SMTA International Conference Proceedings


CONTROLLING COPPER BUILD UP IN AUTOMATIC SOLDERING EQUIPMENT USING LEAD-FREE SOLDER

Authors: David Suraski and Karl Seelig
Company: AIM
Date Published: 9/26/2004   Conference: SMTA International


Abstract: Since "nothing solders like solder", HAL (Hot Air Leveling) will continue to hold a significant place in the surface finishing industry. Furthermore, the wave soldering process will continue to be a viable means of electronics assembly. However, as automatic soldering processes using lead-free alloys have become increasingly prevalent, questions have arisen about copper dissolution into these alloys.

The Sn/Ag/Cu family of alloys is the leading candidate for a lead-free alternative. The first part of this study was to determine if there is any significant difference between Sn/Ag/Cu alloys when used in automatic soldering equipment in terms of copper build-up in the system. The study compared two Sn/Ag/Cu alloys to determine if at processing temperatures one alloy would absorb less copper than the other alloy.

The second part of this experiment was to determine how to effectively control copper build-up in automatic soldering equipment. Presently, manufacturers have been able to limit the copper in a solder bath by precipitating the copper out using a simple gravimetric separation of Cu6Sn5.

Unfortunately, because the density of high-tin lead-free alloys is lower than that of Cu6Sn5, the Cu6Sn5 intermetallics sink and are dispersed through the lead-free alloy in the pot. Therefore a procedure for separating copper intermetallics from lead-free pots has had to be developed. Yet another issue is that there is not yet an agreed upon industry specification for lead-free pot maintenance. Clearly, this will be needed as a guideline for the users of these alloys. To accomplish this, a specification is proposed based upon these experiments.



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