[Arm-netbook] HDMI High-Frequency Layout: Recommendations--Taper

Richard Wilbur richard.wilbur at gmail.com
Sat Jan 6 06:24:35 GMT 2018

On Jan 5, 2018, at 21:28, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> still doing these tiny little changes, it's just the way it goes:
> every time you look at the board in close zoom, it's like... "hmmm,
> yeah that could be improved" and this latest one, it's the (now pair
> of) capacitors for the main DDR3 power stabilisation.
> previously this was a single 0805 capacitor lined up vertically.
> there was plenty of connecting VIAs down to layer 4 DDR3 1.5v power
> plane.... but because there were a MASSIVE array of tracks underneath
> the GND pads there were no GND vias.  whoops.  and when replacing with
> two 0603 4.7uF capacitors, i maintained that mistake.
> i decided to turn both 0603 capacitors horizontal and then to beef up
> the number of GND vias.  this has the unintended side-effect of
> drilling quite a lot of holes into the layer 4 DDR3 1.5v power plane
> however as the GND vias are at the edge of the plane i consider this
> acceptable.  i have however made sure that the plane is free of holes
> for getting the actual 1.5v power *in* to the plane, if that makes any
> sense.

Good stuff.  Should make the power supply more stable for the DDR3 RAM chips!

> anyway a few more things like this... richardt if you're happy with the
> beginning of the HDMI area i'll send the gerbers off straight away.

I am happy with the HDMI but I was going to ask about silkscreen on pads--I saw several instances of silkscreen on areas you'll want covered in solder.  Sorry I didn't bring it up earlier.  Not a problem if you aren't having the silkscreen printed.  Your board fab may also do the right thing and move the offending notations.

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