Surface Mount Attachment Life Testing of a RF Circulator Component Assembled with Pb-Free or SnPb Solder
Authors: Richard Coyle, Robert Kotlowitz, Peter Read, Richard Popowich, and Debra Fleming, and Robert Quigley and Robert O’Neill Company: Alcatel-Lucent and M/A-Com Technology Solutions Date Published: 10/16/2011
Abstract: Accelerated temperature cycling was used to evaluate the thermal fatigue reliability of a circulator component used in RF power amplifiers for wireless hardware applications. The package design of the circulator uses surface mount technology (SMT) butt-type solder connections, rather than the traditional flat-lead attachments where the component is mounted within a cavity in the heat-sink. The butt-type attachment of the circulator presents potential challenges for solder joint assembly quality, thermal fatigue reliability, and overall mechanical integrity. This study compared the thermal fatigue performance of Pb-free Sn-3.0Ag-0.5Cu (SAC 305) and Sn-63Pb37 SnPb eutectic surface mount solder assemblies. The attachment reliability was evaluated using industry-recognized practices for accelerated thermal cycling (ATC) testing. The solder attachment integrity and failure mode under ATC are discussed in terms of the microstructural evolution during testing. The attachment robustness of the SnPb and Pb-free solders is compared using recognized industry models for solder thermal fatigue behavior. The overall test results indicate that the Pb-free solder attachment is at least as robust as SnPb, and provides acceptable long-term reliability in typical thermal use environments for wireless hardware.