Electroless Tin on Lead-Tin Pads for Corrosion Inhibition
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Electroless tin processing of semiconductor wafers just prior to polyimide processing avoids formation of polyamic acid carboxylate lead salt films on lead-tin (Pb-Sn) pads. This lead salt can inhibit proper wetting in the process of chip to module joining. Vacuum deposition through a mask from a Pb-Sn alloy source creates pads on a semiconductor chip which have high tin content on their outer surface. Reflow annealing, time at room temperature with air exposure, and test probing, all contribute to there being lead and lead oxide on the top surface of the Pb-Sn pads. Reaction during the subsequent polyimide and photo hole opening processes forms polyamic acid carboxylate lead salt.