Homebrew PCBs

Hi Folks

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.

-- 
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy