Homebrew PCBs

Leon Heller wrote:
> 
> 
> For home use, collimated light isn't really necessary, as most of us can't 
> create high-resolution artwork that can make use of it. In fact, none of the 
> low-cost UV exposure boxes that one can buy use it, they just have two or 
> four tubes quite close to the PCB/artwork. I get quite good results with a 
> couple of tubes about 15 cm from the PCB. Exposure is quite long at 13 
> minutes, I keep meaning to add another two tubes.
> 


I agree, the level of collimation depends on the resolution required. 
However I found the artwork produced by inkjet printers has sufficient 
high resolution to require a collimated light source to get the most out 
of the printer. For standard 0.35mm (1.3mills) dry film photoresists and 
traces/spaces <= 0.3mm (12mils) then a collimated light source should be 
used. At times I've needed to put a 0.18mm (7mil) trace between a two 
pads on a 1.27mm pitch SOP package. At this detail, the developing and 
etching steps can just as easily cause problems.

In general the smaller the features on the PCB the more attention must 
be paid to each step of the PCB processs. They all come into play when 
the detail goes up.