Cracking phenomena on flexible-rigid interfaces in PCBs under thermo cycling loading

Purpose - The purpose of this paper is to develop simulation models for flexible-printed circuit boards' flex-rigid interfaces and to perform experimental tests in the laboratory in order to evaluate the cracking phenomena when these devices are submitted to thermal cycling.Design methodology approach - A device was proposed in order to evaluate the reliability of flex-rigid interconnections. Thermal cycling tests were performed in an environmental chamber and failure mechanisms investigated using optical and scanning electron microscope techniques. The failure modes were analyzed using computational modelling via the finite element method.Findings - Through failure analysis, it was observed that device design and thermal expansion contraction could contribute to the occurrence of high stresses in the copper pad connections. The simulation model proposed was able to identify the critical regions, as they had occurred in the tests. Thus, the qualitative approach may be considered successful enough to be applied in the early stages of design.Research limitations implications - The materials proprieties were considered as being linear. Thus, in order to enhance the simulation models to provide a quantitative model for the evaluation of product life, non-linear (visco-elastic) behaviour in the material properties and a fracture model should be considered.Originality value - Typical causes of cracking failure in electronic devices are related to mechanical stress, moisture, heat from transportation and field use. Thus, finite element analysis is an important tool in order to evaluate the reliability of electronic components regarding these types of loads in the early stages of design.