Repurposing FPGAs for Tester Design to Enhance Field-Testing in a 3D Stack

We propose an architecture for a Field Programmable Gate Array (FPGA) based tester for a 3D stacked integrated circuit (IC). Due to the very short distances between dies in a stack that can make SerDes connections very efficient and the high density of through silicon vias (TSVs) that may be available, it is possible to connect the FPGA to the die under test through a very high bandwidth connection that can feed multiple short scan chains. We propose and evaluate two designs that exploit the underlying structure of the FPGA, allowing it to be used to efficiently store and apply predefined test patterns, reducing the FPGA resources required and the switching activity in the circuit under test when compared to a more traditional on-chip decompressor implemented to feed short scan chains. For the largest circuit we studied, the switching activity was reduced about 80% and the test time by 90%.