Lead-free plating for semiconductor devices qualification & implementation

This paper presents the findings of a series of experiments to evaluate various commercial lead-free plating alternatives, including tin, tin-copper and tin-bismuth products. Three different IC package types (TSOP 48, PLCC 32 and SOIC44) were used in both off line and in a production environment to evaluate solderability aspects including plating thickness, ionic impurity, morphology grade, solder whisker growth, solderability (tests under steam-age and bake conditions) and lead pull tests of mounted packages. Since no lead-free plating standards of quality were available at the time of the study, normal solder plating standards were used as a reference. Initial experiments revealed solderability issues (especially poor morphology grades and whiskering with both tin-bismuth and tin-copper materials). Tin plating looked the most promising material. Tin and tin-bismuth plating were further investigated in production processes to attempt to eliminate the initial quality issues, and to develop, fine-tune and optimize the plating process. The extensive experiments of this study of lead-free plating has yielded a great amount of information pertaining to the different chemistries of the different plating types, has identified a number of production concerns, and suggests process parameters for tin and tin-bismuth plating types that makes these materials viable replacements for tin-lead plating.