Homebrew PCBs

Good idea! I'll try that with another (small) board. Expose a strip 
at one end for 30 seconds then try the developer. If the whole board 
is stripped clean then I know its developer. If not, I'll keep 
trying to see how things go.

Come to think of it, the light did come with a plastic cover for the 
bulb. The fixture itself didn't work properly so I put the light 
into a small fixture I already had and used that. No plastic cover 
for the light. Perhaps it was filtering some of the UV and the 
manufacturer factored in the weaker UV source... Guess I'll find out 
pretty quick.

Thanks much for the fast response. I can start experimenting 
tonight :D As with any new toy, its hard sitting around and waiting.


--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell 
<adam_seychell@y...> wrote:
> The most likely cause of the problem you describe is overexposure.
> For fix problem one you need to determine minimum exposure time. 
You 
> do this by taking a blank board with photoresist and expose it for 
> different lengths of time using a sliding cover. You must let the 
> light pass through the transparency material to compensate for any 
> absorption of light energy. Expose the blank board in steps of say 
30 
> seconds for total of 5 minutes, and leave one section completely 
> unexposed. I use a piece of black plastic and slide it across.
> 
> Prepare your developer and develop the board. You then get a good 
idea 
>   on how long the resist must be exposed for the developer to 
dissolve 
> away the resist. If the section exposed for 30 second completely 
> dissolves in the developer (assuming positive resist) then your 
> exposure times are obviously much shorter than a few minutes. 
Exposure 
> time measurement is essential for anyone first starting out with a 
> particular photoresist and exposure unit.
> 
>