Homebrew PCBs

I've just noticed something that might be useful to other people using 
pre-coated boards.

I was using up some rather old off-cuts while I waited for some new material 
to arrive, without much success. The new material arrived this morning and I 
noticed that the faint yellow pattern on the resist after UV exposure was 
much more noticeable than it had been on the old stock.

Leon
--
Leon Heller
Amateur radio call-sign  G1HSM
Yaesu FT-817ND transceiver
Suzuki SV1000S motorcycle
leon355@...
http://www.geocities.com/leon_heller

> Leon wrote:
>
> I've just noticed something that might be
> useful to other people using pre-coated
> boards.
> 
> I was using up some rather old off-cuts
> while I waited for some new material to
> arrive, without much success. The new
> material arrived this morning and I
> noticed that the faint yellow pattern on
> the resist after UV exposure was much
> more noticeable than it had been on the
> old stock.

Leon,

At least with the brand I have they will
still work years out of date.

The issue is that they loose a lot of
sensitivity and a little bit of contrast.

As long as your photo tool is nice and
dark just try increasing the exposure
time and see how you go.  As an example
2 year out of date boards with a vellum
photo-tool will take me 10 minutes where
as fresh stock will be about 3 minutes.

Leon wrote:
> I've just noticed something that might be useful to other people using 
> pre-coated boards.
> 
> I was using up some rather old off-cuts while I waited for some new material 
> to arrive, without much success. The new material arrived this morning and I 
> noticed that the faint yellow pattern on the resist after UV exposure was 
> much more noticeable than it had been on the old stock.
> 

They could be a different brand/formula photoresist. could you explain 
what problems you had ? Is it negative or positive resist ?
Was it a exposure, developing issue, or copper residue problem. The only 
problem I've experienced with aged resists (>2 years) is a stubborn 
residual invisible film left behind on the copper surface after 
developing. It requires rigorous developing to remove it, and etching to 
remove the rest.

Adam

Quoth Adam Seychell at 2008-06-05 18:23...
> They could be a different brand/formula photoresist. could you explain 
> what problems you had ? Is it negative or positive resist ?
> Was it a exposure, developing issue, or copper residue problem. The only 
> problem I've experienced with aged resists (>2 years) is a stubborn 
> residual invisible film left behind on the copper surface after 
> developing. It requires rigorous developing to remove it, and etching to 
> remove the rest.

Adam - I'll fire the same question back at you - with which brand did 
you have this specific problem - Kinsten?  If so, I'd be interested to 
hear as I've got a load of "mature" Kinsten stock that I'm about to use, 
having been out of the game for a couple of years.


-- 
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy

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

From: "Adam Seychell" <a_seychell@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Thursday, June 05, 2008 9:53 AM
Subject: Re: [Homebrew_PCBs] Out-of-date pre-coated boards


> Leon wrote:
>> I've just noticed something that might be useful to other people using
>> pre-coated boards.
>>
>> I was using up some rather old off-cuts while I waited for some new 
>> material
>> to arrive, without much success. The new material arrived this morning 
>> and I
>> noticed that the faint yellow pattern on the resist after UV exposure was
>> much more noticeable than it had been on the old stock.
>>
>
> They could be a different brand/formula photoresist. could you explain
> what problems you had ? Is it negative or positive resist ?
> Was it a exposure, developing issue, or copper residue problem. The only
> problem I've experienced with aged resists (>2 years) is a stubborn
> residual invisible film left behind on the copper surface after
> developing. It requires rigorous developing to remove it, and etching to
> remove the rest.

The actual material was Fotoboard 2 (positive resist). The main problem 
(with my standard exposure) was incomplete removal of the resist during 
development. I could probably have got over the problem with more separation 
between the tracks and rubbing the board during development, but I wanted to 
use 10/10 mil tracks. It was easier to dump it and order some fresh boards. 
I've had the problem before.

Leon
--
Leon Heller
Amateur radio call-sign  G1HSM
Yaesu FT-817ND transceiver
Suzuki SV1000S motorcycle
leon355@...
http://www.geocities.com/leon_heller

Matthew Smith wrote:
> Quoth Adam Seychell at 2008-06-05 18:23...
>> They could be a different brand/formula photoresist. could you explain 
>> what problems you had ? Is it negative or positive resist ?
>> Was it a exposure, developing issue, or copper residue problem. The only 
>> problem I've experienced with aged resists (>2 years) is a stubborn 
>> residual invisible film left behind on the copper surface after 
>> developing. It requires rigorous developing to remove it, and etching to 
>> remove the rest.
> 
> Adam - I'll fire the same question back at you - with which brand did 
> you have this specific problem - Kinsten?  If so, I'd be interested to 
> hear as I've got a load of "mature" Kinsten stock that I'm about to use, 
> having been out of the game for a couple of years.
> 
> 

I think the resist was Macdermid brand, negative active. I got a roll of 
it several years ago and apply it myself. Because I develop the PCB 
almost immediately after applying, I never have the residue problem. 
Apparently the professionals never leave resist on any more than 24 
hours or it becomes too difficult to develop.
The only way around the problem is to develop about 2 or3 times longer. 
If its really bad then the resist will get damaged due to excessive 
developing before all the residue has had a change to be removed.

I develop in 1% NaCO3 30~40 deg.C as you do for all negative resists. I 
I use a paint brush for the scrubbing.

The problem I found is the residue is invisible so it looks like the 
developing is complete. But when you go to etch , the photoresist 
residues are quickly revealed by un-etched copper areas.

Adam Seychell wrote:
> Matthew Smith wrote:
>> Quoth Adam Seychell at 2008-06-05 18:23...
>>> They could be a different brand/formula photoresist. could you explain 
>>> what problems you had ? Is it negative or positive resist ?
>>> Was it a exposure, developing issue, or copper residue problem. The only 
>>> problem I've experienced with aged resists (>2 years) is a stubborn 
>>> residual invisible film left behind on the copper surface after 
>>> developing. It requires rigorous developing to remove it, and etching to 
>>> remove the rest.
>> Adam - I'll fire the same question back at you - with which brand did 
>> you have this specific problem - Kinsten?  If so, I'd be interested to 
>> hear as I've got a load of "mature" Kinsten stock that I'm about to use, 
>> having been out of the game for a couple of years.
>>
>>
> 
> I think the resist was Macdermid brand, negative active. I got a roll of 
> it several years ago and apply it myself. Because I develop the PCB 
> almost immediately after applying, I never have the residue problem. 
> Apparently the professionals never leave resist on any more than 24 
> hours or it becomes too difficult to develop.
> The only way around the problem is to develop about 2 or3 times longer. 
> If its really bad then the resist will get damaged due to excessive 
> developing before all the residue has had a change to be removed.
> 
> I develop in 1% NaCO3 30~40 deg.C as you do for all negative resists. I 
> I use a paint brush for the scrubbing.
> 
> The problem I found is the residue is invisible so it looks like the 
> developing is complete. But when you go to etch , the photoresist 
> residues are quickly revealed by un-etched copper areas.

Beware of swimming pool NaCO3 as it seems to be contaminated with something;)

> MatthewS wrote:
> I've got a load of "mature" Kinsten stock
> that I'm about to use, having been out of
> the game for a couple of years.

Matthew - it is kinsten stuff I had that I
found to have lost a lot of sensitivity and
a little bit of contrast when many year out
of date.

However sometimes when I order the Kinsten
boards from Perth they come in different
shades depending on batch.  They range from
drab green to bright green.  So there may
even be marked difference in the "past used
by" performance in the one brand.

Quoth Andrew at 2008-06-06 08:46...

> Matthew - it is kinsten stuff I had that I
> found to have lost a lot of sensitivity and
> a little bit of contrast when many year out
> of date.
> 
> However sometimes when I order the Kinsten
> boards from Perth they come in different
> shades depending on batch.  They range from
> drab green to bright green.  So there may
> even be marked difference in the "past used
> by" performance in the one brand.

Thanks Andrew.  The moral of this story is, therefore, to run a test 
strip on every batch of stock.  Have a small strip of board and a film 
of parallel lines.  Partially cover the strip, expose for a minimum 
length of time.  Uncover a bit more strip, expose for a little longer. 
Rinse, then repeat.  Develop - and possibly even etch - the strip and 
see which exposure time worked best.  I think that the term is 'bracketing'.

Cheers

M


-- 
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy

Matthew Smith <matt@...> writes:
> of parallel lines.  Partially cover the strip, expose for a minimum 
> length of time.  Uncover a bit more strip, expose for a little longer. 

Or just get a step transmission gauge and calibrate your exposure.