Low stress flip-chip package for pressure sensors operating at 500 °C

This work presents a method for a reliable assembly and interconnection of MEMS for very high temperatures. A flip-chip concept for resistive micromechanical pressure sensors with a platinum thin film was developed and sensor-assemblies were fabricated. The investigated metallized ceramic substrates were AlN, Si₃N₄, a Low-Temperature-Cofired-Ceramic (LTCC) and a zirconia-silicate (ZrSiO₄). A borosilicate glass-solder was the die-attachment material and gold stud-bumps were the interconnection. The thermal-mechanical stresses in the sensors, induced by the packaging process due to material-dependent mismatches were analyzed with FEM and optical deformation measurements from 20 to 500 °C. The comparison of the obtained experimental and FE-results revealed a strong influence of the applied substrate on the thermal-mechanical stresses in the chip-membrane which is affecting the output-signal and reliability. Both methods were in good accordance. The two specific silicon-matched ceramic substrates LTCC and ZrSiO₄ reduced the stresses in the sensor-element significantly. Furthermore, the electrical characterization of assembled test-sensors revealed a correlation between the package-induced stresses in the chip-membrane and the shift of the sensor-signal after the assembly-process.