Printed circuit boards populated with twenty-five 0.4 mm pitch, 256-pin plastic quad flat packs (QFP) containing no-clean and water-clean solder joints were subjected to thermal cycling in order to induce thermal fatigue failure. QFPs failed from a minimum of 0.27 cycle to a maximum of 5310 cycles. Solder joints in both types of units were examined in the scanning electron microscope, and a relative comparison of the extent of fatigue damage is presented. The failure associated with cracking in the eutectic composition Sn/Pb solder initiated at the stress concentration sites. Crack propagation continued either along the pin-solder interface or solder-pad interface and ultimately resulted in the separation of the pin/pad junctions. In addition, a qualitative and quantitative comparison of the resulting solder micro-structure and the failure mode between the no-clean and the water-clean QFP solder joints was made and discussed.
Failure Analysis of No-Clean and Water-Clean Solder Joints 0.4 mm Pitch, 256-Pin Plastic Quad Flat Pack
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Govila, R. K., Pao, Y., Larner, C., Lau, J., Twerefour, S., Erasmus, S., and Dolot, S. (September 1, 1994). "Failure Analysis of No-Clean and Water-Clean Solder Joints 0.4 mm Pitch, 256-Pin Plastic Quad Flat Pack." ASME. J. Electron. Packag. September 1994; 116(3): 184–190. https://doi.org/10.1115/1.2905684
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