A Scan Chain is a Design-for-Testability (DFT) technique used to improve the testing of digital integrated circuits by connecting flip-flops into a shift register during test mode.
It allows test patterns to be shifted into the chip and captured responses to be shifted out, making internal nodes controllable and observable.
A Scan Chain is a series of scan flip-flops connected together to form a shift register for testing purposes.
In a normal circuit:
Inputs → Logic → Flip-Flops → Outputs
Many internal flip-flops cannot be directly controlled or observed.
As chip complexity increases:
❌ Difficult fault detection
❌ Low test coverage
❌ Hard to debug manufacturing defects
Scan chains solve this problem.
A scan flip-flop has an additional: