James
Dryfilm foto sensitive resist is a kind of a foil, well, it's a
chemical, foto sensitive layer that is put on a plastic film, and that
layer then also is having a plastic film on top of it. So, it's a
sandwich kind of foil with the foto sensitive layer in the middle.
The process to use it is as follows:
- You remove the lower protective plastic film, then laminate this onto
a copper cladded piece of PCB. You can do so with a standard office
laminator (there are some constrains here, see my other posts from
yesterday).
- The resulting PCB is then photo sensitve, quite the same like coated
PCB material, that said you can expose it. However, exposure time is a
lot shorter. Usually the process is three to ten times times faster
depending on the exposer method used.
- You then remove the other protective foil and put it into a developper
bath. That bath is however not natrium hydroxid (not sure if that's the
propper term in english), but what I think is called caustic soda
(sodium carbonate solution).
- You then can etch the result. If you have a tru plated board, you just
make the film so as the holes remain covered. Note that usually the
dryfilm fotosensitive resist is a negative. That said, exposed areas
will protect the underlaying copper from being etched away, where as the
unexposed areas are taken away by the developper and alas the copper
there will be etched away
.
- After the etching you stripp of the remaining resist in a natrium
hydroxid bath (the same you otherwise use with standard coated boards
for developping). That's the same step as with a regular board where you
may would use aceton or something like this to remove the remaining
parts of the protective laquer.
There are some advantages over standard coated sensitive boards. In
particulare those advantages are:
- If you see after either exposing or developping that the result is not
satisfactory, you simply strip the resist off (see above) and start all
over where as with standard coated material you would have to dump the
whole board
- You can tent the holes. That's of course important only if the holes
are tru plated.
- You can easily "abuse" the resist for all kind of other photo
sensitive work like etching other metal foils etc.
- You can use much cheaper base material, and you can also use non
standard thinkesses which is important if you intend to produce a
multilayer board.
HTH
Markus
James Newton schrieb:
>
> First, thanks so much for sharing this information. I've taken the
> liberty of quoting you on my web site and when you have a web page, I
> will be very happy to link to it... Or even help you set it up.
>
> Now: This is probably a really stupid question, but when you
> say "dryfilm resist" what exactly do you mean?
>
> --
> James.
>
> --- In Homebrew_PCBs@yahoogroups.com
> <mailto:Homebrew_PCBs%40yahoogroups.com>, Markus Zingg <homebrew-pcb@...>
> wrote:
> >
> > James,
> >
> > Regarding "keep the holes from being eched off ". That's the point
> why
> > you have to use dryfilm resist. The resist "tents" the holes (this
> is
> > called tenting) and therby protects them from being etched away.
> That
> > works very reliably. You just must take care to adjust the artwork
> > precisely with the previousely plated holes. Once you get the hang
> of
> > working with dryfilm resist you realize how flexible this method is
> and
> > you hardly will return to anything else. I meanwhile sometimes even
> > strip old base material that is coated with a photosensitive laquer
> and
> > laminate it therafter just because of the advantages of this
> method. One
> > advantage is i.e. that you can always start over if after exposing
> and
> > developping you discover that something is not shart enough etc. by
> just
> > stripping the resist away and relaminate the board.
> >
> > Markus
>
>