This paper describes the development of a device for measuring the removal rate and polishing pad surface asperity on both upper and lower platens in double-sided polishing. A previous measurement device developed by the author's research group cannot evaluate the polishing pad on the upper platen because of the deadweight system, and can be applied to the lower platen only. Therefore, we developed a novel measurement device for the upper platen using the restoring force exerted by the springs. In this study, the conditioning characteristics and removal rate were examined from the viewpoint of the polishing pad surface asperities and profiles in double-sided polishing. The results indicated that the spacing of contact points and the dispersion level of the contact regions markedly affect the removal rate. Furthermore, the effect of the polishing pad on the upper platen on the removal rate is higher than that on the lower platen.

View full abstract

Single-crystal GaN has many excellent features, including high thermal conductivity, heat dissipation, possibility of operation at high temperature, high speed of electron saturation, and high dielectric breakdown voltage. Therefore, it is expected to be utilized for power devices with low power loss. GaN has a hardness of 1800 – 2000 Hv and is brittle, so it is very difficult to process. This research was performed to clarify the crack generation mechanism in the GaN semiconductor grinding process. To investigate the process of crack generation during single grinding, scratching experiments were conducted on the Ga polar plane of a GaN substrate using a single-crystal diamond indenter. The scratching results indicated that it is necessary to set the depth of cut of the tool to ≤ 180 nm to grind in the ductile state.

View full abstract

To evaluate the wear of cutting tools, fractal dimension was proposed as a measure of the complexity of the cutting edge shape, and the changes in fractal dimension and cutting edge shape were evaluated. The cutting edge of the tool repeated microchipping and flattening, occasionally accompanied by large chipping, and eventually reached the end of its life. In this study, further experiments were conducted, and the relationship between fractal dimension evaluation of tool edge and tool life was examined. The cutting experiment of SCM 435 C using a cermet tool indicated that the value of the fractal dimension near the end of life varied depending on the rake angle (1.18 at a rake angle of 0° and 1.16 at a rake angle of 14° ). For small rake angle, many small (micro) chips were generated. Conversely, the scale of the chipping increases toward the end of life at large rake angle. In comparison with conventional flank wear width, cutting resistance, and shear angle, the fractal dimension is stable near the end of life and is an effective measure for tool life prediction.

View full abstract