JP2001085580A - Substrate for semiconductor module and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive substrate for semiconductor module with excellent heat transfer/dissipation characteristics, especially at a part for mounting a semiconductor chip, while preventing of cracking due to thermal stress. SOLUTION: The substrate for semiconductor module mounting a semiconductor chip 20 comprises a first heat sink 11, an insulating substrate 13 bonded onto the first heat sink 11 while having an opening at a part for mounting the semiconductor chip 20, and a second heat sink 17 bonded onto the first heat sink 11 at the opening 13a of the insulating substrate 13 and being bonded with the semiconductor chip 20. The second heat sink 17 is composed of a material having a thermal conductivity higher than that of the insulating substrate 13 and a coefficient of thermal expansion close to that of the semiconductor chip 20. The compositional material includes Mo, W, Mo-Cu, W-Cu, and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor module substrate and a method of manufacturing the same, and more particularly, to a semiconductor module substrate such as a power module substrate for mounting a semiconductor chip which generates a large amount of heat and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a conventional semiconductor module substrate of this type, for example, a power module substrate as shown in FIG. 3 is known. This power module substrate 30
Has a structure in which a wiring metal plate 33 is bonded to an upper surface of an insulating substrate 31 made of a ceramic substrate via a brazing material 32, while a heat sink 35 is joined to a lower surface of the insulating substrate 31 via a brazing material 34. I have. In such a power module substrate 30, the semiconductor chip 20 is mounted on the wiring metal plate 33, and the pad electrode (not shown) formed on the upper surface of the semiconductor chip 20 and the pad electrode portion 33a of the wiring metal plate 33 are connected by wires. At 21, bonding is performed.

[0003]

The semiconductor module substrate has excellent heat radiation characteristics, especially when used as a power module substrate, since the mounted semiconductor chip 20 generates a large amount of heat when a large current flows. Is required. Therefore, the insulating substrate 31 located between the semiconductor chip 20 and the heat sink 35
Is also required to have excellent heat radiation characteristics, that is, to have high thermal conductivity. However, a ceramic substrate having a high thermal conductivity, such as an AlN substrate, is generally very expensive. Therefore, if such a ceramic substrate is used as the insulating substrate 31, the price of the semiconductor module substrate will increase. Therefore, development of an insulating material that is inexpensive and has a high thermal conductivity or development of a semiconductor module substrate having an excellent heat transfer characteristic from the semiconductor chip 20 to the heat sink 35 and having an inexpensive structure has been desired.

In a semiconductor module substrate such as a power module substrate, a difference in thermal expansion coefficient between components occurs due to a periodic temperature change (temperature cycle) due to operation / pause of a mounted semiconductor chip. Thermal stress is generated. If the thermal stress is excessive, cracks or the like may occur in the insulating substrate or the semiconductor chip, and the reliability may be reduced. Therefore, in the development of the above-mentioned insulating material and structure, it is premised that the development considering both the heat radiation characteristic and the difference in the coefficient of thermal expansion between the constituent elements is taken into consideration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an excellent heat radiation property, particularly, a portion on which a semiconductor chip is mounted has excellent heat conduction properties, and prevents cracks and the like caused by thermal stress. It is an object of the present invention to provide an inexpensive semiconductor module substrate and a method for manufacturing the same.

[0006]

In order to achieve the above object, a semiconductor module substrate (1) according to the present invention is a semiconductor module substrate for mounting a semiconductor chip, comprising: a first heat sink; An insulating substrate joined to the first heat sink and opening the mounting portion of the semiconductor chip; and a second joining the semiconductor chip to the first heat sink at the opening portion of the insulating substrate. 2 heat sinks.

According to the semiconductor module substrate (1), the mounting portion of the semiconductor chip required to have excellent heat transfer characteristics to the first heat sink is constituted by the second heat sink, Since the second heat sink is directly joined to the first heat sink from an opening portion thereof without passing through the insulating substrate, the second heat sink is connected to the second heat sink.
When the semiconductor chip is mounted on the heat sink, the heat generated by the semiconductor chip can be efficiently transferred from the second heat sink to the first heat sink to release the heat. Further, since a semiconductor chip is not directly mounted on the insulating substrate, it is not necessary to use a material having particularly excellent thermal conductivity. For this reason, as a constituent material of the insulating substrate, for example, among inexpensive alumina (Al ₂ O ₃ ) and AlN, AlN having a relatively low thermal conductivity and relatively inexpensive can be used.

Further, it is easy to form the second heat sink from a material having a small difference in thermal expansion coefficient from that of the semiconductor chip, and cracks occur in the semiconductor chip and the like due to thermal stress generated by a temperature cycle. And the reliability with respect to the temperature cycle can be improved.

Also, in the semiconductor module substrate (2) according to the present invention, in the semiconductor module substrate (1), the second heat sink has a higher thermal conductivity than the thermal conductivity of the insulating substrate. It is characterized in that it is formed using the above-mentioned material.

According to the semiconductor module substrate (2), the second heat sink, which is a portion on which the semiconductor chip is directly mounted, is formed of a material having higher thermal conductivity than the insulating substrate. Therefore, when a semiconductor chip is mounted on the second heat sink, heat generated in the semiconductor chip can be extremely efficiently radiated from the second heat sink via the first heat sink. Therefore, a semiconductor module substrate having excellent heat radiation characteristics can be realized.

In the semiconductor module substrate (3) according to the present invention, in any one of the semiconductor module substrates (1) and (2), the second heat sink may have a coefficient of thermal expansion of the semiconductor chip. It is characterized by being formed using a material having a similar thermal expansion coefficient. According to the semiconductor module substrate (3) described above,
Since the difference in the coefficient of thermal expansion between the semiconductor chip and the second heat sink is small, when the semiconductor chip is mounted on the second heat sink, the semiconductor chip and the second
Excessive thermal stress does not act on the junction between the heat sink and the semiconductor chip. Therefore, it is possible to prevent the destruction of the semiconductor chip and the like due to thermal stress, and it is possible to enhance the reliability with respect to the temperature cycle.

Further, in the semiconductor module substrate (4) according to the present invention, in the semiconductor module substrate (2) or (3), the second heat sink is made of Mo,
It is characterized by being formed using any of W, Mo-Cu, and W-Cu. Mo, W, Mo-
Both Cu and W-Cu have high thermal conductivity and a thermal expansion coefficient close to that of a semiconductor chip. Therefore, according to the semiconductor module substrate (4) on which the second heat sink is formed using any of these as a constituent material, heat transfer of the mounting portion of the semiconductor chip can be achieved.
It is possible to provide a highly reliable substrate for a semiconductor module which has excellent heat dissipation characteristics and does not cause breakage due to thermal stress in a semiconductor chip or the like.

Further, according to the present invention, there is provided a method of manufacturing a semiconductor module substrate for mounting a semiconductor chip, the method comprising the steps of: Disposing a substrate via a brazing material, and arranging, via the brazing material, a second heat sink to which the semiconductor chip is bonded on the first heat sink at the opening of the insulating substrate; And heating and melting the brazing material to simultaneously bond the insulating substrate and the second heat sink to the first heat sink.

According to the method of manufacturing a semiconductor module substrate described above, the first heat sink and the brazing material between the insulating substrate and the second heat sink disposed on the first heat sink are heated and melted. , To simultaneously join the insulating substrate and the second heat sink to the first heat sink, on the first heat sink,
An increase in the number of steps caused by fixing the second heat sink separately from the insulating substrate can be suppressed. In addition, since the portion on which the semiconductor chip is directly mounted is the second heat sink and is not mounted on the insulating substrate, an inexpensive substrate can be used for the insulating substrate. Therefore, the semiconductor module substrate can be manufactured at low cost.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a semiconductor module substrate and a method of manufacturing the same according to the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view showing a semiconductor module substrate as a power module substrate according to an embodiment, and FIG. 1 shows a state where a semiconductor chip is mounted.

As shown in FIG. 1, in the semiconductor module substrate 10 according to the embodiment, the first heat sink 11
The insulating substrate 13 joined by the Ag brazing material 12 is provided on the upper surface of the substrate. The first heat sink 11 is made of a material having a high thermal conductivity, such as Cu, Mo, or a mixture thereof. The insulating substrate 13 has an opening 13a in which the mounting portion of the semiconductor chip 20 is opened.
Al ₂ O ₃ substrate or AlN substrate having a thickness of about 0 mm (however, AlN has a relatively low thermal conductivity, for example, 13
Relatively inexpensive AlN of about 0 W / m · K), and an inexpensive ceramic substrate such as a SiN substrate. A wiring metal plate 15 joined by an Ag brazing material 14 is provided on the insulating substrate 13.

On the first heat sink 11, an opening 13 a of the insulating substrate 13 is provided with a second heat sink 17.
Are arranged. The second heat sink 17 is made of a material having a higher thermal conductivity than the insulating substrate 13 and having a thermal expansion coefficient close to that of the semiconductor chip 20 made of silicon, for example, having a thermal expansion coefficient of 3 to 10 (× 10 ^{−). 6} /
C.) (RT to 300 ° C.) using a first heat sink 11 and an Ag brazing material 16, for example.
Are joined by Here, as the metal material having a thermal expansion coefficient close to that of the semiconductor chip 20, more specifically, for example, a Mo material, a W material, a Mo—Cu mixed material, a W material
—Cu mixed material.

The thickness of the second heat sink 17 is such that when the semiconductor chip 20 is mounted on the second heat sink 17, the upper surface of the semiconductor chip 20 is positioned on the upper surface of the wiring metal plate 15 on the insulating substrate 13. The thickness is set so as to be in the vicinity or at the same height position as the upper surface position of the wiring metal plate 15. In this embodiment, the thickness is set to, for example, about 0.05 mm to 1.50 mm. In addition, the second heat sink 17 is connected to the opening 13.
It is arranged with a gap between it and the insulating substrate 13 constituting the side wall of FIG.

Here, the second heat sink 17 is Mo,
First heat sink 11, insulating substrate 13, wiring metal plate 1 when composed of W, Mo—Cu, and W—Cu, respectively
Table 1 shows examples of combinations of the constituent materials of Table 5, and Table 2 shows the thermal conductivity and thermal expansion coefficient of each material shown in Table 1.

[0020]

[Table 1]

[0021]

[Table 2] The second configuration of the semiconductor module substrate 10 having the above configuration
A semiconductor chip 20 is mounted on a heat sink 17 of the semiconductor chip 20, and a pad electrode (not shown) formed on an upper surface of the semiconductor chip 20 and a pad electrode portion 15 of a wiring metal plate 15 are mounted.
a are bonded by a wire 21.

Next, a method of manufacturing a semiconductor module substrate according to an embodiment of the present invention will be described with reference to an example of manufacturing a semiconductor module substrate 10 having the above configuration.
In manufacturing the semiconductor module substrate 10,
An insulating substrate 13 in which a mounting portion of the semiconductor chip 20 is cut off and an opening 13a is formed in advance is manufactured. Then, the Ag brazing material 1 is placed on the first heat sink 11.
2. The insulating substrate 13, the Ag brazing material 14, and the wiring metal plate 15 are arranged in a stacked state in this order, and the second portion is formed in the opening 13a of the insulating substrate 13 on the first heat sink 11.
Is disposed via the Ag brazing material 16.

Thereafter, while maintaining this state, the mixture is passed through a furnace maintained at about 800 ° C., and the Ag brazing materials 12, 14, 1
6, the first heat sink 11, the insulating substrate 13, the wiring metal plate 15, and the second heat sink 1
7 are simultaneously bonded. Through the above steps, the semiconductor module substrate 10 is manufactured. When manufacturing a semiconductor module using the manufactured semiconductor module substrate 10, the semiconductor chip 20 is soldered and mounted on the second heat sink 17, and then the semiconductor chip 20 is mounted.
The pad electrode formed on the upper surface and the pad electrode portion of the wiring metal plate 15 are wire-bonded.

According to the semiconductor module substrate 10 having the above structure, the mounting portion of the semiconductor chip 20 which is required to have excellent heat transfer characteristics to the first heat sink 11 is M
o, W, Mo-Cu, W-Cu, and the like. The second heat sink 17 is made of a metal material having a high thermal conductivity. Are joined on the first heat sink 11. For this reason, when the semiconductor chip 20 is mounted on the second heat sink 17, the heat generated in the semiconductor chip 20 can be efficiently transferred from the second heat sink 17 to the first heat sink 11 and radiated. .

Further, since the semiconductor chip 20 is not directly mounted on the insulating substrate 13, it is not necessary to form the insulating substrate 13 using a material having particularly excellent thermal conductivity.
Therefore, as a constituent material of the insulating substrate 13, for example, among inexpensive alumina (Al ₂ O ₃ ) and AlN, AlN having relatively low thermal conductivity and relatively inexpensive can be used.
The cost of manufacturing the semiconductor module substrate 10 can be reduced.

Further, the second heat sink 17 is made of Mo, W, Mo-Cu, W-Cu which has a high thermal conductivity and a small difference in thermal expansion coefficient from the semiconductor chip 20. In addition, it is possible to prevent cracks from being generated in the semiconductor chip 20 or a joint portion between the semiconductor chip 20 and the second heat sink 17 due to thermal stress caused by a temperature cycle, thereby improving reliability with respect to a temperature cycle. Can be.

In the mounting portion of the semiconductor chip 20, an independent second heat sink 17 is provided on the first heat sink 11, so that the thickness of the second heat sink 17 can be adjusted by adjusting the thickness of the second heat sink 17. When the semiconductor chip 20 is mounted on the second heat sink 17, the upper surface position of the semiconductor chip 20 is changed to the wiring metal plate 1.
5 can be easily set in the vicinity of the upper surface position or approximately the same position as the upper surface position of the wiring metal plate 15. Therefore, the pad electrode and the wiring metal plate 15 formed on the upper surface of the semiconductor chip 20 mounted on the second heat sink 17 are formed.
Wire bonding with the pad electrode portion on the upper surface can be easily performed.

In the method of manufacturing the semiconductor module substrate 10 according to the embodiment, the Ag brazing materials 12, 14, 16 are used.
The first heat sink 11 and the insulating substrate 13, the wiring metal plate 15 and the second heat sink 17 are simultaneously joined by heating and melting the first heat sink 11 and the second heat sink 17. Even if two heat sinks 17 are provided, an increase in the number of steps can be suppressed.

As described above, according to the method of manufacturing the semiconductor module substrate 10 according to the embodiment, the semiconductor chip 2
The semiconductor module substrate having excellent heat transfer and heat radiation characteristics can be manufactured at a low cost especially at the mounting portion of No. 0, and the semiconductor module substrate has high reliability with extremely low probability of occurrence of cracks and the like due to thermal stress. 10 can be obtained.

In the present embodiment, Mo, W, Mo-
Although an example using Cu and W-Cu has been described, in another embodiment, another material having higher thermal conductivity than the insulating substrate 13 may be used. Also in this case, it is needless to say that a material having a thermal expansion coefficient close to that of the semiconductor chip 20 is more preferable. In the above embodiment, the semiconductor module substrate 10
Has been described as an example of a power module substrate, but the present invention can be applied not only to a power module substrate but also to various semiconductor module substrates.

Further, in the method of manufacturing the semiconductor module substrate 10 according to the present embodiment, the case where an Ag brazing material is used as the brazing material has been described as an example, but in another embodiment, the wiring metal plate 15 is formed by heat. It is also possible to use another brazing material as long as the brazing material has a melting point low enough not to break.

[0032]

Next, an embodiment of a substrate for a semiconductor module according to the present invention will be described. In the embodiment, the constituent materials of the insulating substrate 13, the first heat sink 11, the wiring metal plate 15, and the second heat sink 17 of the semiconductor module substrate 10 shown in FIG. Samples of four types of semiconductor module substrates 10 of A to D were manufactured. After mounting the semiconductor chip 20 on each of the types A to D, as shown in FIG.
Was measured between the upper surface of the heat sink 11 and the lower surface of the heat sink 11. Eutectic brazing materials were used for the Ag brazing materials 12, 14, and 16 of each sample (types A to D).

Further, a temperature cycle (T / C) test in which a temperature change of -65 ° C. → 150 ° C. → −65 ° C. is repeated 3000 times is performed, and the insulating substrate 13 and the semiconductor chip 20 after the test are performed.
Was evaluated for the presence or absence of peeling or cracking. Table 3 also shows these thermal resistance ratios (relative ratios when the conventional example (type E) is set to 100) and evaluation results after the temperature cycle test.

Further, with respect to the power module substrate 30 having the conventional structure shown in FIG. 3, the constituent materials of the insulating substrate 31, the heat sink 35, and the wiring metal plate 33 were changed to Type E shown in Table 3.
After mounting the semiconductor chip 20 and mounting the semiconductor chip 20, the measurement of the thermal resistance and the temperature cycle test were performed in the same manner as above as a comparative example, and the results are also shown in Table 3.

[0035]

[Table 3] As is evident from Table 3, in the semiconductor module substrate 10 according to the example, the types A to D all have a lower thermal resistance value than the type E having the conventional structure, and the heat generated in the semiconductor chip 20. Was efficiently conducted from the second heat sink 17 to the first heat sink 11.

In any of the types A to D according to the examples, no peeling or cracking was observed in the insulating substrate 13 or the semiconductor chip 20. From the results of the temperature cycle test, it was confirmed that the reliability of the semiconductor module substrate 10 according to the example was equal to or higher than that of the conventional semiconductor module substrate 30. This is because the second heat sink 17 is made of Mo having a coefficient of thermal expansion close to the coefficient of thermal expansion of the semiconductor chip 20, so that excessive thermal stress can be prevented from acting on the semiconductor chip 20. Conceivable. Also, the insulating substrate 1
Since the semiconductor chip 20 is not mounted on the insulating substrate 1, the insulating substrate 1
It is considered that thermal stress caused by a difference in thermal expansion coefficient between the semiconductor chip 3 and the semiconductor chip 20 does not act between these members.

From the above results, it was confirmed that an inexpensive semiconductor module substrate having excellent heat dissipation characteristics, high heat load reliability after mounting the semiconductor chip 20, and low cost can be realized.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a semiconductor module substrate according to an embodiment of the present invention.

FIG. 2 is a schematic side cross-sectional view showing how a thermal resistance of the semiconductor module substrate according to the embodiment is measured.

FIG. 3 is a side sectional view showing an example of a conventional power module substrate.

[Explanation of symbols]

 Reference Signs List 10 substrate for semiconductor module 11 first heat sink 12, 14, 16 Ag brazing material 13 insulating substrate 13a opening 15 wiring metal plate 17 second heat sink 20 semiconductor chip

Claims (5)

[Claims] 1. A semiconductor module substrate for mounting a semiconductor chip, comprising: a first heat sink; an insulating substrate joined to the first heat sink, the mounting portion of the semiconductor chip being opened; and the insulating substrate. A second portion to be joined to the first heat sink at the opening portion and to be joined to the semiconductor chip.
A substrate for a semiconductor module, comprising: 2. The semiconductor module substrate according to claim 1, wherein the second heat sink is formed using a material having a higher thermal conductivity than the thermal conductivity of the insulating substrate. . 3. The semiconductor according to claim 1, wherein the second heat sink is made of a material having a coefficient of thermal expansion close to a coefficient of thermal expansion of the semiconductor chip. Module substrate. 4. The method according to claim 1, wherein the second heat sink is Mo, W,
The semiconductor module substrate according to claim 2, wherein the substrate is formed using one of Mo—Cu and W—Cu. 5. A method of manufacturing a semiconductor module substrate for mounting a semiconductor chip, comprising: arranging, via a brazing material, an insulating substrate having a semiconductor chip mounting portion opened on a first heat sink;
Disposing a second heat sink to which the semiconductor chip is bonded via a brazing material on the opening portion of the insulating substrate and on the first heat sink; and heating and melting the brazing material, Bonding the insulating substrate and the second heat sink to the first heat sink at the same time.