Intermediate and High Strain-Rate Fracture of Lead-Free Solder Joints as a Function of Mode Ratio
Authors: Amir Nourani and Jan K. Spelt Company: Department of Mechanical and Industrial Engineering, University of Toronto Date Published: 5/13/2014
ICSR (Soldering and Reliability)
Abstract: The fracture properties of SAC305 solder joints under intermediate (0.05-1 s-1) and high (10-60 s-1) strain-rate loading conditions were measured as a function of mode ratio using Cu-solder-Cu double cantilever beam (DCB) specimens of 2 mm long discrete solder joints with a thickness of 150 µm. To perform intermediate strain-rate experiments, a servo-electric testing machine was employed while high strain-rate tests were carried out using a newly-designed drop tester. The failure of the solder joints in the DCB specimen was evident as an abrupt change in the load cell or strain gauge output for intermediate and high strain-rate experiments, respectively. In the latter case, the strain gauge was mounted on the copper bar at the location of the solder joint. This maximum strain was used to find the corresponding failure load. The critical strain energy release rate for crack initiation, Jci, of the solder joint was then calculated using a finite element model. The results showed a substantial effect of strain rate and mode ratio on the fracture of solder joints. There was a significant decrease (about 70%) in mode I Jci when the strain rate was increased from intermediate to high values. At all strain rates, the effect of an increasing mode ratio (more shear loading) was to increase Jci so that when the mode ratio was raised from 8° to 38°, Jci increased by a factor of about 5. These fundamental fracture properties can be used to predict the fracture of this joint system (solder+finish+processing conditions) in arbitrary geometries at strain rates to 60 s-1.
solder, fracture, initiation strain energy release rate, strain rate, mode ratio