Microfluidic Chip using Bonding Technique
Bonding process : The sealing of the open microchannels is necessary to produce the final enclosed fluid paths, and thus a critical step in the fabrication process invariably involves bonding a caping layer to the microchannel substrate. Bond strength is a critical consideration and bond interfaces must provide suitable chemical or solvent compatibility to prevent degradation during use, without compromising dimensional control of the microchannels due to deformation during the bonding process.
Other important considerations for the bond interface include surface chemistry, optical properties, and material compatibility and homogeneity of the channel sidewalls.
Additional issues such as manufacturability and compatibility with off- microfluidic chip interconnects can limit the selection of bonding methods.
Microfluidics bonding techniques may be categorized as either indirect or direct. Indirect bonding involves the use of an adhesive layer to seal two substrates and encapsulate microchannels fabricated in one or both of the substrates. In contrast, direct bonding methods fix the two substrates without any additional materials added to the interface.
While in direct bonding the bulk polymer itself comprises the adhesive giving a as a result microchannels with homogeneous sidewalls, indirect bonding methods require an intermediate adhesive that results in channel sidewalls with different chemical, optical and mechanical properties than the bulk polymer.
In general, bonding forces between mating surfaces arise from either molecular entanglement or charge interactions. Entanglement can occur by mechanical interlocking of diffusion between surfaces, while bonding due to charge interactions can result from electrostatic or chemical (covalent) bonding, acid-base interactions, or van der Waals forces.
Thermoplastic bonding methods like thermal fusion bonding, solvent bonding, localized welding and surface treatment and modification bonding are mainly achieved by molecular entanglement.
Adhesive bonding is achieved from charge interactions. In most cases bonding at high temperatures can greatly enhance polymer entanglement and interaction at the bonding interface resulting in high bong strength. However, bonding methods for microfluidic chips must be adapted and optimized for the task of enclosing micron-scale fluidic channels without excessive deformation of the channel cross sections.
Sealing injected pieces, both flat and structured pieces, is one of our well-established fabrication procedures. Alignment accuracy is around units of microns and the bonding yield reaches the 97% of the total area.
We are sealing polymers such as COC, COP, PMMA, PET and also PS, PC, but we are able to create a bonding setup for any polymer needed, doing short series or mass production.
This setup enables:
1. Accurate Flatness (Deformation ± 1 micron)
2. Ideal products for optical applications
3. Impurities-free product, done in clean room