On Wed, Jun 21, 2017 at 6:26 PM, Wolfram Kahl kahl@cas.mcmaster.ca wrote:
On Wed, Jun 21, 2017 at 12:00:07PM +0100, Luke Kenneth Casson Leighton wrote:
.On Wed, Jun 21, 2017 at 9:35 AM, mike.valk@gmail.com
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
So it doesn't have to be a problem. As long as you control the layers that have traces have the same thicknesses.
technically correct but far too much risk and hassle. you end up tying the PCB layout to a specific PCB manufacturing factory.
Are there high-frequency risks/problems with switching back and forth between the layer pair
there are. the more VIAs you have the more EMI there is. R.F. (and HDMI is R.F.) does not travel in a straight line: if you have an abrupt change of direction (a corner or a VIA) the signal actually tries to just keep going in a straight line!
the best track layouts use curves not 45 degree transitions. the best layouts have no track changes at all, are as symmetrical as possible, are completely surrounded symmetrically by the exact same amount of space on either side, and the exact same number of vias on both sides of the track. and also are impedance matched in terms of distance between the pairs, width of the tracks, *and* the distance between layers *and* the dielectric constant of the insulation between the layers.
it's a pretty heavy-duty amount of requirements.
l.