Significance of contamination delay in sequential circuit timing

Q: What is the significance of contamination delay in sequential circuit timing?
Fact: 70-80% of designers who deal with timing closure daily are unaware of this fact.

So, what is contamination delay anyway?
Look at the figure below. tcd is the contamination delay.


















Without understanding contamination delay you "should not" complete timing estimation of any sequential circuit.

What do you mean by that?
Contamination delay tells you if you meet the hold time of a flip flop. To understand this better please look at the sequential circuit below.











The contamination delay of the data path in a sequential circuit is critical for the hold time at the flip flop where it is exiting, in this case R2.

mathematically,
th(R2) <= tcd(R1) + tcd(CL2) Contamination delay is also called tmin and Propagation delay is also called tmax in many data sheets.