Understood Robin, although I have not encountered problems with the
Kinsten positive pcb in terms of registration or under-cutting etc.
I must check my Riston stock for polmerization, as it is also of 1980s
vintage. Last time I looked, about 7 years ago, it was still red.
cheers
Bill, VK7MX
On 19/05/2012 12:31 AM, Robin Whittle wrote:
> 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/29673
>
> Bob 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.html
>
> that 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
>
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>
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