Interfacial Fracture Toughness of PCB/Epoxy Interfaces Under Three Point and Four Point Loading with Sustained High Temperature Exposure

Electronic components used in defense and aerospace applications may be exposed to extreme thermo-mechanical shock loading and high-g shock forces. Reinforcing surface mount electronic components with epoxy potting and underfills, has shown to improve survivability under harsh extreme environments. Potting of electronic components has been shown to offer structural support, shock damping and protection for the components from environmental conditions such as moisture. Interfacial delamination is a dominant failure mode in high-g shock loading of electronic assemblies and often a precursor for solder joint failures. Exposure to sustained storage in non-climate-controlled conditions has been shown to influence the interfacial reliability. Mechanics of interface delamination and fracture toughness of the epoxy potted PCB assemblies under sustained high-temperature storage has been studied. PCB/Epoxy specimens are prepared, and their fracture behavior is observed under both quasi-static three-point and four-point bend loading owing to the difference in the deformation mechanics. In three-point bending, the peak-stress acts at the midpoint of the specimen. In four-point bend loading, the peak stress is along whole area of the specimen under load (load span). The curing temperature providing the best fracture resistance is selected and followed throughout the study. The samples are exposed to 100°C for 30 days and 60 days. The experimental results have been used to provide the peak critical load, from which the fracture toughness parameters are calculated. A comparison has been made on fracture toughness and crack initiation of the PCB/Epoxy systems, based on flexure method and thermal aging.