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The Issues Connecting Lead-Free Solders, Microelectronic Device Moisture/Reflow Sensitivity, Tin Whiskers and False Military Exemptions
Keywords: Pb-Free, Electronics, Standards
We cannot ignore or derail the lead-free (Pb-Free) train that is coming at all of us involved in microelectronics. Pb-Free is here or on its way and if you haven’t started to prepare for it, even if your portion of the industry is “exempt”, you need to get on the train or deal with the future consequences. Pb-Free by itself sounds harmless enough and it would be good for the environment, after all, we already removed lead from paint and gasoline years ago. When you start looking at the consequences of moving towards Pb-Free however, there are many challenges and limitations: some old, some new. The removal of lead from solder has three direct effects; 1) higher costs, 2) higher reflow temperatures and 3) questionable reliability of solder joints. The higher reflow temperatures have a direct effect on the reliable attachment of surface mount devices to PCBs without damaging them during the reflow process. Devices previously classified for SnPb (tin-lead) solders are not likely to qualify for Pb-Free solders, or if they do, it will be at several Moisture Sensitivity Levels (MSL’s) below its current MSL. Semiconductor manufacturers have redesigned devices for qualification and classification at Pb-Free temperatures, which will eventually make SnPb parts obsolete. Not a good scenario for “exempt” industries, such as Defense, who are only a small percentage of the market. Without market clout, currently “exempt” portions of the microelectronic industry, like Defense, will also become Pb-Free. Also, linked to Pb-Free are old issues that are showing up again, such as “Tin Whiskers”. Standard tests are now being put in place by such organizations as JEDEC to begin characterizing the extent of this problem, which was originally resolved by adding lead (Pb). In the short term, tin whiskers may not cause a problem, but for longer-term storage it is likely to be an issue. Nobody is completely “Exempt” from Pb-Free!
Steven R. Martell, Manager, Technical Support Services
Sonoscan, Inc.
Elk Grove Village, IL
USA


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