GB1476888A - Method for making printed circuitry - Google Patents

Abstract

1476888 Printed circuits MINNESOTA MINING & MFG CO 14 May 1975 [16 May 1974] 20423/75 Heading H1R A printed circuit strip 10 (Fig. 1) comprises a thin insulant substrate 12 carrying a predetermined repetitive pattern of conductive areas 14 bonded to one surface and spaced apart with converging inner ends 16. Conductive columns extend through the substrate from the latter and are exposed at 21 to define conductive areas forming a site for an integrated circuit chip or semiconductor connected thereto by thin wires, or bonded thereto, e.g. by thermocompression. The printed circuit is fabricated by applying negative or positive photoresist 24 to a thin, e.g. copper, aluminium, nickel, copper alloy, nickel alloy flexible conductive sheet 22, exposing to define a required image, and developing to leave areas of insoluble photoresist defining conductive areas 21 (Fig. 2B). After development the soluble photoresist is removed and a portion of the conductive sheet is etched out; after which the insoluble photoresist is removed leaving a conductive sheet 22 with upstanding columns 28 (Fig. 2E). Alternatively the conductive sheet may be selectively plated with etch resistant metal to define the upstanding, columns, and etched out. Flexible electric material 30, e.g. polyamide, polyester, acrylic, polyamide, polysulphone, polyolefin. fluorocarbon resin, or the like is applied to the conductive sheet leaving the faces of columns 28 exposed, the sheet is etched on the underside to define conductive areas 14, and the tops of the columns 28 are plated with, e.g. nickel, gold, solder, gold tin alloy, tin nickel alloy, or successive layers of gold, nickel, tin nickel alloy or aluminium to produce projecting bumps (Fig. 2G) to which the connections of an integrated circuit chip may be attached, while the pattern of conductive areas, on the opposed face may be connected to external circuitry. Plural circuits may be bonded together in multilayers.