Homebrew PCBs

----- Original Message ----- 
From: "dl5012" <dl5012@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Tuesday, February 07, 2006 7:41 PM
Subject: [Homebrew_PCBs] Re: Toner transfer experiments and a fix for cheap, 
low-temp laminators


> Hi Leon,
>
> What resist (positive or negative) are you using and where do you buy
> it?  How do you apply it to boards?  When I was in junior college, we
> used to spin it on.  How long will presensitized boards keep?  How do
> you dispose of your expended chemicals?  I'm on a septic system and am
> very careful about what I put down the drain because I or my neighbors
> will eventually end up drinking some of it...

I use pre-coated FPC-16 board (positive-working resist) from Mega 
Electronics:

http://www.megauk.com/

The board is best used within six months, I've found.

I simply pour the NaOH and any exhausted etchant down the drain. The small 
amounts I use don't matter.


>
> I'd like to try doing boards with a positive resist.  It would
> probably give more predictable results, once you got exposure and
> developing times down, with less pitting.

My UV exposure takes 13 minutes, but I can get on with something else during 
that time. Etching is in hot FeCl3 with continuous manual agitation; it 
takes about 5 minutes with fresh etchant. I use a large plastic container 
half-filled with hot water, with a smaller container in it holding the 
etchant and PCB. The etchant lasts for several weeks if I occasionally add a 
little HCl. I dispose of it when the etching time gets to about 15 minutes.

Leon 

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