On Wed, 2008-12-24 at 10:51 -0800, rq1...@q7.com wrote:
> During check-out 'scope the gates during ignition. If there's
> oscillation or hash then a resistor in the 10-100 Ohm range should fix
> it. IMO don't go above ~2k, because at that point the switching
> transition will start to slow down.
I put 100 parts in the schematic/bom, so that's probably what I'll load
on the first boards. Will definitely scope things out.
> If the battery polarity was successfully reversed, i'm as confident as i
> can get without trying it, that stuff will smoke.
> I don't put traces as close to the board edge as you have shown. Same
> for component U4. Typically there would be a design rule of perhaps
> 1.5mm between components/traces and the board outline. This can be
> handled at saw-out rather than in the gerbers.
I ended up pulling everything in at least 10 mils. I realize many would
still consider that tight, but it meets the fab's DFM rules. We'll see
how it goes.
> I'm not sure to what extent your RF layout follows TI, but for example,
> the hole between silkscreen indicators C23 and C24, what will surface
> tension do to those adjacent components? I'm not sure, but it doesn't
> look to me like they'll come out quite straight. But maybe i'm wrong.
I started with TI's layout but didn't stay entirely with it. Andrew
also expressed concern about via - pad distances, I spent some time
pulling them all apart before sending the artwork out. Again, we'll see
how things turn out.
> Typically manufacturers don't recommend full solder paste coverage of
> the exposed pad on parts bigger than ~3-4mm. They want to give the
> solder paste farts somewhere to dissipate. The CC1111 data sheet
> (SWRS033G p41) has a similar recommendation. I haven't seen the
> tic-tac-toe pattern shown in the datasheet before. Seems like it would
> work. All i typically do is reduce the paste coverage to ~60% and leave
> the mask alone, but i don't have any high-volume experience, maybe their
> way is more reliable?
It took me a couple hours, but I finally figured out how to bludgeon
gEDA's pcb tool into giving me a footprint that matches the TI
recommendation including the resist and paste masks.
> I don't like mechanical power switches for high reliability devices, nor
> for rechargeable batteries.
There's nothing to prevent you from soldering a jumper across the pins
to hard-wire the board 'on'. If you're using the connector for the LiPo
as we plan, pulling the battery would become the choice for a hard
shut-down. Keith's comment about hard switches is actually a NAR
requirement that the circuits to the e-matches be interruptable with a
safe/arm switch... there's no requirement that there be power switches.
I like having them, and am willing to pay for good switches and know how
to mount them to avoid thrust-related spurious issues. [shrug]
At this point, we're waiting. Parts order from Digi-Key and the stencil
are likely to get here first, raw boards not promised to ship until the
5th... hoping they're earlier than that, but we'll see.
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