A low-cost massively-parallel interconnect test method for MCM substrates

This paper introduces a new approach for interconnect testing of unpopulated MCM substrates. Defect detection and diagnosis is performed using a variation of methods that have traditionally been applied using Boundary Scan registers. The new approach involves parallel application of digital signatures to all nets, while capturing the responses at every node. The responses of fault-free nets are identical to the applied signatures, while faulty nets exhibit corrupted signatures. Defect classification is accomplished by comparison of the faulty signatures, thereby isolating such fault mechanisms as: (1) shorts to ground, (2) shorts to power, (3) open nets, and (4) bridging shorts between nets. Current methods for unpopulated substrate testing utilize either resistive or capacitance probing techniques which rely on the use of moving probes. Therefore test times may be excessive for large area MCMs. The new approach is significantly faster due to the parallel nature of the test. Thousands of nets may be tested and diagnosed in a fraction of a second with this technique.