Photoimageable solder resists - Optimising the Processing. Greatest care must be taken when applying and subsequently processing today's photoimageable solder resists if they are to fulfil the requirements of maximum resolution and an homogeneous ink surface as well as achieve their specific mechanical, chemical and electrical properties. This paper describes possibilities for increasing the coating quality of photoimageable solder resists applied by curtain coating by modifying equipment and making potential alterations to the processing steps. In detail, these possibilities are measures to achieve a minimum of bubbles in the coating and to incresase the coating thickness on conductor edges while applying the same wet ink weight, optimisation of the exposure process, further improved free-development also of micro through-plated holes and prevention of surface contamination of freely-developed metal substrates (e.g. SMD pads) by ink constituents during the developing process which may lead to incomplete hot-air levelling or incomplete wetting during electroless Ni/Au of the affected surfaces.
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