Grain boundary sliding in surface mount solders during thermal cycling

The growth of fatigue cracks in near-eutectic, surface-mount solder joints during cyclic, thermal displacement-controlled loading is reported. Ceramic leadless chip carriers (LLCC) are subjected to thermal fatigue with a frequency of 1/hr and over two ranges of temperature: -36 degrees C to 125 degrees C and -20 degrees C to 75 degrees C. Surfaces and cross-sections of the solder joints are inspected using scanning electron microscopy. Individual grains (colonies of lamellae and globulae) are found to slide relative to one another during thermal cycling. Sliding causes fatigue cracks to initiate at the surface.<
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