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Anodized Resists for Ammonium Persulfate

IP.com Disclosure Number: IPCOM000095339D
Original Publication Date: 1965-Dec-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

York, ER: AUTHOR

Abstract

In the process for making fine-line printed circuits, eutectic tin-lead is deposited in the positive circuit pattern on a copper-clad board and etched in ammonium persulfate. Before etching, the tin-lead plated circuits are electrolytically anodized in warm sodium borate solution to confer increased corrosion resistance on the tin-lead to the ammonium persulfate etchant.

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Anodized Resists for Ammonium Persulfate

In the process for making fine-line printed circuits, eutectic tin-lead is deposited in the positive circuit pattern on a copper-clad board and etched in ammonium persulfate. Before etching, the tin-lead plated circuits are electrolytically anodized in warm sodium borate solution to confer increased corrosion resistance on the tin-lead to the ammonium persulfate etchant.

The anodizing treatment results in a significant improvement in the yield and quality of the etched circuits. Without this treatment the tin-lead is subjected to chemical attack by ammonium persulfate forming side reaction products which greatly interfere with etching. This problem becomes more critical when etching fine-line circuits.

As another resist for ammonium persulfate, immersion tin deposited on a copper-clad board in the positive circuit pattern is electrolytically anodized in warm sodium borate solution to black, dense stannous oxide. Stannous oxide is inert toward ammonium persulfate and serves as an excellent resist. After etching and removal of oxide in 50% HCl, the tin remains on the board for subsequent processing.

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