I am designing a flexible PCB to carry two types of differential signals. One is about 1.2Gbps 100R differential impedance, while the other is only 3Mbps, with much more tolerance on the impedance.
It was very hard to achieve a differential impedance of 100R with such a thin dielectric, so it was suggested that I used a hatched ground plane to increase the impedance. However, it's hard to make the high speed pairs properly balanced on all parts on the hatching, since they go around some odd corners. Furthermore, the outer pairs are unbalanced all the way.
As an alternative, I was wondering about literally placing diamonds along the route of the pairs, like this:
This way I could achieve good balance for the whole route, and I could leave the outer pairs with a solid plane, rather than unbalancing them.
Lastly, I wonder if it's worth using circles instead of diamonds to reduce the stress concentration at the corners.
I wonder if what I am trying to do makes sense?