Effects of materials and processing on the reliability of silver-glass die attach pastes

The benchmark tests for goodness of silver-glass pastes have been the postfire adhesion and residual moisture present in package cavity head-space. However, as die sizes have increased in edge dimensions and silicon design rules have progressed below 1 μm, processing and evaluation criteria have become more stringent. Evaluation criteria have begun to focus more heavily on the mechanical behavior of the die bond joint. Temperature cycling from -65° to +150° has become a standard procedure for evaluation of silver-glass die bond materials. The percent degradation in tensile adhesion immediately following die attach and after 500 or 1000 cycle tests has become an important criterion for determination of paste robustness. Experimental results have shown that the composition of the glassy phase and the ratio of silver to glass affect the durability of the die bond zone. Several glass compositions were investigated to determine optimum firing conditions and resistance to both mechanical and chemical (ambient gas) degradation. The effects of various metal-to-glass ratios were studied. Optimum ratios other than the traditional 4:1 by weight ratio were identified to give superior performance from the standpoints of chemical and mechanical durability