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From: | |
Reply To: | (Leadfree Electronics Assembly Forum) |
Date: | Thu, 21 Nov 2002 21:28:18 EST |
Content-Type: | text/plain |
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Hi Keith,
Without getting the test details, concluding that "Lead-free joints are
usually stronger and survive thermal fatigue better than tin-lead joints" is
dangerous. Unless the testing follows the guidelines of IPC-SM-785 or
IPC-9701, serious fallacious conclusions can result.
Most of the fatigue results reported are from tests designed to totally
ignore the creep-characteristics of solder [no dwell times at T-extremes] and
also use an extreme cycle condition [-55/-40<=>+125C] that assures
confounding damage mechanisms. Thus, no valid conclusions regarding product
reliability are possible. To date, virtually all properly run accelerated
T-cycling tests have shown inferior creep-fatigue reliability for almost all
LF-solders.
Werner Engelmaier
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