PCB fabrication - Dry film resist method - bubble problems

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Hi All,

I've been using Toner Transfer method for many years and happy with it for general electronics. But my current application requires 10mil precision (or better).

I've been experimenting with negative dry film from eBay. The processes I am using are good: My exposure is good. Development is good (I can develop without having to contact the PCB, which I am happy about, as many youtube videos show the presenters rubbing resist off the board with their fingers or a brush.. anyway, that aside...). I've tuned up most of my methods and am happy with them.

However, the problem I'm having is when I put the dry film over copper laminate, I get very small bubbles (maybe 5-10 bubbles, 0.5mm in size) appear between the resist film and copper board. I am not able to remove them. The laminator I am using (a configurable temperature, a cold roll laminator) has been experimented with by setting different temperatures. I have even put the board through with another on the reverse side to that the rollers have more pressure on the board (Nb/ I am experimenting with 0.032" FR4).

The problem appears to be that the resist is too sticky. It is like sticking shelf liner to a flat surface and getting bubbles, but I would say shelf liner is easier to work with than the stuff I have to be honest. There is no hope of my cold roll laminator removing these bubbles. I am now wondering if my dry film is defective ?

Could anyone tell me what negative dry film (DuPont Riston) should handle like when placed on a copper board ?

Many thanks

[wotnot]

Found an interesting read about this J ->

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Thanks

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