Homebrew PCBs

I'm wondering if developing photoresist in an immersion tank would be a 
good idea. Unexposed resist must be washed away with help from a moving 
brush or sponge. All professional developing machines use spray. I found 
the resist behaves a bit like clay stuck to the surface and it doesn't 
dissolve away when just rocking the PCB in developer solution.
I was wondering if anyone has tried sticking a two pieces of sponge or a 
pile fabric (see link) to the inside walls of a vertical tank. When the 
PCB is immersed and moved around, it rubs on the fabric.

http://www.jongstit.com/product.php?product=Pile&Type=High%20Pile

I use a 4 liter tank for developing, but I keep the board moving in
the tank.  For SS boards, I double-sided tape the board to a stick to
make a "handle", for DS I usually clip a clothespin to an edge or
something.

Note: I picked up some MG film, and it's especially needful of the
motion - otherwise the film just sits there on the board, mushy.

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

From: "Adam Seychell" <a_seychell@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Saturday, September 12, 2009 10:15 PM
Subject: [Homebrew_PCBs] developing immersion tank


> I'm wondering if developing photoresist in an immersion tank would be a
> good idea. Unexposed resist must be washed away with help from a moving
> brush or sponge. All professional developing machines use spray. I found
> the resist behaves a bit like clay stuck to the surface and it doesn't
> dissolve away when just rocking the PCB in developer solution.

I don't have any problems. The resist just dissolves in about 30 seconds, 
with a bit of agitation of the container. I use precoated positive resist 
boards.

Leon

leon Heller wrote:
>  
> 
> I don't have any problems. The resist just dissolves in about 30 seconds,
> with a bit of agitation of the container. I use precoated positive resist
> boards.


Ok then, it is probably a characteristic of dry film negative resist. Of 
the 3 different brands of negative dry film I have used, all form a 
lightly adhering 'mushy' coating that needs more than just light 
agitation to be removed. Once the PCB goes in the acid etch, any 
photoresist residues immediately become solid again, leading to shorts 
between traces. Its really frustrating when that happens.

Adam.

> Ok then, it is probably a characteristic of dry film negative resist. Of 
> the 3 different brands of negative dry film I have used, all form a 
> lightly adhering 'mushy' coating that needs more than just light 
> agitation to be removed. Once the PCB goes in the acid etch, any 
> photoresist residues immediately become solid again, leading to shorts 
> between traces. Its really frustrating when that happens.
>

That "defect" of negative dry film photoresists is really an advantage to be reliable and stronge. If you clean, laminate, and image properly, the dry film adheres so well that it can be handled with security and without peel-off risks.

The kind of fabric that you point in your first link would be useless since it is too soft. You should use a real sponge with medium abbrasive action.

One solution is to make an spray developing tank, which is easier and not so critical than a spray etching tank.

I use the MG Chemical positive Resist boards 600 series.  I use a glass casarole dish.  Right after you put the board in you can see the resist coming off and soon can make out the traces.  I use a foam brush to lightly go over the board a few times.  If I don't use the foam brush sometimes it may leave a thin film that slows down the etching.

Ben

How about using a nylon brush?

ST

> How about using a nylon brush?
> 
> ST


I would think that a nylon brush would work also.  I started using the foam brushes as that is what M G Chemicals recommended to use.  Whatever you use needs to be something that does not scratch the Resist.

Ben

bhleavi wrote:
>  
> 
>  > How about using a nylon brush?
>  >
>  > ST
> 
> I would think that a nylon brush would work also. I started using the 
> foam brushes as that is what M G Chemicals recommended to use. Whatever 
> you use needs to be something that does not scratch the Resist.
> 

The problem would be damaging fine traces. Some nylon brushes have very 
stiff bristles and would easily destroy photoresist. A toothbrush would 
be too aggressive. A synthetic paint brush is good, but I think it 
doesn't give even abrasion as a foam brush. I too often get spots where 
the paint brush hadn't completely removed resist residue. The foam brush 
seems to do a better job.

Adam

No, professional pcb maker use spray developing only for fine structures,
6mil and down, where 6mil can be done on immersion tank.
The point is, that developing on spray method is critical, because 
it needs anti foam agent and the developer don\ufffdt last long.
For 10mil and 8mil, the immersion tank is prefered, eventually 6mil
with agitation (pump+filter, Co2, mecanical) too.

-- 
Neu: GMX Doppel-FLAT mit Internet-Flatrate + Telefon-Flatrate
f\ufffdr nur 19,99 Euro/mtl.!* http://portal.gmx.net/de/go/dsl02

nisma@... wrote:
>  
> 
> No, professional pcb maker use spray developing only for fine structures,
> 6mil and down, where 6mil can be done on immersion tank.
> The point is, that developing on spray method is critical, because
> it needs anti foam agent and the developer don�t last long.
> For 10mil and 8mil, the immersion tank is prefered, eventually 6mil
> with agitation (pump+filter, Co2, mecanical) too.
> 

All the data sheets I've read have only mentioned developing with spray. 
In my experience the resist simply does not wash away with simple 
immersion or bubble agitation.

 From the data sheet http://www.dryfilmresist.com/pds/kg5100.pdf

"To affectively clean between circuit traces to remove all developing 
residue, the panels must be throughly rinsed
with water at temperatures ranging from 15 to 30\u2103 (59-86F) and pressures 
greater than 1.4 bar(20psi). Poor
rinsing may promote ragged edges, rough plating, step plating, resist 
lifting. Rinsing is a most important part of
the developing process."

Adam

But this is the step after developing, done with water, not developer.

To me it seems the resist will turn into gunk in the developer even
without much agitation, and that gunk is washed away in the next step?

ST

On Sun, Sep 13, 2009 at 11:50 AM, Adam Seychell <a_seychell@...> wrote:

>
> All the data sheets I've read have only mentioned developing with spray.
> In my experience the resist simply does not wash away with simple
> immersion or bubble agitation.
>
>  From the data sheet http://www.dryfilmresist.com/pds/kg5100.pdf
>
> "To affectively clean between circuit traces to remove all developing
> residue, the panels must be throughly rinsed
> with water at temperatures ranging from 15 to 30℃ (59-86F) and pressures
> greater than 1.4 bar(20psi). Poor
> rinsing may promote ragged edges, rough plating, step plating, resist
> lifting. Rinsing is a most important part of
> the developing process."
>
> Adam
>

Adam Seychell wrote:

> I was wondering if anyone has tried sticking a two pieces of sponge or
> a pile fabric to the inside walls of a vertical tank. When the PCB is
> immersed and moved around, it rubs on the fabric.
> 

Developing solutions run something above pH 10, i guess that every easy
to find fabric will not last in such solution.

I just can't answer you with a low space requirement solution that
works. It's dry film and i use TT (until i get a direct print
something). But where i used dry film, after the spray developer we used
a first rinse, then a running water rinse, take look and finally 2 times
in the spray rinse. We only had considerable problems when was time to
change the developer. The spray machine used fan-cone nozzles and the
first rinse the water was only changed along the developer, the spray
rinse used rows of straight nozzles. If you build a spray developer make
it with a square box, the board enters in diagonal and the nozzles are
on the other 2 corners, it's more simpler to build and smaller. 

But i can give one suggestion. I guess by your words you don't have a
spray rinse (very useful for who owns a plating system like you). So you
may try to use a bubble tank for developing and clean water spray right
after, or maybe going from one to other more than once. You won't need
any pump for this since tap water have enough pressure for 8 or so (4
per side) small spray nozzles. If you go right from one to other should
give results. I can't promise that will work since water pH is not high
enough to make dry film soluble. But it can shake the dry film a bit and
is my simplest idea.

I cobbled together something that might work. After experimenting with 
various abrasion materials I found velvet to be most effective at 
removing photoresist in developer. See photo links below.

Top view of my immersion developing tank showing the 200W heater (set 
28C), and the velvet/foam stuck to inner walls. PCB is inserted between 
the velvet and moved up and down to rub on the photoresist. Takes ~80 
seconds to develop.
http://members.optusnet.com.au/eseychell/tmp/dev_tank_top.jpg

Cross section view of padded velvet block. Velvet is made from 
nylon/rayon mix. Contact adhesive applied between velvet and stainless 
sheet. Two screws fasten the stainless steel base plate to tank wall.
http://members.optusnet.com.au/eseychell/tmp/dev_foam.jpg

Test PCB before developing. Pattern of grid with 0.2mm lines & 0.2mm spaces.
http://members.optusnet.com.au/eseychell/tmp/dev_board_1.jpg

50% developed
http://members.optusnet.com.au/eseychell/tmp/dev_board_2.jpg

100% developed
http://members.optusnet.com.au/eseychell/tmp/dev_board_finished.jpg


A 0.2mm diameter hole incompletely developed. The dark copper is etched, 
while shiny copper is covered in resist scum. This problem was caused by 
  overexposure.
http://members.optusnet.com.au/eseychell/tmp/dev_scum1.jpg

A 0.2mm diameter square hole successfully developed.
http://members.optusnet.com.au/eseychell/tmp/dev_good.jpg

Adam

Hi Adam.

Could you give me any details on the actual tank itself? Did you make 
this yourself?

Thanks

Trev

The Foam brushes do work good and they are cheap and will last for some time.

I use the M G Chemicals Positive Resist boards.  When I develop them just after I drop the board in you can see the resist coming off.  I would not describe it as Gunk more like a Blue ink.  Then just lightly brush over the board several times with a foam brush then rinse good with water  I have never used the Neg. resist before.

Ben

Trevor White wrote:
>  
> 
> Hi Adam.
> 
> Could you give me any details on the actual tank itself? Did you make
> this yourself?
> 
> Thanks

Hi Trevor,
That tank is 3mm PVC sheet welded with hot air welder. External 
dimensions are 330 x  36 x 226 mm. Liquid capacity 2.0L. If I were doing 
a new tanks I'd make them from 3mm acrylic sheet bonded with the 
capillary type solvent adhesive.

Adam