Applying Solvent Based Masking Lacquers In Electroplating


To ensure 100% success in the use of lacquers for masking, the first requirement is that the work shall be clean and dry.  One of the dangers of lacquering work that has been in the plating shop overnight is that of contamination from dust and residual fumes.  Equally important is the fact that as the shop temperature falls overnight, a thin but invisible layer of moisture condenses on the surface, resulting in unsatisfactory adhesion.

Cleaning:  The use of chlorinated solvents or vapour degreasing is practised in many electroplating shops, but with some soils it can leave a residue which will affect lacquer adhesion.  The proven method of wet cleaning is to be preferred, with a final hot air drying. Where there are difficult materials involved the use of a phosphate conversion coating, or even a “wash primer” is advised to ensure 100% adhesion. It is vital to apply the lacquer to a clean dry surface at 15 - 180C. before the lacquer is applied.  Where-ever possible, masking lacquers should be applied over phosphate or other conversion coating where absolute assurance of adhesion is required.  This simply improves on the excellent adhesion inherent in “Miccro” Lacquers.

 

Applying the lacquer:  Most lacquers can be applied by spray, dip or brush, although addition of thinners to achieve the correct consistency may be required.  Silk screening of lacquer resists is also practised.  Lacquers that are used for masking, dry by solvent evaporation, but because evaporation of the solvent is never uniform over the work surface, small drops of lacquer can remain trapped in the film.  These subsequently migrate through the film, but leave behind small pinholes.  For this reason it is normal to apply 2 coats, which should eliminate the possibility of pinholes coinciding and providing a path through the lacquer for the electrolyte.  It is especially important to follow the application instructions contained in the Technical Information Data Sheets, since there are minor, but important differences in the application instructions for the various lacquers in the “Miccro” range.

 

Thickness of the lacquer: It is important to try to maintain a consistent film thickness/weight by checking either the thickness of the applied coating or the weight per unit area. Normally two coats will be applied though three coats are sometimes necessary.

 

Drying of masking lacquers: Adequate drying is an important contribution to the performance of the masking lacquer. Air drying is preferable and normally left overnight for a least 12 hours. The process can be accelerated by drying in a hot air oven. The specific instructions contained in the data sheets for the appropriate lacquer should be consulted since there are important minor differences in drying and stoving between the various lacquers.