Original Publication Date: 1979-May-01
Included in the Prior Art Database: 2005-Feb-20
The use of a dual-density mask for patterning chrome-copper-chrome ceramic substrates involves exposing a positive photoresist applied over the metal layers. The mask is composed of opaque areas as well as semitransparent areas. After exposure to ultraviolet light, the images are developed out in two stages. First, the fully exposed areas are developed out and etched. Then the partially exposed areas are developed out, usually in a more concentrated developer, and etched. This process allows fully exposed, nonactive areas to be etched out. The partially exposed areas, such as lands, lines, or interconnecting pads, are subsequently unmasked with additional developing, and the chrome is then etched off leaving the desired copper features.