COOLING SYSTEM FOR ELECTRONIC COMPONENTS

Abstract: An IC substrate (3) carrying IC's (14) is fitted into a connector frame (2). Heat passes to a heat-conductive block (6), and thence to a plate (8) provided with coolant channels, by way of a flexible adhesive layer (4) and a low melting point metal or wax layer (5), these layers ensuring good, gap-free thermal contact between a substrate (3) and the block (6). The layer (5) can be melted when it is necessary to replace the substrate (3).

Description: Background of the Invention The present invention relates to a cooling system used for a package mounting a plurality of heat-generating electronic components such as integrated circuits (IC's) on a substrate. A prior art cooling system for a package mounting electronic components on a substrate is disclosed in U.S. Patent No. 4,109,707. The system comprises a micropackage 10 mounting a plurality of IC's on the upper surface of a substrate 12, a connector 20 connected to the package 10, and a heat exchanger 26 in contact with the lower surface 24 of the substrate 12 mounting no IC. Liquid coolant such as water flows inside the exchanger 26. The exchanger 26 is provided with a flexible thin plate 31 on the bottom thereof. The surface 24 of the package 10 is not completely flat. In order to efficiently conduct the heat generated from the IC's into the coolant, it is critically necessary to force the flexible plate 31 to come into close contact with the surface 24 without clearances therebetween. To obtain such close contact, the system tries to bring the plate 31 in close contact with the surface 24 by deforming the plate 31 with the pressure of water circulating inside exchanger 26. In the system, the plate 31 provided on the bottom of the exchanger 26 is made of an extremely thin copper sheet having a thickness of 0.05 to 0.25 milimeters in order to obtain superior flexibility. However, since it is made of such a thin sheet of material, the water pressure used to press the plate 31 against the surface 24, which is a determinant factor of the thermal resistance between the plate 31 and the surface 24, cannot be increased to thereby present an impediment in reducing the thermal resistance between the substrate 12 and the exchanger 26. Because of its weakness, the plate 21 must be handled with utmost care when it is removed from the package 10 at the time of replacement. If the plate 21 is damaged, the water inside the exchanger 26 may leak to malfunction the IC's. Summary of the Invention According to an aspect of the invention, there is provided a cooling system which comprises: a substrate mounting electronic components; a first layer made of adhesive provided on one surface of the substrate; a second layer made of a material having a low melting point and provided on the first layer; and a heat-­ radiating means provided on the second layer to outwardly radiate heat transmitted from the components through the substrate, the first layer and the second layer. Brief Description of the Drawings An object of this invention is to provide a cooling system which is free of aforementioned problems. FIG. 1 is a perspective view of an embodiment of the invention; and FIG. 2 is a cross-sectional view of the embodiment. In the figures, the same reference numerals represent the same structural elements. Preferred Embodiment Referring to FIGs. 1 and 2, an embodiment of the invention comprises a printed circuit board 1, a connector 2, a wiring substrate 3, adhesive 4, a metal layer 5 made of a material having a low melting point, a radiating conducting block 6, a holder 7, a cold plate 8, through holes 9, threaded holes 10, screws 11 for engaging with the holes 10, an inlet 12 for coolant, an outlet 13 for coolant, IC chips 14, threaded holes 21 and through holes 22. In the drawings, the upper surface of the substrate 3 is provided with a plurality of heat-generating components including the IC chips 14. The holder 7 is attached to the connector 2 by the screws 20 which penetrate through the holes 22 to engage with the holes 21. As a result, the substrate 3 is forced against the connector 2 with the holder 7 to electrically connect the IC chips 14 with wiring patterns in the board 1. The layer 5 made of solder or wax material is formed on the lower surface of the block 6. The layer 5 is fixed to the lower surface of the substrate 3 by the adhesive 4 obtained by mixing silicone rubber and a filler of high thermal conductivity. In the manner mentioned above, there is formed a module comprising the substrate 3, the adhesive 4, the layer 5 and the block 6. In the embodiment, no gap or clearance between the substrate 3 and the block 6 is caused by deformations such as warps on the substrate 3 or the block 6 which are often seen in the above-mentioned prior art structure. Since the flexible adhesive 4 is used, there will be no gaps or clearances between the substrate 3 and the block 6 due to such a difference even if the thermal expansion coefficient of the substrate 3 may differ from that of the block 6. The block 6 is snugly fixed to the cold plate 8 inside which liquid coolant is circulated. The opposed surfaces of the block 6 and the plate 8 are finished to give a particularly high flatness. The heat generated from the IC chips 14 is conducted through the substrate 3, the adhesive 4 and the layer 5 to the block 6. Since there is no gap or clearance on the heat conductive path, the thermal resistance of the path can be kept low. Further, because the block 6 and the plate 8 are closely pressed to each other with a high pressure applied by the screw 11, the thermal resistance there­ between can also be kept low. The heat generated from the IC chips 14 reaches the cold plate 8 to be carried away outside by the coolant circulating through the plate 8. As is described above, unlike the prior art structure the embodiment does not use any flexible thin sheets to enhance mechanical strength and avoid possibility of any water leakage which may be caused by careless handling. When the block 6 is to be removed from the substrate 3 at the time of replacement of defective one or ones of the IC chips 14, it would be extremely difficult to separate one from the other if they are adhered to each other with the adhesives 4 alone. However, since the embodiment uses the layer 5, they are easily separated simply by melting the layer, and the adhesive 4 can be easily removed from the substrate 3 after the separation. When re-assembling them, the layer 5 is formed again on the lower surface of the block 6 and the block 6 is then ready to be adhered to the substrate 3 with the adhesive 4. Although the plate 8 through which the coolant is circulated is used in the embodiment, a heat sink for air cooling may be used in place of the plate 8.

Claims: 1. A cooling system comprising a substrate (3) carrying electronic components (14), a first layer (4) made of an adhesive provided on one surface of the substrate, a second layer (5) made of a material having a relatively low melting point and provided on the first layer, and heat-removing means (6, 8) provided on the second layer to disperse heat transmitted from said components through said substrate, said first layer and said second layer. 2. A cooling system according to claim 1, characterised in that the heat-removing means (6, 8) comprise a heat conductive block (6). 3. A cooling system according to claim 1 or 2, characterised in that the heat-removing means (6, 8) comprise a plate (8) with coolant channels therein.

Inventors: MIZUNO, TSUKASA
Applicants: NEC CORPORATION
Application year: 1987
Main classification: H01L23
IPC codes: H01L23