SMTA International Conference Proceedings


REFLOW PROCESS ENHANCEMENT AND WETTING ANALYSIS IN 63Sn/37Pb AND Sn-Ag-Cu LEAD FREE ALLOY

Authors: Scott J. Anson, Ph.D., PE, and Jacob G. Slezak
Company: Rochester Institute of Technology
Date Published: 10/11/2007   Conference: SMTA International


Seika Machinery, Inc.

Abstract: Lead free electronics soldering is driven by a combination of health and environmental concerns, international legislation and marketing pressure by lead free electronics manufacturing competitors. Extensive testing by the electronics community has determined that Sn – Ag - Cu (SAC) alloy is the preferred choice for lead free Surface Mount Technology (SMT) soldering. 96.5Sn/3.0Ag/0.5Cu (SAC305) will be analyzed in this study and compared with 63Sn/37Pb.

Lead free soldering requires an increase in reflow peak temperatures, which further aggravates component moisture sensitivity risks and thereby decreases assembly yield. Prior research has revealed a counterintuitive enhanced solder spreading phenomena at lower peak temperature and shorter time above liquidus with 63Sn/37Pb solder and SAC305.

A summary of several investigations in solder wetting will be presented. The studies span the following four conditions: 1) air and nitrogen reflow atmospheres; 2) 63Sn/37Pb and SAC305 alloys; 3) water soluble and no clean fluxes; and 4) ENTEK® Cu-56 and ENTEK® Plus Gold (106AX) Organic Solderability Preservatives (OSP). All studies were conducted using materials and manufacturing systems that are industry relevant. The objective of each study was to produce practical industry relevant reflow processes. One key aspect was to develop processes that effectively forms solder joints while avoiding heating the assembly any hotter than necessary, which would increase the risk of component damage due to rapid moisture outgassing and associated popcorn delamination. An overview of results will be presented with an emphasis on reflow process improvement.

Key words: Reflow, Lead Free, SAC, Solder, Wetting, Spreading, Temperature, OSP, Organic Solderability Preservative



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