Fracture Behavior of Lead-Free Solder Joints under Bending as a Function of Joint Width
Authors: Sadegh Mirmehdi, Amir Nourani, Farid soroosh and Gholamhossein Farrahi Company: Sharif University of Technology Date Published: 6/6/2017
ICSR (Soldering and Reliability)
Abstract: The fracture behavior of lead-free solder joints has been shown to be influenced by the level of constraint on the joint deformation. The joint constraint is a measure of joint size/geometry, adherend stiffness and loading type. Among these parameters, there is no data on the effect of solder joint width (i.e. joint size in the out-of-plane dimension) in spite of its possible role in defining the degree of solder joint deformation. The fracture load of 2.5 mm long SAC305 solder joints with a thickness of 250 µm was measured under mode I intermediate strain-rate loading (0.03 s-1) for three different widths of 8, 11 and 14 mm using Cu-solder-Cu double cantilever beam (DCB) specimens. The adherend thickness was 14 mm in all the cases. A hydraulic tensile testing machine with a cross-head speed of 5 mm/s was employed with the failure of the solder joints evident as an abrupt drop in the load cell output. The fracture load over the width of the specimen, F/w, was then measured and the critical strain energy release rate for crack initiation, Jci, of the solder joint was calculated using a finite element model (FEM). The fracture load increased by almost 75% from a solder width of 8 mm to 14 mm, while F/w changed only by 10% over this range. The statistical analysis on the three groups showed that this difference was statistically insignificant. Also, Jci remained almost unchanged with the joint width suggesting that the data obtained from each width can be used to predict the fracture loads of the solder joints having different widths. This promising conclusion can be applied to real ball grid array (BGA) solder joints used in microelectronic package-on-board systems subject to bending type of loading.
solder joint, width, fracture, constraint, plastic zone size