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|Methods for Providing a Dry Seal Environment|
|Keywords: moisture, hermetic, seal|
|Reliability concerns associated with moisture in electronic devices have been documented in the literature. This paper, will identify sources of water, and suggest methods used to minimize it. We will simplify the problem by assuming true hermetic packaging. We can analyze the case of non-hermetic packaging by assuming a water leak rate and/or diffusion constants through a permeable package wall. However, for purposes of this paper we will concentrate on some common internal sources of moisture. It is well known that organic materials such as adhesives and die attach materials can adsorb and desorb water vapor. It is important to consider all sources of moisture, including the water adsorbed on various surfaces as well as the water vapor concentration in the seal gas. A pre-seal bake also can assist in driving water vapor out of organic materials. What is less commonly known is that even a hermetic package that contains no organic material can be a source of considerable water vapor. In this paper, we will show current work aimed at quantifying the amount of water that can be sealed inside a package. We will also show how water may become concentrated in specific locations that affect device performance.|
|Thomas E. Salzer, President