Non-metal hermetic encapsulation of a hybrid circuit

Abstract A cheap hermetic non-metal encapsulation was evaluated for use with a high reliability hybrid circuit subject to severe climatic environment for precise magnetic field measurements over 20 years lifetime. For this purpose a literature scan has been carried out establishing roughly the following results: 1. a) Humidity is the largest single risk faktor concerning reliability and expected life time of the device. 2. b) Plastic sealing does not represent a barrier against humidity for a long time. 3. c) There is no off-the-shelf solution available as usual real hermetic encapsulations are ruled out due to electrical, magnetic and price considerations. Therefore a simple ceramic cover soldered by an AuSn preform directly to the ceramic substrate supporting the sensor and the thick film circuit has been developped to meet all requirements of a cheap, hermetic enclosure. This paper presents both the considerations taken into account to evaluate an appropriate encapsulation method as well as the final solution.