Evaluation of Thermo-Mechanical Fatigue Life of Microvias Under PCB Substrate's Influence During Reflow Process

The growing reliance of the automotive sector on miniaturized electronic packages necessitates HDI technology printed circuit boards with robust microvia connections. To reduce failure rates, automotive manufacturers demand zero-failure reliability for microvias. Achieving this goal requires identifying and understanding uncontrollable factors associated with substrates that affect microvia structures during the reflow process. The substrate layer contains a complex structure that impacts the microvia reliability at elevated temperatures. The effect of interaction between microvia structure and substrate layer was overlooked in the conventional microvia studies highlighting the need for reliability estimation of microvia structures within the substrate layer. This paper develops a finite element model of a composite substrate layer including fiberglass and epoxy resin with a microvia interconnect hole inside to investigate the effect of substrate on microvia life. The results show that the microvia life is not the same at every possible location on the substrate layer due to the uneven distribution of fiber and resin. Out of 4 microvia positions on the substrate used in the DOE, microvias in 2 positions did not survive 1000 thermal cycles. Regions with greater resin concentrations than fiber have a higher possibility of microvia early failures. Furthermore, the developed model was correlated with the literature models and experimental observations to verify the accuracy.