Homebrew PCBs

Hello all!

  Searched part of the archives (this search engine isn't real good)
and couldn't find assistance with the folowing:

  I've recently started using photoresist after using toner transfer
and  plotting direct plotting since I finally have to use SMDs and
double sided PCBs.  Did my first test run today and have a few questions:

  Once I peeled off the backing paper, I found that the edge of the
board wasn't covered in photoresist - in some places a strip of up to
an inch of copper wasn't covered in resist.  Is this normal??

  I presume that if the exposure time is correct then once developed
you get clean copper where etching is to occur?  My test board on the
longest exposure time I've tried (~8mins) still had a touch of green
on the etched areas of the board and they handn't appeared to be
touched when I etched in Amonium Persulphate.

  Is the resist still UV sensitive post developing in sodium
metasillicate?  
  
  Should I etch in low-light conditions or once developed I can the
etch in 'normal' bright sunlight and/or leave lying around in
sun/florescent lighting for a couple of hours before etching?

  Thanks for your help

  Trev.

  By the way - I'mm currently printing my artwork via Lexmark inject
to two copies of acetate transparencies.  Matching both copies of each
side then exposing using a 2nd hand UV light box and through a glass
sandwich.  ie glass, 2 x component artwork, PCB, 2 x solder side
artwork, glass, UV lightbox.  The glass sheets I'm using don't
actually fit in the lightbox, so I'm resting them on the lip of the
box which moves the artwork about 1 inch above the box's glass surface.

  I'm thinking of using tracing paper primarily for cost reasons
though - any thoughts??

"Once I peeled off the backing paper, I found that the edge of the board
wasn't covered in photoresist - in some places a strip of up to an inch of
copper wasn't covered in resist.  Is this normal??"

I've never had that from MG Chemicals boards.  The stuff came right up to
the edge.

Robert
:)







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I've had that problem on some of the MG Chemical boards.  Overall the 
whole setup works very well.  I've made a lot of boards this way.

http://www.kd7lmo.net/tech_pcb.html

On Wed, 8 Jun 2005, Robert Hedan wrote:

> "Once I peeled off the backing paper, I found that the edge of the board
> wasn't covered in photoresist - in some places a strip of up to an inch of
> copper wasn't covered in resist.  Is this normal??"
> 
> I've never had that from MG Chemicals boards.  The stuff came right up to
> the edge.
> 
> Robert
> :)
> 
> 
> 
> 
> 
> 
> 
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBs
> 
> If Files or Photos are running short of space, post them here:
> http://groups.yahoo.com/group/Homebrew_PCBs_Archives/ 
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
> 
> 
> 
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBs
> 
> If Files or Photos are running short of space, post them here:
> http://groups.yahoo.com/group/Homebrew_PCBs_Archives/ 
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
>

doesn't make a good etch when spreading the silicone so thin that the  
paper shines through.
Uneven surface leads to spots with too little toner and pinholes after  
etch, even tho all the toner is tansferred.

Using more silicone (just enough to cover all paper fibers) works ok.

Problem is with inkjet paper pinholes are much easier covered.

Did make good PCBs tho, and it works without any problems for component  
legend.


ST

Well I never saw where he said he was using M.G. Chemicals boards, I 
have used 100's of their 600 series boards over the years noramlly 
8x10 or 8x12 boards, that I cut up into smaller boards after etching.  
I see one of my board pictures has made it on the Home Page.  Never 
had any kind of problem with resist being missing like that.  Might 
have a few small bad places along a edge where they cut it, but 
normally not a problem, and maybe had a couple that had a small 
scratch on them, there again not normally a big problem.  M G 
Chemicals boards seem to me to be some of the best available, I don't 
buy anything else anymore.  No they are not the cheapest in price 
either.

First off, you must have your artwork in direct contact with your 
board, ink side towards the board. The glass to do any good must be 
flat against the Artwork.  Transparencies is what I find to work best, 
they must be for inkjet printer for best results.  I use a HP and use 
HP transparency only, other brands may not work as good even those 
that say they are for your machine.  I have tried the tracing paper or 
veluem paper, really does not work as good, Black ink seems to work 
best on the veluem paper if you want to try.  What I have found to 
work best is printing to Transparency using yellow ink.  I am told 
that using photo cyan (green & yellow together) if you have a photo 
printer works even better. Also find it is good to run your printer 
thru it cleaning process, seems to help keep it from streaking some.

Yes UV is correct, I use the Black Light tubes, I use 4 of the 
F15T8/BLB lamps, I think that is the right #.  Having the light source 
back a little ways seems to help stop undercutting.  Have not tried 
yet but some have talked about using the egg crate you put in lights 
to only get direct light downward.

Developer I use the M G Chemicals which is Sodium Hydroxide also 
believe called Lye.  Find it works best if you mix it with warm water 
just before you are to use it.

I use Ferric Chloride, yes it can be messy if your not careful with it 
but you need to be careful with any of the etchants or other chemicals 
one might use in making PCB's.  Works best Heated, and needs some way 
to keep the etchant moving.  I have a 5 Gal. tank with air bubbles to 
move the etchant.

My exposure time is using the yellow ink on transparency is about 5 
min, Black ink ran about the same but did not work as well, got more 
pitting and small breaks in traces but where still good.
My Etch Time is about 6 to 12 Min if the etchant was Heated well and 
depends on how fresh the etchant is also.

If you are planning on making board on a regular basis then I would 
recommend that you have you a place you can leave setup and have 
access to running water.

Myself I leave the resist on the board, load it and solder it then 
spray with a clear lacquer.

Cutting methods I have found that work best are Table Saw, but need 
good dust colection system in place and filter protect you motor from 
sucking in the dust.  I use a wet/dry diamond blade, use it dry.  You 
do have to account for the blade kerf in spacing your boards on the 
larger board.

Other method is a bench shear,  I use one by Kepro, not cheap but I 
found mine used on ebay.  They are still available from a company that 
took over Kepro, link to them should be in the Links section.


Hope that helps.

Ben