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Visual Method for Monitoring the Surface Composition of Lead-Tin Alloys

IP.com Disclosure Number: IPCOM000059744D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Linde, HG: AUTHOR

Abstract

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.

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Visual Method for Monitoring the Surface Composition of Lead-Tin Alloys

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. By a simple dip tank method, wafers are submerged in octanoic acid which reacts with lead to produce an insoluble soap product. Reflowed lead-tin IC solder balls on the wafer (or other alloys) are allowed to react by soaking in a 10% solution of octanoic acid in xylene for a period of 10 minutes at room temperature. Samples are then rinsed briefly in pure xylene. The lead-tin surfaces are then observed microscopically. Growth of white soap crystals indicates reactivity and potential polyamic acid interaction. The table below shows observed reactivity with known alloys and gives respective surface and bulk analysis. Polyamic acid film formation on these alloys was correlated...