Homebrew PCBs

Hi guys,

Here's a step wedge from my latest attempt to make Fotoboard2 work properly:
http://img413.imageshack.us/img413/8161/xyzvm.jpg

Exposure time was 340 seconds for Step 1; step 2 is 1.414x less (divide 
time by 1.414), step 2 is another 1.414x less, and so on. Layering was 
as follows:

Base: PCB
L1: OHP transparency, inkjet printed, printed side flat on PCB
L2: Stouffer 21-step exposure wedge

What I'm getting is severe pitting of the photoresist layer, which is 
causing the photoresist to be breached during etching. My ground planes 
look like they've been applied with a sponge...

I've aimed for a Step Held of 8, which worked fine for other photoresist 
laminates (Microtrak and CIF), but doesn't seem to work on Fotoboard2.

I've also noted that the coating quality on FB2 seems to be somewhat 
poorer than MT -- for a start, the coating seems to "blob" and "bubble" 
towards the edge of the PCB, and in a few cases I've had boards where 
patches and strips in the middle have been had photoresist missing. Most 
odd. Although maybe this is down to the coating method used (FB2 is 
roller-coated; MT is dip-coated).

So onto my questions:
   1) Am I doing something wrong here? Should my "step held" be lower 
for this laminate? The image (link above) suggests a step reduction of 
around 3 or 4 (i.e. reduce time from 340secs to 120 or 85 seconds) might 
be more suitable, but this seems a bit low based on my experiences with 
other photoresists.
   2) What would be a typical exposure time for FB2? Mega seem to shy 
away from making any recommendations, simply stating in the datasheet 
that "exposure times will depend on the UV unit and artwork in use".
   3) For those who are using Fotoboard2, what process parameters are 
you using? Exposure time, developer type, that sort of thing would be 
useful.

Thanks,
-- 
Phil.
ygroups@...
http://www.philpem.me.uk/