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G. Siroky, E. Kraker, J. Magnien, D. Melinc, D. Kieslinger, E. Kozeschnik, W. Ecker:
"Effect of solder joint size and composition on liquid-assisted healing";
Microelectronics Reliability, 119 (2021), 114066; 1 - 10.

This work presents an experimental and numerical investigation of liquid-assisted healing with respect to solder
joint composition and size. A damage-healing model is formulated based on entropy generation of damage and
viscous material transport during healing. The model accounts for a composition-dependency of healing by
introducing the liquid film thickness, the liquid viscosity and a microstructural mobility parameter. The size
dependencies enter the healing model in form of the local capillary pressure of the solder joint. A viscous flow
experiment illustrates the compositional dependency of local material transport and a cyclic tensile experiment
shows the regain of mechanical properties, such as, stiffness and strength after healing. The flow experiment
shows that material transport is retarded for solders of low liquid fraction and crack healing is limited due to
partial filling of the crack. Simulation results of a solder array suggest the capillary pressure as the driving force
for healing, which leads to a size-dependency of the healing evolution. The required time for complete healing
increases with reduced solder dimensions due to higher capillary pressures. Microstructural mobility due to high
liquid fractions also promotes healing.

Liquid-assited healing, Damage Healing, Fatigue Solder, FEM, BGA, Solder array

http://dx.doi.org/10.1016/j.microrel.2021.114066