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Hi all,

I picked up a large sheet of surplus single sided copper clad board that is coated with a reddish colored photoresist. I don't know anything about it or whether it's positive or negative. I would like to remove the photoresist and just leave the copper layer so I can use it for toner transfer. The resist is not affected by acetone, turpentine or naphtha.

Any advice on where to go from here would be much appreciated.

Thanks,

Morris

Acetone will do a quick job of this.

Tom

Alas not, I've tried both acetone and IPA and they don't touch it. I'll try MEK but I'm reluctant to try paint stripper because of methylene chloride toxicity.

Morris

Received from Morris Odell at 10/13/2021 23:31 UTC:

Alas not, I've tried both acetone and IPA and they don't touch it. I'll try MEK but I'm reluctant to try paint stripper because of methylene chloride toxicity.

If you try methylene chloride, just use it outdoors where it will work as well as it does inside, but you don't have to breathe it.

I suggest something alkaline... like dishwasher detergent powder... though an alkaline drain cleaner would probably be better. A couple of tablespoons of the cleaner in enough water to just cover the board all in a glass dish. Soak it a few minutes (drain cleaner) or maybe 15 minutes (dishwasher powder) then rinse it carefully (no splashing) down the drain and then the resist will probably come off with a pot scrubber.

Educated guess, not guaranteed. If you can look up the product on the Internet you would have something more specific to go on.

Good luck.

JimH

On 13/10/21 8:11 pm, Morris Odell wrote:

Hi all,
I picked up a large sheet of surplus single sided copper clad board that is coated with a reddish colored photoresist. I don't know anything about it or whether it's positive or negative. I would like to remove the photoresist and just leave the copper layer so I can use it for toner transfer. The resist is not affected by acetone, turpentine or naphtha.
Any advice on where to go from here would be much appreciated.

It's likely to have a plastic film layer to protect it from air.

Lift a corner of it using the stickiness of some stick tape, to get it to peel.

Heat sodium hydroxide NaOH (garage/concrete floor cleaner or over cleaner) in a microwave to over 30degC (higher the better).

Put PCB in and the resist starts lifting in a minute.

If the PCB is small enough, put in the cold NaOH and then put it all in the microwave.

NaOH only needs to be 10g/Lt of water

There's no plastic coating. Not much joy from cold sodium hydroxide either but I'll? try it hot tomorrow.

Morris

In my process, developing uses sodium carbonate (washing soda) and
*developed* resist is removed with sodium hydroxide (lye). So if your
film is undeveloped, you might try the sodium carbonate first, with a
soak in the lye after for anything that remains. Or leave it in the
sunshine for an hour, then the lye.

Note: these are *soaks* not *wipes*. It takes time if you use the
dilutions you'll find in the online guides, since they're for using the
film, not just removing it.

Received from russell shaw at 10/14/2021 04:36 UTC:

If the PCB is small enough, put in the cold NaOH and then put it all in the microwave.

I don't recommend putting a copper clad PCB into an operating microwave oven. You'll have a real mess if you get local hot spots that cause the NaOH solution to splatter.

JimH

On 15/10/21 6:39 am, Jim Higgins wrote:

Received from russell shaw at 10/14/2021 04:36 UTC:

If the PCB is small enough, put in the cold NaOH and then put it all in the microwave.

I don't recommend putting a copper clad PCB into an operating microwave oven. You'll have a real mess if you get local hot spots that cause the NaOH solution to splatter.

The copper is high enough electrical conductivity and the water high enough thermal conductivity that hot spots are never a problem (have atleast 1mm or more depth on top of the pcb).

Arcing due to high Q resonator effects never happen because the conductive solution is a resistive dampener.

I've been doing it for 10+ years.

My thanks to all those who responded. The suggestion of a soak in sodium hydroxide solution was the solution. At first I thought that didn't work because it didn't appear to dissolve the resist but after letting it soak for 5 minutes in hot NaOH solution the coating lifted right off.

I'm delighted to be able to use this PCB material at last!

Morris

Hi Vesselin,

I found it as surplus at a hamfest. Some of the electronics parts places down here in Australia sell boards coated with photoresist but I've never used any.

Regards,

Morris