Polymer thick film materials for integral resistors

Trends in the electronics industry, requiring products to be smaller, lighter, and cheaper, are driving the development of integral passive technology. New design system, test system, and manufacturing processes provide new challenges and the opportunity to employ new passive materials. In general, metal/ceramic based materials provide better resistance stability, however, high processing temperatures, (up to 800°C), make them unusable with organic substrates. In contrast, polymeric materials (e.g. polymer thick films or PTFs), provide a wide range of resistivity with reasonable curing temperatures. However, unstable electrical resistance, especially under high temperature and humidity conditions over a long period of time, is a major hurdle. A structure-property-performance study was conducted on a series of commercially available polymer thick film (PTF) materials. The objective was to identify the fundamental failure mechanisms contributing to unstable electrical resistivity. For the materials studied, interfacial failure was the dominant mechanism and the resistance drift was found to be irreversible. These results suggested that corrosion of the metal substrate at the metal-PTF interface caused the increase in resistance. Based on this finding, a series of new PTF materials have been developed with improved resistance stability. Resistance drift, ((R-Ro)/Ro), has been reduced from 800% for the commercial materials to 15% for the novel PTF materials