Homebrew PCBs

DJ Delorie wrote:
> Adam Seychell <a_seychell@...> writes:
>> So the photoresist professionals say you must expose the resist such
>> that when you put a 21 step gauge, the resist under step 8 should be
>> about "%50" cured. I assume "%50" cured means its gets heavily
>> eroded by the developer but not quite enough to be completely
>> removed.
> 
> More like some parts come completely off, and other parts remain
> intact.  I guess the parts that remain could be thinner, but I didn't
> check.
> 
>> In this situation, the actual energy during PCB exposure will then
>> be 11.3137 times the amount of energy needed for "%50" cure. I think
>> this is what your saying above.

The way i checked mine is to expose a series of areas, where each is
30s longer than the last. I selected a time that was beyond where there
was no visible difference between steps, after developing.