by Doug Coulter » Fri Aug 10, 2012 3:09 pm
I do pcb's here all the time. Essential if you want to do anything SMD, and a lot of parts are SMD-only these days. I've never really seen the toner transfer thing work well enough for what I do. I buy presensitized positive resist boards. I use the laser printer to make the artwork on overhead projector film. I built a UV source on a timer and a printing frame I can use for double sided, even. You no longer need UV, the new boards will do with a regular incandescent (if you can find one these days). The developer is a 1/10th saturated solution of lye - not super friendly, but not super bad either - it washes off your hands easily if you get some on them, it's not going to dissolve you in seconds. It's been the etchant, most use ferric chloride, that's been a pain. Not unsafe (unless you're mixing up your own, talk about exothermic reactions!), but just plain nasty - stains even quartz, permanently. I have found NOTHING that removes these stains, even HF (talk about the cure being worse than the disease).
I'll do it even if I just need one or three units of something. They are easier to "edit" than real wiring - even after the fact - just cut a trace or add a wire as needed, most of the other work is just plain done, and it's going to work and last a lifetime. If I'm going to need a bunch - I still want to see one work here first, before sending off a large order. Too many times I've seen a connector wiring perfectly reversed or some other show stopper to put that money at that much risk.
HCl is a mixed bag around here. It's essential for pickling things I'm going to electroplate. As such, I have a 5 gal pail of it, diluted, to dunk things in - also super to strip off galvanizing an an area about to be welded - one time of zinc-fume-sickness will make you do that one every time. Of course, the top is on the pail when not in use. I note the author of that article got the very best brand I've come across. The stuff at lowes or most hardware stores is junk - already contaminated with iron and yellow. That stuff I have to get at the local concrete company, it's the top purity out there. Probably doesn't matter for this, but that's not the only chemistry I do - I also make my own fluxes for soldering/brazing for example,
Rusting isn't always bad - the key to really nice gun blueing is controlled rusting...
On the other hand...my soon-to-be-ex wife had a TV, and she wanted to have it up here where I hang out instead of the building she was supposed to hang out most of the time in (long story, but upshot - glad she's gone, whew). I hate TV. I conveniently made room for her tv on the bench just above that pot of HCl. Heh, you can guess what happened only 6 months later. Of course I "forgot" and left the top off the pail a few times to speed things along.
Honest, Chris, all this junk stays in the bottles just fine - it doesn't jump out at you. I use plastic trays (like what we get meat from the grocery store in) and either rinse them or just toss them out after pouring the stuff back into the storage jugs - plastic milk jugs work well for that - use a funnel for no spills, and do all this someplace other than your main nice room. You just use normal caution and wash the hands after - unless you get ferric chloride on them, in which case you wait weeks for that skin to die and be replaced with unstained stuff (or gosh, just wear gloves).
At any rate, next time I do boards I'm going to try this stuff - I'll tell y'all how it works.
A PCB house I used to work with did an additive process, though they did start with ultra thin copper cladding - then build it up after drilling the boards and dunking them in PdCl to get the holes conductive so they'd plate too. I don't get that fancy - I don't have a robot to pre-drill the holes for example, but I can get the sides aligned and just solder a short piece of WW wire through for vias. Once I get a design I want, I can then go to apcircuits in Canada for boards. Their proto-1 service is both cheap and has an additional advantage - they plate on solder, just the right amount to make sticking down SMD's easy with only flux. You can then add solder to taste, but this makes putting the parts down and making them stay a heck of a lot easier. This actually is much superior to their more expensive service with solder mask - it tends to hold the chip pins a little off the board - fine for the "real" way most people make those - solder paste through a mask, then vapor phase reflow, but a disaster for hand-soldering. The mask alignment is never perfect either, which can make for issues.
I use another trick, a little OT, but here it is - I make the tracks under big quad flatpacks about 1-2 mils narrower than the pins (opposite of normal practice). If you're then using a metcal solder station/horse hoof tip to wipe down the row with solder - any bridges are between the pins, not down on the board, which makes it simple to come back and just wipe them off with a clean tip. It's far easier than doing a through-hole, to be honest. I discovered this on a CPU board I did for MusiCad - only the tms320-c31 was SMD, and it was far easier to stick down that 132 pin flatpack than all that static ram I had in the design - by orders of magnitude. Now, SMD discretes are still a PITA, but hey...so is folding up component leads to stick them in.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.