Liquid Photoresists

Apply 15-30 drops of the photoresist to the center of the transparency leaving about 2.5 in. between each coverslip and the liquid photoresist. 

Polymer-based liquid photoresist Cu, Mn, Pb, Zn Direct liquid analysis after dilution with propylene glycol monomethyl ether acetate SA Tetramethylammonium hydroxide (TMAH) as modifier for matrix removal. Pd added as modifier for analyte stabiUzation [21]... 

The photosensitive polymeric systems used as photoresists in the interconnect industry are either liquids or dry films formed from a liquid solution. Dry-film photoresists are the industry standard, but liquid photoresists have become widely used, particularly for fine-feature circuits. Both types of photoresist can be used for a variety of processing requirements. 

The nature of the substrate itself in terms of topography and surface features must also be considered. Is the photoresist required to cover or tent plated through holes or tooling features, and must it conform to existing circuitry This consideration will dictate if dry-film or liquid photoresists are appropriate and, in some instances, the required tone. 

FIGURE 26.5 Chemistry mechanism of positive-acting liquid photoresists. 

The technique used to apply the photoresist to the substrate depends on the type of photoresist selected.The various techniques used with dry-fUm and liquid photoresists are discussed. 

The spray head traverses a larger area than the substrate to be coated, and the amount of liquid photoresist that becomes overspray can be significant. Exact characteristics of the coating in terms of thickness and topographical coverage depend on spray-head configuration, nozzle backpressure, droplet size, and conveyor speed. ... 

Sutter,T.C., Liquid Photoresist Systems An Overview, BoardAut/iority supplement to CircuiTree, Vol. 1, No. 3, October 1999, p. 22. 

Liquid Photoresist Liquid resists work well in a print-and-etch process. They have excellent adhesion and a tolerance for surface flaws and are relatively low in cost. The disadvantage of a liquid photoresist is the need to produce a perfect coating. Foreign material, skips, thin spots, and dewetting all cause serious image problems. The use of a wet coating can also cause problems due to resist contamination of the transport system. 

Dry-film and liquid photoresist materials are capable of yielding the fine-hne (0.003 to 0.005 in) circuits needed for production of surface-mount circuit boards. Like screened resists. 

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