JPH04323856A - Semiconductor device with heat sink - Google Patents

Abstract

PURPOSE:To mount in a high density by adhering a heat sink to both upper and side surfaces of a package. CONSTITUTION:A heat sink 3 is adhered to both upper and side surfaces of a ceramic case 8 with adhesive 4. Thus, a size of the case 8 for obtaining the same heat dissipating performance can be reduced as compared with that of a conventional structure. That is, when a heat transfer area of the upper surface of the case 8 is A3, a heat transfer area to be transferred from the side 2 of the sink 3 to a fin 1 of the sink 3 is A1, a thermal conductivity of the case 8 is lambda, and thermal conductivity of the sink 3 is lambdaH, A3/A1=lambdaH/lambda is obtained, and the heat transfer area can be reduced in the amount corresponding to larger conductivity of the sink 3. Thus, a size of a semiconductor device can be reduced, and a high density mounting is performed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device with a heat sink.

0002

2. Description of the Related Art Conventionally, as shown in the cross-sectional view of FIG. 3, for example, a semiconductor device has a structure in which the surface on which a semiconductor chip 5 is mounted is opposite to the surface on which external leads 7 are attached (hereinafter referred to as cavity-up). When power consumption is large, a heat sink 3 is attached on top of the ceramic case 8 in order to efficiently dissipate heat generated from the semiconductor chip. This heat sink 3 is equipped with fins 1, and is usually made of Al.
Or made of Cu. Ceramic case is Al2O
3, and the thermal conductivity of each is shown in Table 1.

0003

[0004] The heat sink 3 is bonded to the ceramic case 8 with a resin 4. Heat generated from the semiconductor chip 5 is transmitted to the heat sink 3 through the ceramic case 8, and is radiated to the outside air.

As can be seen from Table 1, Al2 O3 has the lowest thermal conductivity. Therefore, the amount of heat transferred from the ceramic case to the heat sink is controlled by the thermal conductivity of Al2O3, and if the amount of heat is Q, then Q=λAΔT/l

...It is represented by (1). Here, λ is the thermal conductivity, A is the heat transfer area, l is the distance, and ΔT is the temperature difference between two points l apart.

[0006]

Problem to be Solved by the Invention In order to increase the amount of heat transferred to the heat sink, it is necessary to increase the heat transfer area A according to equation (1). However, in the conventional semiconductor device with a heat sink shown in FIG. 3, the heat sink is attached to the top surface of the ceramic case, so in order to increase the heat transfer area and improve the heat dissipation performance, the ceramic case must be made larger. This means that conventional semiconductor devices with heat sinks cannot be mounted at high density on a mounting board. With the increasing demand for miniaturization of electronic devices, the large size of the ceramic case precluded high-density packaging, which was a fatal problem. Another problem was that the larger the ceramic case, the higher the material cost.

[0007]

Means for Solving the Problems The semiconductor device with a heat sink of the present invention is characterized in that the heat sink is bonded to both the top and side surfaces of the package.

[0008] Here, the package refers to a case in which a semiconductor chip of a semiconductor device is mounted, excluding a heat sink.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor device with a heat sink according to an embodiment of the present invention. The heat sink 3 is attached to both the top and side surfaces of the ceramic case 8 with an adhesive 4. The other parts are the same as the conventional example shown in FIG. With such a structure, the size of the ceramic case for obtaining the same heat dissipation performance can be made smaller compared to the conventional structure shown in FIG. 3. The reason is explained as follows. In Figure 3, the thickness of the ceramic case 8 is t, and the heat transfer area of the width t of the top surface of the ceramic case is A.
3. Similarly, in Figure 1, the side part 2 of the heat sink 3
The thickness of the heat sink 3 is W, and the heat sink 3
Let A1 be the heat transfer area transferred to the fin 1. The thermal conductivity of the ceramic case is λ, and the thermal conductivity of the heat sink is λ.
H, the amount of heat passing through the heat transfer area A3 in Figure 3 is
Q=λA3 ΔT/l
...(2)
Similarly, in Figure 1, the amount of heat passing through the heat transfer area A1 is Q = λH
A1 ΔT/l
...(3) In order for the heat dissipation effect to be equal in Figures 1 and 3, from formulas (2) and (3), A3 /A1 = λH /λ
…
(4) That is, the heat transfer area can be reduced because the heat sink has a high thermal conductivity. Therefore, the size of the semiconductor device can be reduced.

FIG. 2 is a sectional view showing a second embodiment of the present invention. Materials having different thermal conductivities are used for the fins 1 of the heat sink and the side portions 9 of the heat sink. The rest is the same as the previous embodiment. The effect is the same as the first embodiment.

As an adhesive between the heat sink and the ceramic case for realizing the embodiment of the present invention, there is a resin sold by Toray Silicone Co., Ltd. under the trade name SE4400. Further, the present invention is not limited to ceramic cases, and can be similarly applied to resin-sealed semiconductor devices.

[0013]

[Effects of the Invention] As explained above, in the present invention, the heat sink is bonded not only to the top surface of the package but also to the side surface, so compared to conventional semiconductor devices, the size of the semiconductor device can be made smaller while maintaining the same heat dissipation performance. As a result, it has the effect of enabling high-density packaging. Also,
Since the size of the package is reduced, material costs are reduced, which has the effect of reducing costs.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the invention.

FIG. 3 is a cross-sectional view showing a conventional semiconductor device.

[Explanation of symbols]

1 Fin 2,9 Side part 3 Heat sink 4 Adhesive 5 Semiconductor chip 7 External lead 8 Ceramic case

Claims (1)

[Claims] Claim 1: In a semiconductor device in which a package containing a semiconductor chip is attached with a heat sink having a thermal conductivity equal to or higher than that of the package, the heat sink is bonded to the top and side surfaces of the package. A semiconductor device with a heat sink.