Microfluidic Bonding Technology Guide for Polymer Consumables

Figuring out the key criteria to consider and how several technical choices, at different stages of the process impact each other can be stressful when choosing the right microfluidic bonding technique. As an engineer, you must address design and process issues early to produce a high-quality consumable product.
laser welding_edited
But what are key criteria to consider? And how do several technical choices in different stages of the process impact each other? Figuring out these and more questions can be stressful with the amount of information around.
At Axxicon and within the Flow Alliance, we have been working on several projects were bonding is an important part of the product’s functionality. This article summarizes some of the knowledge we gained:
  • Requirements for the selection of your bonding process
  • Common bonding technologies
  • How to decide?
Continue reading to find out more.

Requirements for the selection of your bonding process

Each microfluidic product and application has unique requirements, and the bonding process you choose must meet those criteria as well. Common requirements are:
  • Optical properties
    In some applications it is essential to compromise the optical properties of the consumable like transparency, prevent autofluorescence
  • Chemical and biological compatibility
    Biocompatibility, contact of reagents or samples with glues, VOCs
  • Pressure stability
    For some applications pressures within the consumable can increase.
  • Channel dimensions integrity
    The dimensions of structures like channels or cavities should stay within tolerance after bonding
  • Design limitations
    Not all bonding processes might be compatible with all designs. Distance of features, available surface for bonding, this all can be relevant
  • Reagent storage on chip (before bonding)
    For example coatings or bio-reagents can be stored on chip, but can they also survive the bonding process?
  • Material compatibility
    Not all bonding processes work with all materials
  • Shelf life
    How will the consumable be stored? Will there be reagents in the consumable during storage?
  • Scalability and cost
    In product development scalability and cost is always relevant. In the end the bonded product has to be produced in volumes and for a certain target price.
It can be challenging to put these requirements together and choose a suitable process as there is not black and white answer. Luckily, we have outlined methods for selecting the best process for your specific application requirements in the remainder of this article. Also our webinar on demand will give you additional insight. Keep reading to learn more!

Common bonding technologies

There are a variety of bonding techniques available, some of which are more advanced than others. Let's look at the more mature ones that are commonly utilized in microfluidic consumables currently. We briefly summarized some of the bonding methods, as well as their advantages and disadvantages below.

Solvent Bonding

With this technique, a solvent is used to form a strong, long-lasting bond between two polymer layers. This method is extremely adaptable and can be used with virtually any microfluidic design.
However, if you add bio-reagents before bonding, this will not be a suitable option. The time required to bond a product is relatively long (10s of seconds), which will have an impact on the final price of the polymer consumable.

Thermal Bonding

Because no additives are used, this method provides a very pure and very strong material bond. As this process involves heat, no biochemicals or bio-materials should be present on the chip prior to bonding. The used heat can also cause some deformation of the microfluidic structures.
The time it takes to bond layers together with this technique is longer, making it a costly operation with limited scaling possibilities.

Adhesive Bonding

This bonding process is extremely versatile due to the numerous options for application techniques, adhesive types and curing parameters when necessary. Almost any structure can be bonded, and the process simple to optimize. It is an easy to scale up process and offers a low-cost solution for producing microfluidic consumables in small to large quantities.Adhesive curing station for microfluidic bonding
However it might not be compatible with all assays and is some cases might affect the dimensions of the microfluidic structures. Not all microfluidic designs might be compatible with the application methods. Shelf life varies per adhesive.

Tape assisted bonding

There is a wide range of tapes available that are suitable for a broad variety of products and assays. It is a low cost process that is ideal for rapid testing and development. Tape surface properties can be customized.
However, high hydrophilic tapes are hard to come by. Thinner tapes are difficult to process and can present difficulties, such as tape folding, and trapping bubbles.

Laser welding

Using this process the bond is formed by melting layers together with a laser. It creates very pure and strong bond. The time required to form this type of bond is short, and it provides in-line capabilities for a production line.
However as the process time increases with the complexity of the microfluidic structures it might not be a low cost process for some consumables. Also most laser welding processes available need a non-transparent part for bonding.

Ultrasonic welding

In this technique, energy directors use the ultrasonic vibrations to create a pure bond between the layers. It is a fast process using a well-established technology with a low development effort.
This process, however,has an impact on your microfluidic design because energy directors must be implemented. Also if your product has very small and intricate features, this may not be the most accurate bonding method for your product.

But how to decide?

With all of this information, how do you choose the bonding process that is best for your unique polymer consumable, assay and set up?
Returning to the requirements for microfluidic bonding mentioned earlier, we can examine the various bonding technologies that can meet those requirements. The image below depicts the most appropriate microfluidic bonding technologies for the aforementioned requirements.
Bonding process considerations overview
As you can see, some of the processes mentioned appear several times. These combinations could be the significant to your process. Because each application, assay, and consumable has its requirements, there might be solutions or (combination of) processes that would surprise you. Our experts at Axxicon and the Flow Alliance will gladly discuss the best process for your specific microfluidic consumable.
How to move forward? Read on.

Webinar bonding process considerations

Do not miss our on-demand webinar on microfluidic bonding process considerations to learn more about the individual processes and decision criteria. The presentation will be followed by a question and answer session with our Flow Alliance expert panel from Axxicon and Micronit who will give valuable insights to pressing questions around that topic. 
Get your webinar on demand here.

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