New testing approach using near electromagnetic field probing intending to upgrade in-circuit testing of high density PCBAs

Abstract

With the density increase of today's printed circuit board assemblies (PCBA), the electronic test methods 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. Current test methods must be rethought to include a large panel of physical phenomena that can be used to detect electrical defects of components, absence, wrong value, and shorts at component level on the board under test (BUT). We will present the possibility of using electromagnetic signature to diagnose faulty components contactlessly. The technique consists in using small diameter near electromagnetic field probes, which detect the field distribution over powered sensitive components. A giant magnetoresistance (GMR) sensor was used as well to detect variations in low frequency components. The loading of the BUT is specifically chosen to enhance the sensitivity of the EM measurements. Reference EM signatures are extracted from a fault-free circuit, which will be 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. As a result, we will show that the amplitude of a specific harmonic acts as a sensing parameter, which is accurately related to the variation of the component value.