[Arm-netbook] EOMA68-A20 2.7.4 pre-production prototypes received and working

Luke Kenneth Casson Leighton lkcl at lkcl.net
Sat Jun 17 10:17:07 BST 2017

On Fri, Jun 16, 2017 at 8:40 PM, mike.valk at gmail.com
<mike.valk at gmail.com> wrote:

> Bleh. It looked so pretty in my mind. ;-(

 i knoow...   btw can you possibly investigate why, when you hit
"reply", the ">"s are not added?

> So different layers have different copper thickness.

 in a stack you tell the factory what thicknesses you want, as well as
what material in between, and what thickness of that, too.  so you get
different capacitance on different layers.  thus, the problem is: you
cannot guarantee the impedance will be identical on different layers.
so having differential pairs on different layers is the worst possible
thing you could do.... *unless* you have access to PCB simulators.
which are ultra-expensive.


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