nanoFAB Knowledge Base

Space shortcuts

Page tree

Equipment or ProcessPDMS Processing
Process Area

PDMS

SynonymsTBAF, PDMS

Introduction

PDMS casting using Si or other moulds generally results in residual PDMS remaining on the mould over time.  PDMS has been proven difficult to remove using standard cleaning methods, as it tends to absorb and swell when cleaning using standard cleaning solutions (piranha or solvent-based), rather than dissolve.  In the case of plasma cleaning, a fluorine and oxygen based plasma is required due to the silicone structure of PDMS, and is detrimental to most standard mould materials (Si or SiO2/glass).

To effectively remove PDMS residue, a 1% solution of tetrabutylammonium fluoride (TBAF) in PGMEA has been proven to work effectively without affecting the mould.  The nanoFAB stocks a 75% in H2O solution of TBAF, which can be diluted to 1% using PGMEA as the solvent.  SU-8 developer is 99.5-100% PGMEA, and is used as the solvent.  Room temperature soaking of PDMS moulds will effectively remove residual PDMS.  A dissolution rate of 1.0-1.5 µm/min has been shown using a heated bath at 50 °C.

Procedure

This procedure must be performed in one of the general-use wet decks (1A/1B/1C/2A).

  1. Determine the volume of 1% TBAF required to fully immerse the mould.
  2. Calculate the volume of PGMEA and TBAF required.  In general, 1.3 mL of 75% TBAF is required for every 100 mL of PGMEA.  Scale accordingly.
    • N.B. TBAF is corrosive (serious skin/eye irritation):  treat as HF when preparing the PGMEA/BAF solution, wearing full acid gear (face shield, chemical apron, chemical-resistant gloves).
  3. Mix the solution, either with a stir bar/stir plate or by hand with a stir rod, until thoroughly mixed.
  4. Load samples into the solution.
  5. If heating, use a stir bar, and slowly heat the solution until it reaches 50 °C.  Alternatively, a longer, room temperature soak is effective, and can be left overnight to clean.
  6. A second "clean" bath may be used following the initial bath.  Prepare if required.  If there are residual streaks or redeposited PDMS, a second bath is recommended.
  7. Follow the cleaning step(s) with an IPA soak to remove PGMEA.
  8. N2 dry.  Inspect the sample, and repeat the cleaning procedure if required.
  9. The TBAF/PGMEA solution, and any IPA used, must be disposed of in the solvent waste containers in the wet decks (waste bottles in 1A/1B/2A, cup sink in 1C).


Tetrabutylammonium fluoride solution (Sigma-Aldrich)

SDS - Tetrabutylammonium fluoride solution

SDS - SU-8 Developer

Reference

R.Dahiya, G.Gottardi, N.Laidani, PDMS residues-free micro/macro structures on flexible substrates, Microelectron. Eng., 136, 57–62 (2015)