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Negative dry film problem in removing second protective film

dashy1981

Jun 19, 2013
83
Joined
Jun 19, 2013
Messages
83
Hey Guys !!!
I recently started back on homemade pcb with negative dry film method. After experimenting for two weeks I've calibrated my process to satisfying results.
However, I always have great problems in removing the 2nd protective sheet on the dry film after exposure. 1st protective sheet removal is quite easy with attaching tape at both sides and peeling off. But once the film is put on copper clad board and exposed after that I only get second layer removed with 30-40% accuracy. I've screwed many pcb's at this stage in last two weeks.

The method I use is try to put tape on one corner of dry film and try to peel off... But most of the times while dry film starts to peel off instead of just the protective sheet. After looking at multiple YouTube videos and reading through blogs and pages, I am yet to find a solution to it. I even tried removing it with a tweezer, but to no awail. I don't seem to get to the sheet, rather whole thing comes out.

My process is as follows:
1. Cleanup pcb with acetone and scrubbing.
2. Use tape on both sides of dry film and pull it apart exposing the photo material on one side.
3. Apply the dry film on pcb face down. Remove any bubbles with gentle presssure.
4. Heat the pcb with hair dryer or medium hot iron.
5. Expose in uv light : 12 s gives a good exposure with LED torch.
6. Remove the second protective layer
7. Develop in sodium carbonate solution
 

Bluejets

Oct 5, 2014
5,852
Joined
Oct 5, 2014
Messages
5,852
Think you will find those all have a limited shelf life, at least that was my experience so 20 years ago.

These days one can get 5 boards made (under a certain size) for $2.00.
Postage racks that up quite a bit but still, professional quality stuff, short turn around, free design software with one click up loads to the manufacturer.
 

dashy1981

Jun 19, 2013
83
Joined
Jun 19, 2013
Messages
83
Think you will find those all have a limited shelf life, at least that was my experience so 20 years ago.

These days one can get 5 boards made (under a certain size) for $2.00.
Postage racks that up quite a bit but still, professional quality stuff, short turn around, free design software with one click up loads to the manufacturer.
Yes, that's true but to enhance longavity we can use uv mask. Point here is it's a hobby for me and in india it's not easy to get it sourced from china. Moreover, quickly doing a prototype is much faster than sourcing it.
 
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