Thermal Cycling Ramifications of Lead-Free Solder on the Electronic Assembly Repair Process

摘要

The conversion from tin–lead to lead-free electronics has created concern amongst engineers about the reliability of electronic assemblies and the ramifications that reliability changes may have on the life cycle cost and availability of critical systems that use lead-free electronics. In order to analyze the impact of the tin–lead to lead-free electronics conversion in terms of life cycle cost and availability, a simulation of fielded electronic systems to and through a board-level repair facility was created. Systems manufactured with tin–lead parts or lead-free parts that are fielded, fail and have to be repaired are modeled. The model includes the effects of a finite repair process capacity, repair prioritization, multiple possible failure mechanisms, no-fault-founds, and un-repairable units. The model is used to quantify and demonstrate the system- and enterprise-level risks posed by the conversion from tin–lead to lead-free electronics. Example analyses were performed on electronic assemblies that use SAC (tin, silver and copper) and tin–lead solder using a repair process modeled after a NSWC Crane Aviation Repair Process (8000 assemblies with 30 year support lives were modeled). The components considered consisted of ball grid array, column grid array and leadless chip carrier packaged parts that experienced three different thermal cycling profiles. The case studies revealed that when exposed to usage profiles characteristic of consumer electronics, low maximum and mean thermal cycling temperatures with long dwell times, SAC exhibited significantly reduced repair costs compared to tin–lead. For usage profiles characteristic of aerospace and high-performance applications, high maximum and mean thermal cycling temperatures with short dwell times, SAC exhibited significantly increased repair costs when compared to tin–lead.