Elasto-Hydrodynamic Interaction in the Free Abrasive Wafer Slicing Using a Wiresaw: Modeling and Finite Element Analysis

Abstract

Free abrasive machining (FAM) process associated with the wiresaw wafer slicing involves a three body abrasion environment. During the process, the cutting action is caused by fine abrasives freely dispersed in the slurry, which get trapped between an axially moving taut wire and the ingot being sliced. In this paper a model is proposed wherein the entry of abrasives into the cutting zone is governed by elasto-hydrodynamic (EHD) interaction between the slurry and the wire. An EHD film is formed by the abrasive carrying viscous slurry, squeezed between the wire and the ingot. This phenomenon is analyzed here using the finite element method. The analysis of such an interaction involves coupling of the basic Reynold’s equation of hydrodynamics with the elasticity equation of wire. Newton–Raphson algorithm is used to formulate and solve this basic coupling. The finite element discretization of the resulting nonlinear equation is carried out using Galerkin’s method of weighted residuals. Basic hydrodynamic interaction model and the incorporation of the entry level impact pressure into the inlet boundary conditions are the two novel features introduced in this work. The analysis yields film thickness profile and pressure distribution as a function of wire speed, slurry viscosity, and slicing conditions. A perusal of results suggests that the wiresawing occurs under “floating” machining condition. The minimum film thickness is greater than the average abrasive size. This is practically very important since the wiresaw is used to slice fragile semiconductor wafers with severe requirements on the surface finish. The possible mechanism by which a floating abrasive can cause material removal is also touched upon in this work. Material removal rate has been modeled based on energy considerations. [S0742-4787(00)00702-5]

Mechanisms of wafer sawing and impact on wafer properties

“…This parameter determines whether the abrasive is simultaneously in contact with the wire and the silicon. Most of the research in this area has been carried out with the help of simulations, with results ranging from 30 mm [12] to more than 100 mm [4]. This is wide range, from the abrasive size to much larger than its size, or from a situation where there is a direct contact between the wire, the abrasive and the silicon ingot to a situation where there is no direct contact.…”

“…The hydro-dynamic characteristics of the slurry have been studied [4], as well as its impact on the wire vibrations [5,6]. Furthermore, it is known that the size and concentration of the abrasive grains is of paramount importance to the quality of sawing [7,8].…”

Tribologically-induced Damage in Cutting and Polishing of Silicon

“…As a semiconductor process usually involves cutting grooves, lubricants not only actively remove swarf from the grooves, but also prevent adhesive contact between the cutting surface and the work piece. A direct or partial-contact is thought to occur in slurry sawing [16,17]. The lubricants will also exert shear stress that can increase the material removal rate.…”

Nanomanufacturing : nano-structured materials made layer-by-layer.

“…The theory of lubrication flow has been in use for well over a century, beginning with Tower's 1883 experiments of a rolling bearing [Tower (1883) Booker and Huebner (1972), Christensen (1972), Higgins and Scriven (1980), Anturkar et al (1990), Heil and Pedley (1995), Bhagavat et al (2000), Kothmann and Stefani (2001), Hori (2006), Szeri (2010)]. Many extensions of this basic theory exist, including elastohydrodynamic lubrication [Greenwood (1972), Taylor and O'Callaghan (1972), Oh and Huebner (1973), LaBouff and Booker (1985), Jones (1993) [Constantinescu (1959), Ng (1964), Elrod and Ng (1967), Hirs (1973)], and lubrication of non-Newtonian fluids [Ng and Saibel (1962), Swamy et al (1977), Johnson1993, Bhattacharjee and Das (1996), Hryniewicz et al (2001), Nair et al (2007), Mongkolwongrojn and Aiumpronsin (2010)], among others [Christensen (1971), Eringen and Okada (1995), Feng and Weinbaum (2000), Stone (2005), Jang and Khonsari (2005), Bujurke and Kudenatti (2007), Rojas et al (2010)].…”