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

[mike.valk at gmail.com]

2017-06-17 11:17 GMT+02:00 Luke Kenneth Casson Leighton <lkcl at lkcl.net>:
> 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?

I was using gmail in HTML mode, apparently. I've found a switch.
Hopefully this works better.

N.B. Was this a problem before the auto HTML conversion on the list?

>
>> 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.

So it doesn't have to be a problem. As long as you control the layers
that have traces have the same thicknesses.