Influence of the metal migration from screen-and-fired terminations on the electrical characteristics of thick-film resistors

To understand the effects of resistivity changes and temperature-coefficient-of-resistance variations caused the migration of metal particles from terminations into the resistor film, the electrical characteristics of Ru-based thick-film resistors with different conductive terminations (PtAu and Ag based compositions) and with different aspect ratios were examined. The data were collected using Ag-based terminations, since Ag diffusion processes and relevant electrical effects are emphasized. Scanning electron microscopy, electron microprobe analysis, and x-ray diffraction analysis were used to study the diffusion processes and the thick-film microstructures. The experimental data can be explained simply by a conduction model that assumes percolative tunneling of electrons through conductive grains embedded in the glass matrix of the resistors. Using simple hypotheses, the model theory gives a good quantitative fit of the experimental results.