5]
Japanese Utility Model Publication No. Sho 63-20448 [0004]
[Problems to be solved by the invention]
However, since the size of the bonding portion of the plate-like lead is larger than that of the wire or the like, the amount of thermal expansion generated at the bonding portion also increases. Further, while the plate-shaped lead and the like are often made of a material having a large thermal expansion coefficient such as Cu, the semiconductor element to be joined is made of a material having a small thermal expansion coefficient such as Si. For this reason, for example, the difference in the amount of thermal expansion generated between the electrode of the semiconductor element and the joint of the plate-shaped lead is considerably larger than that in the case of wire bonding. In particular, the difference in the amount of thermal expansion increases around the joint of the plate-shaped leads. As a result, a large tensile stress or a large compressive stress acts on a peripheral portion thereof due to a temperature cycle or the like, and cracks are generated from the peripheral portion, and the cracks are liable to be separated and the bonding portion is easily peeled off. This can lead to reduced reliability.
[0005]
The present invention has been made in view of such circumstances. That is, an object of the present invention is to provide a semiconductor module capable of improving reliability when wiring a semiconductor element using a plate-like lead. It is another object of the present invention to provide a plate-shaped lead suitable for such a lead.
When the semiconductor element is joined to the substrate, the heat spreader is interposed between the electrode of the semiconductor element and the wiring layer of the substrate to absorb the difference in the coefficient of thermal expansion between the two. It is disclosed in Japanese Patent Publication No. 20448. However, as the name implies, this heat spreader diffuses the heat of the semiconductor element, which is a heating element, to a substrate or the like, and is not used as an electrode wiring in the first place. In other words, it should be noted that they have different functions and there is no direct relationship between them.
[0006]
Means for Solving the Problems and Effects of the Invention
The inventors of the present invention have conducted intensive research to solve this problem, and as a result of repeated trial and error, as a result, the amount of thermal expansion at the electrode joint of the plate-shaped lead has been suppressed, and the heat dissipation at the electrode joint has also been ensured. The inventors came up with a plate-like lead that can be made, and have completed the present invention described below.
(Semiconductor module)
That is, the semiconductor module of the present invention comprises a substrate, a semiconductor element mounted on the substrate and having an electrode on a surface on the opposite side of the substrate, an electrode bonding portion bonded to the electrode, and an external part of the semiconductor element. A semiconductor module comprising: a plate-shaped lead having a wiring joint to be joined to a wiring part, and a connecting part connecting the electrode joining part and the wiring joining part,
The plate-shaped lead is characterized in that at least the electrode joint is made of a composite material including a low-expansion material in a high-thermal-conductivity material (claim 1).
[0007]
In the case of the semiconductor module of the present invention, the electrode joint of the plate-shaped lead wired to the semiconductor element is made of a composite material having low thermal expansion and high thermal conductivity.
First, since the outer periphery of the composite material, which is in contact with the electrode of the semiconductor element, is made of a high thermal conductive material, heat of the semiconductor element is efficiently transmitted and conducted to the plate lead through the high thermal conductive material. That is, the high heat conductive material plays a role of a large heat passage. Then, the heat absorbed by the plate-shaped lead is radiated from the connecting portion and the wiring joint portion of the plate-shaped lead, and further radiated to another substrate, a heat sink, or the like.
Thus, even when the plate-shaped lead is used, it is possible to prevent the electrode joint from being extremely heated. As a result, the difference in the amount of thermal expansion between the electrode of the semiconductor element and the electrode joint of the plate-shaped lead is reduced, and the thermal stress generated at the joint between the two due to the difference in the amount of thermal expansion is also reduced.
[0008]
Next, the composite material includes a low expansion material in the high thermal conductive material. Therefore, when viewed as a whole of the composite material, the thermal expansion coefficient is lower than that of the high thermal conductive material alone. As a result, when the plate-like lead is made of the above-described composite material, the difference in the amount of thermal expansion between the electrode of the semiconductor element and the electrode joint of the plate-like lead is smaller than when the plate-like lead is made only of the high thermal conductive material. Therefore, the thermal stress at the joint due to this is also reduced.
As described above, according to the present invention, the occurrence of cracks and peeling between the electrodes of the semiconductor element and the electrode joints of the plate-like leads is suppressed and prevented by the synergistic effect of the two, and as a result, the entire semiconductor module is reduced. Reliability is improved.
[0009]
(Plate lead)
The present invention is not limited to the above-described semiconductor module, and may be grasped as the plate-like lead itself.
That is, the present invention provides an electrode bonding portion bonded to an electrode provided on an opposite surface of a semiconductor element mounted on a substrate, and a wiring bonding portion bonded to a wiring portion outside the semiconductor element. Part, and a plate-shaped lead having a connection part for connecting the electrode joint part and the wiring joint part,
At least the electrode bonding portion may be a plate-shaped lead made of a composite material in which a low-expansion material is included in a high-thermal-conductivity material.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in more detail with reference to embodiments. The following contents are applicable to the semiconductor module and the plate-shaped lead of the present invention as appropriate.
(1) Plate-shaped lead The “plate-shaped” lead is a lead having a width w larger than a thickness t. Although the specific size does not matter, usually, the width w is approximately the same as the electrode of the semiconductor element to which the plate-shaped lead is joined. Of course, the width w may be reduced so that a plurality of plate-shaped leads are provided for one electrode.
[0011]
The composite material of the plate-like lead is made of a high thermal conductive material and a low expansion material. Here, the high thermal conductive material is a material having a higher thermal conductivity than the low expansion material. The low expansion material is a material having a smaller linear expansion coefficient than the high thermal conductive material. The low expansion material preferably has a smaller linear expansion coefficient than the electrode of the semiconductor element. This is because the high thermal conductive material has a substantially higher linear expansion coefficient than the electrode of the semiconductor element, and effectively brings the linear expansion coefficient of the entire composite material closer to that of the electrode.
[0012]
Examples of the high thermal conductive material include a pure metal or an alloy containing Cu or Al as a main component. Since the high thermal conductive material naturally has conductivity as a plate-like lead, those metallic materials are preferable. When the high thermal conductive material corresponding to the outer skin is soldered to the electrode of the semiconductor element, and when the solder wettability is not good, Ni, Au, Ag plating or the like may be appropriately applied to the surface.
[0013]
An example of the low expansion material is an invar alloy. Invar alloys are preferred because they are inexpensive and have excellent moldability. The invar alloy includes various types such as a ferromagnetic invar alloy, an Fe-based amorphous invar alloy, and a Cr-based antiferromagnetic invar alloy. In consideration of the working temperature range, workability, cost, presence / absence of magnetism, etc., those suitable for the use of the plate-shaped lead are selected. In the present invention, the type, composition, and the like are not particularly limited. For example, ferromagnetic invar alloys such as Fe-36% Ni (unit is mass%, the same applies hereinafter) and Fe-31% Ni-5% Co (super-invar alloy) are famous.
[0014]
The above-mentioned composite material includes the low expansion material in the high thermal conductive material, but its inclusion form (such as the arrangement of the low expansion material) is not limited. It is not necessary that the periphery of the low expansion material be completely surrounded by the high thermal conductive material. This is because heat transfer from the semiconductor element to the plate-shaped lead and heat conduction in the plate-shaped lead may be achieved within a desired range. For example, the low-expansion material may be arranged in the high-thermal-conductivity material in a single state, or may be divided and arranged.
However, the arrangement of the low-expansion material in the high-thermal-conductivity material is preferably at least vertically centered. Thereby, it is possible to prevent warpage at the electrode joining portion of the plate-like lead, and to suppress cracking and peeling at the joining portion. Further, it is preferable that the low-expansion material is disposed in a symmetrical position between the left and right centers in the composite material. This is because the thermal expansion at the electrode joint of the plate-shaped lead becomes uniform, and it is possible to avoid applying unnecessary stress to the joint.
[0015]
In addition, by appropriately adjusting the volume ratio between the high thermal conductive material and the low expansion material, the thermal conductivity and the low expansion property of the composite material can be controlled. For example, the volume ratio of the low-expansion material can be increased to reduce the amount of thermal expansion of the entire composite material forming the electrode joint.
Although there is no limitation on the method of manufacturing such a plate-shaped lead, it can be manufactured by, for example, wrapping a thin plate-like invar material with a similarly thin plate-like Cu plate and pressing the same. That is, a clad material can be used as the composite material.
It is sufficient for the plate-shaped lead of the present invention to provide the above-mentioned composite material at the electrode joint portion, but other wiring joint portions and connection portions may be made of the composite material. Of course, only the electrode joints may be made of a composite material, and the wiring joints and the connecting parts may be made of a single material such as a Cu material.
[0016]
(2) Semiconductor Element The semiconductor element is not limited in its type, shape, standard, size and the like, but it is needless to say that the semiconductor element includes an electrode joined by a plate-like lead. For example, when the semiconductor element is a (power) MOSFET, a (power) IGBT, or the like, its electrodes are a source, an emitter, a drain, a collector, a control electrode (gate), and the like. The electrode to be joined to the plate-shaped lead also differs depending on which electrode is joined to the wiring layer on the substrate or the like. For example, when a drain electrode is soldered on a wiring layer of a substrate, a source electrode and / or a gate electrode are connected to a wiring layer or an external terminal on the substrate by a plate-like lead. In this case, only the source electrode having a large amount of current may be joined by a plate-like lead, and the gate electrode may be wire-bonded.
[0017]
(3) Substrate The substrate may be a ceramic substrate or a metal substrate, and is provided with a wiring layer on one or both sides as appropriate. The wiring layer may be, for example, a Cu wiring layer or an Al wiring layer. In any case, the type and shape of the substrate, the form of the wiring layer, and the like do not matter.
In the present invention, the semiconductor element is `` mounted '' on the substrate, even when the semiconductor element is directly mounted on the wiring layer of the substrate, even when another member such as a heat spreader is interposed between them. Means good. Usually, a heat sink or a heat radiating plate for heat radiation is often bonded to this substrate. This heat radiating plate may be used also as a housing of the semiconductor module.
[0018]
(4) Wiring part The wiring part is outside the semiconductor element and is joined to the electrode of the semiconductor element by a plate-like lead. The wiring section may be composed of external terminals, or may be on a wiring layer of the substrate. The substrate on which the wiring portion is provided may be different from the substrate on which the semiconductor element connected by the plate-like lead is mounted.
[0019]
(5) Support The support referred to here supports the semiconductor element and the wiring portion. When the wiring portion is on a substrate on which the semiconductor element is mounted, the substrate serves as a support. In addition, a heat sink on which a substrate is mounted, a heat sink, a housing, or the like may be used as a support. As described above, the support serves as a base for supporting the semiconductor element and the wiring portion.
By the way, both the support and the plate-like lead receive heat from the semiconductor element, become high temperature, and expand thermally. At this time, the amounts of thermal expansion of the two materials are usually different due to the difference in thermal expansion coefficient and the difference in temperature distribution of the materials used for the two materials.
[0020]
If the amount of thermal expansion on the side of the plate-like lead is smaller than the amount of thermal expansion on the side of the support, a tensile force acts on the plate-like lead as the semiconductor element generates heat. In order to reduce the tensile stress acting on the entire plate-like lead by absorbing the tensile force, for example, a low-rigidity portion may be provided in the connecting portion. This low-rigidity portion may be the entire connecting portion or a part thereof. Examples of the low-rigidity portion include a thin portion having a smaller thickness than a joint portion, a narrow portion having a smaller plate width than a joint portion, a bellows-like bellows portion, a mesh-like expanded portion, and the like. By providing such a low rigidity portion, a difference in the amount of thermal expansion acting on the plate-like lead is absorbed, and the tensile stress acting on the entire plate-like lead is alleviated. As a result, the stress finally acting on the electrode joints and the like of the plate-like lead is also alleviated, and it is also useful for suppressing and preventing cracks and peeling of the electrode joints and the like due to temperature cycling and the like.
As a case where such a difference in the amount of thermal expansion between the plate lead and the support becomes a problem, for example, the plate lead is mainly made of a Cu material containing Cu as a main component, and the support is made of Al. It may be made of an Al material as a main component.
[0021]
(6) Use The semiconductor module of the present invention is not limited in its use, but is suitable for equipment requiring high reliability. In particular, the semiconductor module of the present invention is suitable for a device (e.g., a vehicle-mounted device) on which a semiconductor element for power electronics is mounted and in which the use environment changes drastically such as a temperature change (temperature cycle).
[0022]
【Example】
The present invention will be described in more detail with reference to examples.
(First embodiment)
A semiconductor module 100 according to a first embodiment of the present invention is used for an inverter device for controlling driving of a three-phase induction motor (three-phase motor). FIG. 1 is a sectional view of a main part of the semiconductor module 100.
[0023]
The semiconductor module 100 includes an element-side metal base wiring board 10, a semiconductor element 20, a plate-like lead 30, a terminal-side metal base wiring board 40, a support 50, and a heat sink 60.
[0024]
The element-side metal base wiring board 10 has the semiconductor element 20 surface-mounted. The element-side metal base wiring substrate 10 includes an Al base substrate 11 and Cu wiring layers 13 and 15 stretched on both surfaces thereof with insulating layers 12 and 14 therebetween. Note that the insulating layer 14 and the wiring layer 15 may be omitted as long as the element-side metal base wiring board 10 is soldered to the support 50 or the like.
[0025]
The semiconductor element 20 is an IGBT element having a drain electrode 22 on the lower surface of a main body 21 and a source electrode 23 and a gate electrode (not shown) on the upper surface.
[0026]
The plate-shaped lead 30 has an electrode joint 31 and a terminal joint (wiring joint) 32 at the ends, and both are connected by a connecting part 33. In the case of the present embodiment, the electrode joint 31 to be soldered to the source electrode 23 includes a thin copper plate (high thermal conductive material) containing an invar alloy (Fe-36% Ni) plate material (low expansion material). It consists of a laminated material (composite material) formed by pressing. The terminal joining portion 32 and the connecting portion 33 do not include the Invar material, and are formed by simply stacking the above-described copper plates. The details of the method of manufacturing the plate lead 30 will be described later.
[0027]
Thus, the electrode joint 31 of the plate-shaped lead 30 has a three-layer structure of the Cu layer, the Invar alloy layer 34, and the Cu layer. Each of these layers has a thickness of about 1/3 of the whole, and the Invar alloy layer 34 is formed symmetrically at the center in the thickness direction. As a result, warpage at the electrode joint 31 is prevented. Incidentally, the overall thickness of the plate-like lead 30 is about 0.05 to 1 mm.
The size of the Invar alloy layer 34 substantially matches the size of the source electrode 23. As a result, the coefficient of linear expansion of the electrode joint 31 approaches the coefficient of linear expansion of the source electrode 23, the difference in the amount of thermal expansion between the two becomes smaller, and the thermal stress acting on the joint is alleviated.
[0028]
Further, since the Cu layer surrounds the Invar alloy layer 34, the end portion of the electrode joint portion 31 (the right end portion in FIG. 1 and the front and rear portions in FIG. 1) is smaller than the source electrode 23 by that amount. It protrudes slightly. Thereby, the heat of the semiconductor element 20 moves efficiently from the semiconductor element 20 side to the heat radiating plate 60 side so as to go around the periphery of the Invar alloy layer 34 without being blocked by the Invar alloy layer 34 (that is, Heat conduction).
[0029]
The terminal-side metal base wiring board 40 constitutes an external terminal, and similarly to the element-side metal base wiring board 10, an Al base board 41 and Cu And wiring layers 43 and 45 made of the same. Also in this case, the insulating layer 44 and the wiring layer 45 may be omitted as long as the terminal-side metal base wiring board 40 is soldered to the support 50 or the like.
[0030]
The support 50 is a heat sink made of an Al alloy. However, the support 50 may also serve as a housing of the semiconductor module 100.
The heat radiating plate 60 is also a heat sink made of an Al alloy and includes a large number of fins 62 projecting from the base 61.
[0031]
Next, the joining relationship between the members will be described.
First, the element-side metal base wiring board 10 is fixed to the inner bottom surface of the support 50 via the solder layer 91. On the wiring layer 13 of the element-side metal base wiring board 10, the drain electrode 22 of the semiconductor element 20 is joined by a solder layer 92. The terminal-side metal base wiring board 40 is fixed on the protrusions 51 of the support 50 via the solder layer 95. The source electrode 23 of the semiconductor element 20 is connected to the electrode joint 31 of the plate-shaped lead 30 via the solder layer 93, and the wiring layer 43 of the terminal-side metal base wiring board 40 is connected to the plate-shaped lead 30 via the solder layer 94. Are respectively joined to the terminal joining portions 32. Thus, the source electrode 23 and the wiring layer 43 serving as the source pattern are electrically connected by the plate-shaped lead 30. Further, a heat radiating plate 60 is bonded to the electrode bonding portion 31 of the plate-like lead 30 (on the opposite side of the semiconductor element 20) via a solder layer 96.
[0032]
In this embodiment, the heat of the semiconductor element 20 is transmitted to the Cu layer of the electrode joint 31 through the source electrode 23 and the solder layer 93. Then, the Cu layer of the electrode joint portion 31 conducts heat from the semiconductor element 20 side to the heat sink 60 side. Here, since the Cu layer is a high thermal conductive material, heat hardly stays at the joint between the electrode joint 31 of the plate-shaped lead 30 and the source electrode 23, and the surface area of the surface of the electrode joint 31 via the solder layer 96 is small. Is transmitted to the heat radiating plate 60 having a large size, and the heat is radiated efficiently by the heat radiating plate 60. In this manner, the temperature of the electrode joint portion 31 is prevented from being abnormally high.
[0033]
Further, in the present embodiment, due to the presence of the invar alloy layer 34, the linear expansion coefficient of the electrode joint 31 is partially reduced, and the difference in the amount of thermal expansion between the electrode joint 31 and the source electrode 23 is also reduced.
Thus, the temperature rise at the junction between the electrode junction 31 and the source electrode 23 is suppressed, and the difference in linear expansion coefficient between the two is reduced, so that the thermal stress acting on that portion is further reduced. Therefore, cracks, peeling, and the like at the joints between them are effectively suppressed and prevented, and the reliability of the semiconductor module 100 is improved.
[0034]
Next, a method for manufacturing the plate lead 30 will be described with reference to FIG.
First, the Invar alloy thin plate 1 is placed substantially at the center of the Cu thin plate 2 slightly larger than that (FIG. 2A). Next, the Cu thin plate 2 is folded in the direction of the arrow shown in FIG. 2A so as to grip the end of the Cu thin plate 2 and enclose the Invar alloy thin plate 1.
[0035]
Next, the Invar alloy thin plate 1 and the Cu thin plate 2 which are partially formed into three layers are formed by pressing from upper and lower surfaces in a high temperature atmosphere, that is, hot press forming. While maintaining this state for a while, each layer is diffusion bonded.
Then, when the obtained raw material is cut into a desired size, a plate-like lead 30 is obtained.
[0036]
(Second embodiment)
FIG. 3 shows a semiconductor module 200 including a plate-like lead 230 having substantially a three-layer structure of an Invar alloy layer and a Cu layer as well as an electrode junction. The same members as those in the first embodiment are denoted by the same reference numerals.
In this case, since the entire structure has a three-layer structure, the manufacture of the plate-like lead 230 is facilitated, and the cost of the semiconductor module 200 is reduced.
This plate-shaped lead can also be manufactured by the above-described manufacturing method. In addition, the plate-like lead 230 can be manufactured by a method of plating the periphery of the Invar alloy thin plate with Cu, or the like.
[0037]
In addition, in the above-described embodiment, the size of the low expansion material in the electrode junction is substantially equal to the size of the electrode of the semiconductor element. However, for example, the area ratio between the two may be adjusted to -60% to + 60%.
[Brief description of the drawings]
FIG. 1 is a sectional view of a main part of a semiconductor module according to a first embodiment of the present invention.
FIG. 2 is a schematic view showing one manufacturing method of a plate-like lead used for the semiconductor module.
FIG. 3 is a sectional view of a main part of a semiconductor module according to a second embodiment of the present invention.
[Explanation of symbols]
10. Device side metal base wiring board (board)
Reference Signs List 20 semiconductor element 30 plate lead 31 electrode joint 32 terminal joint (wiring joint)
33 connecting part 34 invar alloy layer 40 terminal side metal base wiring board 43 wiring layer (wiring part)
Reference Signs List 50 Support 60 Heat sink 100 Semiconductor module

Claims (5)

Board and
A semiconductor element mounted on the substrate and having an electrode on a surface opposite to the substrate;
A plate-shaped lead having an electrode bonding portion bonded to the electrode, a wiring bonding portion bonded to a wiring portion outside the semiconductor element, and a connecting portion connecting the electrode bonding portion and the wiring bonding portion; A semiconductor module comprising:
The semiconductor module according to claim 1, wherein the plate-shaped lead is formed of a composite material in which at least the electrode joint portion includes a low-expansion material in a high-thermal-conductivity material. The semiconductor module according to claim 1, wherein the low expansion material is made of a material having a smaller linear expansion coefficient than the electrode. The semiconductor module according to claim 2, wherein the low expansion material is an Invar alloy. The semiconductor module according to claim 1, wherein the high thermal conductive material is a pure metal or an alloy containing copper (Cu) or aluminum (Al) as a main component. An electrode bonding portion bonded to an electrode provided on the opposite surface side of the semiconductor device mounted on the substrate, a wiring bonding portion bonded to a wiring portion outside the semiconductor device, and the electrode bonding A plate-shaped lead having a portion and a connecting portion for connecting the wiring joint portion,
At least the electrode joint is made of a composite material in which a low expansion material is included in a high thermal conductive material.

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