Hermetic Encapsulation

‘Hermetic sealing’ is defined by the Shorter OED as “air-tight closure of a vessel by fusion, soldering or welding”. The term ‘hermetic package’ used in the electronics industry is however at best slightly misleading, in that the term is used to describe components where the die and associated bonds are sealed within a cavity in a hollow package (as distinct from being embedded in a resin), and at worst wholly inaccurate, in that these seals are generally far from air-tight. Although the packages use materials which show the greatest resistance to the passage of water vapour (Figure 1), examination of typical package contents by Residual Gas Analysis (Figure 2) shows that complete isolation from the ambient is rare.