Effect of Solder Alloy, Aging and Tal on High Strain-Rate Fracture of Lead-Free Solder Joints
Authors: Amir Nourani and Jan K. Spelt Company: University of Toronto Date Published: 9/28/2014
Abstract: Fracture experiments at a strain rate of 30 s-1and a loading phase angle of 38° were performed using Cu-solder-Cu double cantilever beam (DCB) specimens of 2 mm long discrete solder joints with a thickness of 150 µm. Three different lead-free solder compositions, SAC305, SAC0807 and SAC0307, were examined using a drop tester. Some specimens were aged at 100°C for 300 h to assess the effect of aging, while the effect of the time above liquidus (TAL) was investigated using values of 120 s and 240 s. These parameters were of interest since they can change the microstructure and fracture behavior of solder joints. The failure of the solder joints in the DCB specimen was apparent as a distinct peak in the output of a strain gage that was bonded to the lower arm of the specimen at the location of the solder joint. This maximum strain at break was used to find the corresponding failure load using a finite element model (FEM) of the DCB. The critical strain energy release rate for crack initiation, Jci, of the solder joint was then calculated using the FEM. The standard deviation of Jci obtained from different test batches was between 11% and 18% of the mean value. Although other studies showed that these parameters significantly affected on fatigue life and reliability of solder joints, a statistical analysis on multiple repeat tests showed that the mean values of Jci were essentially the same for the three solder alloys, and were unaffected by either the aging or the change in TAL.
solder, fracture, initiation strain energy release rate, aging