Method of chemical machining utilizing same coating of positive photoresist to etch and electroplate

The method of chemical machining a sheet of sheet metal to define one or more components that have their marginal edgings formed by voids in the sheet but which remain integrally connected in the sheet for handling purposes, which method includes selective plating of said components while they remain integrally connected in the sheet, which method is to include the plating of a precious metal on selected portions of one or more of said components on restricted areas of same, which method comprises:

• taking the sheet and passing same through a trichlorethylene solvent bath,
• immersing the sheet in a 10 per cent aqueous solution of hydrochloric acid at approximately room temperature for approximately 5 minutes,
• removing the sheet from the hydrochloric solution and rinsing same with deionized water,
• dipping the sheet into an isopropyl alcohol bath and then drying the sheet metal,
• passing the dried sheet through a liquid positive photoresist to provide each side of the sheet with a positive photoresist coating of uniform thickness across the sheet,
• curing the photoresist coatings,
• placing the sheet between a set of photomasks bearing registered images of the front and back sides of the metal components to be formed, respectively,
• photographically exposing said images to a high intensity light source to transfer the respective images to the respective coatings in registered relation by exposure of same to said light source through the respective masks,
• immersing the sheet following said exposure in a positive photoresist developer to remove from the sheet only the portions of said coatins that were exposed by the exposing step to bare the portions of said sheet underlying said photographically exposed portions of said coatings,
• etched the sheet on both sides to remove the bared portions of said sheet through the thickness of said sheet to form the sheet voids that define said components,
• rinsing and drying the etched sheet,
• applying to the etched sheet in registered relation thereto and in overlying registered relation to one of the coatings a photomask bearing an image delineating for exposure one or more selected areas of the etched sheet where selective plating of a precious metal is desired,
• photographically exposing the photomask and said one coating to a high intensity source of light to transfer to said one coating the image of the second mentioned photomask,
• immersing the sheet after the last mentioned exposure in a positive photoresist developer to remove from the sheet only the newly photographically exposed portions of the one coating to bare the portions of said sheet underlying said newly exposed portions of said coating,
• baking the sheet and coatings under conditions providing a surface temperature in the range of from about 250.degree. F. to about 300.degree. F. for about 10 minutes,
• cleaning the sheet in an acidic bath for plating purposes,
• electroplating in an electrolyte bath of the type to which said coatings remain plating resistant the newly bared sheet portions with the precious metal to the exclusion of the sheet portions still bearing said coatings,
• and thereafter removing the remainder of the photoresist coatings,
• whereby said selected areas of said sheet are plated while said sheet bears said coatings that resist plating of the portions of said sheet remaining coated therewith.