Reservation  -     

Center of MicroNanoTechnology CMi

PDMS line

PDMS zone12 access is only possible with CMi_BM+1 ISO 6/7 clothing. Access with CMi_BM-1 ISO5 clothing is strictly forbidden.
See gowning regulation HERE


Printable user manual is available HERE

New PDMS dispenser details HERE

Contents: CMI

  1. Material requirements
  2. PDMS molds
  3. Typical process flow
  4. Surface conditioning
  5. Mixing - Degassing
  6. Pouring - Spin coating
  7. Baking - Curing
  8. Alignment - Demolding - Access ports by punching
  9. Surface activation for bonding

I. Material requirements CMI

Handling. Safety glasses, gloves, tweezers, Petri dishes, pipettes, spoons, cups, razor blades, scalpels, aluminum foil.

Machines. Ventilated fume hood, high precision scale, mechanical mixer, vacuum desiccators, spin coater, manual hole-punching machine, binocular, oven/hot plate, oxygen plasma.

Products. Sylgard 184 silicone base, Sylgard curing agent, silanizing agent (TMCS: Chlorotrimethylsilane, 33014 from sigma).

Please read with great attention the Material Safety Data Sheets (MSDS) and the Standard Operation Procedures (SOP) of products mentioned above

II. PDMS molds CMI

The first step in PDMS molding is designing molds and creating them. SU-8 processing and silicon etching are the two protocols commonly used to realize molds for PDMS micro-molding. Procedures for creating these molds are not presented in this present document.

III. Typical process flow CMI

Process Flow

IV. Surface conditioninghaut CMI

The surface conditioning of the mold is important to prevent PDMS sticking. A silanization allows passivation of the surfaces to aid release from PDMS.


Conditioning01


Conditioning02

V. Mixing - Degassing CMI

ADDITIONAL SINGLE USE GLOVES REQUIRED. DO NOT TOUCH ANYTHING IN THE ZONE (chairs, tables, computer, doors...) BUT ONLY THE EQUIPMENT NEEDED FOR MIXING AND DEGASSING THE PDMS. DO NOT HESITATE TO THOROUGHLY USE PAPER WIPERS TO QUICKLY CLEAN PARTS AND TO AVOID UNDESIRABLE CONTAMINATION.

Aluminum foil is used as a liner for protecting equipments in contact (Petri dishes, scale...).
A single use plastic cup is to be used for preparing the PDMS mixture. The plastic cups are compatible with the mechanical mixer and their maximum capacity is 50g. This means the total mixture must weigh 50g maximum.


Mixing01

Caution: adapter weight of 115g to be added to the weight of your cup
Clean well the scale before switching it off and clean the products bottles

Mixing02

Final degassing may be performed using the desiccator.

VI. Pouring - Spin coating CMI

ADDITIONAL SINGLE USE GLOVES REQUIRED. DO NOT TOUCH ANYTHING IN THE ZONE (chairs, tables, computer, doors...) BUT ONLY THE EQUIPMENT NEEDED FOR POURING  SPIN COATING THE PDMS. DO NOT HESITATE TO THOROUGHLY USE PAPER WIPERS TO QUICKLY CLEAN PARTS AND TO AVOID UNDESIRABLE CONTAMINATION.

Pouring.
Pour the PDMS mixture over the passivated mold placed in a Petri dish. The interior of that dish should be protected with aluminum foil. Be careful not to create bubbles while pouring the mixture (proceed slowly). The mixture is then degassed in the desiccator to remove any remaining entrapped bubbles. If large bubbles form at the surface, vent vacuum slowly so the mixture does not foam out. Put it back under vacuum until no bubbles are visible. This also improves the filling of small structures.

Pouring


Spin coating. Programming instructions are available HERE. After spin-coating, it is essential to leave the substrate at atmospheric pressure for ~15min to homogenize the thickness on the edges. Also, an additional degassing step in the desiccator may help removing remaining entrapped air.
A spin curve of a 10:1 ratio spun onto silicon wafers is available HERE.

The spinner can operate up to 9999rpm. Chucks for 4" wafers, microscope slides and 1x1cm samples are available.

Spin

VII. Baking - Curing CMI

PDMS can cure without heating in ~24 hours. To decrease cure time, put the Petri dish in an oven for at least 2 hours at ~80C. Curing time depends on temperature and on the thickness of PDMS. After curing, the wafer is stable and can be stored for months if necessary.

Baking

VIII. Alignment - Demolding - Access ports by punching CMI

DEMOLDING-CUTTING IS TO BE DONE IN THE DEDICATED TRAY PRESENT ON THE CENTRAL TABLE. A SECOND ALUMINUM LINER IS TO BE PUT BEFORE CUTTING-DEMOLDING AND IS TO BE DISPOSED OF BEFORE LEAVING THE PLACE. NO CUTTING-DEMOLDING ALLOWED OUTSIDE THIS TRAY FOR CONTAMINATION REASONS.

After cooling, the PDMS is easily peeled off and cut. Use adequate tools to perform it (tweezers, razor blades...). Cut the PDMS into the desired shape.

Alignement01


Create access ports using the manual hole-punching machine fitted with a light source and a video camera. Alignment of PDMS samples with other glass/PDMS/silicon pieces can be done using the binocular.

CLEAN WELL THE PLACE BEFORE LEAVING. DISPOSE OF THE SECOND ALUMINUM LINER. BE SURE NO RESIDUES OF PDMS ARE REMAINING.

Alignement02


IX. Surface activation for bonding CMI

PDMS can be bonded to glass, silicon and itself using oxygen plasma surface activation. PDMS is hydrophobic, with a low energy and non reactive surface. It is therefore difficult to bond it with other surfaces. By exposing PDMS to oxygen plasma, its surface becomes hydrophilic and more reactive. This results in irreversible bonding when it contacts glass, silicon, or even another PDMS piece that was exposed to the same oxygen plasma. Contact should be made quickly after plasma exposition because the PDMS surface will undergo reconstitution to its hydrophobic and non reactive state within hours. The bonding is accelerated if a post-bake is then performed.

Activation


A fine tuning of the oxygen plasma is necessary: