On 22/03/2010 18:04, Philip Pemberton wrote:
> 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,
I don't have any problems using Fotoboard 2 with my home-made UV
exposure unit (two tubes about 15 cm from the glass. I found the optimum
exposure level (11 minutes) by using the old strip technique that used
to be common in photography. Transparencies are printed on Mega's
Jetstar Premium film using an HP 5940 printer (1200 dpi). Over exposure
doesn't seem to matter too much, I've missed the alarm before now and
probably left it for 20 minutes, on one or two occasions.
I develop in NaOH (12 gm/litre). It takes about 20 seconds.
I've found that the edges of the material sometimes don't work properly,
probably because it's been exposed to fluourecent lighting, which has
leaked under the protective coating.
It's important not to use outdated material, the resist seems to go off
after about six months.
Leon
--
Leon Heller
G1HSM