| 摘要 |
An improved printed wiring board (PWB) with solder mask coatings is achieved by means of a two layer composite coating. One inner adhesive photopolymer layer is applied to the PWB in the liquid state, displacing air from PWB surface. The outer layer of the composite is dry and is carried on a thin plastic sheet and overlaminated onto the liquid inner layer, without the need for a vacuum laminator. The dry film solder mask so laminated is then exposed through a phototransparency to harden the light struck dry film solder mask and light struck inner layer photopolymer, thereby cojoining the dry film solder mask, inner layer and PWB surface. A solvent washout step removes unexposed dry film solder mask and unexposed inner layer photopolymer. This provides a faster process, requires less equipment, and improves adhesion to metal conductors. The outer layer need not be photoimaged. Thus, pre-patterned expoy solder masks may be printed on the carrier sheet, partially hardened and overlaminated in register onto liquid photopolymer-coated PWB, then exposed to light source through a phototransparency and through the pre-patterned solder mask, thereby permanently adhering the outer layer to PWB. The composite coating can be a combination of known solder mask materials, dry film, UV-curable and thermal-curing epoxy, chosen for desired characteristics including electrical performance, printing resolution and cost.
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