Santosh,
can you elaborate how the number of scan chains is controlled by " test time( cost of the device per million parts) and number of flops in the chain". Please talk about a practical design. Dont say that a design with 5 flops cannot have 6 chains.
Also, I would again say it is always best to have the number of scan chains equal to the number that can be supported by the tester.
If you see any scan compression technique,, all we are trying to do is to maximize the number of scan chains.
-cheers
vlsi_eda_guy