SMTA International Conference Proceedings


LEAD-FREE SELECTIVE SOLDERING: THE WAVE OF THE FUTURE

Author: Bob Klenke
Company: ERSA, Inc.
Date Published: 9/22/2002   Conference: SMTA International


Abstract: The pending legislation and market trends leading toward the implementation of lead-free electronic assemblies have raised several issues including the need to increase the thermal tolerances of electronic components. Lead-free solder alloys such as tin-silver-copper (SnAgCu) with a melting point of 217° C, require higher processing temperatures than traditional tin-lead (SnPb) alloys thereby reducing the process window and focusing on the need for rigorous control of the thermal process during soldering. This paradox between higher melting points of lead-free alloys and the thermal thresholds of electronic components forms the basis of the lead-free challenge.

Raising component thermal tolerances will place a significant economic burden on electronics manufacturers since they will be faced with higher overall thermal processing costs. This increase in costs associated with the thermal process will drive electronics assemblers to maximize the efficiency of their thermal processes.

This is especially true when soldering through-hole (TH) components in complex mixed technology printed circuit boards (PCB’s), where greater thermal demands are placed on the process capabilities of existing soldering methods such as wave soldering. One potential solution to this problem is the utilization of site-specific selective soldering to form TH interconnections for lead-free assemblies.

This paper describes the use of selective soldering as a viable alternative to wave soldering for lead-free soldering of TH interconnections. This paper outlines the quality and cost advantages that TH selective soldering offers for improving lead-free manufacturing cost efficiencies. Despite this fact, technological obsolescence of end-of-life (EOL) electronic products resulted in 21 million used computers being dumped into the solid-waste recycling process in 1998.

An additional concern is that although the electronic solder contained in electronic products represents less than 1.0% of total lead consumption, 28.5% of all lead bearing materials going into municipal solid waste (MSW) in the U.S. is from associated cathode ray tubes (CRT’s) contained in television sets and computer monitors. If leadacid storage batteries could be 100% recycled and thereby removed from MSW, electronic solder and CRT’s would represent more than 83.7% of the remaining lead bearing source material.2



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