Homebrew_PCBs

Matthew Smith <matt@...> writes:

> Hi Folks

Hi!

> 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.

Beware that Eagle has some nasty DRM built-in to it, some folks have
found themselves locked out of their own designs due to it. Be *very*
careful about any library you use other than that which you create
yourself. I use gEDA and PCB (and help maintain PCB), which have no
limits, no cost, and use text file formats.

> Last week, I took delivery of a Dremel and press - hopefully this
> process should get a bit easier for me.

I use a dremel in a home-made press. Since switching to my own press,
I haven't broken a drill bit (except when I drop them on the floor)
and I use mostly 13 mil (vias).
http://www.delorie.com/pcb/dremel-stand/

> (I still prefer larger SMDs though - anything that saves drilling is
> worth it!)

I use mostly 0.5mm pitch and 0603 discretes. But then again, others
have commented on my small-part-insanity.
http://www.delorie.com/pcb/smd-challenge/

> * 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.

My technique (although for toner) is to tape on a paper pattern and
drill through some alignment holes just outside the board outline
(i.e. in the "waste" board). Then I poke pinholes in the toner sheets
so I can align each side to the holes. I can get within a few mil
this way.

> * Tinning boards. Tinning solution is just too expensive for what I am
> doing. Hand-tinning with solder doesn't seem to suit smaller components.

I use MG Chemical's "Liquid Tin". Just soak for a few minutes and rinse.
http://www.delorie.com/pcb/liquidtin/

> * Making vias.

I use 13 mil holes with a 28 mil pad, which is just enough to ensure
copper all the way around the hole. I wrap some 20 mil solder around
the board to hold it up off my work surface, and cut a bunch of
lengths of wire wrap wire. Each length is about 2-3 inches. I flux
the wire, and, for each via, poke it through the hole, solder the top,
and cut it off. This leaves all the vias with the wire sticking 20
mil out the other side, so just flip and solder them all.

> * 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.

Hot plate and solder paste. http://www.delorie.com/pcb/hotplate/
and http://geda.seul.org/projects/djs_pcbs/

Others have put large vias under the pad, so they can solder through
from the other side.

> * 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.

Hot plate again. It's *really* easy to fix shorts with copper braid,
so aim for slightly more than enough paste.