Robust scan-based logic test in VDSM technologies

The customer expects defect-free chips, at consumer prices, making thorough manufacturing test mandatory. With increasing chip density, the addition of say 10,000 gates is no longer of great impact (these would occupy only 0.1 mm² on a 0.18-μm die); satisfying timing requirements and not exceeding package or system power requirements are the principal implementation objectives. The new availability of silicon real estate has transformed the design-for-testability environment. Implementing contemporary application-specific integrated circuit (ASIC) designs based on standard-cell and gate array technologies now requires design flows that incorporate DFT. Robust design for testability in very deep-submicron (VDSM) technologies is essential to volume manufacturing. The most common structural test method is scan-based logic test, which is now the backbone of manufacturing test. Using this method, commercial ATPG tools rely on test-mode reconfiguration of the circuit to a pseudo-combinational one, ensuring its access, controllability, and observability. Each state bit is transformed into a stage (either a flip-flop or master-slave latch pair) of a shift register or scan chain accessible from chip pins. The author points out ways to avoid pitfalls in implementing effect scan-based test. These include modifying register-transfer-level circuit representations for testability, using a single clock edge design, and providing clock control.