Homebrew_PCBs

On 18/05/2012 3:54 AM, Boman33 wrote:
> Thanks for a detailed post with good information.
>
> A quick question: Why not also consider positive resist?
>
> =============================
>
> From: Robin Whittle Sent: Thursday, May 17, 2012 11:12
> I am a newbie to this list and am keen to set up for using Riston
> (negative) photoresist for making small quantities of relatively small
> PCBs. I used it in mid-1980s but then I had a process camera and could
> make really good phototools.
>
> The developer and stripper chemicals are cheap and easy - sodium
> carbonate (washing soda) and caustic soda respectively.
>
> My initial tests with a novel exposure technique are encouraging - I
> will describe this in another message.
>
> It is possible to buy Riston coated single-sided 1.6mm FR4 PCB material
> in Australia: (Asterisks added to force indents in the Yahoo Groups
> archives, which gobble leading spaces.)
>
> * http://www.jaycar.com.au/productView.asp?ID=HG9970
>
> but it is expensive: $24.95 for 152 x 152mm (6 inches square). This is
> what I used for tests. According to the instructions in the pack, this
> material comes from http://www.rcsradio.com.au, a business established
> in 1943 but which has ceased trading since the proprietor Bob Barnes died:
>
> * http://www.thebackshed.com/forum/forum_posts.asp?TID=3574
>
> so it would not be surprising if Jaycar discontinued this.
>
> Kalex in Melbourne: http://www.kalex.net.au advertise 1.6mm single-sided
> Riston-coated PCB material in their pricelist. I called them and was
> told that this is only for large quantity - they don't keep any in stock.
>
> I couldn't find any other sources of FR4 already coated with Riston, so
> this lead me to buying the Riston film itself, and looking at techniques
> for laminating it to the PCB material. This will allow me to choose
> 1.6mm and 0.8mm material with normal (1 ounce) copper or thinner (0.5
> oz) copper. I understand the finer tracks can be achieved with the
> thinner copper because the etch time is reduced, leaving less time to
> undercut the photoresist, and I guess with the copper being thinner and
> less accessible to the etchant. If I get adventurous I may even try
> double-sided PCBs.
>
> This is for prototyping - and for the satisfaction of making things at home.
>
> The Riston information is at:
>
> *
> http://www2.dupont.com/Imaging_Materials/en_US/tech_info/product_selector.ht
> ml
>
> I found 3 sources of Riston film. I also found some Chinese sources of
> generally un-named dry negative photoresist film. The last one mentions
> it is Hitachi photoresist:
>
> * http://stores.ebay.com/Led-Light-Bulb-World/_i.html?_nkw=photoresist
> * http://stores.ebay.com/Digole-Digital-Solution/_i.html?_nkw=photoresist
> * http://stores.ebay.com/oneworldonedream2010/_i.html?_nkw=photoresist
> * www.ebay.com/sch/dr_ho_000/m.html
>
> The first Riston source is Think and Tinker in the USA. They sell rolls
> of "M115", which I assume means Riston MM115 or MM115i. This is 50
> microns thick. However, I don't need such large quantities.
>
> http://www.thinktink.com/products/Photopolymers.asp
>
> The second source is in Sweden. They sell sheets of Riston FX515 which
> is 15 microns thick.
>
> * http://www.ebay.com/sch/karass/m.html
>
> The third source is in the Czech Republic. They sell A5 sheets of
> Riston MM540. This is 38 micron. I ordered some sheets today.
>
> * http://www.ebay.com/sch/gaminn/m.html
>
> Can anyone comment on the merits of Riston or alternative brands of
> negative photoresist, or on the three thicknesses: 15um, 38um and 50um?
>
> - Robin Melbourne Australia http://www.firstpr.com.au/rwi/dfish/
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>


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

>> Very, very good indeed once you've mastered the art
>> of laminating. Definitely worth shelling out the ?10 or so for a
>> cheapo laminator. Very cheap chemistry. No shelf life that I've
>> seen. Very consistent results. Can also be used as a poor man's
>> solder mask. Buy flat sheets (eBay China) not the cheap roll ends
>> which curl up every other whichway when you're trying to apply it.

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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