Visual Method for Monitoring the Surface Composition of Lead-Tin Alloys
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
A process to rapidly indicate potential soldering (chip joining) difficulties due to reactive lead-tin alloy surface regions is featured. Polyamic acids used in some integrated circuit (IC) processing steps react with lead and low tin alloys to form a salt residue which inhibits the chip joining process. Lead-tin alloys of >4% tin tend to retard this reaction. To rapidly evaluate the surfaces of reflowed lead-tin alloys, i.e., IC chip joining solder balls, and determine the reactivity and uniformity of the surface regions prior to polyamic acid processing, a method of detecting potential alloy reactivity with polyamic acid, and the degree of surface passivation resulting from tin or tin oxide coverage, has been developed.