Lead Profile Optimization and Stress Analysis for Hermetic Metal Package

Glass seal is commonly utilized in hermetic metal package to assure hermeticity and protect electronic devices. However large stresses may exist in glass seal and induce failure or cracks. To reduce stresses, lead profile is optimized and stepped leads are utilized in metal packages of TO-254A. Stresses in glass seals were simulated and investigated using ANSYS. Simulation results showed that maximum tensile stress and maximum compression stress for packages with stepped leads are about 1~3% of that of packages with conventional leads. Furthermore, lead integrity experiments were carried out and simulation results were validated. Lead integrity experiments showed that no cracks were found in metal packages with stepped leads but failure occurred in other metal packages with conventional leads. And seal tests indicated that measured leak rate of packages with stepped leads was quite low, smaller than 1 x 10^-3 Pa cm³ /s, while the leakage rate was about (2.0 ~ 6.0) x 10^-2 Pa cm³ /s for metal packages with conventional leads. Both simulation and experimental results demonstrate that stepped leads are critical to reduce stresses and enhance the reliability of hermetic metal packages.