[Arm-netbook] libre 15in laptop progress: pcbs and parts

[Luke Kenneth Casson Leighton]

okaaaay sooo, whew :)

spent the entire day online looking up digikey part numbers... eyes
are going funny (square _and_ crossed....) but i got there.  65 items
from digikey, then another 5 or so that need to be sourced from china
(only) -  a special narrow 3.5mm jack which can re-route both outputs
to speakers if the headphone jack's not plugged in, a CM108AH USB
Audio IC, GL850G hub, SY6280 USB power control IC and a SY7201 step-up
converter for the 3.5 watt LCD backlight.  they're all easy to get...
just not outside of china.

i also ordered qty2 of the PCB1 (main laptop interface board) and PCB2
(embedded controller, keyboard/mouse) as "bare prototype" boards,
0.5oz copper, from eurocircuits.  the 4 boards came to a total of $EUR
100, which is pretty amazing for europe, and they were very tolerant
about me making a mistake and having to cancel the order, make some
changes, and re-submit even after i'd actually paid (they don't
normally allow that!).

i did have to redesign all the PCBs to use a 24mil surround around the
10mil drill holes - and change all the track-to-track min clearance to
7mil and the min track width to 8mil.  this was the *absolute* minimum
that eurocircuits "prototype pool" would allow.

*sigh* i'm also going to have to go back and adjust the casework to
cope with a 1.6mm PCB thickness.... i'd designed it for 1.2mm and yes,
really, 0.4mm makes a huge difference, it will be about a day's work
to adjust all the 3D parts.

the power board (PCB3).... yyyeah i am having fun, there.  the example
board layout i got from linear tech's online resources says that 2oz
copper is needed.  *nobody* does 2oz copper with anything below 12mil
track and 12mil track-to-track.... yet the distance between the pads
on an LTC4155 are 7.8mil (0.2mm)... what's up with that??

soo... hmmm, i'm looking up current handling calculators online to see
if i can get away with 1oz copper.... and i believe i can.  which
would be good, if it was the case, as i can go to eurocircuits....
BUT, i would have to make a "standard" order not prototype because the
proto boards are only available in 0.5oz copper...

oh!  and the 1kW IR solder station arrived.  it's.... much more basic
than i was expecting :)  there are two thermistors that you're
supposed to like stick somewhere around the PCB when the 800W
pre-heater and the 200W IR lamp are on....

.... i got them in the wrong place on the first board i tried (a 1in
prototype board) and was fascinated to see it sizzle within about 15
seconds, this little black spot about 8mm in diameter appeared and i
spent the rest of the day with the smell of cooked fibreglass up my
nose...  mmmm looovely :)

anyway it appears that it actually works, must get some solder paste,
start doing some desoldering of components on random boards as an
experiment, it'll be fuuuun....

l.