PCB Etching Nightmare

[Charles Jean]

On Sun, 17 Aug 2003 20:12:34 GMT, bjenkins@direct.ca (Bill Jenkins)
wrote:

What exposure lamps did you use? It seems like they didn't expose
long enough to get thru the resist. Try repositioning your layout and
re-exposing again. What type of artwork did you use?

I looked at the replies and your answers, and I think you said the
board was 5" away from your light source.
Did you use a piece of glass to hold the layout against the board?
If you did, and you used just any old piece, it may have had lead in
it. This will impede the uv which exposes the resist. Get a piece of
6mm no lead content plate glass from your local glass house and try
again.

I use F15T8BL uv lamps or the latest eqv in cheap fluroscent holders
I buy from Home Depot. I remove the plastic cover, replace their lamp.
I built a box big enough to hold 4 holders, with 6" high sides and
rabbitted a groove on the top inside edge, for the glass to sit in.
With the holders 3" apart, I can expose a 12" x 12" board without
problems. Since my lamps are 15 years old, I expose 5 minutes and can
easily do .01" traces. I have used MG boards and resist for years,
but now they don't supply resist. I coat my own boards with positive
resist and use MG418 developer mixed .1part dev, to 6 parts water.
This is my "stock" solution. When I need developer, I mix 1 part stock
to 1 part water. It can be cold and put it in a glass dish. I watch
the resist change color, and remove the board when it is quite dark. I
wash it off and put it back into the tray to finish developing, then
wash and etch.
The developer can be reused until it get too dark to see the board.
Keep the used developer in a different bottle.

If you need any assistance please contact me and I will try to help.

Bill Jenkins
On Tue, 12 Aug 2003 20:57:27 -0400, Bennet Williams
brwilliams@adelphia.net> wrote:

I have tried my first positive photo resist etch. The light exposure /
developing step went great. All the exposed parts of the PCB looked
like copper and all the unexposed parts looked like photo resist. So
far, so good. After rinsing and drying, I put my board in a tank of
Radio Shack's best etching solution. Unfortunately, I don't have a
good etching tank, just a pan. After stirring for 30 minutes, barely
any of the copper was etched. After leaving it overnight, still only
1/2 of the copper is etched and some of my traces are starting to
erode - aargh! I used to etch standard PCBs all the time with Radio
Shack etchant with no problem (about 30 minutes etch time). Is there
something special about photo resist PCBs that standard etchant won't
work? Am I doing something wrong? Please help.

BRW
___

I tried looking for some positive photoresist at MG, but couldn't find
any. Where can you get it? Any special tips or tricks about applying
it to the boards?

 

[Bill Jenkins]

Positive photo resist has not been available to us users for three
years or so. At least not in Canada where I am. I bought 5 gallons
from the company who made the original resist that MG sold. Now due to
WHMIS and all those regulations, it's difficult to send it in liquid.
The fines are disgusting.
I had thought that a way to do it would be to coat boards and sell
them. There would be a learning curve to be able to coat them in
quantity for resale. I usually coat a 36" x 12" piece and cut when and
as needed. This works for me.

I coat the boards by first wiping the copper with a paper towel soaked
in some acetone. This removes the surface grease and allows the resist
to coat quite nicely. I pour some resist into a glass or metal tray,
hold the board vertical and use a fine foam brush to "paint" a layer
of resist over it. Excess resist will run down into the tray, for use
again, then when most of the excess is off, I take the board into my
darkroom and place it upright and onto a pad of paper towel to sop up
the resist drips. Then pour the tray resist back into the bottle.

The new resist I have is quite forgiving, it doesn't matter if there
are run lines, making some areas thicker than others, (within reason).
I just expose a little longer and these runs develop out and I get a
etchable board.

Resist is green and exposed resist turns red in the developer making
it easy to see areas needing to be developed longer. As I said
previously, I take the board out of the developer just after it turns
red and wash the developed resist off, then back in for more develop
time.

Hope this helps

Bill




On Mon, 18 Aug 2003 03:01:06 GMT, Charles Jean
<alchemcj@earthlink.net> wrote:

On Sun, 17 Aug 2003 20:12:34 GMT, bjenkins@direct.ca (Bill Jenkins)
wrote:

What exposure lamps did you use? It seems like they didn't expose
long enough to get thru the resist. Try repositioning your layout and
re-exposing again. What type of artwork did you use?

I looked at the replies and your answers, and I think you said the
board was 5" away from your light source.
Did you use a piece of glass to hold the layout against the board?
If you did, and you used just any old piece, it may have had lead in
it. This will impede the uv which exposes the resist. Get a piece of
6mm no lead content plate glass from your local glass house and try
again.

I use F15T8BL uv lamps or the latest eqv in cheap fluroscent holders
I buy from Home Depot. I remove the plastic cover, replace their lamp.
I built a box big enough to hold 4 holders, with 6" high sides and
rabbitted a groove on the top inside edge, for the glass to sit in.
With the holders 3" apart, I can expose a 12" x 12" board without
problems. Since my lamps are 15 years old, I expose 5 minutes and can
easily do .01" traces. I have used MG boards and resist for years,
but now they don't supply resist. I coat my own boards with positive
resist and use MG418 developer mixed .1part dev, to 6 parts water.
This is my "stock" solution. When I need developer, I mix 1 part stock
to 1 part water. It can be cold and put it in a glass dish. I watch
the resist change color, and remove the board when it is quite dark. I
wash it off and put it back into the tray to finish developing, then
wash and etch.
The developer can be reused until it get too dark to see the board.
Keep the used developer in a different bottle.

If you need any assistance please contact me and I will try to help.

Bill Jenkins
On Tue, 12 Aug 2003 20:57:27 -0400, Bennet Williams
brwilliams@adelphia.net> wrote:

I have tried my first positive photo resist etch. The light exposure /
developing step went great. All the exposed parts of the PCB looked
like copper and all the unexposed parts looked like photo resist. So
far, so good. After rinsing and drying, I put my board in a tank of
Radio Shack's best etching solution. Unfortunately, I don't have a
good etching tank, just a pan. After stirring for 30 minutes, barely
any of the copper was etched. After leaving it overnight, still only
1/2 of the copper is etched and some of my traces are starting to
erode - aargh! I used to etch standard PCBs all the time with Radio
Shack etchant with no problem (about 30 minutes etch time). Is there
something special about photo resist PCBs that standard etchant won't
work? Am I doing something wrong? Please help.

BRW
___
I tried looking for some positive photoresist at MG, but couldn't find
any. Where can you get it? Any special tips or tricks about applying
it to the boards?

 

[Bill Jenkins]

Loved these when they were available. Sprayed a little, used the foam
brush to smooth it out and give a level coating.

MG dropped these years ago. Never found any others here. Have seen
them mentioned in newsgroups.

Bill

On 19 Aug 2003 01:39:56 -0400, Allan Adler <ara@nestle.ai.mit.edu>
wrote:

Bill Jenkins wrote:

Positive photo resist has not been available to us users for three
years or so. At least not in Canada where I am. I bought 5 gallons
from the company who made the original resist that MG sold. Now due to
WHMIS and all those regulations, it's difficult to send it in liquid.

What about in a spray can?

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************

 

[Allan Adler]

Bill Jenkins wrote of spray cans of positive resist:

Loved these when they were available. Sprayed a little, used the foam
brush to smooth it out and give a level coating.
MG dropped these years ago. Never found any others here. Have seen
them mentioned in newsgroups.

Others will probably mention them, if they are still available.
But I'm just wondering how hard it is to make one's own spray cans
for this purpose. People do home canning and people use CO2 cartridges
to make their own seltzer and several decades ago, in lieu of canned bug
sprays, people had DIY bug spray using some clumsy mechanical contraption
that came with the liquid insecticide. So maybe it is possible to improvise.

I'm no good at practical stuff like this, although I succeed occasionally,
but what would be wrong with an arrangement using a CO2 cartridge and
positive resist in a seltzer bottle and a suitable kind of nozzle to shape
the spray better, just as some kinds of shower heads do?

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************

 

[JeffM]

I think your new agitator
will quickly tell you whether it is depleted etchant.
I'm lucky that there was a stirring hotplate
in my lab when I got there.
A pyrex baking dish, a teflon-coated magnet
(stirred by the magnet clutch of the hotplate),
and some ceramic blocks to elevate the PCB
make life easy.

CadSoft USA (divison of a German company)
http://www.cadsoftusa.com/
has a nice PCB layout package called EAGLE
(Easily Applicable Graphical Layout Editor).
The free version does 100mm x 80mm double-sided (4" x ~3").
It will output Gerber;
many PCB houses also take native EAGLE files.
Like anything else, it has its quirks but it is very popular.
The upgrade path is also reasonable.
There is a user's newsgroup and a factory-guys newsgroup
(caution: Tilmann doesn't suffer fools lightly).

boards like a nice warm sauna
dan williams

I've decided to...buy a $40 etch tank with a heater and bubbler.
...professional PCB house...
...I don't have the PCB layout software that they need.
Bennet Williams

..After stirring for 30 minutes...
..After leaving it overnight
...some of my traces are starting to erode
Bennet Williams

 

[Terry J. Ilardi]

Allan Adler wrote:

Bill Jenkins wrote of spray cans of positive resist:


Loved these when they were available. Sprayed a little, used the foam
brush to smooth it out and give a level coating.
MG dropped these years ago. Never found any others here. Have seen
them mentioned in newsgroups.


Others will probably mention them, if they are still available.
But I'm just wondering how hard it is to make one's own spray cans
for this purpose. People do home canning and people use CO2 cartridges
to make their own seltzer and several decades ago, in lieu of canned bug
sprays, people had DIY bug spray using some clumsy mechanical contraption
that came with the liquid insecticide. So maybe it is possible to improvise.

I'm no good at practical stuff like this, although I succeed occasionally,
but what would be wrong with an arrangement using a CO2 cartridge and
positive resist in a seltzer bottle and a suitable kind of nozzle to shape
the spray better, just as some kinds of shower heads do?

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************
There's no need to go throught that effort, at least in the US. Your

local hardware store, or at least a local home center such as Home Depot
carries Preval units. These come with compressed cartridges and a small
glass sjar and are made specifically for for the purpose of making your
own spray "cans". They are cheap (under 10 USD) and widely
available-at least in the US.

Terry Ilardi