Characterization of interfaces involving electrically conductive adhesives using electron-beam moire and infrared microscopy

The complimentary techniques of electron-beam moire and infrared microscopy were used to determine the mechanical and thermal degradation of interfaces involving electrically conductive adhesives. The infrared microscopy technique was used to examine the changes in heat transport across the interfaces in electronic packaging materials. The electron-beam moire technique is capable of measuring displacements at a spatial resolution of 50 nm and was used to measure displacements in materials due to mechanical or thermal loading. We overlaid these two techniques to achieve a more complete understanding of the degradation mechanisms in electronic packages. We made a specimen with sandwiched layers of FR4 printed wiring board, silver-filled conductive adhesive, carbon-filled conductive adhesive, and stainless steel. We thermally cycled the specimen from -55°C to 125°C. We paused the thermal cycling for testing with both techniques. Measurements show that after only 3 thermal cycles, there were already changes in the interfacial thermal resistance seen by the infrared microscope. SEM observations showed no detectable damage at the surface of the specimen at this number of cycles. Moire images at different temperatures showed the origins of the degradation mechanism, as images at the extreme temperatures showed how the differential thermal expansion and contraction of the different materials strain the various layers. The combination of these two techniques gives a unique perspective on analysis of interfaces in electronic packaging materials systems