Work out scan chain length instantly with clear inputs, formula shown and shareable results.
Scan test time is patterns times chain length divided by the scan clock, so doubling the number of chains halves test time. The limit is the number of available scan pins, which is why on-chip compression is used to drive hundreds of internal chains from a handful of pins.
Scan test time
chain length = flops / chains; test time = patterns x (chain length + 1) / scan clock
Automated test equipment time is charged per second and ATE is capital intensive. Test time often exceeds a second per die and directly adds to unit cost.
It decompresses a small input stream into many internal chains and compacts responses on the way out, cutting both data volume and time by 10-100 times.