So called hotmelt materials are wax based and printed at elevated temperature. Their main use is in metal etching and plating application because of their excellent chemical resistance. Some hotmelt materials contain a UV curable component to make them also more mechanically resistant. Hotmelt materials hold up for a long time in different etch and plating chemistries, still they are easy to strip in typical caustic or amine based stripping solutions. Therefore inkjet process often fits seamlessly into existing production processes. It replaces resist coating, exposure and development, while existing pre-treatment and stripping steps can be maintained. Good results have also been achieved on glass and silicon substrates achieved with hotmelt inks. Under less harsh conditions, also UV curable acrylate based resists can be used for the same applications. Typically such materials hold up well during shorter etching times, so these materials are mainly targeting etching of thin metal layers.
In some cases a chemically resistant, but permanent resist is required. For these cases polyimide and SU8 epoxy based materials are available in inkjet printable formulations.
Inkjet printing can also be applied for full area (blanket) coating of substrates with UV curable resist for optical and (nano-) imprint lithography. One of the advantages of inkjet is the efficient use of materials. Spin and spray coating processes waste a significant amount of material in order to achieve homogeneous layers. On large and square substrates, or on substrates with high topologies (eg cavities) spin coating is actually limited in delivering homogeneous coatings, which makes inkjet an attractive alternative, specifically in combinations.