Recommendations on Solder Scavenging Systems| 1 May, 2009
Scavenging Methods [Improve Solder Scavenging of Large Area-array Sites, SMT, Laurence Harvilchuck, process research engineer, Unovis Solutions, email@example.com]
Two common methods exist for scavenging residual solder on the site for simplified component replacement: * Solder wicking with copper braid and a hot iron. * Vacuum-assisted desoldering with specialized tooling.
In the simplest cases, where there is a coarse pad pitch and known-good laminate and alloy, wicking is performed. This involves heating the copper braid with the soldering iron tip to a point above the solder alloy's melting temperature. Passing the hot braid over the solder will then melt the solder and draw the liquid off the pad and into the wick. Alternatives such as a metallic block, wool, or foil � that will wet the solder and draw the excess liquid away from the pad by virtue of wetting and capillary action � may be used.
Vacuum desoldering evolved partially out of the need to remove higher-melting structures such as high-lead spheres or columns from the site, without the need to completely melt the high-lead alloys at temperatures that would damage organic material sets. As the complexity of electronics assemblies increased to include such factors as package-on-package (PoP) components, systems-on-chip (SoC), and the EU RoHS regulations, amongst others, so did the selection of alloys, giving less of a safety margin between the necessary reflow temperatures and the thermal damage thresholds for material sets. New material systems that were introduced, as a result, demanded more careful attention to the thermal profile during repair, and the need for further sophistication of the solder scavenging process increased.