ICSR (Soldering and Reliability) Conference Proceedings


Authors: Craig Hamilton and Matthew Kelly
Company: Celestica Inc. and IBM Corporation
Date Published: 5/16/2008   Conference: ICSR (Soldering and Reliability)

Abstract: Ever since the inception of the RoHS legislation was known, the search for a replacement to the well established 63Sn-37Pb alloy has taken place. To date, the majority of the Electronics Manufacturing industry has implemented either SAC305 or 405 alloys to manufacture Pb-free (E.U. RoHS, compliant) products, for both the SMT and PTH card assembly processes. This original alloy composition choice, dating back to 1999, was based on early research into the metallurgy and reliability of the alloy/s and agreement amongst top companies involved in iNEMI, JEITA and within the European Union. Over the past few years, a shift towards SAC305 has been observed within the industry, primarily due to its lower cost when compared to SAC405. However, at this point in time, there does not seem to be one clear alloy of choice, for use within both the SMT and PTH processes for manufacturing all product types. For example, over the past year, BGA manufacturers have been developing variations of low-silver content type alloys (i.e. SAC105) in order to improve drop and shock resistance for use within portable electronic type devices. In addition, there are many lead free alloy options currently available for use within the wave solder and PTH rework processes, each having differing compositions and physical properties compared to the SAC305/405 alloys. Standardizing on one alloy across the industry is what we all would like to strive for - but is there currently one lead free alloy available which will provide the solution for all applications?

This study focused specifically on researching 4 available alternative lead free alloys used in the wave and solder fountain processes. All of the alternative lead free alloys were compared against a SAC405 baseline. The results from earlier trials characterizing each of the alternative lead free alloys copper dissolution rates will be discussed. In addition, the process performance of three of the alternative alloys within the wave solder process, based on the results of the Phase 1 trials will be discussed, which includes profile optimization and process yield analysis using an internally designed wave test vehicle.

Key words: Alternative Pb-free Alloys, Cu Dissolution, Quality, Defects, Process Window

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