STP942: Fatigue of Solder Joints in Surface Mount Devices

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

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

    Pages: 23    Published: Jan 1988


    Abstract

    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).

    Keywords:

    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


    Paper ID: STP24508S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP24508S


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