Calculation and Correction on Water Vapor Content Value in Sealing Devices

The volume fraction 0.5% is the acceptance criterion of water vapor content in the internal atmosphere of hermetic sealing devices according to the GJB548 standard. It is based on the assumption that the gas pressure inside a hermetic sealing device is one standard atmospheric pressure. However, the hermetic packaging achieved by current sealing process technologies typically results in an internal gas pressure that is always less than 1 standard atmospheric pressure. The higher the sealing process temperature, the lower the total internal gas pressure of the device. Taking the three most common hermetic sealing processes-parallel seam welding, gold tin alloy solder sealing, and low temperature glass frit sealing- as examples, devices sealed by parallel seam welding exhibit the highest internal gas pressure, which is around 0.8 standard atmospheric pressure. Devices sealed with gold tin alloy solder sealing have an internal gas pressure of around 0.6 standard atmospheric pressure, while those sealed with low temperature glass frit sealing show the lowest internal gas pressure of around 0.4 standard atmospheric pressure. That means the actual measured values in the internal water vapor content test could not represent the real water vapor pressure inside the device because the dew point temperature corresponding to a water vapor content of 0.5% is significantly below zero degrees Celsius. This paper discusses the relationship between measured water vapor content values and the internal gas pressure of hermetic sealing devices. Through theoretical calculations, a correction method for water vapor content test results is proposed, which shows when the actual dew point temperature is zero degrees Celsius, the corresponding internal water vapor content levels for devices using parallel seam welding, gold tin alloy soldering and low temperature glass frit sealing are 0.7487%, 1.1234% and 1.3410%, respectively. These values are all larger than 0.5%.