| The properties of Lead-Free solder joints continue to change over a very long time while in service. The assessment of long-term service life of electronics packages invariably misses the effect of solder joint size and configuration, and may thus end up to be seriously misleading. One of the goals of the present research is to develop a fundamental understanding of the effects of solder joint size on the mechanical properties of microstructure and aging kinetics. This understanding will help in the assessment of the reliability of Lead-Free solder joints. For this purpose, two different room temperature properties, namely, shear strength and micro-hardness, are studied and the microstructure is also evaluated to find the correlation between them. These properties are measured before and after aging for different lengths of time at different temperatures.;Five common Lead-Free alloys are selected for the present study, which are SAC105, SAC205, SAC305, SnCu and SnAg. The study also addresses effects of solder joint size by focusing on 20 mil (508&mgr;m) and 30 mil (760&mgr;m) diameter solder spheres reflowed onto solder mask defined OSP coated Cu pads with a typical manufacturing Lead-Free reflow profile. Isothermal aging is conducted for up to 500 hours at temperatures of 70, 100, and 125°C. As expected, the resulting room temperature properties decrease with aging time, and at a faster rate for higher aging temperatures. The acceleration factors that are extracted for the evolution of each property are different for the selected alloy and joint sizes. |
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