Homebrew PCBs

I once tried to built a bubble agitated developer but found the 
bubbles could not reliably remove the dry-film from the board. In the 
end I found best results using something similar to what Tom described 
  with the brush.
I also agree with Tom that you could be suffering dry-film residue, 
which is an invisible scum left behind after developing and is 
impermeable to the etchant. I am only familiar with negative dryfilm, 
are you sure the boards are this film or is it positive pre coated PCB 
material often sold at hobby shops ?
The way to check if you have a residue problem is after about 1 minute 
in the etchant you should see the copper turn matte pink. If it still 
shows shinny scrubbing marks then its dry-film scum. This happens when 
the dry film has been on the board longer than a few weeks. I have 
some stuff that's over a year old and is a problem to develop. The way 
to develop these boards is to extend the developing time (brushing 
over the board for upto 3 minutes). I put it in the etcher and if the 
copper doesn't become matte pink over the entire board then I take it 
back to the developer and brush over it for another minute. The second 
pass usually gets it all. I apply my own dry-film these days and 
develop the board the same day so I never have residue problems.

Ron Amundson wrote:
> I'll give the brush solution a try tomorrow. As I purchase my boards pre
> laminated with dry film, I'm sure cleanliness is not the issue, but
> underdeveloped dry film resist probably is.
> 
> I do my developing in a tray with agitation too, looks like I'll need to set
> up a simple to do spraying.
> 
> Thanks
> Ron
> ----- Original Message -----
> From: <twb8899@...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Tuesday, January 21, 2003 10:09 AM
> Subject: [Homebrew_PCBs] Ferric Chloride
> 
> 
> 
>>Ron mentioned in a previous post that he was getting uneven etching
>>with ferric chloride. When this happens it's usually due to under
>>development of the photoresist. I am assuming that dry film resist is
>>being used. The best way to develop dry film is with a spray tank set
>>up with a 1% sodium carbonate (soda ash)solution. Find out how long
>>it takes to "break through" to bare copper and then go about that
>>same time again for final developing. For example if the bare copper
>>shows up in 1 minute then continue the process for an additional 1
>>minute and then you can etch.
>>
>>Another good idea is to make up a tray of weak etchant from a couple
>>of ounces of ferric chloride in one gallon of water. If a developed
>>board is put into this solution for a minute or so the areas that are
>>fully developed will turn a dark color and the under developed spots
>>will show bright copper. This will amaze you the first time you see
>>it because the panel still has some dry film "scum" on the surface
>>when the board looked like it was fully developed. If the board has
>>scum, just put back in the developer for a bit longer and try again.
>>When a uniform dark color appears across the entire surface you will
>>be ready for final etching and obtain excellent results.
>>
>>If developemnt is being done in a tray, try using a very soft
>>bristled brush to gently work the solution across the board surface.
>>This will help to break through any scum on the board. The bottom
>>line is that this scum must be removed or you will never obtain
>>uniform etching. Hope this idea helps out.
>>
>>Tom
>>
>>
>>
>>
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>>
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> 
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