Abstract
If not hermetically encapsulated, thin film hybrid circuits require passivation for various reasons: protection against mechanical attack, long-term humidity diffusion, oxidation of metal films during heat treatment and destruction of oxide layers in electroless plating baths. An inorganic (Al 2O 3, SiO 2 etc.) or organic (photoresist, polyimide) passivation alone cannot meet all requirements simultaneously since most organic coatings do not resist temperatures of more than 150°C whereas evaporated oxide layers are too thin (1 μm or less) for mechanical protection and are often destroyed by non-neutral plating baths. We present a double-layer protective coating for thin film circuits consisting of an evaporated Al 2O 3 thin film and a photoresist layer baked at temperatures near the solder bath temperature. This passivation layer sequence is shown to avoid all the shortcomings of its constituents.
Published Version
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