GB1303851A - - Google Patents

Abstract

1303851 Printed circuits PHOTOCIRCUITS CORP 9 March 1970 11089/70 Heading H1R A method of making a printed circuit board provided with holes having metallized hole walls the surface of the said board being completely or substantially completely free of exposed conductor lines, which comprises the steps of establishing metallic conductor lines forming one or more printed circuit patterns in one or more planes of an insulating base; substantially covering exposed conductor lines of the circuit pattern or patterns on the surface plane or planes with a non-removable, insulating mask, the said mask covering completely or substantially completely all of the exposed surface of the said base; establishing a thin layer of metal on the surface of said non-removable mask, said metal layer being provided with a superimposed, temporary, insulating layer or coating, prior to or after establishing the said thin metal layer providing at least one hole extending through the board; providing a thin layer of metal on all exposed hole walls; forming an additional metal deposit on the hole walls by electroplating, the said additional metal deposit extending substantially to the exterior surface of the mask and this way forming a small ring-like metal deposit or land on the horizontal surface of the edge of a mask surrounding the hole or holes, and subsequently removing said temporary insulating layer or coating and the said thin layer of metal on the surface of the permanent mask. An insulating base 3000, Fig. 1D, clad with a metal layer and etched to form circuits 3004, 3006 is coated all over with an insulating, solder resistant layer 3010. Holes 3014 are then made through the base and a thin electroless plating 3016 is applied after sensitization with stannous ions, amine boranes or alkali borohydrides together with palladium ions. After applying a strippable mask 3020 the holes and lands 3015, Fig. IE, are built up by electrolytic deposition. The mask 3020 is then removed. In another embodiment, Fig. 2H, before the hole 4023 is made, the insulating layer 4010 is electrolessly coated with metal 4016 and two removable masks 4018 and 4020 are applied. All exposed surfaces are then sensitized and the mask 4020 removed to leave only the hole wall sensitized for electroless deposition. The electrolessly through plated hole is built up electrolytically and the mask 4018 and layer 4016 are removed to leave lands 4022, 4024, Fig. 9K. The layer 4016 may be laminated on instead of electrolessly deposited.