Efficient observation-point insertion for diagnosability enhancement in digital circuits

Chip designers typically do not consider design-for-diagnosis (DfD) for manufacturing defects while implementing an integrated circuit and its design-for-test features. The lack of emphasis on DfD results in low diagnosis resolution and limited physical failure analysis (PFA) success rate when diagnosis is carried out using advanced techniques. To the best of our knowledge, no practical solution is available today to analyze the diagnosability of a design and improve it before tapeout. Furthermore, techniques that are specific to a given design cannot be reused for other chips. Therefore, we first propose a general structure-based diagnosability scoring model that can be used to analyze the diagnostic resolution for any chip. After the diagnosability analysis, we consider inserting additional observation points (OPs) for diagnosability enhancement. Given a constraint on the maximum number of inserted OPs, we propose a three-stage OP insertion (OPI) method, which includes: (i) selection of hard-to-diagnose (HTD) faults; (ii) mixed location ranking based on a structure-based diagnosability “repair” scoring model; (iii) information update and final location selection for a better diagnosability “repair” effect. The use of OPI results in higher fault “repair” rates and significant improvement in diagnosability. Experiments on benchmark circuits and industrial designs demonstrate the effectiveness of the proposed DfD solution.