Hi Boman33, Don and Bill,
I am responding to your replies to my message "Riston precoated FR4 in
Australia, Riston sheets and rolls".
I am pursuing Riston, or potentially other negative photoresist films,
because its my impression it can reliably produce finer lines than the
other alternatives.
For instance, from this list (2012-02-14):
∗
http://tech.groups.yahoo.com/group/Homebrew_PCBs/message/29673Bob Balderstone wrote to the effect that Toner Transfer was not as easy
or repeatable as Riston type laminated film, that spray-on or sponge-on
photoresists don't work, and that "pre-coated boards" (negative,
positive? - at least as distinct from laminating your own Riston
negative resist) were:
>> Good sometimes but expensive and sometimes poorly cut
>> (raised edges have to be filed down before exposure)
>> and occasionally unevenly coated meaning it's hard to
>> get consistent results. My experience is they have a
>> shelf-life (older = longer exposure time) which again
>> causes inconsistencies if you don't make many boards
>> at one go.
I have read about toner transfer, and my impression is that it would be
tricky to get the transfer lamination process working reliably, with
expensive transfer film required for each attempt. Also, it is clear
from the Pulsar documentation:
∗
http://www.pcbfx.com/main_site/pages/direct_etch/the_8min_pcb.htmlthat the toner itself is not good enough, so there has to be a second
step of applying a "Green TRF foil" so the combined bonded "foil" and
toner will keep the etchant reliably off the copper.
These steps involve melting the toner on a flat surface and pressing it,
so I would expect it to spread out and so make lines wider, with fuzzier
edges.
If I can laminate my own Riston or similar to FR4 material, rather than
buy pre-laminated FR4 material, then I can choose whatever thickness of
FR4 I want, with one or two copper layers, with the copper thickness
whatever I want, without having bunches of laminated boards degrading
over time.
I have some single-sided Riston FR4 from the 1980s. It is all
polymerized dark blue - so it can't be used. I understand the thin
mylar film is to protect the Riston from oxidation, which I guess causes
the photoresist to polymerize. I guess this can be avoided if the dry
film is stored correctly. Maybe it goes off after a few years, but the
dry film is cheap. Pre-laminated Riston FR4 boards are difficult or
impossible to obtain and would be much more expensive.
The low cost and simplicity of Riston developer and stripper would be
hard to beat.
There are plenty of etching options, so the remaining problems are:
1 - Choose and purchase some Riston film. I should have some 38 micron
MM540 in the next few weeks.
2 - Figure out how to laminate it onto single and double sided boards
- probably A5 size will be fine for me. I will write a separate
message about the laminator I bought today.
3 - Expose the Riston without too much fuss. I have a promising
technique which I will write to the list about once I have tested
it further.
- Robin