GB1441781A - Electric circuit fabrication - Google Patents

Abstract

1441781 Printed circuits INTERNATIONAL BUSINESS MACHINES CORP 29 Oct 1973 [30 Nov 1972] 50287/73 Heading H1R A process for manufacturing a printed circuit board having closely spaced, fine line circuitry comprises depositing on a substrate 2 a metal layer 6, optionally after a metal an interlayer 4 which improves bonding of layer 6, covering the coated substrate with a liquid positive photoresist, allowing the resist layer to dry partially for 15 sees to 45 mins, spinning the assembly to produce uniform resist coating, baking, exposing and developing the resist to produce a desired circuit pattern, electroplating the exposed portions of layer 6 to the thickness of resist layer 8, removing the resist, and etching the non-plated portions of layer 6 and of layer 4 if present. The substrate may be glass, ceramic, a silicon wafer or, for miniature recording heads, magnetic material, e.g. permalloy. Layer 4 may be evaporated Ta, Ti, W, Nb or Cr, and layer 6 evaporated Cu or Au. If the desired circuit pattern is not uniformly distributed on the substrate, "dummy" portions of layer 6 may also be exposed to provide a more even distribution of plating current and these portions are subsequently removed by a masking and etching process. The plated layer may be gold or copper with a surface layer of gold. In the case of magnetic recording heads the plated layer is covered with an insulating layer then a layer of magnetic material. Prior to plating, a second resist coating may be applied, baked, exposed and developed using an identically aligned mask.