Homebrew_PCBs

The 'turkey bag' method you describe below sounds like a very good idea.
Having used the dry film I can imagine how this will work. Once the film is
laid down without wrinkles or visible signs of trapped air, then the iron
simply does the final fusion between the copper/dryfilm interface.

However one advantage of the cold wet lamination method I described earlier
is that the water used to wet the board also washes most foreign particles
off the copper surface. I found it difficult to keep a surface free of dust,
even in my workshop shed were there is very little dust, compared to say
inside my house were fabrics, and carpet are continuously shedding fibers.

I'm glad you mentioned liquid resists. I have been looking for a liquid
resists for some time. I've only been able to find one product costing AU$250
(US$125) for 1 liter, that was a negative acting resist. Does this sound
like a normal price ? There is one local PCB shop that I know of who uses
liquid resists (not sure which type) and they apply it with a silk screen
exactly as you describe. This sounds messy and wasteful to cover just one
panel. How do you clean up the equipment afterwards ?

Application of photoresists is a big topic in itself. I'm still experimenting
with dry film and I'm happy with the results so far. Do you know shelf life
of the dry film when stored in the refrigerator ? What happens to out of
date film ?


twb8899 wrote:

> Adam,
>
> You are correct about using the iron and wrinkles. I didn't go into
> much detail on the process. I lay down the dry film like you
> suggested and then put the panel in a nylon turkey bag. Then I use a
> small vacuum pump to evacuate the air and iron it down. There are no
> wrinkles and its easy to do. Another way is to lay down the dryfilm
> on a panel and then run it through the heated roller from an old copy
> machine or pouch laminator as you suggested.
>
> Your comments about cleaning the board are absolutely correct as any
> oils or finger prints will mess up the adhesion of the dryfilm.
>
> I do have a roll laminator but rarely use it because anything past a
> prototype I just silkscreen. You will waste 5 or 6 feet of dryfilm
> just getting the laminator "fired up". The dry film I have on my roll
> laminator is called KOLON and is made in Korea. It cost approximately
> $0.25 per square foot. The best resist I have used is DuPont 4715
> which was around $0.38 per square foot last time I ordered. I keep
> these rolls refrigerated to extend the shelf life.
>
> Here is something else to consider, there is a liquid resist made by
> Peters in Germany. You just mask off an area on a blank silk screen
> and print the entire blank board. The blank panel is then dried in an
> oven at about 180 degrees F for 20 or so minutes. It dries with no
> pin holes and any small dents or imperfections are covered.
>
> All other processing and development is the same as dryfilm. I used
> this resist to process inner layers on multilayer boards and it
> worked even better than dry film but the cost was higher. We had
> almost zero defects when using this method so it was worth the added
> cost.
>
> This type of resist would do an excellent job on hobby boards if you
> want to get the silk screening equipment for coating the panels. You
> can coat a batch of panels and store them for future use. The silk
> screening equipment can be used to print equipment panels as well and
> is a good thing to have around.
>
> Tom
>
>
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Adam,

The liquid photo resist I use is made by Peters in Germany. The name
of the company is Lackwerke Peters GmbH + Co KG. Their web site is
www.peters.de and the product is called Elpemer SD 2054. This resist
can be applied by masking off a blank silkscreen and flood printing a
blank copper panel. Any excess can be scraped from the screen and put
back in the container. There is very little waste involved. Cleanup
is with laquer thinner or acetone. The data sheet states that 50 um
lines and spaces are possible with this resist.

Your "wet" lamination method for dry film is an excellent idea. Some
of the better lamination machines use a water mist in addition to
heat and pressure. It is supposed to be a superior method and many of
the shops are starting to use it. I have never tried the wet method
but after hearing about your success I'm going to give it a try. I'll
post a message with my results.

If there is any interest I would be willing to supply blank FR-4
panels coated with dry film and sealed in an opaque light tight
container.

Tom

Just a note...

> Cleanup is with laquer thinner or acetone.

They state clean-up is done with caustic-soda (Lye) solution...

hans w




[Non-text portions of this message have been removed]

--- In Homebrew_PCBs@y..., Hans Wedemeyer <hans@c...> wrote:

> Just a note...
>
> > Cleanup is with laquer thinner or acetone.
>
> They state clean-up is done with caustic-soda (Lye) solution...
>
> hans w

Hans,

We use solvent just to clean the screens. All other processing is
water based chemistry.

Thanks for pointing that out. You wouldn't want to use solvent on the
finished parts!

Tom