Fatigue of Solder Joints in Surface Mount Devices

    Published: Jan 1988

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    Lifetime studies of a 16 I/O surface-mounted solder joint array undergoing isothermal cyclic fatigue in torsion shear under fixed plastic strain range show a strong correlation with creep fatigue and a creep-cracking mechanism. Experimental lifetime data follow an inverse dependence on matrix creep. Experimental measurement of the steady-state shear creep rate versus shear stress defines the creep characteristic that is sensitive to changes in metallurgical structure. The amounts of grain boundary and matrix creep taking place during a fatigue cycle are derived from experimental creep data combined with stress-strain hysteresis data obtained in steady-state cycling. Initially, thicker solder joints have a larger grain size than thinner solder joints, giving more matrix creep during fatigue and a faster failure rate. Fatigue increases the mean grain size of the solder joint as determined by the creep-rate-versus-stress characteristic and microstructure. Effects of grain size and joint thickness on lifetime are discussed. A maximum in the creep fatigue rate occurs at 333 K (60°C).


    creep fatigue, creep cracking, matrix creep, grain boundary creep, lifetime inverse relationship with matrix creep, surface-mounted solder joint array, torsion shear, fixed plastic strain range, creep characteristic, fatigue rate

    Author Information:

    Shine, MC
    Principal Engineer and Consulting Engineer, Digital Equipment Corporation, Andover, MA

    Fox, LR
    Principal Engineer and Consulting Engineer, Digital Equipment Corporation, Andover, MA

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP24508S

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