Homebrew PCBs

Les Newell wrote:
> Hi Mike,
> 
>>Les, I agree that that is the ultimate method of making PCBs 
>>but...you forgot to mention follwing problems:
>>1. You must have a good UV exposure box-- let's not start another 
>>dicussioon today what that means. It is not a trivial issue although 
>>for some it might be.
> 
> I have no problems with a very basic setup. I admit I tend to stick to 
> 12 thou track/gap because I know it will work every time. For one-offs 
> size isn't usually a problem so you can afford to space things out a bit.

I've done 10cm x 10cm boards full of 8mil tracks and spacing for fine pitch
128pin DSP chips and FPGAs using the uv method and there was no track
breakages or shorts.

>>2. Once you have the box you need to calibrate the bloody box and 
>>depending what light it uses the timing might be all over the map, 
>>depending on the preheated condition of the lamp. Depending on what 
>>you are using. Calibration alone is not for weak people either.
>>  
> Leaving the box on for 10-15 minutes before use solves the warmup 
> problem. Calibration is a little tedious but it isn't exactly difficult. 
> You only have to do it once.

I've found with my 4-flouro tube box, results are consistant as soon as
i use it, which is usually less than 1-2mins after switch-on.

I use a 125 Watt HID box mostly now, and it certainly needs a warm-up
of 5-10mins. Exposure works to ~80-90% in 30secs with precoated negative
pcb, so i use 90secs for excellent results. Calibration was easy.

>>3. PCB material: buy ready made (expensive),

I get my pcb vendor to coat and cut a whole panel, and it works
out very cheap. I store the stuff in the fridge.