--- In
Homebrew_PCBs@yahoogroups.com, "gandolfreefer" <synchronousmosfet@...> wrote:
>
> I really appreciate all the answers; very helpful, and I'm still rereading them all and ruminating on it all....
>
> ....part of figuring out what method I'm going to commit to is I'm now in the philipines, doing medical mission work and R & D, here for quite a while, and I have to consider local supplies, and it turns out getting all my PCB fab stuff sent to me is not as simple as I thought it would be.....
>
> So, I'm now considering building a 3D router table/stepper-controlled, and just route the PCB's....which would also include being able to drill the holes automatically...
>
> The nice thing about this, is that even though it's expensive to setup, once it's done, no worries about type of paper, type of printer, etchant, etc., etc....
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> I just wouldn't be able to do very fine stuff, I presume...but I wasn't planning on making boards for surface mount IC's anyway...
>
Hmm - I've got an EverPrecision EP-2002 machine, which I use to do all sorts of fine-line work. I can happily do a 208-QFP device (and have done, several times).
The machine does have one special feature, it does a surface-scan at intervals of (typically) 10mm across where it will mill prior to milling - the tip is conductive so when the drill meets the copper it completes the circuit and the machine can tell how the copper varies over X and Y. This lets it automatically compensate for that variation which helps a lot with the fine traces.
Milling is done with one type of bit (a "milling" bit :) and drilling with a variety of others (one for each hole size). The milling bit has a V-shape cross-section, but since the machine knows the height of the copper, it can tailor how deep to cut in order to make sure it doesn't over-cut (which can thin the trace to an unusable width, or undercut (which leaves a conductive layer of copper between two traces). All this is automatic.
Doing two-sided milling is almost trivial - you drill two 2-mm holes (one on each side of the copper plate, away from the work-area), drilling down into the sacrificial bakelite beneath, then use pegs in those holes to locate the board in the right place after it's been flipped. Again, the software handles this nicely.
All I use to create the input to the device is Eagle. There's an ULP to generate G-code from an eagle BRD file, but in fact the software that controls my machine accepts a Gerber input, so I just use the CAM processor in Eagle to produce Gerber and I can even draw an outline on the Gerber "milling" layer to get the machine to route out the board from the copper plate.
What I really like about it is the repeatability. I guess I was crap at the toner method because I never could guarantee that I'd have registered the two sides properly, and exposed for the correct time, and etched for the correct time. As often as I got a perfect part, I got an hour of wasted time... With this system I just set it up (5 mins), change drills as necessary (5 mins), do side A (5 mins) and then side B (5 mins)... The side-A and side-B times can get longer if I want to clear out the copper for some reason but normally I use ground/VCC planes and want the copper there...
The machine cost me ~$4000 (IIRC) second-hand from a dealer who had moved on to selling a competitor's product. Best thing I ever bought in this hobby :) For me, it's not the price that matters though, it's the time. With the machine I feel that if I've made a mistake, I can just walk back into the house, change the layout in Eagle, and whack out a new one. In the past, I've sent stuff off to board-houses ready to work on during a planned vacation, only to find that I'd mirror'ed a part and there are now 100 traces going the wrong way - by the time I've corrected the error (10 minutes) and re-ordered the part (10 minutes) then waited for it to turn up (5 days), my vacation was over. Sad but true - it was then that I decided my time was far more important to me than the cost of purchase :)
The only drawback is that you still don't get plated-through holes (although I've found a chinese company that makes something almost-affordable). I'm hoping Santa will drop off a hefty contribution and then I'll be able to get a PTH machine in the New Year...
Simon