Flexural Strength of Bga Solder Joints with Enig Substrate Finish Using 4-point Bend Test

PCB assembly and handling operations involving excessive monotonic bending at high strain rates can cause brittle solder joint failures in BGA packages. This paper deals with brittle fracture of flip-chip BGA packages with electroless Nickel immersion Gold (ENIG) substrate pad finish. A high speed 4-point bend test has been used to evaluate the flexural strength of different component sizes and pincounts with eutectic Sn/Pb and lead-free Sn/Ag/Cu solder. The devices were electrically monitored for the duration of the tests, along with the load, displacement, and PCB strain. The tests were performed at three different strain rates. Results show that the high strain rate 4-point bend test is capable of replicating the brittle fracture failure modes observed in PCB assembly operations. The PCB strain to failure and the failure mode were found to be strongly dependent on the strain rate. A significant outcome of this work is the determination of the PCB strains which, if exceeded, could pose a substantial risk of brittle fracture in assembly, test, shipping, and handling operations.