Contents lists available at ScienceDirect Precision Engineering journal homepage: www.elsevier.com/locate/precision On form accuracy and surface roughness in micro-ultrasonic machining of silicon microchannels Dungali Sreehari a,b , Apurbba Kumar Sharma b, ⁎ a Department of Mechanical Engineering, National Institute of Technology, Uttarakhand, Srinagar, Pauri (Garhwal), Uttarakhand, 246174, India b Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Roorkee, Haridwar, Uttarakhand, 247667, India ARTICLE INFO Keywords: Surface roughness Overcut Stray cut Medium viscosity Feature plot ABSTRACT Accuracy in manufacturing microchannels is important in order to achieve their intended function. Smooth and high aspect ratio microchannels on silicon wafer substrate are needed in the heat removal application in various microelectronic components. Generally, etching techniques are used to fabricate silicon microchannels; how- ever, the maximum achievable limit for the channel depth is a major concern. Micro-ultrasonic machining (micro-USM) is capable of machining high aspect ratio microchannels on hard and brittle material such as silicon, glass, ceramics, etc. However, achieving reasonable form accuracy and surface roughness of the mi- crochannels is challenging. Overcut and edge damage (stray cut) are undesirable for precision machining while surface roughness of the microchannels can be set at an optimized value to attain maximum heat transfer. In the present study, silicon microchannels were fabricated using the micro-USM technique. In order to improve the precision and quality of the fabricated silicon microchannels in terms of surface roughness, overcut and stray cut; viscous fluids with different viscosities were considered for investigation in combination with other machining conditions. The experimental investigation revealed that using low viscous fluids yields better surface roughness compared to high viscous fluid; however, overcut and stray cut were minimized while using high viscous fluids. Machining at higher feed rates could minimize the surface roughness, over cut and stray cut irrespective of the abrasive concentration percentage. Possible interactions between the tool, abrasive and workpiece in the ma- chining zone were analyzed vis-à-vis the experimental results. 1. Introduction Focus in improving the capabilities and accuracies in micro- machining has been on the rise with an increase in the demand for miniaturized components in various applications such as lab-on-chips, micro heat exchangers, electronic systems, micro-reactors, micro-elec- tromechanical systems (MEMS), micro-fluidic systems, etc. Fabrication of precise microchannels for the intended components is one of the most primary requirements in all such applications. Microchannels have attained prominence in miniaturization, especially in the elec- tronic industry, due to their capability of removing high heat fluxes. Aluminum, copper, stainless steel and silicon are commonly used sub- strate materials to fabricate microchannels due to their good mechan- ical and thermal properties. However, silicon microchannels are pop- ular in heat transfer applications in microelectronic devices. The first silicon microchannel was developed by Tuckerman and Pease in 1980’s by an orientation dependent etching technique [1]. These microchannels were used to remove a high heat flux (∼790 W/ cm 2 ) from a small area with deionized water as a working fluid. Later, research was mostly focused on fabrication of precise microchannels with different cross-sections, aspect ratios and surface conditions using different micromachining techniques such as micro-EDM, micro-ECM, micro-LBM, micro-USM, LIGA, photolithography, micro-cutting, micro- casting, etc. [2,3]. Heat transfer characteristics were investigated ex- perimentally by Qu et al. and compared the results with numerical data on trapezoidal silicon microchannels fabricated by anisotropic etching technique [4]. They reported significant difference between these re- sults which was attributed to the surface roughness of the microchannel walls. Wu and Cheng had fabricated differently sized silicon micro- channels of trapezoidal cross-section by varying surface conditions by the wet etching technique and studied the heat transfer characteristics [5]. The studies revealed that both the surface roughness and geometric parameters of the microchannels had significant effect on their heat transfer characteristics. Attempts were made to improve the surface finish of the walls and bottom of the silicon microchannels by (i) varying the temperature of silicon etchant, (ii) controlling the compo- sition of the etchant and (iii) orientation of the masking pattern [6]. The wet and dry etching techniques are commonly used to fabricate https://doi.org/10.1016/j.precisioneng.2018.04.014 Received 14 January 2018; Received in revised form 10 March 2018; Accepted 16 April 2018 ⁎ Corresponding author. E-mail address: akshafme@iitr.ac.in (A.K. Sharma). Precision Engineering xxx (xxxx) xxx–xxx 0141-6359/ © 2018 Elsevier Inc. All rights reserved. Please cite this article as: Sreehari, D., Precision Engineering (2018), https://doi.org/10.1016/j.precisioneng.2018.04.014