Homebrew PCBs

Adam Seychell <a_seychell@...> writes:
> Following the recent posts on BGAs, I'm curious what people consider the 
> lower size limit for SMD to when doing home brew PCBs and projects.

I use 0603 by default; I see 0805 as "big".  I don't usually use 0402
but I don't find it difficult.  I've done 0201 and 01005 with
home-etched boards, just to see what each size is like:
http://www.delorie.com/pcb/smd-challenge/

The nice thing about 0603s is that you can put the pads on 100x50 mil
grids.  Likewise, SOT-323s fit on 100 mil spacing.  See the LED raster
board at http://www.delorie.com/electronics/usb-gpio/

I do 0.5mm pitch TQFP's all the time, no problem.  I've done 0.4mm
pitch too.

I just finished a board with 0.65mm and 0.5mm QFNs on it: 
http://www.delorie.com/electronics/powermeter/

The 0.65mm were easy.  The 0.5mm all worked, but usually required some
touch-ups after reflow.  I.e. flux pen along the edges and wipe an
iron over them, which cleans up all the connections.  The hardest part
is placing them accurately over the paste.  I think you can only
hand-solder the ones where the pad extends up the side of the chip,
but the ones where the pad is *only* on the bottom, I think reflow is
the way to go.

I did some 0.5mm CSPs as a test: http://www.delorie.com/pcb/inkjet/
(view the last picture)

Other than forgetting that they're lead-free (longer reflow time), I
was able to solder them.  The problem I had is that the connections
are "brittle" - flexing the pcb popped the chip off, leaving the
solder balls behind.  Of course, my boards are much more flexible than
stock PCBs.