METHODOLOGY FOR EVALUATING DATA FOR “REVERSE COMPATIBILITY” OF SOLDER JOINTS
Authors: Bill Russell, Dennis Fritz, and Gary S. Latta Company: Raytheon Professional Services LLC, SAIC Corp., and Crane Division, Naval Surface Warfare Center (NSWC Crane) Date Published: 10/11/2007
Abstract: Particular attention is being paid today to lead-free components and/or solder alloys being used to repair legacy military electronics. Military hardware, manufactured for decades with eutectic tin/lead solder, is now being caught up in the global shift to lead-free solder. A “backward compatibility” problem occurs as parts suppliers due to market concerns (military <5% of market share) eliminate eutectic tin/lead solder as a component finish substituting other finishes (usually electroplated matte tin) on existing part numbers. In addition, the proliferation of commercial off the shelf (COTS) hardware into military systems greatly increases the probability of mixing tin/lead and lead-free solders and component finishes within the assembly during repair. The intermixing of tin/lead and lead-free solders raises long-term reliability issues that are yet unanswered. A large database of information was assembled from publicly available data on mixed solder assembly. Methodology was developed for comparing information sources by analyzing Weibull reliability charts for data consistency. Using these comparisons, reliability predictions will be made for mixed solder assembly of military electronics, to guide rework and repair options and making informed decisions possible.