A constitutive model for creep of lead-free solders undergoing strain-enhanced microstructural coarsening: A first report

Abstract

Lead-free solder joints in microelectronic applications frequently have microstructures comprising a dispersion of intermetallic particles in a Sn matrix. During thermomechanical cycling (TMC) of the solder joint, these particles undergo strain-enhanced coarsening, resulting in a continuously evolving, creep behavior. Because the extent of coarsening is dependent on the stress/strain state, which is dependent on the location within a joint, it is important that creep models used in joint-life prediction incorporate these effects. Here, an approach for incorporating the effect of in-situ second-phase particle coarsening in a dislocation-creep model applicable to lead-free solder alloys is proposed. The formulation, which can be expressed in a closed analytic form following some simplifications, incorporates the effects of both static-and strain-enhanced coarsening and accounts for the effects of inelastic-strain history and hydrostatic constraint. Predictions of coarsening based on the model agreed reasonably well with experimentally observed trends. Because of its simplicity, the microstructurally adaptive creep model proposed here can be easily incorporated in current finite-element codes for joint behavior simulation.

Recrystallization and Precipitate Coarsening in Pb-Free Solder Joints During Thermomechanical Fatigue

“…During TMF testing, thermal aging and strain-enhanced precipitate coarsening lead to ongoing softening. [30][31][32][33][34] It is also commonly noticed that TMF testing tends to produce recrystallization of the Sn grains across the high-strain region before failure. We propose that the development of recrystallization depends directly on the precipitate distribution, and thus on its coarsening.…”

Optimal design toward enhancement of thermomechanical reliability of polyimide layers in a flip-chip-on-lead-frame dual flat no-leads package with copper pillar bumps

“…During ATCs, electronic packaging is uniformly heated up and cooled down in order to induce thermomechanical strains and stresses in interconnections and interfaces of the packages due to mismatch of the coefficient of thermal expansion(CTE). Under the thermomechanical stressing condition, the solder joint or bump is a critical reliability issue on which many studies have been focusing [1][2][3][4][5][6].…”

Dynamic Mechanical Properties and Microstructural Studies of Lead‐Free Solders in Electronic Packaging

“…The emphasis has been on areas such as product-level tests [7,8], boardlevel tests, simulation involving drop tests [9][10][11], bending tests [12,13], thermomechanical effects [11,14,15], low-strain-rate tensile properties [15][16][17], creep and stress relaxation [18][19][20][21], vibration [22,23], and microstructure [19,20,24].…”