mixed FR4 and microwave dielectrics

Back in 1988, we specified isocyanate resin bonded teflon (PTFE) cloth as t he outside layers of our six-layer delay board, so we could route the 800MH z clocks and the sub-nanosecnd logic transistions around without losing too much edge speed. The inner layers were all FR4 epoxy resin bonded glass fi bre.

It was a triple extended Eurocard (big), but came out flat.

What did you do wrong?

John Larkin wrote in news: snipped-for-privacy@4ax.com:

So, the other type of MEMS....

Macro Electro-mechanical systems.

Needs a more stable spin.

IIRC, the fab told them it was a bad idea, customer said go ahead and make it, and evidently the fab believes the customer is always right.

You ALWAYS make the board stack symmetrical. Whatever you're doing on one side, you're doing on the other side. Same cores, same prepreg, same copper thickness, same copper density. Otherwise you get something like this. :-)

Tim

Except for cost, what is wrong with using mixed PPO (Panasonic, Isola)