How to uncurl photosensitive dry film?

[rcbuck]

I purchased dry film for circuit boards like this:
https://www.ebay.com/itm/30cm-1M-Photosensitive-Dry-Film-for-Circuit-Production-Photoresist-SheetsASS/263587365246?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908103841%26meid%3D86042eb9c41743d9ae85b8648cf44c27%26pid%3D100227%26rk%3D3%26rkt%3D15%26mehot%3Dag%26sd%3D173645405698%26itm%3D263587365246&_trksid=p2054502.c100227.m3827

It comes on a very small roll that is tightly wound. It works fine but is a pain to use because it wants to curl up due to being wound on the spool. Does anyone know how to make it lay flat again? I tired leaving it between the pages of a large book with more books on top overnight but that didn't work.

The dry film used to be widely available in flat cut sheets on Ebay but no one seems to be selling the sheets anymore. I did find one seller but their cost was about 10 times more than the rolls.

[helius]

You could try using a print de-roller or weight.

[sleemanj]

Can't say I've ever had a problem dealing with curl, but I mostly do small boards less than 7x10 cm and apply using water spray method.

I would try warming the film and allowing it to cool held flat.

Edit to add: way back when I first started selling dry film, I tried sending it in cut flat sheets, it was a massive PITA trying to stack up a load of flat sheets and get them into  a flat package so postage would be cheap... I imagine this is why nobody does it, it's certainly why I gave up on the idea.

[M4trix]

@helius,

unfortunately that won't help much. When it curls up it stays curled till the moment you peel off the polyolefin foil prior to the lamination process.

Edit: I did a lot of trials and errors with dry films and I found only one method which guarantees you a perfect laminated PCB without those
entrapped notorious air bubbles and foil distortions.

You can see how to do it here -->

https://www.thinktink.com/stack/volumes/volvi/modulam_lam.htm

The only thing that I found better is:

1. Push the carrier into the laminator just enough till the rollers grabs the carrier.
2. Then stop the laminator by stepping on the foot pedal. Btw, having a foot pedal is mandatory and I really mean it ! Every laminator
    can be simply modified/hacked with this feature.
3. Completely peel off the polyolefin foil. Do not let the dry film fall over the PCB cuz it might stick to it.
4. Then grab the two corners of the dry film and pull them outward making a slight tension. This tension must be kept through the
    whole lamination process !
5. Release the foot pedal and make no jerky movements with hands untill the process is finished ! If you have shaky hands, you're doomed.
    A glass of cold beer might help 

There. Repeat the process for the other side of the PCB.

[rcbuck]

Thanks for the replies.

M4trix, I will try the method your referenced. In the past I never had a problem with the flat sheets. I haven't had a problem with air bubbles or foil distortions with the curled film. It has just been a problem trying to keep it flat when applying it to the board prior to laminating. The method shown where the film is applied as it enters the laminator looks like it will solve the problem.

[BravoV]

I am assuming you own a laminator right ? As this film will stick perfectly to pcb using these laminator to prevent any bubbling and even out the stress at the film surface, compared to manual handling just by hand.

Usually I set the temperature just luke warm, not hot, then feed film slowly and carefully as it needs fully attended during feeding time as its curl. And if you did it right, the whole film will come out perfectly flat and no kink at all.

Random image from Google of laminator

[M4trix]

I got mine from eBay for 100 bucks. GBC HeatSeal H600 Pro in a very good condition. Since it was for the US market, the working voltage is 110V so
I had to make a step down converter 220-110V, 1500W. Added a tattoo foot switch and a RCA 6,3mm connector. I simply cut the wire which feeds the main DC motor and soldered it to the connector. Of course, you have to drill a 9mm hole on the front panel. The foot switch has a reverse switching option. Thank God. 

Foot switch