Sougata Hazra 1 Department of Mechanical Engineering, Stanford University, Stanford, CA 94305 e-mail: shazra@stanford.edu Ki Wook Jung Department of Mechanical Engineering, Stanford University, Stanford, CA 94305 e-mail: lupin000@stanford.edu Madhusudan Iyengar Google LLC, Mountain View, CA 94043 e-mail: miyengar@google.com Chris Malone Google LLC, Mountain View, CA 94043 e-mail: cmalone@google.com Mehdi Asheghi Department of Mechanical Engineering, Stanford University, Stanford, CA 94305 e-mail: masheghi@stanford.edu Kenneth E. Goodson Department of Mechanical Engineering, Stanford University, Stanford, CA 94305 e-mail: goodson@stanford.edu Thermal and Manufacturing Design Considerations for Silicon-Based Embedded Microchannel Three- Dimensional-Manifold Coolers (EMMC)—Part 3: Addressing Challenges in Laser Micromachining-Based Manufacturing of Three- Dimensional-Manifolded Microcooler Devices Laser machining is an inexpensive and fast alternative to conventional microfabrication techniques and has the capability to produce complicated three-dimensional (3D), hier- archical structures. It is especially important while performing rapid prototyping and quick design studies of extreme heat flux cooling devices. One of the major issues plagu- ing the use of laser micromachining to manufacture commercially usable devices, is the formation of debris during cutting and the difficulty in removing these debris efficiently after the machining process. For silicon substrates, this debris can interfere with sur- rounding components and cause problems during bonding with other substrates by pre- venting uniform conformal contact. This study delves deep into the challenges faced and methods to overcome them during laser micromachining-based manufacturing of such complicated 3D-manifolded microcooler structures. Specifically, this work summarizes several postprocess techniques that can be employed for complete debris removal during etching of silicon samples using an Nd/YVO4 ultraviolet (UV) laser, detailing the advan- tages and drawbacks of each approach. A method that was found to be particularly prom- ising to achieve very smooth surfaces with almost complete debris removal was the use of polydimethylsiloxane (PDMS) as a high-rigidity protective coating. In the process, a novel technique to strip PDMS from silicon surface was also developed. The result of this study is valuable to the microfabrication industry where smooth and clean substrate surfaces are highly desirable and it will significantly improve the process of using UV lasers to create microstructures for commercial applications as well as in a research environment. [DOI: 10.1115/1.4047847] Keywords: laser, debris, bonding, microcooler, micromachining, cooling, embedded microchannel 1 Introduction Lithography-based fabrication is an immensely popular tool used by researchers in industry and academia which helps create precise microstructures with dimensions ranging from millimeter to submicron and nanometer scale, with mass production capabil- ities in a contaminant free environment. However, microfabrica- tion techniques suffer from several drawbacks like large overhead cost for purchase and maintenance of expensive instruments [1]. Furthermore, fabrication of etched microstructures with hierarchi- cal features or through holes in silicon wafers involves compli- cated, expensive, and time-consuming steps using multiple lithography tools. A much faster and cost-effective alternative to cleanroom fabrication is laser-based micromachining for creating precise micron level hierarchical structures. Laser-assisted 1 Corresponding author. Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received January 15, 2020; final manuscript received April 21, 2020; published online August 17, 2020. Assoc. Editor: Sukwon Choi. Journal of Electronic Packaging SEPTEMBER 2020, Vol. 142 / 031119-1 Copyright V C 2020 by ASME Downloaded from http://asmedigitalcollection.asme.org/electronicpackaging/article-pdf/142/3/031119/6558192/ep_142_03_031119.pdf by Stanford University user on 19 April 2021