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Solder Pad Cratering - A Growing Concern for Lead Free Soldered Electronics
Keywords: Cratering, Lead-Free, Failure mode
Cracking through the resin under the solder joint contact pads on printed circuit boards and/or components (‘cratering') is gaining increasing attention in different sectors of the electronics industry. In fact, EMS providers report that the combination of lead free solders and the greater brittleness of lead free compatible laminates is making cratering a more common solder joint failure mode than cracking through the solder itself. This of course depends very much on the application. Pad cratering is usually believed to require the kind of high strain rates only occurring under certain isothermal loading conditions. A typical example is wear out of the laminate in repeated drops, which is of course a concern for portable electronics. Certain high performance products, such as servers, are well protected and ‘only' subject to thermal cycling after installation. The manufacturers of these are therefore only concerned about immediate failure by cratering due to an overstress during testing (bending) or transport (drop). The failure mechanisms and resulting trends, including dependencies on laminate and processes, are very different in this case. However, manufacturers and users continue to overlook a major risk associated with invisible damage induced by a much lower load in assembly, testing, handling or transport. Such damage has been seen to significantly reduce life in subsequent thermal cycling. This presentation will offer an overview of the above issues, providing examples of very different sensitivities to various factors, and illustrating the lack of correlation between laminate strength and fatigue resistance. This will be followed by recommendations as to different test methods and the development of standards.
Venkatesh Raghavan,
SUNY Binghamton; System Science and Industrial Engineering Department
Binghamton, NY
USA


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