Evaluation of diffusion patterning as an alternative substrate technology for automotive applications

In automotive applications, electronic circuits are becoming more sophisticated in terms of functionality, power, and density. Specifically, the engine control unit (ECU) is being moved to direct engine mounting, minimizing interconnection length, reducing interference, and simplifying assembly and testing. This type of mounting will reduce the overall manufacturing cost. Therefore, the electronics have to survive higher working temperatures, vibration, and wider temperature excursions during on/off and temperature cycles. These requirements have been the driving force for robust multilayer substrates. Diffusion patterning (DP), a multilayer dielectric technology developed by DuPont Electronics, is evaluated for next generation ECUs. This high density thick film technology achieves via formation through a complex chemical reaction utilizing an imaging paste. Moreover, the DP technology may incorporate buried resistors and capacitors. Using the DP technology, engine controllers with both four-layer and six-layer structures have been built. The six-layer substrate contains several buried resistors and capacitors. This paper discusses the critical parameters in fabrication of these substrates. The processibility and capacitance variations with different process parameters and firing conditions are also presented. Another aspect of DP technology is that it is compatible with surface mount and flip chip technology. Long term reliability testing of flip chips on DP substrates has been performed. After 4000 cycles, reliability data were excellent; no failures were identified. Reliability test results will be reviewed.