Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Thanks for a detailed post with good information.

A quick question: Why not also consider positive resist?

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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/





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