Lock-in IR thermography for functional testing of solar cells and electronic devices

Abstract

Lock-in thermography (LIT), which is a standard tool in nondestructive testing (NDT), is also very advantageous for electronic device testing (EDT). In this contribution the special points of view of LIT applied in EDT are reviewed. In EDT it may be useful to display not only the amplitude or the phase image but also images of the magnitude of special phase components. The “0°/-90°” image as a new kind of representation is especially advantageous to display microscopic lock-in thermograms of integrated circuits (ICs). Just as the phase image, the 0°/-90° image is inherently emissivity-corrected, but it provides a considerably better spatial resolution. The quantitative interpretation of EDT thermograms in terms of a lateral power distribution is reviewed with special emphasis to the measurement of local power sources and the numerical inversion of lock-in thermograms enabling a higher spatial resolution. Experimental details of a lock-in thermography system specialized to electronic device testing are introduced with a number of representative application examples demonstrating the universal applicability of this technique in EDT.