Pb-free plating for peripheral/leadframe packages

Leadframe packages utilize SnPb plating on terminals to protect the base metal from corrosion and to provide a solderable surface. However, customers are moving to environmentally conscious products establishing a need to develop alternative Pb free plating finishes for terminals. The most promising solution is Sn-based electroplating. Several Sn-based plating chemistries are commercially available at comparable costs to SnPb. However, Sn-based plating finishes are not free of issues. Whisker growth can cause a component to electrically short. In addition, there is little data on solderability and solder joint reliability for Pb free terminal finishes with Pb free solders, as well as, SnPb solders. Sn, SnCu, SnBi, and SnAg plating finishes were evaluated for whisker growth, solderability, and solder joint reliability. For the packages SnBi out-performed the other Sn-based finishes in terms of whisker free life, needle length, and quantity. Solderability for the Pb free finishes was poor in comparison to the SnPb finish, which passed all solderability preconditioning and test methods. Lastly, solder joint reliability appears to be comparable for all Pb free finishes to the SnPb finish.