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