Optical Contact Bonding Synthetic Quartz Substrates
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Solution Overview
Problem
The existing methods for bonding glass substrates in microfluidic devices, such as thermal fusion, face challenges with productivity and surface defects like non-bonding and air bubbles due to insufficient surface smoothness and the need for pressure-welding, which can lead to substrate breakage and transfer of surface irregularities.
Innovation Solution
A synthetic quartz glass substrate with a specific surface roughness characterized by a maximum cyclic average power spectral density of 5.0 × 10^15 nm^4 or less, measured over a 6.0 mm × 6.0 mm area, is used for optical contact bonding, enhancing adhesion and preventing defects like non-bonding and air bubbles at the bonded interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermal fusion bonding is used to bond glass substrates, then strong adhesion is achieved, but productivity is reduced due to the need for pressure-welding and heating treatment
Solution Approach 1:
The patent replaces thermal fusion bonding with optical contact bonding, substituting a thermal-mechanical process with a simpler optical-physical process. By controlling surface roughness to specific standards, the substrates can be bonded through direct contact without heating or pressurizing equipment, dramatically improving productivity while maintaining bond strength.
Solution Approach 2:
The patent changes the surface roughness parameter of the glass substrates to specific ranges (arithmetic average roughness Ra of 0.3 μm or less, maximum roughness Rmax of 1.2 μm or less). This parameter optimization enables optical contact bonding to achieve sufficient adhesion without requiring thermal fusion conditions, thus improving manufacturing efficiency.
2Strength
If thermal fusion bonding with pressure-welding is used, then adhesion is enhanced, but substrate breakage and surface irregularity transfer occur
Solution Approach 1:
The patent eliminates the pressurizing jig and heating treatment steps by using optical contact bonding. This substitution removes the mechanical stress and thermal stress that cause substrate breakage and surface irregularity transfer, while still achieving strong adhesion through optimized surface roughness control.
Solution Approach 2:
The patent performs preliminary surface preparation by controlling the surface roughness parameters before bonding. By pre-optimizing the surface quality to specific standards, the bonding process can proceed without requiring high pressure or heat, thus preventing substrate damage and surface defect transfer.
3Strength
If polishing is performed to smooth the bonding surface, then adhesion is improved, but manufacturing complexity and time increase
Solution Approach 1:
The patent establishes specific surface roughness parameter ranges (Ra ≤ 0.3 μm, Rmax ≤ 1.2 μm) that enable optical contact bonding. By defining these precise parameters, the manufacturing process can control surface quality through standardized polishing procedures rather than requiring complex multi-step polishing, simplifying the overall process while ensuring adequate adhesion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables high productivity and robust bonding in microfluidic devices by ensuring strong adhesion and preventing defects such as non-bonding and air bubbles, allowing for efficient manufacturing without the need for pressure-welding and reducing the risk of substrate breakage.
Implementation Method 1
it is based on van der Waals force between the glass surfaces or hydrogen bonding between silanol groups on the surface of the glass which are formed by adsorption of water
Implementation Method 2
a channel forming step of forming a channel in at least one of the two surfaces which are to constitute bonded surfaces of the two or more synthetic quartz glass substrates by wet etching using a hydrofluoric acid solution
Data Source
Figure 1A~1D
Figure 2A~2D
AI summary
Provided is a synthetic quartz glass substrate for use in a microfluidic device to which bonding by optical contact can be applied in manufacturing a microfluidic device, and which has high adhesion in a bonded interface and does not cause defects such as non-bonding and breakage of the substrate and a defect in which air bubbles are sandwiched at the bonded interface. A synthetic quartz glass substrate for use in a microfluidic device, wherein a maximum value of a cyclic average power spectral density at a spatial frequency of 0.4 mm-1 or more and 100 mm-1 or less is 5.0 × 1015 nm4 or less, the maximum value being obtained by measuring any given region of 6.0 mm × 6.0 mm on a surface of the synthetic quartz glass substrate with a white interferometer.