Evaluation of Water Soluble and No-Clean Solder Pastes with Palladium Plated and Solder Plated SMT Devices

In response to increasing environmental concern over the use of chlorofluorocarbons (CFC's) to clean printed circuit assemblies, many surface mount operations are converting to water soluble or no-clean type solder pastes. Current trends indicate that this conversion will progress rapidly until water soluble and no-clean pastes constitute the majority of the product mix. With the introduction of water soluble and no-clean solder pastes many users have a need to understand which factors influence performance of these new generation pastes in their reflow process. The purpose of this evaluation was to determine to what degree the solder paste, reflow profile, and component shelf storage time impacted solder joint quality for both palladium and solder plated surface mount devices. Designed experiments were performed to understand the individual impact of each factor on the mechanical strength of the solder joint and contact angle of the solder with the lead on surface mount devices. Several water soluble and no-clean solder pastes were included in the evaluation. Identical test matrices were performed for both palladium and solder plated devices. The test results indicate that the solder paste formulation had the strongest influence on the contact angle of the solder joint for both palladium and solder plated leads. The reflow profile and the component shelf storage time had minimal impact on the contact angle, regardless of the plating material. The solder paste formulation also had the strongest impact on the shear strength of the solder plated units.