JPH06163764A - Structure for mounting semiconductor chip - Google Patents

Abstract

PURPOSE:To prevent the interface of a bonding layer from being cracked or stripped due to thermal fatigue by a method wherein a heat-dissipating material is formed of aluminum whose purity is specific. CONSTITUTION:A conductor substrate 12 for circuit formation use is bonded to the surface of an insulating substrate 11. An aluminum heat sink 13 is fixed and bonded to the surface of the conductor substrate 12 by a solder 14. A plated layer 15 which makes wettability to the solder 14 good is applied to the surface of the aluminum heat sink 13. A silicon chip 16 is mounted on the surface of the aluminum heat sink 13 so as to be fixed and bonded by a solder 17. In this case, aluminum whose purity is 99.9% or higher is used for the heat sink 13. In addition, the thickness of the heat sink 13 is set at 0.2mm or higher. In such a structure, the deformation resistance of a heat-dissipating material is small, and the material is plastic-deformed easily. As a result, the relaxation effect of a thermal stress generated inside a solder layer bonding the silicon chip can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor chip mounting structure, and more particularly to a semiconductor chip mounting structure capable of easily absorbing strain and stress due to thermal expansion of a silicon chip.

[0002]

2. Description of the Related Art Semiconductor devices, particularly power transistors and semiconductor rectifying devices, consume a large amount of power per operating area. Therefore, the generated heat amount cannot be completely discharged only by discharging the heat amount from the case or the lead of the semiconductor element, and the internal temperature of the semiconductor element rises, causing thermal destruction. Therefore, a heat sink for absorbing the heat generated by the semiconductor element is required, and conventionally, a heat sink is interposed between the insulating substrate and the silicon chip (semiconductor element) to absorb and dissipate the heat.

Cu has been used as the material for the heat sink because of its good thermal conductivity. In particular, when a large amount of heat is generated, a Cu-W alloy or a Cu / Mo / Cu clad material having a thermal expansion coefficient close to that of the silicon chip is used as the heat dissipation plate.

[0004]

As described above, although Cu has a high thermal conductivity, it has a high rigidity as an inherent property thereof, so that it is hard to undergo thermal deformation and absorb the thermal stress generated in the silicon chip. For example, 0.2% proof stress (4.
9 MPa), the elastic deformation range is wide when an external force is applied, and the work hardening is also large. That is, the rate at which thermal stress is absorbed by plastic deformation is small. Also, Cu-
Both the W alloy and the Cu / Mo / Cu clad material have the drawbacks of not only extremely low thermal conductivity but also high cost. Further, the heat dissipation plate using the Cu-based material has a problem that the weight of the whole substrate becomes excessive.

An object of the present invention is to mount a semiconductor chip on which a crack or peeling thereof due to thermal fatigue at the interface of a bonding layer interposed between a silicon chip and a heat sink is less likely to occur due to a thermal cycle or intermittent energization of the semiconductor element. To provide.

[0006]

According to the present invention, a heat dissipation material is made of aluminum having a purity of 99.9% or more, and the thickness of the heat dissipation material in the stacking direction is 0.2 mm or more. By using aluminum, which is a metal having high flexibility, the above object can be achieved.

[0007]

In the present invention, the coefficient of thermal expansion of pure aluminum used as a heat dissipation material for mounting semiconductor chips is almost equal to that of Cu. Also, its thermal conductivity is Cu-W.
It is comparable to alloys and Cu / Mo / Cu clad materials, and is slightly inferior when compared to Cu alone, but it has less deformation resistance and is very effective as a thermal stress absorber. For example, 0.2% proof stress (2.9MP
Since a) is small, plastic deformation easily occurs. That is, since it is easy to adapt without resisting the thermal stress, the thermal stress is effectively absorbed. Further, since work hardening is less than that of Cu, it is possible to flexibly cope with external force. That is, when an external force is applied to a metal to cause plastic deformation, the external force is removed once, and then the external force is applied again, most of the metal including Cu does not undergo plastic deformation again unless the external force is considerably larger than the initial external force. However, aluminum causes plastic deformation with a smaller external force.

In the present invention, the purity of this aluminum is set to 99.9% or more. Below this range, the effect of the present invention is not exhibited. Further, in the present invention, the thickness of the aluminum heat sink in the stacking direction is set to 0.2 mm or more. When the thickness is less than this value, not only the effect of relaxing the thermal stress decreases, but also the thermal storage does not function effectively. The aluminum heat dissipation material is lighter in weight than the Cu-based heat dissipation material and has a lower cost than the Cu-W alloy and the Cu / Mo / Cu clad material.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. As shown in this figure, a circuit-forming conductor substrate 12 made of, for example, aluminum is joined to the upper surface of an insulating substrate 11 made of ceramics, resin, an aluminum insulating substrate, or the like by a brazing material or the like. An aluminum heat dissipation plate 13 is fixed to the upper surface of the conductor substrate 12 with solder 14. A plating layer 15 is deposited on the surface of the aluminum heat dissipation plate 13 to improve wettability with the solder 14. Then, a silicon chip 16 is mounted on the upper surface of the aluminum heat dissipation plate 13 while being fixed thereto by, for example, solder 17. Here, the heat dissipation plate 13 uses aluminum having a purity of 99.9% or more. FIG. 2 is a graph showing the influence of impurities on the tensile properties of aluminum.

The thickness of the heat dissipation plate 13 is 0.2 mm or more, preferably 0.2 to 2.0 mm. If the thickness exceeds this range, it is not practical. Nickel or Au / Ni is used as the plating material used for the plating layer 15 attached to the front and back surfaces of the heat dissipation plate 13 in order to improve the wettability with the solder layers 14 and 17. As the solder layers 14 and 17 which are provided with the plating layer 15 sandwiched between them, ordinary Pb-
Sn system, Su-Sb system, Pb-In system, Au-Si system,
Alternatively, Au—Sn solder is used. In particular, Pb-
If Sn-based solder is used, the nickel plating layer 15 may be formed only on the portion of the silicon chip 16 that needs to be soldered when the silicon chip 16 to be mounted is small.
This is preferable because the displacement of the silicon chip 16 can be prevented.
In the mounting structure having such a configuration, the heat dissipation plate 13 transmits and dissipates heat even when the power transistor or the like is formed on the silicon chip 16. And
Solder 1 even for repeated use of transistors, etc.
The cracks and peeling of Nos. 4 and 17 and the crack of the silicon chip 16 are unlikely to occur. This is because the aluminum heat sink 13 is easily plastically deformed to absorb and absorb thermal stress.

Table 1 shows the results of the heat resistance cycle test. In this table, the product of the present invention has a purity of 99.
9% of aluminum was used as a heat sink, and Cu was used as a heat sink as a comparative product. The test conditions are as follows. That is, for one cycle, after holding the insulating substrate at −40 ° C. for 60 minutes, holding it at room temperature for 10 minutes, further holding it at 125 ° C. for 60 minutes, and then holding it at room temperature for 10 minutes.
Hold for a minute.

[0012]

[Table 1]

FIG. 3 is a micrograph showing a crack of the solder portion of the comparative product after the thermal cycle test, magnified 100 times.

[0014]

According to the semiconductor chip mounting structure of the present invention, since the heat-dissipating material has a small deformation resistance and is easily plastically deformed, the effect of alleviating the thermal stress generated in the solder layer for joining the silicon chips is high, It is possible to effectively prevent damage to the silicon chip during the thermal cycle or intermittent energization of the silicon chip.

[Brief description of drawings]

FIG. 1 is a sectional view showing a semiconductor chip mounting structure according to an embodiment of the present invention.

FIG. 2 is a graph showing yield stress and proof stress of high-purity aluminum according to the present invention.

FIG. 3 is a micrograph of a comparative product for explaining the present invention.

[Explanation of symbols]

 11 Insulating substrate 13 Heat sink 16 Silicon chip

Claims (2)

[Claims] 1. A semiconductor chip including an insulating substrate, a semiconductor chip mounted on the insulating substrate via a bonding layer, and a heat dissipation material interposed between the insulating substrate and the bonding layer. 2. The mounting structure for a semiconductor chip, wherein the heat dissipation material is formed of aluminum having a purity of 99.9% or more. 2. The thickness of the heat dissipation material in the stacking direction is 0.2 m.
The mounting structure for a semiconductor chip according to claim 1, wherein the mounting structure is at least m.