Effect of humidity and temperature on the tensile strength of polyimide/silicon nitride interface and its implications for electronic device reliability

A new strategy for improving, predicting, and optimizing the mechanical reliability of interfaces appearing in electronic devices, substrates, and their packages, is introduced. An essential feature of this strategy is to measure the fundamental tensile strength of interfaces devoid of any material plasticity and geometry effects and quantify changes in the measured strengths by exposing interfaces to varying levels and duration of in-situ temperature rise and relative humidity. These fundamental strength charts can now to be used in conjunction with simulations capable of predicting time-dependent stress concentrations, moisture accumulation, and temperature rise at critical interfaces during processing and service, and thus, predict device reliability from a fundamental standpoint. Since these latter simulations are already well developed and largely available, implementation of the proposed strategy requires development of largely unavailable database on the degradation of the interfaces’ intrinsic tensile strengths. As a start, this paper presents such a data for the polyimide/Si3N/Si interface system, which besides serving as an exemplar, has importance in device fabrication. The strength data is gathered using the laser spallation technique, in which a laser-generated stress wave on the backside of the substrate pries off the coating deposited on its front surface. This work extends this technique for multilayer testing. Interestingly, the degrading effect of each variable was found to fall in two separate regimes of moderate and strong effect. Uncovering of such transition zones is of obvious importance in reliability studies.