Replica molding - NanoLabStaff/nanolab GitHub Wiki

by Jonas M. Ribe

Steps	Process
1. Mix	1:10 ratio curing agent/base by stirring for >5 min
2. Degas	30-45 min. in desiccator
3. Pour	>3g per 2” wafer
4. Cure	2h at 65°C in oven
5. Peel	Slowly by hand and cover feature side w. plastic foil

1. Make mold

   See SU-8.

2. Silanize mold (optional)

    Silanization facilitates the release of the PDMS from the mold. 
    This improves the durability of the mold. Silanize the mold by 
    placing it in desiccator together with a drop of silane. 
    Pump down and leave for 1-2h.
   

3. Mix PDMS

    Mix PDMS from Dow Corning’s Sylgard 184 two component silicone elastomer 
    kit with a ratio of 1:10 curing agent (cross-linker) to base (siloxane) 
    measured using a digital scale. Stirr using a plastic spoon for ∼5 min.
   

4. Degas PDMS

    Remove the bubbles created by mixing, by degassing PDMS for 30-45 min. 
    in a desiccator. Vent the chamber every 15 min. to improve the pumping 
    efficiency.
   

5. Make holder:

    Place mold in a ”cupcake” holder made from aluminum foil. 
   

6. Pour PDMS

    Pour PDMS slowly in center of the wafer. ∼3g PDMS is typically 
    sufficient for thinner devices. Push down the wafer to ensure an even 
    height of PDMS. If new bubbles are formed when pouring they can be 
    removed using the spoon, otherwise another degas step is required. 
   

7. Cure PDMS

    Cure the PDMS in a Termaks oven at 65°C for 2h.
   

8. Peel PDMS

    Once cool, peel the aluminum foil off the cured PDMS. 
    Start at the edge of the wafer and peel slowly. 
    Cover the features side with a plastic film to protect 
    the features and improve visibility when punching. 
   

9. Punch inlets (optional)

    Punch inlet holes for tubings using UniCore punchers.
   

10. Tape clean

     Pick up particles and PDMS debris made by the puncher by covering the 
     device with Scotch tape and peeling.
    

11. Plasma bond

    Treat the surfaces to be bonded (glass or PDMS) with a short oxygen 
    plasma (e.g. 12s 50% O2, 50% power). Bring the surfaces in contact. 
    Finalize the bond by baking the device at 80°C for ~15 min.
    

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