Debugging and Diagnosing Scan Chains

Scan chains help detect and identify failures in integrated circuits, but they are also susceptible to failure themselves. When scan chains break, it does not necessarily render them useless. Normally, scan chains can be debugged and diagnosed so that they can be fixed or used while masking out vector bits associated with broken or corrupted portions of the chain. This article describes the different ways that scan chains can break and how it tends to affect their performance. It explains how to repair various types of scan chain failures or at least regain partial use for limited testing purposes.