Multi-chip package thermal management of IBM z-server systems

The recently announced IBM z9 server system presents unique cooling requirements from a packaging perspective. Cooling has to be achieved for sixteen chips mounted on a common glass ceramic chip carrier. Eight of the sixteen chips dissipate significant power. A recently described small gap technology (SGT) is used to attain customized chip to cap gaps. An advanced thermal compound (ATC) is used as the interface between the chips and the cap. The package thermal and mechanical design is first described. Design optimization is achieved by detailed finite element thermo-mechanical modeling. The complex encapsulation process to attain the correct chip to hat ATC gaps is outlined. Verification of the ATC gaps is an integral part of the assembly process. The reliability qualification is then discussed. Issues found during the qualification were the structural fragility of the glass ceramic chip carrier flange and ATC thermal degradation. The structural robustness of the chip carrier was improved by modifying its design. ATC degradation is quantitatively related to the shear strain