PLASTIC-DEFORMATION KINETICS OF 95.5SN4CU0.5AG SOLDER JOINTS

The plastic deformation kinetics of 95.5Sn4Cu0.5Ag solder joints were determined in monotonic loading shear over the temperature range of 25 degrees-150 degrees C using three types of tests: (a) constant shear rate, (b) constant shear stress (creep), and (c) differential tests (c hanges in shear rate or temperature duping an otherwise isothermal con stant shear rate test). The deformation kinetics were evaluated in ter ms of the Dorn high temperature plastic deformation equation gamma(p) = A mu b/kT D(b/d)(P)(tau/mu)(n) where gamma(p) is the shear rate, mu the shear modulus, b the Burgers vector, D the appropriate diffusion c oefficient d the grain size and tau the shear stress. A, p, and n are constants whose values depend on the rate controlling mechanism. It wa s found that n increased with stress from similar to 4 at 2 MPa to sim ilar to 20 at 25 MPa, relatively independent of temperature. The activ ation Delta H was determined to be 21.1 +/- 2 kcal/mole. The constant A, however, decreased with temperature from a value of similar to 10(1 8) at 25 degrees C to similar to 10(10) at 150 degrees C. The values o f n and Delta H suggest that dislocation glide and climb is the rate c ontrolling mechanism and hence that p approximate to 0. It is speculat ed that the large decrease in A with temperature may be the result of an effect on the microstructure.