Fracture resistance evaluation of RuO2-based thick film resistor material by in situ crack extension observation in a scanning electron microscope

Parameters for the fracture mechanics of thick film materials are scarce in the literature. One reason is that for many such materials it is very difficult to produce a bulk specimen as required for most standard tests. This paper describes an alternative method for measuring the fracture resistance of a ruthenium dioxide (RuO2)-based thick film resistor material for electronic applications. The method is based on an in situ investigation of crack propagation in the loaded material. The investigated material is printed as a thick film on a substrate of low-temperature-co-fired-ceramic. An initial crack in the film is introduced with a Vickers indenter. The crack is subsequently loaded with a four-point bending equipment in a scanning electron microscope, which allows for in situ crack length measurement. The crack growth measurements reveal that once a certain crack length is achieved the load required to extend the crack becomes independent of the crack length. Beyond this length, the crack propagates in the so-called steady-state region, which is used in the present method to estimate the fracture resistance of the film. Both tensile stresses resulting from bending and tensile residual stresses are taken into account. Although a brittle substrate was used, the crack did not penetrate into the substrate. The measured fracture resistance of 0.69 +/- 0.14 MPa√m is found to be realistic for the investigated thick film material with high silicate glass content.