Plasma Cleaning for PDMS Bonding

Plasma Cleaning for PDMS/PDMS and PDMS/Glass Bonding: Plasma cleaning is commonly used technique for surface preparation for various applications, including bonding PDMS (Polydimethylsiloxane) to PDMS or glass. Here’s how it works and why it’s beneficial for such bonding processes:

How Plasma Cleaning Works:

Plasma cleaning involves subjecting surfaces to a low-pressure plasma environment, typically using gases like oxygen, argon and even room air. When RF energy is applied to the gas, it ionizes and forms a plasma, which contains highly reactive species such as ions, radicals, and UV photons. These species can chemically react with the surface, removing contaminants and functionalizing it.

Benefits of Plasma Cleaning for PDMS Bonding:

• Contaminant Removal:  Plasma cleaning effectively removes organic contaminants, dust, and other particles from the surface. This is crucial for ensuring a clean bonding interface, which enhances the strength and reliability of the bond.
• Surface Activation:  Plasma treatment activates the surface by introducing reactive functional groups such as hydroxyl (-OH) and carbonyl (-C=O) groups. These groups improve the surface energy and wettability of PDMS, promoting better adhesion between PDMS layers or between PDMS and glass.  Several Customers want to see a hydrophilic surface, and take measurements to confirm the contact angle prior to plasma processing and after plasma processing.
• Improved Bonding Strength:  By removing contaminants and activating the surface, plasma cleaning significantly enhances the bonding strength between PDMS layers or between PDMS and glass substrates. This is particularly important for applications where a strong and durable bond is required.
• Uniform Treatment:  Plasma cleaning offers uniform treatment across the entire surface, ensuring consistent bonding properties and reducing variability between samples.

 

Procedure for Plasma Cleaning for PDMS/PDMS and PDMS/Glass Bonding:

 

• Selecting Gas:  Choose a suitable gas based on the specific requirements of your application. Oxygen is commonly used for PDMS bonding as it promotes oxidation of the surface, enhancing its adhesion properties.
• Plasma Parameters: Optimize plasma parameters such as power, pressure, and treatment duration based on the material and desired surface modification.
• Cleaning Procedure: Place the PDMS or glass substrates in the plasma chamber and evacuate the chamber to create a low-pressure environment. Then introduce the plasma gas and apply RF power to generate the plasma. Allow the plasma to treat the surfaces for the desired duration.  Often the best results are with a short time.  See this application note:
• Post-Treatment Handling: After plasma cleaning, it’s important to handle the substrates carefully to avoid recontamination of the surfaces before bonding. Bonding should ideally be done immediately after plasma treatment for best results.

By following these steps, plasma cleaning can effectively prepare PDMS surfaces for bonding, whether it’s PDMS/PDMS or PDMS/glass bonding, resulting in strong and reliable bonds suitable for various applications such as microfluidics, biomedical devices, and lab-on-a-chip systems.

Here are notes from Customers that use our plasma systems for this application:

From MIT:  The Auto is a single chamber 4” barrel asher, with a 300W RF maximum power supply, generating an air or oxygen plasma. Plasma causes chemical and kinetic energy to either modify the top levels of a substrate surface, if Using lower energy air plasma, or to removal organic materials, such as photoresist, if Using higher energy O2 plasma, on substrates no larger than 4”. Lower pressures equate to higher energies due to fewer inter gas collisions. Typical usages of low power are PDMS to glass bonding, often done for .2 min. (12 sec) at 100 W in air at 1 torr, and high power is typified by resist ashing done at 200 W and .5 torr, with time depending on resist thickness. RF Power of up to 250 or even 300 W can be used for short periods, but causes exhaust overheating after about 5 minutes. chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/http://web.mit.edu/scholvin/www/mq753/Documents/SOP.asher-EML.pdf

From Duke University:   Applications   AutoGlow 200 plasma system:

https://smif.pratt.duke.edu/capabilities/56203

 

“The silicon chip (etched side) was then bonded to the common channel layer atop the punched hole using oxygen plasma (Glow Research AutoGlow). All plasma bonding steps were performed at 30 W for 30 seconds.”    chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.rsc.org/suppdata/lc/c4/c4lc01366b/c4lc01366b1.pdf

 

 

Click HERE for an application note using air as a process gas for bonding

Click HERE  for more information on the GLOW plasma system

Click HERE for more information on the AutoGlow 200 plasma system