Evolution of Potting-PCB Interfacial Reliability After Long Term High Temperature Operation

Abstract

Abstract Fine Pitch Electronic Components are reinforced using epoxy potting compounds and underfills to improve reliability and survivability, in extreme environments. Potting of electronic components offers structural support, shock damping and protection for the components from environmental conditions like moisture. Potting is one of the cost-effective and viable way to improve the survivability of the electronic components. On dynamic shock loading, interfacial delamination occurs between the potting material and the PCB, which further propagates to solder interconnect failures. The interfacial properties change with long-term exposure to temperature during operating and storage conditions. Mechanics of interface delamination of the epoxy potted PCB samples with thermal aging is a primary focus on this paper. Determination of fracture parameters such as fracture toughness and strain energy release rate at steady state stress is important in selection of the potting material and the reliability study of the supplemental restraint systems. PCB/Epoxy specimens are prepared, and their fracture behavior is observed under quasi-static three-point and four-point bend loading. 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 30days and 60 days. Under dynamic loading, damage at the interface is studied. The experimental results 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.