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An Etch Resistant Banking Agent

IP.com Disclosure Number: IPCOM000098168D
Original Publication Date: 1960-Apr-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Hoffman, HS: AUTHOR

Abstract

The addition of a palladium salt to a copper etchant, ammonium persulfate, causes a significant reduction in undercutting the foil pattern of an etched circuit.

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An Etch Resistant Banking Agent

The addition of a palladium salt to a copper etchant, ammonium persulfate, causes a significant reduction in undercutting the foil pattern of an etched circuit.

When a conductive printed circuit pattern is etched, it is desired that the conductor line sides and hole walls should be vertical and not undercut. Usually, as etching proceeds, an ordinary acid tends to etch laterally and thus undercut the resist to cause weakening and distortion of the pattern. Some banking techniques call for repeated powdering of the foil, i.e., applications of resist between partial etching operations. operations. However, such repeated banking operations are time consuming and difficult to apply.

In using the improved etching agent it is found desirable to impinge the etchant bath against the foil surface to be etched, as by splashing. The special etchant forms a partially etch-resistant film on the resist free metal surfaces, and when the bath is impinged against the surface to be etched in a direction normal to that surface, the film is broken. As a differentiation, when the bath hits the side walls of a pattern, the film is generally not broken because there is insufficient striking force, and etching of the side walls (or undercutting) is reduced substantially.

The etchant is prepared with the following formulation:

Ammonium persulfate 285 g. per liter

Sodium palladium chloride 1.5 g. per liter

The solution is heated to 15O degrees F and poured into a splash etcher. A copper-clad laminate with a fine line resist pattern is placed in the etcher. The time required to etch 1.35 mil copper foil is about 1 minute and 15 secon...