MEM 417_Lab_II_Polymer Micromachining

MEM - Fall 2008 MEM 417 Polymer Micromachining Lakir Patel Drexel University Fall 2008 The objective of Lab 2(Polymer Micromachining was to

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Fall 2008 Lakir Patel Drexel University Fall 2008 MEM 417 Polymer Micromachining
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The objective of Lab # 2 (Polymer Micromachining was to familiarize ourselves with the process of micromachining and the implementation of its use as well as application throughout the MEMs industry. The lab was divided in to three parts, PDMS Replica Molding/ Casting, Hot Embossing and Parylene Deposition. PDMS Replica Molding / Casting: Polydimethylsiloxane (PDMS) is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or flow) properties. PDMS is viscoelastic, meaning that at long flow times (or high temperatures); it acts like a viscous liquid, similar to honey. However at short flow times (or low temperatures) it acts like an elastic solid, similar to rubber. PDMS was used because of the following properties: 1) Good biocompatibility and Chemical Inertness, 2) Suitability for molding (Casting), 3) no swelling in water, permeable to gasses, 4) optical Transparency, isotropic and Homogeneous properties, 5) Good thermal stability (upto 200 ˚ C in air) and mechanical durability, 6) good bonding (sealing) with glass, silicon and plastics, 7) surface modification via plasma etching. (MEM 417 Lab Handout, 10/15/08) After polymerization and cross-linking, solid PDMS samples will present an external hydrophobic surface. This surface chemistry makes it difficult for polar solvents (such as water) to wet the PDMS surface, and may lead to adsorption of hydrophobic contaminants. Plasma oxidation can be used to alter the surface chemistry, adding silanol (SiOH) groups to the surface. This treatment renders the PDMS surface hydrophilic, allowing water to wet (this is frequently required for, e.g. water-based microfluidics). The oxidized surface resists adsorption of hydrophobic and negatively charged species. The oxidized surface can be further functionalized by reaction with trichlorosilanes. Oxidized surfaces are stable for ~30 minutes in air, after a certain time hydrophobic recovery of the surface is inevitable independently of the surrounding medium whether it is vacuum, air or water. Summary of Lab Procedure: The PDMS used was DOW corning sylgard 184 Elastomer Kit. SU-8 micro pattern on glass substrates or silicon wafer was used as a master mold. Plastic Petri dishes were used to accommodate the experiment, weighing scale to properly measure the weight of the samples. Vacuum desiccators and Vacuum pump to remove the air from the sample, an oven and Harrick Plasma was used as plasma cleaner. For the Casting Process, first the sample was cleaned with IPA. Then the PDMS was mixed with resin with a ratio of 10:1 (Resin: Curing Agent), which was then poured on the master mold and degassed for 30 minutes. This was left to cure at 80 ˚ C for 20 minutes. After casting procedure, the sample was removed from the mold, inspected for
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any visual defects, in which holes were punched for inlet and outlet of micro channel. This was
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This note was uploaded on 11/30/2008 for the course MEM 417 taught by Professor Noh during the Fall '08 term at Drexel.

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MEM - Fall 2008 MEM 417 Polymer Micromachining Lakir Patel Drexel University Fall 2008 The objective of Lab 2(Polymer Micromachining was to

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