Following a two-year study on the effect of impurity limits on the performance of lead-free solder, the IPC Solder Products Value Council (SPVC) has announced the publication of a white paper, "Take Action Limits (TAL) for SAC305 Lead-Free Soldering Processes Utilizing Solder Baths/Pots." The paper provides electronics manufacturers with better-defined limits to guide them on a more efficient use of solder and, as a result, improve yields.

Take action limits, also known as "dump pot specifications," are important to any electronics manufacturing company using flow soldering techniques either in selective soldering or wave soldering. The report is based on testing of eight common SAC alloys that were subjected to strenuous tests, including wetting and electron microscope examination. The IPC TAL white paper identifies three action levels:

• Normal operation -- the level one would expect contamination levels to be, based on running at a steady state.
• Increased monitoring -- a level that is not a danger but indicates an upward trend that should be monitored more closely.
• Adjust pot -- the level at which the pot should be adjusted to ensure reliable performance of solder joints.

Paul Lotosky, global director of customer technical support at Cookson Electronics, and chairman of the IPC SPVC technical subcommittee, explained that current specifications for contamination are for either tin-lead alloys or for component and board acceptance. "The white paper we published reports on a series of tests to validate take action limits of solder pot contamination for SAC305 lead-free solder."

The report also sets TALs for 14 materials that can commonly be introduced during normal board production, such as gold, nickel and bismuth. In addition, scatter plot diagrams for all wetting test results as well as statistical analyses of wetting data are included.

"The report is another example of how the industry can come together and work together to create a coherent set of technical requirements that the industry can use to increase efficiencies and eliminate unnecessary waste," added Karl Seelig, AIM Inc. and chairman of the IPC SPVC.

IPC members can download the IPC TAL white paper for free. Nonmembers may purchase the report for $25. See the reference link below.