Homebrew PCBs

Gary

Thanks for reply. Helpful.

I also want to get rid off the bicromate. As you mentioned can you name the chemical name so that i can also try that.
Secondly the adhesion problem on copper i am also facing - Can i try other things in resin other than Elmer glue. Any idea,.

ATHAR 

--- On Fri, 7/30/10, garydeal <garydeal@...> wrote:

From: garydeal <garydeal@ucom.net>
Subject: [Homebrew_PCBs] Re: Photo Resist Gelatin Bicromate Process
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 30, 2010, 4:07 PM







 



  


    
      
      
      >But any way you cut it, ammonium dichromate is a nasty substance that just 

>loves to crosslink collagen; of which there is plenty in the human body. 

>So be careful with this stuff.



Yes, quite. If you've seen the "Erin Brockovitch" (sp?) movie, the 

substance that was getting into the groundwater (and ruining people) was 

hexavalent chromium, which is the ammonium, potassium, sodium, etc., 

dichromates.



I believe that the information on chromated gelatin over at the 

holography site includes something regarding mixing waste dichromate 

solutions and wash water containing dichromates with used photographic 

developer, which changes it to an insoluble form. This drastically 

reduces it's impact.



I used to be involved in the corporate use of this process on a 

relatively small scale, and they eventually had to stop and find a 

replacement. An industrial silkscreen-making goop (diazo?) ended up being 

the thing, it dropped right into the process (being sprayed on, resisting 

acetone, coming off with bleach, etc). The toughest part was figuring out 

how to measure it out for amounts much smaller than the one-gallon kit.



In the above process, I was aware that a competing company would add 

Elmer's white glue to the mix when they had adhesion problems with the 

plain gelatin/dichromate mixture. I'm not sure if they realized that the 

glue was also crosslinking.



The green pigment may not be the best choice for sensitizing (the 

base mixture requires UV). Look on the holography site for information on 

red-sensitive DCG - although then you'll have to use a dark green 

safelight, which gives rise to the phrase "working in the green 

darkness". It's probably easier to come up with enough UV, I expose UV 

sensitive resist with a cheap 500 watt halogen with the UV shield glass 

removed (~4 minutes at 18 inches through an old glass-topped photo 

contact printer).





    
     

    
    


 



  






      

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