A comprehensive surface mount reliability model (CSMR) covering several generations of packaging and assembly technology

An extensive set of surface mount reliability data gathered by several AT&T organizations between 1984 and 1992 has been integrated in a single design-for-reliability tool, AT&T´s Comprehensive Surface Mount Reliability (CSMR) model. This analytical/empirical model fits AT&T´s database with a correlation coefficient of 0.97, a significant improvement over a correlation of 0.40 for the existing Figures of Merit. The new solder joint life prediction capability spans test conditions with a wide range of frequencies and temperature limits and covers three orders of magnitude in cyclic life. The validity of the model has been verified for evolving families of components, substrates and assembly technology, including 0.5 mm pitch Alloy 42 leaded TSOPs and large, 25 mil pitch devices. The extension of the model to land grid arrays is in progress and the present fit to accelerated test results looks promising. This paper presents the innovative features of the CSMR model and illustrates its application to several design examples. Important benefits of the model are more accurate attachment reliability predictions and less conservative design decisions than from previous models