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Solvent Use & Transition to Aqueous Processing in PCB Fabrication & Assembly

Looking back over the last 50 years of electronic manufacturing one will notice that solvents, in particular halogenated hydrocarbons, were widely used in a variety of process steps. They were used as developers and strippers in photoresist processing, to remove plater tape residues from board surfaces after nickel/gold plating, and to clean fluxes after soldering components in assembly. Due to health and environmental concerns, as well as cost issues, these solvents were phased out and replaced by aqueous chemistries or water-miscible solvents that present a lower health risk. To enable these transitions, new photoresists and new fluxes had to be developed, as well as plater tapes that release cleaner from the board surface without compromising adhesion during plating.

Imaging of Circuit Patterns

Screen printing of an etch resist and/or plating resist pattern, followed by etching (or plating and etching) was quite common in the ‘50s and ‘60s. Today, this process is only used for simple, single-sided boards. The screen is coated with a photosensitive emulsion, dried and exposed through a phototool. Unexposed emulsion is washed off with water. The emulsion stencil pattern and residual resist ink were typically stripped with trichloroethylene or a toluene based stripper for re-use of the screen. In today’s remaining applications other solvents are likely to be used.

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Editor's Note: This article originally appeared in the April 2013 issue of The PCB Magazine.