How to decide that how many scan chains are required??

[deepen talati]

We have tester available. Its memory is fixed and channels available to it also fixed.
Now we have also idea about the gate count/flops available in design.
So now how many chains are needed?
Who will decide it and how?

 

[rca]

The external scan chain number is for me limited by the smalest between the pads available or the tester channel available.

 

[deepen talati]

Yeah..That thing is fine.
But what about internal scan chains and scan chain length?
Can you pls. tell me.

Thank you and Regards,
Deepen

 

[rca]

internal scan chains is different only if you used a compress technic.
and the scan length is manage by the DFT tool to have equivalent length over all scan chains.