In the HITACHI MP6000 (HDS Skyline Trinium TM), the bipolar-CMOSprocessor dissipates about 600 W, and the new direct solder-attachedcooling (named DiSAC) method has been developed for use with it. In thiscooling method, the HDM is supported by the 97Sn/Ag C4 (or CCB;controlled collapse bonding) bumps, which are affected by almost all thedeformation that occurs in the power on/off cycle. Hence, the fatiguelife of the C4 bumps is most important in the application of thiscooling method. In this paper, the causes of C4 bump strain are analyzedby the finite element method, and several techniques for reducing strainare simulated. A new method of estimating the fatigue life of the C4connections, pseudo-elastic plastic creep analysis (EPC), is developedin order to improve the accuracy of fatigue life calculations, and isused to evaluate the creep strain in a 3D model. Using EPC andexperimental C4 power cycle damage data, a new strain-fatigue life curveis defined. Process defects in the direct solder attachment are found tomarkedly shorten the fatigue life of the C4 connections, and the effectsare estimated. All the technological developments presented areimplemented in the DiSAC model, and the improvement in reliability isverified by experiment
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