Measurement and modeling of in situ lead stiffness of surface mounted packages

An approach to the experimental determination of in situ lead stiffness has been used to measure selected surface mount component (SMC) lead stiffness under simulated service conditions. Good agreement was obtained between the experimental data and three-dimensional elastic beam finite element analysis (FEA). The agreement was achieved through the use of a stiffness matching point, which provided insight into the level of constraint provided by the solder joint at the lead foot. When adequate solder was available, the solder served as a built-in boundary. When there was insufficient solder creep relaxation in the solder because of the high level of stress in the joint permitted rotation of the lead and the solder served as a pinned joint. Location of the stiffness matching point was found to be approximately 0.08 mm (0.003 in) below the solder fillet on the lead for the lateral stiffness component and about 0.15 mm (0.006 in) above the land for the transverse stiffness component.<
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