Soft-errors (SEs) and delay faults (DFs) frequently occur in modern high-density, high-speed, low-power VLSI circuits. Therefore, SE hardened design and DF testing are essential. This thesis introduces two novel methods for soft-error detection and delay fault propagation in nanometre technology. A new idea is proposed to propagate those delay faults that are not causing logic failure at the site of the defect, but the delay makes the circuit more prone to soft-errors that manifest the effect of delay faults. This approach propagates the fault from the fault location by mapping a nine-valued voltage model on top of a five-valued voltage model to convert delay faults to static faults. This original idea reduces the complexity of delay fault propagation. This thesis introduces an original approach toward soft-error detection based on the strength violation in the circuit. This research shows that transient pulses of less than threshold voltage will cause soft-errors without altering the logic value at the strike location. This method will increase the Soft-Error Rates (SER) for all existing methods if strength-based Soft-Error detection will be considered. The offered approach uses a novel coding system that carries both logic and strength which applies to certain logic functions that are sensitive to strength variations. A wide range of soft-errors are the result of strength violation in switch-level that have never been investigated before.