Thermal stress analysis of a multichip package design

A thermal analysis of a package design that emphasizes thermally induced stress, in the most critical package components is presented. The package uses flip-chip solder bonding and thin-film interconnections between chips. Indium was chosen as the die-attachment medium for use between the chips and the water-cooled heat sink. A method for estimating the stress on a solder bump array when the indium die bond deforms during a power-up is given. It is found that stress can be reduced by decreasing the die bond thickness. However, very thin die bonds will have a reduced fatigue life due to increased plastic strain per power cycle. Therefore, the package design can be optimized by using the thinnest possible indium die bond which has an adequate fatigue life