Printed Wiring Design Aspects of Using Permanent Photopolymer (Dry Film Solder Mask) Coatings

The advantages of incorporating permanent photopolymer (dry film solder mask) coatings into high density printed wiring designs to obtain maximum component density and high reliability are discussed. Although originally developed for use as solder masks, these materials offer significant advantages to the PCB designer. Specific items to be discussed include high density conductor routing, in accordance with the proposed MIL STD 275D, on the solder side and under closely spaced components, component and heat sink mounting, the use of permanent polymer coatings to avoid metallic growth problems, new industry and military specifications and standards that relate to the incorporation of photopolymer masks into PCB designs and effects of coatings on high density, controlled impedance transmission lines.