Homebrew PCBs

I've read a million post on the net about how to create a pcb with 
photosensative spray, and UV light and after about 30 failed attempts 
I'm almost ready to give up.

If someone could please check my method and advise me where I'm going 
wrong:

1) Clean pcb - this is not a problem as its really shiny afterwards 
with no oil on etc
2) Spray with photoresist. I've tried various thicknesses from almost 
see through to a nice clear purple film on the board. Left it to dry 
for 24 hrs. 
3) Created a artwork on tracing paper  (90 gsm) with a deskjet 
printer. 
4) expose using uv lamps - ive  tried various exposure times. 4 mins 
seems to give the best results. 
5) My caustic soda solution is 3 teaspoons to 1.5L water. Again this 
is from trial and error and sometimes seems to give the best results. 

From the 30 attempts I've had - one board was almost usable. The 
problem is that nothing seems consistent. One day I'll create a pcb 
and all of the photo resist gets removed in the CS, the next day with 
the same quantities, the outsides of the board gets removed - the 
purple photo resist film toward the middle of the board refuses to
get 
removed. I've even tried rotating the board under the UV light. 

Help!! Does everyone else have hassles like this? Is there any method 
I can use to produce good pcb's every time.

>From: "gmc_za" <gmc_za@...>
>Reply-To: Homebrew_PCBs@yahoogroups.com
>To: Homebrew_PCBs@yahoogroups.com
>Subject: [Homebrew_PCBs] Photoresist spray and UV light failures
>Date: Wed, 20 Oct 2004 19:30:20 -0000
>
>
>
>I've read a million post on the net about how to create a pcb with
>photosensative spray, and UV light and after about 30 failed attempts
>I'm almost ready to give up.

I've never been able to get the aerosol resist to work, since they changed 
the formula. It used to be OK.

Leon

Buy just one pre-sensitised photo resist board and try making a board with this.
Then do everything as normal, if it works then it's the aerosol, if it fails then its something else you are doing.

Kev/.

  ----- Original Message ----- 
  From: Leon Heller 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Wednesday, October 20, 2004 9:28 PM
  Subject: RE: [Homebrew_PCBs] Photoresist spray and UV light failures




  >From: "gmc_za" <gmc_za@...>
  >Reply-To: Homebrew_PCBs@yahoogroups.com
  >To: Homebrew_PCBs@yahoogroups.com
  >Subject: [Homebrew_PCBs] Photoresist spray and UV light failures
  >Date: Wed, 20 Oct 2004 19:30:20 -0000
  >
  >
  >
  >I've read a million post on the net about how to create a pcb with
  >photosensative spray, and UV light and after about 30 failed attempts
  >I'm almost ready to give up.

  I've never been able to get the aerosol resist to work, since they changed 
  the formula. It used to be OK.

  Leon




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

gmc_za wrote:
> 
> I've read a million post on the net about how to create a pcb with 
> photosensative spray, and UV light and after about 30 failed attempts 
> I'm almost ready to give up.
> 
> If someone could please check my method and advise me where I'm going 
> wrong:
> 
> 1) Clean pcb - this is not a problem as its really shiny afterwards 
> with no oil on etc

Make sure there is no oil by seeing if a coating of water "beads" on it,
or stays flat.

> 2) Spray with photoresist. I've tried various thicknesses from almost 
> see through to a nice clear purple film on the board. Left it to dry 
> for 24 hrs.

Only enough to give a "sealed" smooth surface is needed.

> 3) Created a artwork on tracing paper  (90 gsm) with a deskjet 
> printer.

Do tests without the tracing paper and using a strip of cardboard
to make the shadow pattern on the pcb.

> 4) expose using uv lamps - ive  tried various exposure times. 4 mins 
> seems to give the best results.

> 5) My caustic soda solution is 3 teaspoons to 1.5L water. Again this 
> is from trial and error and sometimes seems to give the best results.

Buy the developer to eliminate a variable from your tests. Then ditch
the spoon and buy scales.

>>From the 30 attempts I've had - one board was almost usable. The 
> problem is that nothing seems consistent. One day I'll create a pcb 
> and all of the photo resist gets removed in the CS, the next day with 
> the same quantities, the outsides of the board gets removed - the 
> purple photo resist film toward the middle of the board refuses to
> get 
> removed. I've even tried rotating the board under the UV light. 
> 
> Help!! Does everyone else have hassles like this? Is there any method 
> I can use to produce good pcb's every time.

Usually it's problems with cleaning all the oil off or incorrect
developer.

I get %100 consistancy from spray-on PRP (green).

> I get %100 consistancy from spray-on PRP (green).


I'vw tried the electrolube PRP spray (green) without any luck. 
Minutes after I've applied the spray over the surface of the board, 
the coating starts to corrupt, first appearing bubbles on the 
surface. Could you explain what procedure do you use?. 

Thanks.

P.D.: I've tried Seno photoresist with great results.

fjimenezg2003 wrote:
> 
>>I get %100 consistancy from spray-on PRP (green).
> 
> I'vw tried the electrolube PRP spray (green) without any luck. 
> Minutes after I've applied the spray over the surface of the board, 
> the coating starts to corrupt, first appearing bubbles on the 
> surface. Could you explain what procedure do you use?. 
> 
> Thanks.
> 
> P.D.: I've tried Seno photoresist with great results.

Scrub the pcb with any abrasive household bathroom/kitchen cleaner
(usually white creamy stuff), then rinse and observe if the surface
stays wet with a thin layer of water or whether it beads (has oil).
If it beads, you'll need to figure out where the oil comes from.

Some cleaning sponges release their own oil, so try cleaning using
a wet paper towel and kitchen cleaner.

Dry the pcb with one or two swipes against a roll of paper towel,
and blow with hot-air gun for 5-10 secs. Brush surface with clean
paint brush to remove any dust and lint.

Hold the pcb horizontal by a corner with some pliers, and spray with
side-to-side strokes with prp to give a smooth coating. The thinnest
coating that allows all the droplets to join and give a smooth surface
is adequate.

Hold for 10-15s to allow solvent to evaporate a bit. Always hold the
pcb horizontal.

Blow/heat with hot air gun for 30 secs to fully dry. This step can often
be from as little as 15 secs to as long as you want. I can tell by feel
that the pcb is around 50-70 deg C.

PCB is now ready. No need to bake for hours or overnight as the
instructions say.

You can do it in ambient (non-fluoro) room light or outdoors (not in
direct sunlight).

In a lightbox with four 8 Watt black-light (whitish tubes) fluros
at 7-8cm from the pcb, exposure of 5 mins is ideal with a decent
transparency printout.

Beware that if you put your pcb against the ink side of a fresh transparency
printout, the prp may peel/flake off during developing. The vapour from the
ink does this. You'll need to dry the printout in front of a fan heater for
10-15mins, or put the pcb against the non-ink side of the printout (can give
less sharp detail tho). Epson ink/transparency has this problem, but usually
has the sharpest detail printouts because epson transparency has a gelatine
coating that absorbs the ink quickly.