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'[EE] PCB newbie needs advice please.'
2005\07\31@052446 by Peter Onion

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While I've been building electronics projects for over 15 years, I've
never taken the step of moving from hand wiring on stripboard to making
my own PCBs.

However I now want to produce a number of simple PIC boards to
experiment with a network of communicating PICs, so it seems the right
time to investigate making my own PCBs.

I understand the basic principles of etching etc, but what I want some
advice  on is what equipment I need.  Luckily I live near to a large
electronics supplier (http://www.rapidelectronics.co.uk/) where I can
order in the morning and collect on the way home from work.

They have what looks like a useful "Starter Kit" (watch for URL wrap)
http://www.rapidelectronics.co.uk/rkmain.asp?
PAGEID=80010&CTL_CAT_CODE=30343&STK_PROD_CODE=M29467&XPAGENO=1

Of course I will want to be able to move to producing artwork on the PC,
and print it with my HP PSC-1205 inkjet printer, but this where I don't
know what I'll need to make this possible.

For simple circuits will I need some think like this
http://www.rapidelectronics.co.uk/rkmain.asp?
PAGEID=80010&CTL_CAT_CODE=30342&STK_PROD_CODE=M66161&XPAGENO=1
or can normal OHP transparencies be used ?  I only want do make some
small boards with 0.1" spaced DIP devices and for that using a whole
sheet of that (expensive) sheet seems rather wasteful.

Peter Onion

2005\07\31@094936 by Hector Martin

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Peter Onion wrote:
> For simple circuits will I need some think like this
> http://www.rapidelectronics.co.uk/rkmain.asp?
> PAGEID=80010&CTL_CAT_CODE=30342&STK_PROD_CODE=M66161&XPAGENO=1
> or can normal OHP transparencies be used ?  I only want do make some
> small boards with 0.1" spaced DIP devices and for that using a whole
> sheet of that (expensive) sheet seems rather wasteful.

I use normal transparencies fine. Make sure they're inkjet
transparencies though, else the ink won't stick (you probably knew
that already). I've printed 50mil PLCC packages and quite thin tracks
without error, although it takes some practice. Make sure the image on
the transparency is very black, with no tiny holes, etc (you might
have to mess around with the print settings. A black rectangle is OK
for a test pattern to see the uniformity of the print). Some films
work better than others, I've seen some really bad ones.

I have a UV exposure unit, although normal light works fine, just
needs more time. My PCB says recommended 3 minutes UV, I use 2m40s
which works fine for me. For developing, I just follow the directions
on the developer package. For etching I use HCl+H2O2 which is the
standard "fast etchant" kit from my electronics supplier. Others use
other methods, you might want to experiment.

Also, I found that wiping the board after developing helps a lot get
rid of the softened resist. No, the unexposed parts do not go away, it
is quite strong.

--
Hector Martin (spam_OUThectorTakeThisOuTspammarcansoft.com)
Public Key: http://www.marcansoft.com/hector.asc

2005\07\31@100702 by Tom Smith

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I've recently taken the plunge in this area myself because I wanted to make
my own H-bridge/control boards for small robots. I did quite a bit of
research and followed the path that appealed to me from the many choices
available. Rather than transparency film or acetate you can try tracing
paper. The standard weight is 90 gsm but 120 gsm is better if you can find
it. Tracing paper is sufficiently transparent to UV radiation for this
process. The Jetstar film is an interesting product, however. I bought the
MG Electronics (also located in the UK) UV lamp, as well as some of their
chemicals. The UV spectrum output is centered at 375 nm. It's cheesy, but
exposure frames are very expensive, especially for hobby work. A good
alternative is a used small tanning station if you can find one cheap. I was
tempted to build an exposure frame but cost-benefit considerations decided
against it, at least for the present. I've never found an accurate kitchen
timer so I bought a used darkroom timer. An alternative might be an
appliance timer but after searching online I couldn't find one suitable for
my purposes. BTW, Seichi Inoue, who has been mentioned in the past, I
believe, has an interesting homebuilt countdown timer for just this sort of
thing.

You don't need a red darkroom lamp to fasten the artwork to the
pre-sensitized board (cut to size) because the board is not as sensitive as
film, however, you do need subdued light and you might want to use a yellow
bug lamp or gold fluorescent lamp for this step.

Single lamp exposure times can be as high as 20 to 50 minutes, depending on
the type of lamp used and the distance from the lamp to the board. You *can*
use sunlight but it doesn't allow much control of the exposure. Exposure
times are on the order of 20-25 seconds in very bright conditions and you
have to be careful of bleed-through. You really need a light meter to
determine exposure times if you go this route. You might also need a light
meter to calibrate your setup using a UV lamp but once that is done you
don't need the light meter again. As an alternative, if you already have
some idea of the correct exposure time you can sacrifice a small strip of
board to make a step exposure reference, which should be marked and filed
for future reference.

As for wasting a sheet of transparency film: print artwork on ordinary
paper, lay a sheet of film over the print and mark boundaries, cut just the
portion of film you need, align and tape to a fresh sheet of paper and print
on that. For small boards you can probably get four (or more) prints per
film sheet this way.

As for other and cheaper methods, there is dry transfer and drawing the
artwork on the board with a Sharpie ;)

Cheers

{Original Message removed}

2005\07\31@153800 by Peter

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On Sun, 31 Jul 2005, Hector Martin wrote:

> I use normal transparencies fine. Make sure they're inkjet
> transparencies though, else the ink won't stick (you probably knew
> that already). I've printed 50mil PLCC packages and quite thin tracks

Print two copies of each side, one normal and one rotated 90 degrees,
then register and staple them together. This fixes 'streaking' caused by
inkjets and makes the black density better. The stapling is done with
the tacky faces touching. The foils will not keep, the ink creeps
between the tacky surfaces and makes the foil useless after a few weeks.

Peter


'[EE] PCB newbie needs advice please.'
2005\08\02@035927 by Steve Murphy
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I followed these instructions:

http://www.fullnet.com/u/tomg/gooteepc.htm

and had really good luck with a small PCB. I used it to make an SOIC to
DIP converter board and it handled the fine traces really well. The
concept is basically that you use high clay content inkjet paper in a
LASER printer, then you use an iron to transfer the toner directly to
the PCB (and touch it up with a Sharpie permanent marker if necessary).
The paper then essentially peals off/dissolves in warm water. As for
equipment, I used a $0.25 disposable plastic food container. The toner
makes a good etch resist and comes off with acetone (fingernail polish
remover). A side benefit is that you can also make a component side
"silk screen" using the same process.

One detail I read elsewhere that I liked: instead of removing the toner
from the entire board as recommended in the above article, just remove
it from the pads to be soldered, thereby preventing oxidation of the
copper. This months Circuit Cellar has an article that goes into some
depth about doing ones own PCBs (August 2005, pg 75, "Analog Tips and
Tricks"). He also recommends silver plating the board using silver
plating powder (http://www.cool-amp.com). If you buy the commercially available
papers (which usually cost $1.00+ a page), he recommends using *good
quality* scotch tape and just tape a piece of it the size of your board
to a regular sheet of copier paper and running it through your laser
printer. Even at a buck a sheet this would be quite economical.

Hope this helps.

 --Steve.

2005\08\02@094011 by Josh Koffman
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On 8/2/05, Steve Murphy <.....stephmurKILLspamspam@spam@cableone.net> wrote:
> One detail I read elsewhere that I liked: instead of removing the toner
> from the entire board as recommended in the above article, just remove
> it from the pads to be soldered, thereby preventing oxidation of the
> copper.

I've thought of this in the past, but I couldn't figure out an
efficient way of removing just the toner on the pads. Any insight?

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

2005\08\02@192538 by Steve Murphy

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Josh Koffman wrote:

{Quote hidden}

There's the rub (no pun intended). I tried Q-Tips dipped in acetone and
that removed the toner off of the pads all right, but it also smeared it
all over the rest of the board, making a terrible mess. So I ended up
wiping it all off all at once because it wasn't so messy. So, no, I
haven't figured out an easy way to do that. I suppose you could print
out a solder mask and re-iron it on, but that sounds like a lot of trouble.

 --Steve.

2005\08\02@213537 by Josh Koffman

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On 8/2/05, Steve Murphy <.....stephmurKILLspamspam.....cableone.net> wrote:
> There's the rub (no pun intended). I tried Q-Tips dipped in acetone and
> that removed the toner off of the pads all right, but it also smeared it
> all over the rest of the board, making a terrible mess. So I ended up
> wiping it all off all at once because it wasn't so messy. So, no, I
> haven't figured out an easy way to do that. I suppose you could print
> out a solder mask and re-iron it on, but that sounds like a lot of trouble.

I've printed a silkscreen layer once...it sort of worked, but I was
putting it on the blank side of single sided board, and I should have
slightly scuffed the surface for better adhesion I think.

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

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