2017-06-17 11:17 GMT+02:00 Luke Kenneth Casson Leighton lkcl@lkcl.net:
On Fri, Jun 16, 2017 at 8:40 PM, mike.valk@gmail.com mike.valk@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.