Research on twin crystal structure evolution and properties of copper-tin diamond ultra-thin grinding wheel for silicon wafer cutting

Addressing the poor cutting stability and low lifespan of copper‑tin ultra-thin diamond grinding wheels for CSP (Chip Scale Package) chip package cutting, this paper investigates the growth mechanism and evolution patterns of twin phase and high‑tin phases of DC(direct current)-sintered CuSn pre-alloyed binder as a function of the sintering temperature and heat preservation time. The study also demonstrates the correspondence between cutting performance and microstructure, establishing a theoretical foundation for the microstructure control and performance design of ultra-thin diamond grinding wheels for advanced chip package cutting. The research indicates that the twin phase are primarily formed during the heat-up stage of the sintering process, and their size grows significantly as the insulation time increases, while the high‑tin phase evolves from a discontinuous reticulated structure to a massive structure. Besides, the dynamic hardness and elastic modulus change mechanism of the microstructure of copper‑tin binder is discussed in this paper. The dynamic hardness and elastic modulus of the copper‑tin binder decline in general as the sintering temperature rises, and the dynamic hardness of the twins climbs and then reduces, while the elastic modulus rises and then falls. Characterization and analysis of cutting parameters, fracture surfaces, and chip formation at different sintering temperatures lead to the following conclusions: with the increase of sintering temperature, the chip size, cutting current, and wear of the single-crystal silicon all initially increase and then decrease. The grinding wheel sintered at 470 °C exhibits the best overall cutting performance and lifespan. Compared with ordinary copper‑tin grinding wheels, the twin crystal grain distribution in the bond structure of copper‑tin pre-alloyed powder sintered grinding wheels is more uniform, providing a more stable cutting process and longer cutting lifespan. •The twin crystals were formed during the heating stage of powder sintering.•The elastic modulus of the binder decreases as the sintering temperature increases.•Copper tin grinding wheels with smaller twin sizes have better cutting performance.•Pre-alloyed powder wheels offer a more stable cutting process than elemental powder.