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Preventing Etchback Around Holes in Printed Circuit Boards

IP.com Disclosure Number: IPCOM000089020D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Chellis, LN: AUTHOR [+3]

Abstract

Printed-circuit boards include layers of copper circuitry between layers of epoxy. In the example shown above, the copper circuitry is designated 11, and the epoxy is designated 10. Printed-circuit boards frequently have holes therein shown above by the numeral 15. These holes are plated with copper in order to make connections between various layers of circuitry on the board.

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Preventing Etchback Around Holes in Printed Circuit Boards

Printed-circuit boards include layers of copper circuitry between layers of epoxy. In the example shown above, the copper circuitry is designated 11, and the epoxy is designated 10. Printed-circuit boards frequently have holes therein shown above by the numeral 15. These holes are plated with copper in order to make connections between various layers of circuitry on the board.

The copper circuitry 11 has a layer of copper oxide 12 thereon. This layer of copper oxide is formed by treating the copper with an oxidizing agent prior to the laminating process. The purpose of forming oxide layer 12 is to improve the adhesion of epoxy 10 to the copper 11.

It has been found that during the cleaning of holes 15, some of the solvent etches layer 12, forming cracks or discontinuities.

It has been found that if the copper layer 11, which has oxide 12 thereon, is treated with a low viscosity epoxy solution prior to the lamination operation, the amount of etchback around hole 15 is reduced. Any suitable epoxy resin in a suitable solution can be used, such as commercial epoxy - solvent adhesive EC2290*. Such coatings can be further diluted with ketones or other solvents to achieve low viscosity and good wettability. The addition of wetting agents or silicon coupling agents can enhance the wettability. Varnishes which are compatible with the laminating resins can also be used. Also, the use of dilute solutions enables a t...