JP3044952B2 - Semiconductor chip mounting structure - Google Patents

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 distortion and stress due to thermal expansion of a silicon chip.

[0002]

2. Description of the Related Art In a semiconductor device, in particular, a power transistor or a semiconductor rectifying device, power consumption per operation area is large. For this reason, only the release of heat from the case or the lead of the semiconductor element cannot completely release the generated heat, and the internal temperature of the semiconductor element rises, causing thermal destruction. For that purpose, a heat reservoir for absorbing the heat generated by the semiconductor element is required. Conventionally, a heat sink is interposed between an insulating substrate and a silicon chip (semiconductor element) to absorb and dissipate heat.

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

[0004]

As described above, although Cu has a high thermal conductivity, it has high rigidity as an inherent characteristic, so that it is difficult for thermal deformation to occur, and it is difficult to absorb thermal stress generated in a silicon chip. For example, 0.2% proof stress (4.
9 MPa), the elastic deformation range when an external force is applied is wide, and the work hardening is also large. That is, the rate at which thermal stress is absorbed by plastic deformation is small. In addition, Cu-
Both the W alloy and the Cu / Mo / Cu clad material have the drawback that not only the thermal conductivity is extremely small but also the cost is high. Further, there is a problem that a heat sink using a Cu-based material becomes excessively heavy as a whole substrate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor chip mounting structure in which cracking and peeling due to thermal fatigue at the interface of a bonding layer interposed between a silicon chip and a radiator plate due to thermal cycling, intermittent energization, etc. of a semiconductor element are less likely to occur. Is to provide.

[0006]

According to the present invention, a heat dissipating material is manufactured using aluminum having a purity of 99.9% or more, and the thickness of the heat dissipating material in the laminating direction is set to 0.2 mm or more. The above object is achieved by using aluminum which is a metal having high flexibility.

[0007]

According to the present invention, pure aluminum used as a heat dissipating material for mounting a semiconductor chip has substantially the same coefficient of thermal expansion as Cu. Also, its thermal conductivity is Cu-W
Compared with alloys and Cu / Mo / Cu clad materials, they are slightly inferior to Cu alone, but have less deformation resistance than Cu alone, and are thus very effective as thermal stress absorbing materials. 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 can be effectively absorbed. Further, since work hardening is less than that of Cu, it is possible to flexibly respond to an external force. In other words, when an external force is applied to a metal to cause plastic deformation, the external force is removed once, and the external force is applied again, most of the metals including Cu are plastically deformed unless the external force is considerably larger than the initial external force. However, aluminum causes plastic deformation with smaller external force.

[0008] In the present invention, the purity of this aluminum is 99.9% or more. Below this range, the effect of the present invention is not realized. Further, in the present invention, the thickness of the aluminum heat radiating material in the laminating direction is set to 0.2 mm or more. If the thickness is smaller than this value, not only does the effect of relaxing the thermal stress decrease, but also it does not function effectively as a heat reservoir. The aluminum heat radiator is lighter in weight than the Cu-based heat radiator, and is lower in cost than the Cu-W alloy and the Cu / Mo / Cu clad material.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One 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 radiator plate 13 is fixed to the upper surface of the conductive substrate 12 by solder 14. A plating layer 15 is provided on the surface of the aluminum radiator plate 13 to improve the wettability with the solder 14. A silicon chip 16 is mounted on the upper surface of the aluminum radiator plate 13 by being fixed with, for example, solder 17. Here, the heat sink 13 is made of aluminum having a purity of 99.9% or more. FIG. 2 is a graph showing the effect of impurities on the tensile properties of aluminum.

The thickness of the heat radiating 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 a plating material used for the plating layer 15 attached to the front and back surfaces of the heat sink 13 in order to enhance the wettability with the solder layers 14 and 17. The solder layers 14 and 17 provided with the plating layer 15 interposed therebetween include ordinary Pb-
Sn-based, Su-Sb-based, Pb-In-based, Au-Si-based,
Alternatively, Au-Sn based solder is used. In particular, Pb-
When the Sn-based solder is used, the nickel plating layer 15 is formed only in a portion where the silicon chip 16 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, even when a power transistor or the like is formed on the silicon chip 16, the heat radiating plate 13 transmits and dissipates heat. And
Solder 1 even for repeated use of transistors, etc.
Cracks and peeling of 4 and 17 and cracking of the silicon chip 16 hardly occur. This is because the aluminum heat sink 13 is easily plastically deformed, thereby relaxing and absorbing the thermal stress.

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

[0012]

[Table 1]

FIG. 3 is a photomicrograph showing the cracks in the solder portion of the comparative product after the heat cycle test at 100 times magnification.

[0014]

According to the semiconductor chip mounting structure of the present invention, the heat dissipating material has a small deformation resistance and is easily plastically deformed, so that the effect of reducing the thermal stress generated in the solder layer joining the silicon chip is high. During thermal cycling or intermittent energization of the silicon chip, breakage of the silicon chip can be effectively suppressed.

[Brief description of the drawings]

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

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

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

[Explanation of symbols]

 11 Insulating substrate 13 Heat sink 16 Silicon chip

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-348 (JP, A) JP-A-3-125463 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 23/373

Claims (2)

(57) [Claims] 1. A semiconductor chip comprising: an insulating substrate; a semiconductor chip mounted on the insulating substrate via a bonding layer; and a heat dissipating material disposed between the insulating substrate and the bonding layer. 3. The mounting structure of a semiconductor chip according to claim 1, wherein said heat radiation material is formed of aluminum having a purity of 99.9% or more. 2. The thickness of the heat radiating material in the stacking direction is 0.2 m.
The mounting structure of the semiconductor chip according to claim 1, wherein m is not less than m.