Thermomechanical effects in embedded passive materials

Thermomechanical fatigue was measured using electron-beam moire (EBM) and infrared (IR) microscopy. A specimen was made using a FR-4 printed wiring board (PWB), a silver-filled conductive adhesive, and a carbon-filled conductive paste. Both filled polymeric materials are used for embedded resistor applications. We studied the behavior of these materials and, particularly, the interfaces between these materials as a function of thermal cycling. The EBM gives quantitative information on localized strains, whereas the IR microscopy gives quantitative information on changes in heat flow. The filled polymeric materials showed strains of -0.6% at -55degreesC and 1.4% at 125degreesC. The interface between the silver and carbon-filled materials increased in thermal resistance on the order of 10(-6) m(2) . K . W-1 per thermal cycle.