Homebrew PCBs

On Fri, 10 Oct 2008 13:33:03 -0000, you wrote:

There are two things that might be wrong that come to my mind.

1) you may have too strong a developer.  Not sure, never used it.

2) if the film exposes from the top down, insufficient exposure can
cause a bottom layer of film to be unexposed and soluble. The wider
traces stay on because the developer can't dissolve the unexposed
resist fast enough.

Solution for #2 is to expose longer, or use UV lights, or whatever the
manufacturer recommends (never used the product, but experience is
drawn from other photosensitive processes.).

I'd look at doing a test exposure from about 1/4 the amount of time
you think needs to be done to 2 or 4x the amount of time.  Make it a
small board, and see where you get the best results for time and light
intensity.

Harvey



>Hello, new member here.
>
>I joined because I think this should be the best place to solve a
>problem I'm having with a dry film I'm testing (never used this method
>before).
>
>The stuff I'm testing is this:
>http://www.es.co.th/Detail_eng.asp?Prod=WARA%2DDRYFILM
>
>I get it locally (I live in Bangkok), and unfortunately the
>instructions are in Thai... my girlfriend helped me out with it but I
>still think there may be something wrong with them... 
>
>But first let me lay out the scene.
>
>Of course first I prepare the board, just before applying the film
>sand it over with 600 grit sandpaper, buff it up with Brasso polisher,
>rinse and clean with water and then final wiping with alcohol. I get a
>very pleasing mirror finish! =)
>No fingerprints, lint or dust on the PCB before applying the film.
>
>I cut a piece of film slightly larger than the PCB area, remove the
>backing layer and stick it to the PCB starting by and edge and using a
>cloth to easily slide my fingers around the sticking edge as I lay it
>down. No bubbles or anything, it adheres very well on its own.
>
>I place a cloth over the PCB and film and use an iron on Silk setting
>to fuse the film to the board, if I use a higher temperature the film
>seems to liquefy under the backing film and make nasty spots... not
>good. With some practice I've managed to do it right most of the time.
>
>After ironing I place the negative mask over the board and expose it
>with an incandescent light bulb for an hour until the exposed film
>turns a darker blue. So far so good, the traces look perfect and the
>backing film peels off easily.
>
>Everything goes wrong when I try to wash away the unexposed film. Per
>the instructions I used all the developer powder provided (about 50
>grams of calcium carbonate) on 200cc of water. The instructions simply
>say to use a sponge to wipe out the unexposed film, at first seems to
>work but then the finer traces (0.3mm) start to break and by the time
>the unexposed film is gone all looks mangy and frankly quite FUBARed.
>
>I suspect the developing solutions is not correct, but having no
>experience with this method I couldn't tell.
>
>The bulk of my ignorance is the developing process, what is the
>standard way of developing and cleaning the excess dry film?
>-Should I do it right after exposing it, or should I leave the board
>in a dark place for some time?
>-Should I go at it with the sponge right away or first leave the PCB
>submerged on the developing solution for some time?
>
>I would appreciate very much some insight from the people in this group.
>
>Cheers,
>
>Ale