In this paper, we present a general at-speed test method for die-to-die interconnects and demonstrate its particular application to the interposer wires in a 2.5-D IC. At the heart of this method is a pulse-vanishing test technique (called PV-test), in which a short-duration pulse signal is applied to an interposer wire under test at the driver end. If this pulse vanishes at the receiver's output, then it indicates the presence of a delay fault. This PV-test technique is effective for detecting not only resistive open faults, but also resistive bridging faults between interposer wires. This method has several other advantages. For example, the implementation is especially easy as it incorporates only logic cells and can be merged with boundary scan cells. Also, it can support on-the-spot diagnosis which is desirable in applications where subsequent built-in self-repair is needed.

Testing the speed of post-bond interposer wires in a 2.5-D stacked IC is essential for silicon debugging, yield learning, and even for fault tolerance. In this paper, we present a novel at-speed test technique called Pulse-Vanishing test (PV-test), in which a short-duration pulse signal is applied to an interposer wire under test at the d river end. If the pulse signal can successfully propagate through the interposer wire and reach the other end, then the interposer wire is considered fault-free. Otherwise, it indicates the presence of a delay fault. This new test technique has several technical merits. For example, the Design-for-Testability (DfT) circuit for an interposer wire is similar to the boundary scan cell and can be controlled through scan chain. Also, it can be easily adapted to perform at-speed Built-In Self-Test (BIST) supporting on-the-spot diagnosis.