Mainly signal integrity problem falls following category

Timing

EMI

Noise

Timing is complicated field of study by itself in one clock of cycle a certain no of operation will happen this short time must be divided up and allocated in budget in all a various opretions .some time allocated for gate switching , for propagating the signal to output gate ,for wating for clock to get to the next gate , and waiting for gate to read the data data input .

we hear about lot of noise such as ringing , ground bounce , reflection, near end cross talk ,switching noise, non monotonic, power bounce , attenuation and capcitive load .