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PCB Etching Problem

2005

Hi Friend's,
I am faceing lot problem with my PCB Febrication double Sided. Because I am using PTH.(plated throuth hole) Process.My process and problem as below.


1.drilling
2.Electroless copper plate for PTH
3.Electro Copper plate
4.photo Resist Dryflim and
5. photo resist develop
6. pattetn plate with Lead/tin
7. Etch With Sodium persulphate and make problem.Its remove copper with Lead/Tin. So also remove my PTH also.

please help me how I can save my PTH.If I save Lead/tin plate than save my PTH also. please help

Sanjib Roy
Akash Technology - Dhaka, BD, Bangladesh

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Most people use an ammoniacal etch in that process. Second in popularity is a peroxide/sulfuric acid formulation.

James Totter, CEF
- Tallahassee, Florida
2005

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While your statement is probably true, James, I don't think it helps Sanjib solve his problem. He seems to want to know a chemical that will strip Tin-Lead without attacking copper.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

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Actually, Ted, from the process description, I inferred that the question was the opposite...At the point in the process described, the etch is used to remove background copper, with the Sn/Pb being used as an etch resist in order to preserve the defined circuit pattern in a panel plate operation. The Sn/Pb may or may not be removed later.

If the intent is to remove the etch resist in this case, a proprietary chemistry is generally used. However, if the function of the Sn/Pb is solely as an etch resist the industry has moved away from Pb and gone to Sn only plating.

James Totter, CEF
- Tallahassee, Florida
2005

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Thanks, James. Upon rereading the question you're apparently right. Is there a step 6-1/2 missing, or can ammoniacal etch remove the developed photo resist?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

The resist strip step is indeed missing; it is usually done with a KOH solution. An ammonia ⇦this on eBay or Amazon [affil links] etch may remove the resist if it isn't controlled properly; doing that isn't a cost effective method since the etch is usually recycled for copper content and fertilizer raw materials.

James Totter, CEF
- Tallahassee, Florida
2005