Designs of low stress I/O pin attach structures

Three low-stress pin attachment structures were developed for the glass ceramic-copper multilayer ceramic (MLC) packaging technology used in IBM ES 9000 processors. The structures include the multilayer thin-film I/O pads, taper-headed pin and low-stress solder as the joining alloy. All of them were shown to reduce the pin-joint stress significantly and, consequently, are more compatible with the glass-ceramic module. The authors summarize both experimental and finite-element analysis studies to optimize the stress of the pin-attach system such that the pins can be joined to the glass-ceramic MLC with good reliability. The design goal was to have a pin-joint structure in which the ceramic and the pin-joint will survive a pin-pull test up to 10 lbs with a repairable pin-shank failure mode. The combined stresses generated from the braze, pin loading, and I/O pad should not exceed the fracture strength of the ceramic substrate. Finite-element modeling identified high-stress regions and possible failure modes of each pin joint design. The three approaches taken to reduce the stress of the pin-joint are described