Thermal cycling induced plastic deformation in solder joints. II.Accumulated deformation in through-hole joints

摘要

A thermal-cycled through-hole solder joint is studied. Nonlinearelastic/plastic solder properties at different temperatures and asteady-state creep law are used to characterize the deformation of theeutectic Pb-Sn solder. Large geometry changes in the solder and pinstructure are observed experimentally. The deformation observed is muchlarger than expected from a simple thermal expansion mismatchcalculation. This phenomenon is explained as a combination of plasticand creep deformations which accumulate during the thermal cycling.Because of the complexity of multiaxial stresses in the joint due tothermal expansion mismatch, finite-element analysis is required tocharacterize stress and strain in the solder joint. The large plasticdeformation observed in the solder fillet is quantitatively simulated bythe analysis. The majority of the deformation is a result of thetime-dependent creep, while deformation occurring during thetime-independent temperature change is minor. The displacement of the ICpins is recorded after each cycle and approaches the value observed inan actual joint after 1000 cycles. Thermal cycling fatigue lifeprediction based on uniform shear and the Coffin-Manson equation isfound to be insufficient in dealing with the complex deformationmechanism of solder