On Tue, 25 Mar 2008 08:41:56 +1030, you wrote:
>Hi Folks
Double sided boards. If you're doing photo, then the positives should
line up properly. Putting them together, on top of a board, then
drilling the board and positives together gives you matched holes
which can then be aligned.
If you decide to do toner transfer, there's other methods.
I'm somewhat avoiding SMD's and definitely avoiding BGA's. Will
probably have to go to another SMD method, and center pads are not in
the works.
Vias: I've tried both the pins and eyelets, and somewhat prefer
eyelets. Those need to be soldered on both sides, though. I've
gotten designs where the via does not have a parts lead going through
it, which facilitates using parts that do not enable me to solder the
top layer.
Once you do get the design done, though, any one thing on a top layer
becomes much nicer than jumpers. Even eyelets are better, IMHO.
The Dremel is better (often) than the full sized press. Even better
would be a high speed spindle.
Harvey
>
>I was guided here from the 1-Wire weather list[1], so I can stop posting
>off-topic stuff there about board fabrication ;-)
>
>Just by way of introduction, I'm a freelance web applications developer
>(Perl, MySQL, a little PHP, somewhat less C) and general technology
>consultant, having spent many years in IT/network/comms management in an
>engineering multinational.
>
>I have done hobby electronics on and off, in a rather half-hearted way,
>since my early teens. My earliest days were spent working with
>Veroboard which, in hindsight, seems to require more effort to plan,
>assemble and debug than does making up a PCB. First attempts at PCB
>fabrication were using a rub-down 'Letraset' system back in the early
>1990s. I lost interest in this (too much like Hard Work) and only again
>started on PCB fabrication about 7 years ago, when I moved to Australia.
>
>This time around, I had the freeware version of Cadsoft's Eagle, running
>on my Linux laptop. I experimented with printing using both laser and
>inkjet printers, onto OHP transparency film. (I actually found that the
>laser printer with the inkjet film seemed to produce the best results.)
>
>I built myself a UV exposure box using an old file card drawer lined
>with aluminium foil, a pair of UVB tubes and ballast, covered by a sheet
>of thin glass, which sits on top of the rails that used to hold the file
>dividers. This assembly is controlled by the digital timer from a
>deceased microwave oven. (It even says "enjoy your meal" at the end of
>the exposure, which I still find amusing, in a sad way.)
>
>Transparencies are contact printed with the above onto Kinsten
>pre-sensitised board and developed using sodium metasilicate. (I gave
>up with caustic soda - often as not it would remove ALL the etch-resist,
>exposed or not.)
>
>I do my etching using a rocker dish (actually an old Ferrero Rocher box)
>and ammonium persulphate. Having to use thrice-loathsome ferric
>chloride near put me off for life - ammonium persulphate has been my
>saviour.
>
>After three or four years of being too busy/sick/otherwise engaged, I
>find myself with a few projects requiring PCBs[2], so I am getting ready
>to go again. I was going to treat myself to a bubble etch tank but it
>seems that both my sources (at least sources charging sensible prices)
>are out of stock for quite some time. I was rather looking forward to
>the heated tank so that I wouldn't have to fish the PCB out half-way and
>put the solution in the microwave - but looks like I'll just have to
>carry on like that for a while longer.
>
>The one thing that I have acquired this time round is the not-for-profit
>'Standard' version of Eagle. Getting that extra board space is well
>worth it, in my mind. Still waiting for the manuals, which were out of
>stock when I ordered.
>
>Holes are something I hate; I have been trying to use carbide drills in
>a cheap-and-nasty, full-sized drill press. All I will say is that it is
>very expensive in drills. Last week, I took delivery of a Dremel and
>press - hopefully this process should get a bit easier for me. (I still
>prefer larger SMDs though - anything that saves drilling is worth it!)
>
>Issue that I will be needing to address:
>
>∗ I'm still a little shaky when it comes to double-side boards; I have
>yet to perfect a method of aligning top and bottom films in a way that
>suits a) my UV exposure box and b) my shaky hands. If I can get away
>with single-sided and a few jumpers, I generally will.
>
>∗ Tinning boards. Tinning solution is just too expensive for what I am
>doing. Hand-tinning with solder doesn't seem to suit smaller components.
>
>∗ Making vias.
>
>∗ Mounting SMDs with central pads (in addition to the side pads).
>Haven't actually tried this yet, will probably just run a big pad end-to
>end of the device, poking out either end, and put the iron on one of the
>ends.
>
>∗ Mounting SMDs with lots of small pins. At the moment, I'm just trying
>to avoid them altogether. I've read about the toaster oven technique -
>still sounds pretty tricky to me.
>
>The above are challenges that I will be facing when I get back into it,
>but am not worrying about unduly at the moment. When it comes to it, I
>will ferret through stuff on the Group and tap into your combined wisdom...
>
>Cheers
>
>M
>
>
>References
>----------
>
>1 - <http://www.buoy.com/mailman/listinfo/weather>
>
>2 - 1-Wire barometer, Nixie clock, isolation/level conversion boards for
>GPS modules, (wired) remote control board for outside lighting, modified
>quartz clocks that will read Tropical and Lunar years - and various
>other stuff.