Hi guys,
I realise most people in this group are using toner-transfer, but I did notice a few folk talking about the more traditional photo-etch based technologies. Hopefully a few of the more experienced folk might be able to answer my questions...
I've pretty much given up on TT due to the poor yields (and having wrecked the non-stick coating on more clothes irons than I care to count!), especially on double-sided boards (usually the two layers won't align properly).
I managed to find a used UV exposure unit (a Mega AZ210, the smallest of the double-sided vacuum units) on greed-bay for "not very much money". It weighs an absolute ton, but appears to work pretty decently. That is to say, it beeps, counts down, and the "Lamp Failure" light is off.
At this point, AIUI, I need a few more things:
- Photoresist PCBs
- Developer chemistry
- Another developer tray or two (not hard to find)
- Some OHP transfers (I have some Stabilo inkjet ones, but they've been on my shelf for about five years and are in pretty poor condition)
I'm within a 15-minute drive of the Farnell trade counter, so ideally I'd like to get as much from there as possible (with the possible exception of the dev trays, which may well be cheaper at Maplin). What I am stuck with is a "too many choices" problem.
Farnell appear to stock most of Mega's Microtrak range, which is (positive-acting and uses a metasilicate developer), and a couple of other more standard pre-coated boards (from Kelan and CIF) which develop using the old standby of diluted sodium hydroxide. Other than that, the only difference I can see is the shelf life -- six months for the Kelan boards, a year for the Mega ones, or five years "guaranteed" for the CIF boards.
At the moment, I'm leaning towards using Microtrak (on account of the less-harmful developer), but the long shelf life on the CIF boards makes them a bit more interesting. Has anyone tried any of the above products? I did notice Mike Harrison (of Mike's Electric Stuff fame) singing the praises of Microtrak on his "how to make really good homemade PCBs" page.
As far as OHP transfers go, I've got both a laser (Panasonic KX-P7110) and an inkjet (Canon iP4600) printer. Which one is likely to produce better results for PCB work? On the one hand I'd expect the laser to produce more opaque blacks (at a cost of worse linear accuracy -- e.g. roller slip and paper shrinking in the hot fuser), but the inkjet to be more accurate (at a cost of slightly more transparent ink)...
Lastly, I'd like to know if anyone has any hints on aligning the transfers for double-sided work. I've tried the "align on a lightbox and staple three edges" method with toner-transfer, and somehow the top layer always ends up at least 20 or 30 mils out of line with the bottom. Would I be better off adding alignment holes to the master, drilling these to start, then aligning the transparencies on a lightbox and Scotch-taping them down?
Apologies if you're all getting tired of my questions, it's just that I'd rather like to get this right, and waste as little FR4 as possible!
(And yes, I'm planning to get a metal shear of some description to cut the PCBs. It's just that I've spent about 80% of my budget on the UV box!)
Thanks,
--
Phil.
ygroups@...
