Assembly test chips and circuits for detecting and measuring mechanical damage in packaged ICs

Die cracking and stress induced damage to metal conductors in plastic package integrated circuits have become major reliability issues in recent times. Test chips with structures which can detect cracking or metal damage can be used to qualify new types of packaging. The Sandia stress sensing chip, ATC04, can make quantitative measurements of in-plane shearing stress which can in turn be related to the shearing stresses which produce metal motion. Recent stress measurements with liquid encapsulated ATC04 parts are reviewed and accuracy limits discussed. Other types of test chips attempt to detect thin film cracking or delamination by electrical detection of damage to conductor structures in or near chip corners. Several designs of such chips are discussed.