I finally got round to trying out the blue solder mask I'd ordered.
It's an extremely viscous fluid, which doesn't flow noticeably. One consequence of that is that if one applies it with a roller, it doesn't then settle flat, the way paint would. Rather, one's left with an imprint of the roller sponge surface.
The curing time prior to developing depends on the thickness of he layer, and I found that the thickness is next to impossible to get consistent, even when covering it with a plastic sheet and using a laminator.
The stuff itself sticks to anything, and either just doesn't dry unless exposed to UV, or takes a very long time - days - during which any misplaced drop is waiting to be spread around the house (I think I've avoided that so far).
In short, it's a right pain. Maybe one can eventually manage to use it, but I think it's more trouble that it's worth.
Well, it _is_ UV cure -- a good UV cure material wouldn't cure out at all without being exposed to UV, and would pop off either immediately or in a nicely controlled manner when it is.
Have you tried leaving it in the sun?
It's designed for solder mask, which certainly appears to flow out just fine on all of my boards -- it may be designed to flow out when you warm it. I'd hit it with a heat gun and see what happens.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
BTW: if your exposure mask is good enough and you keep it dark during the etching process, you can do a second exposure with only the pads and vias transparent, and can selectively remove the photoresist for those. The remaining resist is not quite as good as a proper solder stop, but usually works, if your iron is not high-powered. Also, it's free.
If I lived somewhere where prototype boards could be sourced at a reasonable price and lead time (say a week), I wouldn't bother. In practice, I either have to wait a month (and that can be variable), or pay a high price either for the board to be made locally (I'm in Australia), or for it to be couriered from somewhere where manufacture is cheaper (e.g. China).
I'm using a UV lamp box I made, which works perfectly well on the etch resist. Indeed, it works on the solder mask - but if the layer's too thick, only the surface cures (and attaches to the plastic sheet covering it), leaving the underlying material uncured. I made quite a nice solder mask on the plastic sheet - which is useless, of course.
ExpressPCB has almost zero lead time,but there are "gotchas" being fixed trace widths, minimum spacing and maybe a few other details one might not like. Their ONLY option for delivery is expensive: FedEx Air. So....sounds like a reputable Chinese PCB house is in order.
OTH,if you are young and rather competent in the fields of PCB making and sales, start your own company and beat the competition on price and thru-put.
If the glop has a thinner or solvent that could be used as a thinner, then dilute it like crazy to make it thin enough to easily pour on and spin (or pour off the board after leveling); let thinner dry in dust-free environment. Makes to perfectly uniform coating that is a joy to use in production. I did that trick with KPR resist, using Benzene as the (highly compatible) thinner, and a TCE (home-built) vapor degreaser (a LOT less expensive than their "developer" which does a poor job).
Maybe you're supposed to spray it on with an airless spray (perhaps thin it a little) and then expose it with a mask covering the solder pad locations and finally wash off the excess.
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