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|Modification to Darveaux Solder Joint Fatigue Life Prediction Method for Flip-Chip Solder Joints|
|Keywords: Flip chip, Fatigue life prediction, solder joint reliability|
|For decades, BGA solder joint fatigue in thermal cycling has been studied by different researchers. Finite element modeling techniques have been used for years to calculate inelastic strain energy accumulated during thermal cycling. Fatigue life prediction methods then are used to measure and predict accumulative fatigue. For years, different stress-based, strain-based, damage accumulation-based, inelastic energy-based theories were proposed and studied by researchers. Robert Darveaux proposed a damage accumulation-based inelastic energy-based theory in 2000 that is being commonly used in industry. Darveaux method measures number of cycles for cracks to initiate and propagate through the joint based on average inelastic energy density accumulated during thermal cycling, and the crack initiation and crack growth constants he calculated for BGA joints. In this paper, Darveaux fatigue life prediction method is modified for flip-chip solder joints where solder joints are smaller with finer ball pitches, and Darveaux constants for BGA solders can not be applied. In this work, modified crack initiation and growth constants are proposed for flip-chip solder joints. Furthermore, Darveaux constants are modified to be able to apply to Tessera’s uPILRTM flip-chip solder joints when copper pins are used in combination with solder to form the joints. This modification is detailed and illustrated on Tessera’s 130um bump pitch flip chip package comparing solder fatigue life for solder-only, C4-bump and uPILRTM flip chip technologies.|
|Bahareh Banijamali, Senior Mechanical Engineer
San Jose, CA