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topic 1960

Stripping tin/lead from PWB / PCBs


(1998)

I have visited the Finishing.com page and saw the article on stripping tin/lead from PWB's. My problem is a little different and so I wonder if you can help or point me in the right direction ......

The article on stripping indicates the following:

-------------------- Copied from Article ----------------------------

However if you have to strip Tin/Lead, Nitric/HF is not the best stripper, Nitric/Ferric Nitrate is the a much better choice. Nitric/HF will leave an insoluble residue of Lead Fluoride, and this residue can act as a barrier and stop stripping in very small, deep holes. The Nitric/Ferric Nitrate system does go through a stage where there is some residue during stripping, but ultimately the residue will dissolve. This dissolution makes this the chemistry of choice for Tin/Lead stripping.

The 4 different chemistries for stripping Tin or Tin/Lead are:
1. Ammonium Bifluoride/Peroxide (the original, & still used for Tips)
2. Two step, Nitric followed by Ferric Chloride
3. Nitric/Ferric Nitrate
4. Nitric/HF

----------------- End of Copy -----------------------------

My problem is the following:
I have a polyimide flex circuit.
On this flex I have conductors which are copper.
At the end of the conductive traces I have a contact pad.
The pad is copper/overplated with nickel overplated with gold.
The purpose of the flex circuit and the contact is to provide a temporary contact to a flip chip device so that it can be tested.
During test solder is being wiped/deposited onto the gold pads.
I would like to remove this solder.
The solder composition is Pb-90/Sn-10.

We have tried a hydrogen peroxide/acetic acid etch and that appears to remove some material. I am concerned about any etch undercutting the nickel and copper since the sides of the traces are not overplated and are open to attack from any chemical.

Any suggestion/recommendations? I am prepared to change the contact plating to something else due to the solubility of gold and lead ..... Are you aware of any surface plating which will enable me to contact a solder pad and provide low contact resistance but which also does not oxidize?

Thanks in advance for your help.

Regards

James

James Forster
- Mansfield, Massachusetts


(2004)

We want to selectively remove solder / tin in the electronic scrap,and to recover both lead and tin and reuse the stripper solution. I would be very thankful if you could kindly send me the informations.

thanking you.

Savari Kulandaisamy
Central Electrochemical Research Institute - Karaikudi, Tamilnadu state, India



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