Homebrew PCBs

On Tue, 25 Mar 2008, Matthew Smith wrote:
Hi,

> The one thing that I have acquired this time round is the not-for-profit
> 'Standard' version of Eagle.

Unfortunately, possibly too late for you now since you've paid, and
probably therefore will want to stick with Eagle... but if you're running
Linux, then PCB is a great PCB layout package:

http://pcb.sourceforge.net

with no arbitrary restriction on size or numbers of layers, and it's Free
as in freedom. I've done some fairly complex layouts using this software,
including a Z80 single board computer (Eurocard sized, double sided), a
remote SPI driven nixie display (again, Eurocard, but single sided), and
I'm just finishing off a rather densely populated 4 layer board (which I'm
going to send off to get fabricated...although some on the list have done
4 layer homebrew PCBs).

> * 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.

You might find toner transfer is easier for double sided. My second ever
board was double sided, and I've never had a 'failed' board yet using
toner transfer.

Basically, for registration, I use a bright light source (sunlight works
well) and put the transfer sheets face to face, then use the light to get
them lined up. PCB prints bold alignment lines to get it close - to get it
perfect, I just line up the pins and vias. Then I tape the sheets together
at one end to form a hinge, re-check alignment, and slip the board between
the sheets and get ironing. Usually, registration is absolutely spot on
using this method.