Evaluation of Solder Pastes for High Reliability Applications
Authors: Scott J. Anson Ph.D., PE; Michael McLaughlin and Abner Argueta Company: LeTourneau University and IEC Electronics Corporation Date Published: 10/13/2013
Abstract: Solder paste is the most important material in Surface Mount Technology (SMT) assembly, and contract manufacturers of high reliability electronics face the simultaneous challenges of multisite operations combined with mission critical customer applications. It is essential to select a solder paste that performs at a high level under optimum conditions and also gives stable performance under suboptimal conditions, such as common environmental and manufacturing time fluctuations. This study examined 63Sn/37Pb solder paste alloy with both 63Sn/37Pb and 96.5/3.0Ag/0.5Sn (SAC305) lead free components in mixed alloy reflow. Both water soluble and no-clean chemistries were evaluated. A design of experiments (DOE) approach was employed to examine solder balling and slump resistance. Additional experiments examined print quality utilizing automated Solder Paste Inspection (SPI) in terms of bridge resistance, CSP and 0201 insufficient resistance, and response to a 45 minute print pause. Assemblies were also built to check for defects, joint quality, and voiding. The result is a holistic approach to solder paste testing that includes weighting of numerous factors to assess solder paste performance and robustness to external variation such as humidity and exposure time.