PDMS Molding

Introduction

Polymethylsiloxane (PDMS) is material that is optically clear, and generally considered to be inert, non-toxic and non-flammable. This document describes how to mix, degas and cast PDMS onto a mold that has been made by your favorite technique (UV lithography, Ebeam lithography...)

Associated documents and references

  • How to process su-8 2015 
  • Soft-Lithography (what is soft-lithography)
    David C. Duffy, J. Cooper McDonald, Olivier J. A. Schueller, and George M. Whitesides, “Rapid
    Prototyping of Microfluidic Systems in Poly(dimethylsiloxane)” Anal. Chem. 70, 1998. pp. 4974-4984.

Equipment used and safety considerations

  • desiccator
  • scale
  • weighting cup

Read PDMS MSDS before processing.

 

Recipe Parameters

PDMS comes in the form of 2 liquid components (component A: the base and component B: the curing agent) that are mixed to a ratio of 10:1 %w. After casting the PDMS on a mold and curing it it becomes solid and can be used for various applications.

  1. Prepare the work area with protective rags so spills won't go on the directly on the table
  2. Grab the 2 components that are located in the blue solvent cabinet of the yellow room
  3. Put the weighting cup on the scale and press TARE
  4. Pour the needed quantity of PDMS (max 30g). Beware of spills. Clean any spills right away with rag and acetone
  5. Press TARE again and pour component B, measure 1/10th of the weight of component A
  6. Mix the two component for 1 minute using a plastic swab
  7. Put the cup in the desiccator located underneath the table of the yellow room
  8. Leave under vacuum for 10min and bring back to atm pressure. Repeat step 8 until no bubble remains in the cup
  9. Place your mold in a closed container and pour the degassed PDMS on it. Degas again if needed. If the mold is made of silicon an anti-adhesion treatment is needed to ease the peeling of PDMS when cured. This can be done is the AMAT P5000 with the recipe CHF3 TREAT.
  10. Place the container in the oven @ 60-70°C for 4 hours or overnight to get it to cure 
  11. Peel off the PDMS and cut it to your needs with a razor blade

PDMS can be cleaned with acetone and IPA. During cleaning PDMS will swallow the IPA and bend. After drying the bending will go away.