Test of integrated digital circuits - Basic notions and evolutions

IC testing is not a new field, but one that is constantly evolving. In the early days of IC production, the design engineer and the test engineer were generally well separated. The former would decide which elements were to be implemented in the circuit, and how these elements were to be drawn on the physical substrate; the latter would decide how to effectively determine, at the end of production, whether the circuit was free from manufacturing defects and could be delivered to the customer. The former had to guarantee design-error-free functionality; the latter had to ensure detection of any physical defects. With the rapid growth in circuit complexity, this clear separation of responsibilities became obsolete. The move towards VLSI (Very Large Scale Integration) meant that it was impossible to test the circuit effectively in production if the test had not been planned for during the design phase; the quality and cost of the test became directly linked to the design choices made and the information provided by the designer in preparation for the test.

The preparation of test vectors is now the responsibility of the designer. This article is essentially devoted to this aspect, which includes the need to choose physical defect models according to technologies. These vectors are then translated into programs for the test equipment (ATE: Automatic Test Equipment) used on production lines.

The notion of Design for Testability (DFT) has also emerged (§ 3) [E 2 461] . In fact, in an increasing number of cases, specific devices need to be added to the circuit to enable the required level of test quality to be achieved within the allotted time. This is the subject of another article detailing the techniques involved, but some fundamental concepts are summarized here.

The aim of this article is to provide an overview of the most important concepts in the field, without claiming to be exhaustive. The information provided in the bibliography will enable you to delve deeper into the points you need to know in a given context. In particular, as this article has been written from the designer's point of view, aspects relating to the implementation of testing in the production phase are barely touched upon. ETA features are only mentioned where they have a direct impact on the designer's work. Furthermore, this article focuses on the testing of digital circuits, and the case of non-CMOS (Complementary Metal Oxide Semiconductor) circuits is only partially...