Homebrew PCBs

Hi guys,

I got a chance to do some more experimenting with the dry film photo 
process.  I did a "step" test doing various exposure times and found 
out that the UV lamp I bought for this purpose simply isn't powerful 
enough.  I have a regular light bulb of the right color range and 
tried that with much better results - exposure time through 
transparncy of only 3 minutes.  I have much more experimenting to do 
to get it better, but was able to make my first board all the way 
through the etching process.

A couple of questions...

1) When I used to have a black and white dark room, I discovered 
that the developer would last a long time and could be reused over 
and over again.  I realize the developer for negative resist film is 
much different than photographic developer, but suspect that the 
chemical will stay "active" and as such, I could be reusing it.  Has 
anyone tried this?

2) While doing the exposure / developer tests, I realized very 
quickly just how tough this resist is.  I was scrubbing with a 
scotch brite pad vigorously without removing the resist. This leads 
me to the next question. Should the resist be removed or can it be 
left on the copper?  If you have to remove it, how do you do it?

Thanks in advance!

Chris

----- Original Message ----- 

From: "lcdpublishing" <lcdpublishing@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Saturday, October 25, 2008 1:21 AM
Subject: [Homebrew_PCBs] Dry film, photo resist - progress and question...


> Hi guys,
>
> I got a chance to do some more experimenting with the dry film photo
> process.  I did a "step" test doing various exposure times and found
> out that the UV lamp I bought for this purpose simply isn't powerful
> enough.  I have a regular light bulb of the right color range and
> tried that with much better results - exposure time through
> transparncy of only 3 minutes.  I have much more experimenting to do
> to get it better, but was able to make my first board all the way
> through the etching process.
>
> A couple of questions...
>
> 1) When I used to have a black and white dark room, I discovered
> that the developer would last a long time and could be reused over
> and over again.  I realize the developer for negative resist film is
> much different than photographic developer, but suspect that the
> chemical will stay "active" and as such, I could be reusing it.  Has
> anyone tried this?

NaOH developer can be reused many times. NaCO3 is probably similar, as it 
forms a weak solution of NaOH which actually does the development..

>
> 2) While doing the exposure / developer tests, I realized very
> quickly just how tough this resist is.  I was scrubbing with a
> scotch brite pad vigorously without removing the resist. This leads
> me to the next question. Should the resist be removed or can it be
> left on the copper?  If you have to remove it, how do you do it?

It can be soldered through, but it's best to remove it. Iso-propyl alcohol 
works very well for positive resist - I rub it with a moistened paper towel. 
It probably works for negative resist, as well.

Leon

"lcdpublishing" <lcdpublishing@...> writes:
> chemical will stay "active" and as such, I could be reusing it.  Has 
> anyone tried this?

So far, my developer and stripper haven't "aged" and I use them very
infrequently.

> Should the resist be removed or can it be left on the copper?

In my case, I strip the film off with a NaOH solution, and tin plate
the copper to protect it.

lcdpublishing wrote:
> Hi guys,
> 
> I got a chance to do some more experimenting with the dry film photo 
> process.  I did a "step" test doing various exposure times and found 
> out that the UV lamp I bought for this purpose simply isn't powerful 
> enough.  I have a regular light bulb of the right color range and 
> tried that with much better results - exposure time through 
> transparncy of only 3 minutes.  I have much more experimenting to do 
> to get it better, but was able to make my first board all the way 
> through the etching process.

Most people use those UV "insect zapper" florescent tubes, also known as 
black lights ("BL") which emit a bluey violet colour. Don't waste your 
money on filtered black lights used for special effects. You can get 20W 
compact florescent blacklight lamps too these days.

> 
> 1) When I used to have a black and white dark room, I discovered 
> that the developer would last a long time and could be reused over 
> and over again.  

There is no shelf life for sodium carbonate solutions, other than water 
evaporation. The Na2CO3 is obviously consumed during development, but 
its actually very small. The data sheet for my resists specifies a 
developer loading capacity of about 9.4E-6 m^3 of resist per litre of 
developer. For your average 40um dryfilm resist and double sided PCB 
with 50% trace coverage then that works out to be 0.23 m^2 of PCB area 
(485 x 485mm square) per litre of developer.


> 2) While doing the exposure / developer tests, I realized very 
> quickly just how tough this resist is.  I was scrubbing with a 
> scotch brite pad vigorously without removing the resist. 

That's normal. You strip it off in 2~5% NaOH, in 5 minutes at room temp. 
  Don't waste your energy scrubbing it off, just let the NaOH do its 
work and it will lift off before your eyes.

tanning tubes (easy to get in europe) works great.

I'm glad to hear (read) that more and more dry film users are here.
for over a couple of years im working with it and found out that a 
normal exposure unit isnt wath you want with negative films.
Specialy with small smt pwb, the lines that are close together melt 
together with negative film.
Or with positive film they get real thin.
I lower the 12 tube's to 60/70cm 25in. and close to te glassplate a 
collimar grid like think&thinkers idea.
i will shoot some pictures this week of it

gr Roel


--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell <a_seychell@...> 
wrote:
>
> lcdpublishing wrote:
> > Hi guys,
> > 
> > I got a chance to do some more experimenting with the dry film 
photo 
> > process.  I did a "step" test doing various exposure times and 
found 
> > out that the UV lamp I bought for this purpose simply isn't 
powerful 
> > enough.  I have a regular light bulb of the right color range and 
> > tried that with much better results - exposure time through 
> > transparncy of only 3 minutes.  I have much more experimenting to 
do 
> > to get it better, but was able to make my first board all the way 
> > through the etching process.
> 
> Most people use those UV "insect zapper" florescent tubes, also 
known as 
> black lights ("BL") which emit a bluey violet colour. Don't waste 
your 
> money on filtered black lights used for special effects. You can 
get 20W 
> compact florescent blacklight lamps too these days.
> 
> > 
> > 1) When I used to have a black and white dark room, I discovered 
> > that the developer would last a long time and could be reused 
over 
> > and over again.  
> 
> There is no shelf life for sodium carbonate solutions, other than 
water 
> evaporation. The Na2CO3 is obviously consumed during development, 
but 
> its actually very small. The data sheet for my resists specifies a 
> developer loading capacity of about 9.4E-6 m^3 of resist per litre 
of 
> developer. For your average 40um dryfilm resist and double sided 
PCB 
> with 50% trace coverage then that works out to be 0.23 m^2 of PCB 
area 
> (485 x 485mm square) per litre of developer.
> 
> 
> > 2) While doing the exposure / developer tests, I realized very 
> > quickly just how tough this resist is.  I was scrubbing with a 
> > scotch brite pad vigorously without removing the resist. 
> 
> That's normal. You strip it off in 2~5% NaOH, in 5 minutes at room 
temp. 
>   Don't waste your energy scrubbing it off, just let the NaOH do 
its 
> work and it will lift off before your eyes.
>