Papers by Keyword: Lubrication Theory

Abstract: Here we use 2-D models of fluid film lubrication and contact mechanics to calculate the contact stress and fluid (i.e., slurry) pressure distributions on the wafer–pad interface in CMP. In particular, the effective rigidity of the wafer (determined by the wafer carrier structure), the retaining ring width and its back pressure are taken to be the design parameters. The purpose is to study the synergetic effects of such parameters on the contact stress non-uniformity (NU), which directly affects the spatial non-uniformity of the material removal rate on the wafer surface. Our numerical results indicate that, for a given wafer rigidity, one may choose a particular combination of the retaining ring parameters to minimize NU. Also, the corresponding minimum NU decreases with the effective wafer rigidity, suggesting that it is beneficial to use a soft (e.g., floating-type) wafer carrier. Moreover, for a soft wafer carrier, the presence of the retaining ring also reduces NU to some extent, but the use of a multi-zone wafer-back pressure profile would be more effective in this regard.

Abstract: This paper describes an investigation about the grinding fluid optimization supply based on lubrication theory. The models for three-dimensional hydrodynamic flow pressure in contact zone between wheel and work are presented based on Navier-Stokes equation and continuous formulae. It is well known that hydrodynamic fluid pressure generates due to this fluid flux, and that it affects overall grinding resistance and machining accuracy. Moreover, conventional methods of delivering grinding fluid, i.e. flood delivery via a shoe or jet delivery tangential to the wheel via a nozzle, have been proved that they can not fully penetrate this boundary layer and thus, the majority of the cutting fluid is deflected away from the grinding zone. Therefore, in this paper, a new delivery method of grinding fluid, the minimum quantity lubricant (MQL)-near-dry green grinding is presented and analyzed for it not only reduces hydrodynamic lift force but also reduces grinding fluid cost to achieve green manufacturing. Experiments have been carried out to validate the performance of the MQL supply compared with conventional flood cooling. The experimental results have shown that the theoretical model is in agreement with experimental results and the model can well forecast hydrodynamic pressure distribution at contact zone between and workpiece and the MQL supply in grinding is feasible. Experiments have also been carried out to evaluate the performance of the MQL technology compared with conventional flood cooling. Experimental data indicate that the proposed method does not negatively affect to the surface integrity and the process validity has been verified.