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Subject: Etching pattern plated PCBs

Date: 05/15/00 at 11:41 PM
Posted by: Adam Seychell
E-mail: aseychell@vet.com.au
Message Posted:

I am interested in knowing more about bath chemical composition of printed
circuit etching tanks manufactured with the pattern plated process. This
process uses a metal plating to resist copper traces in the etching bath
and is the most commonly method used for PCB fabrication. Different metals
can be used for the plating resist, the most common being tin/lead (solder) alloy.
Pure tin is also a widely used plating resist but is more limited to available
etching baths than tin/lead since tin is attacked easier than tin/lead.
I am only interested in etching baths compatible with a pure tin
metal plating resist. So far I have experimented with common etching bath
of ammonium persulphate and showed me that the tin is quickly dissolved
(at faster rate than copper). Ferric chloride is incompatible with all metal
plating resists, except may be gold. A bath mixture of phosphoric acid + ammonium
persulphate was reported in "Printed Circuits Handbook", Clyde F. Coombs, Jr.
3rd sd being acceptable for tin metal plating. No details of the bath
composition were given. Any information on etching baths for pattern plated
boards would be greatly appreciated as I've so far spend weeks researching this.
I know this is not about PCB design but I don't know where else to post my
question, I have tried sci.electronics.design. A forum deticated to PCB fabrication
would probably get some popularity, especially among hobbiests.

regards,
Adam


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