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topic 44254

Removing solder from circuit boards

A discussion started in 1998 but continuing through 2019

1998

Q. 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

Q. 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



2007

Q. I want to remove components from circuit boards by somehow dissolving the solder and leaving the copper tracks.I have tried desoldering with a soldering iron but its too slow and using a heat gun burns the boards. I want the components (in working condition) for for a mate of mine whos kid is into electronics and the circuit boards are for the wife who makes things like drink coasters etc out of the old boards.

Any suggestions. I have just found this site and all I can say is WOW. Nice to see folks exchanging ideas and helping each other for a change.

Greets from Perth WA

Dean Campbell
Hobbyist - Perth, Western Australia, Australia


simultaneous 2007

A. Exactly what you ask for is not possible, BUT, try a higher wattage soldering iron or gun. They go to a higher temperature and stay hot longer when in use. Electronic stores also sell a suction bulb device so that you can remove the glob of solder as soon as it softens so it does not resolder and uses less heat. Next, to preserve the component, invest in a good heat sink, a plier like device to keep heat away from the component.

James Watts
- Navarre, Florida


2007

A. Dean,
The solder on the boards is much thicker than a plated tin lead alloy, and take a long time to strip by chemical. Be careful of nitric based strippers, they generate nasty fumes and will likely ruin the components you want to save. I would say the best bet would be is to seek out a printed circuit board repair supplier. They should have a safe product such as a paste. These days, especially with multi-layer board technology, the whole board is replaced when a component fails. In light of this I'm not sure of the availability of such products.

Mark Baker
Process Engineer - Syracuse, New York


2007

A. Dean

I wouldn't expect such a chemical would exist. If it did it would need to dissolve large amounts of lead without attacking the plating on the component leads or the metal that the leads are made of. An acid etc may leave a non-conductive salt or oxide on the component leads rendering them useless for resoldering and difficult to get any electrical connection through.

I have had some success removing components in bulk with a hot air (paint stripper) gun. I heated a large area of the board on the solder side (sometimes blackening it) and bashed the board edge down against something. Lots of working components and solder splash out.

Hope this helps

Scott Gavins
- Electronic Engineer - Gold Coast, QLD, Australia



How to strip 60/40 tin lead

October 10, 2019

Q. Hi,

I am looking to strip 60/40 tin lead from Nickel plating and the base metal is aluminum. Is there anything out there that will not Turn the nickel black. We previously used a product from Atotech that they no longer make

Thank you

Bob Haines
Plater - Erie, Pennsylvania

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