STM32WB55CGU6T = MASTER
ADS1299 = SLAVE

400ps rise time before I added 100ohm Resistors.
Estimated new rise time = 2ns

Clock Speed = All I need is 100 KHz max

Full Ground plane .11mm under as reference

Grid increments .750mm

Via sizes = Big .3 x .6mm and Small .45x .2mm

 

Did you try to plot a USA flag with traces and vias?

 

Did you try to plot a USA flag with traces and vias?

Lol no but i see what you mean

 

Line up all those 45° bends on the red tracks. You know you want to.

 

I think you could also reduce spacing between traces.
As a good rule, traces of the same bus/interface (i.e. SPI: SCK, MISO MOSI) should be always of equal length.