Method of making multi layer circuit boards

Claim 2

A method according to claim 2 wherein the resin is a cross-linked co-polymer.

Claim 3

A method according to claim 2 wherein the resin is a catalyst hardened resin.

Claim 4

A method according to claim 1 wherein the final stage of the process comprises the following sequential steps, a. prior to said drilling through the assembly, forming an outermost insulating layer of said non-smearing insulating material over a penultimate one of the conductor patterns which in the finished assembly will be adjacent to an outermost one of said conductor patterns, said outermost insulating layer not extending over the edges of the assembly, b. thereafter, effecting said drilling through the assembly at said preselected positions, c. applying a continuous coating layer of a conductive metal over the whole of said outermost insulating layer and internally of the bores, but not over the edges of the assembly, d. masking said continuous layer of conductive metal with a resist shaped to correspond to a negative of the desired outermost conductor pattern and to expose parts of said continuous layer of conductive metal and also to expose said bores, e. applying a readily solderable coating on sAid exposed parts of said continuous layer of conductive metal, said readily solderable coating thereby extending internally of said bores, and f. removing all of said continuous layer of conductive metal except said parts coated with said readily solderable material, by etching, thereby to form said outermost pattern and establish electrical interconnection between said conductor patterns as required.

Claim 5

A method according to claim 5 wherein the final stage includes the additional step of forming an additional continuous layer of conductive metal over said outermost insulating layer immediately prior to drilling through the assembly to form said bores.

Claim 6

A method according to claim 5 wherein said continuous layer of conductive metal which is deposited in the final stage of the process consists of a metal selected from the group consisting of copper and nickel.

Claim 7

A method according to claim 7 wherein the readily solderable coating deposited in the final stage of the process consists of a metal selected from the group consisting of tin, tin/lead, and gold.

Claim 8

A method according to claim 5 wherein said circuit board formed in the first stage of the process comprises a double-sided circuit board with said first conductor patterns on said respective opposed sides thereof, the remaining stages of the process being effected simultaneously on both sides of said circuit board.