METHODS OF ANALYZING THERMOMECHANICAL STRESS IN PLASTIC PACKAGES FOR INTEGRATED-CIRCUITS

Thermomechanical stresses are built up in the plastic packages during the manufacture of an integrated device and also throughout the workin g life of the device, arising due to a mismatch between the coefficien ts of thermal expansion of the package materials. Excessive levels of thermomechanically induced stresses may lead to cracking in the packag es, which could in turn lead to failure of the device. It is important , therefore, to be able to predict and measure thermomechanical stress es in order to improve package reliability. This paper describes the u se of finite-element techniques and strain gauges to determine package stress levels. The effect of delaminations at the interfaces of the p ackage materials is discussed also, and the scanning acoustic microsco pe is introduced as a complimentary tool to identify stress-related de fects in plastic packages.