The Relationship Between Reliability and Bonding Techniques in Hybrid Systems

Differential thermal expansion has been shown to be responsible for many observed failures in ceramic chip capacitors mounted on alumina substrates. The present work has shown that the mounting techniques used in bonding the capacitors have a marked effect upon the thermally induced mechanical stress and thus the failure rate. A mathematical analysis of a composite model of the capacitor-substrate system to predict the magnitude of thermally induced stresses have been conducted. It has been experimentally observed that the stresses in more compliant bonding systems such as soft lead/tin and indium solders are significantly lower than those in hard solder and epoxy systems. The marked dependence upon heating and cooling rate has proven to be a determining factor in the prediction of failure n both the indium and tin/lead solder systems. This study has shown that the harder or higher melting solders are less susceptible to thermal cycling effects but that they are more likely to fail during initial processing operations, in the course of the study, strain gage techniques were used to determine thermally induced expansion stresses of both the capacitors and the alumina substrates. Thus, the compliance of the different bonding mediums were determined. From the data obtained, several recommendations are made concerning the optimum bonding system for the achievement of maximum reliability.