hey guys did you ever thought about the 100nF caps ?
above 5MHz they are pure inductive, so no capacitance left ! EMC-Problem !
you place tons of them on your 33MHz board and you dont need them ! They are useless !

the capicitance needs to be calculatet

you know the current, the time and the max allowed voltage rippel, now you know the cap you need.(for each part)

you know the PCB layerstack, so you know the effective area of the capacitance.

you know the cap value and its parasiteric parameters ( R and L ) so you know its frequency behaviour in frequency domain and therefor its attenunation/damping (at least see datasheet). and then you know what values you will need to keep the impedance under the desired value of your design.

also the layout is very important. keep the area of the loop between foe example vcc and gnd (seen as a short circuit in ac mode) as smal as possible to reduce emc emmision.

regards

michael schmitt