The present invention generally relates to structure for sealing module, and more particularly to a structure for sealing modules which include a plurality of plated printed circuits provided with a thermal conduction type cooling system.
The plated printed circuitry of modern electronic apparatus such as computers generates a large quantity of heat because a large number of integrated circuit elements are provided on a multi-layer ceramic substrate at a high density and the circuits are operated at a high speed. Accordingly, the plated printed circuitry must be effectively cooled in order to ensure stable operation of the circuits. Usually, thermal conduction type cooling systems are employed in which each of the integrated circuit elements is directly cooled using a cooling medium having a large cooling effect.
In thermal conduction type cooling systems, a cold plate having a passage through which a cooling medium flows and a bellows which communicates with the passage are arranged immediately above the integrated circuit elements at the surface of the plated printed circuit and the ambient atmosphere becomes highly humid. For this reason, a sealed space is provided between the cold plate and the plated printed circuit and a gas such as nitrogen or helium is provided within the space at a predetermined pressure so as to maintain a dry atmosphere. Such sealed structure prevents the corrosion of the integrated circuit elements, the circuit patterns and the bonding material, and the reliability of the plated printed circuit is enhanced and deterioration is prevented.
FIG. 1 shows an example of a conventional sealed module including conventional sealing structure, and FIG. 2 shows an essential part of the conventional module sealing structure on an enlarged scale. In FIG. 1, the module includes a plated printed circuit 1 comprising a multi-layer ceramic substrate 2 having a top surface 2a and a bottom surface 2b. A large number of integrated circuit elements 3 are provided on the top surface 2a of the substrate 2, and input/output pins 4 project from the bottom surface 2b of the substrate 2. A thermal conduction type cooling system 5 includes a box shaped cold plate 6 which opens to the bottom. A passage 7 for the cooling medium is provided inside the cold plate 6, and bellows structures 8 communicate with the passage 7. The cold plate 6 is arranged so that a bottom plate portion 9 of each of the bellows structure 8 make close adherence with the corresponding integrated circuit element 3 of the plated printed circuit 1, and a generally ring-shaped metal fitting 10 is mounted at the bottom of the cold plate 6. A flange 10a of the metal fitting 10 projects inwardly thereto and holds the peripheral portion 2c of the bottom surface 2b of the substrate 2. A module 11 is completed in this manner.
The sealing between the bottom surface 2b of the substrate 2 and the flange 10a of the metal fitting 10 is made as shown in FIG. 2. That is, a thin metal film 12 is formed on the peripheral portion of the bottom surface 2b of the substrate 2, and this thin metal film 12 and the flange 10a are fixed together by a solder 13 to provide the sealing between the bottom surface 2b of the substrate 2 and the flange 10a of the metal fitting 10. As a result, a sealed space 14 is formed between the cold plate 6 and the plated printed circuit 1, and a gas such as nitrogen is sealed within the space 14.
Therefore, the integrated circuit elements 3, the circuit patterns on the substrate 2 and the other components on substrate 2 are maintained in a dry atmosphere by the gas sealed within the space 14, and the heat generated from the integrated circuit elements 3 is reduced and eliminated by the cooling medium in the bellows structures 8.
In the conventional module the sealing structure, is formed by directly fixing the flange 10a to the thin metal layer 12 which is formed on the peripheral portion 2c of the bottom surface 2b of the substrate 2 by the solder 13. For this reason, a pushing force exerted by the bellows structures 8 acts directly on the junction between the peripheral portion 2c of the substrate 2 and the flange 10a. In addition, thermal stress is generated at the junction due to differences in the coefficients of thermal expansion of the materials used at the junction, but there is no means for absorbing such thermal stress. As a result, damage such as cracking easily occurs at the junction, and the substrate 2 is easily damaged because it is usually made of a glass ceramic material or the like which is mechanically weak.