You choose a dielectric according to your other requirements.
Other requirements include
packing density of board
accuracy/constancy of dielectric constant
whether low loss is needed
If you are making a high speed logic board, then generally loss and constancy are not too relevant. When you make a transmission line to get good propagation and control ...
I'm very confused that dielectric constant should be selected high or
low to design high-speed boards.
I'll try and answer your question by considering inter-chip communication speeds on a circuit board using copper tracks. With a higher dielectric constant and a given PCB track width, the capacitance will be higher and this inevitably means that the ...
I think the hatched ground plane is more technological technique. It is used for better adhesion of layers on a flexible PCB or to reduce thermal dissipation in manual soldering.
Sometimes a single ground plane cutout is used to optimizing impedance when a signal meets a discontinuity.
It seems that impedance tunung with multiple cutouts is not a good and ...
So, i've finally assembled board with this design and DDR3 portion ended up working @ 333MHz. Although now i think traces is way too close to each other. W/3W rule must be kept.
EDIT: Keep in mind that this design have very short(relatively) clock line. Some calibration algorithms on some systems may not work.
EDIT: Yeah, my trace impedance is ~60Ohms. And ...
The optoisolator has the pin 7 floating. It is common to put a bias resistor from that pin to ground, to help discharge the base charges, which turns off the transistor faster. Not all datasheets mention this. Try for example a 10k resistor there.