MANUFACTURE OF PRINTED WIRING BOARD

PROBLEM TO BE SOLVED: To form fine wiring by boring holes into a copper-plated laminated board and blackening the internal surfaces of the holes after metallization, and then, forming an etching resist by laminating a photosensitive dry film upon the surface of the copper foil, exposing the dry film to ultrasonic rays through a photomask, and developing the film and, finally, selectively etching off the copper foil. SOLUTION: After the surfaces of the copper foil 3 of 100 pieces of both-sided copper-plated laminated boards is blackened with a chemical on a substrate 4, a photosensitive dry film 2 is laminated upon the foil 3. Then 100 pieces of printed wiring boards 100 are formed by exposing the film 2 to ultraviolet rays, developing the film 2, and etching the film 2. The blackening is performed by dipping the foil 3 in a solution composed of sodium chlorite, sodium hydroxide, and sodium phosphate. The light passing through the transparent section of the photomask 1 at the time of exposure is not scattered, but mostly absorbed to the surface of the foil 3, when the light reaches the surface of the foil 3, because a black oxide formed on the surface of the foil 3 is black in color. Therefore, the boundaries between light receiving sections and the other section become distinctive and fine wiring can be formed by transferring the shapes of the transparent sections.