Upgrading In-Circuit Test of High Density PCBAs Using Electromagnetic Measurement and Principal Component Analysis

With the density increase of today's printed circuit board assemblies (PCBA), electronic test methods such as in-circuit test (ICT) reached their limits. In the same time the requirements of high reliability and robustness are greater. Original equipment manufacturers are obliged to reduce the number of physical test points and to find better-adapted test methods to keep adequate test coverage. Current test methods must be rethought to include a large panel of physical phenomena that can be used to detect- electrical defects, absence, wrong value of components, absence and shorts without using test points on the board under test (BUT). In this paper, a test set-up based on the measurement of electromagnetic signature to diagnose faulty components contactlessly is presented. The technique consists in using magnetic field probes, which detect the field distribution over powered sensitive components. To evaluate the relevance of the method, reference EM signatures are extracted from fault-free circuits, which are compared to those extracted from a sample PCBA in which we introduced a component level defect by removing or changing the value of critical components. For more robust detection of multiple defect scenarios, the principal component analysis (PCA) method is used as an outlier detection algorithm.