Bonding Strength of a Glass Microfluidic Device Fabricated by Femtosecond Laser Micromachining and Direct Welding

Abstract

We present a rapid and highly reliable glass (fused silica) microfluidic device fabrication process using various laser processes, including maskless microchannel formation and packaging. Femtosecond laser assisted selective etching was adopted to pattern microfluidic channels on a glass substrate and direct welding was applied for local melting of the glass interface in the vicinity of the microchannels. To pattern channels, a pulse energy of 10 μJ was used with a scanning speed of 100 mm/s at a pulse repetition rate of 500 kHz. After 20–30 min of etching in hydrofluoric acid (HF), the glass was welded with a pulse energy of 2.7 μJ and a speed of 20 mm/s. The developed process was as simple as drawing, but powerful enough to reduce the entire production time to an hour. To investigate the welding strength of the fabricated glass device, we increased the hydraulic pressure inside the microchannel of the glass device integrated into a custom-built pressure measurement system and monitored the internal pressure. The glass device showed extremely reliable bonding by enduring internal pressure up to at least 1.4 MPa without any leakage or breakage. The measured pressure is 3.5-fold higher than the maximum internal pressure of the conventional polydimethylsiloxane (PDMS)–glass or PDMS–PDMS bonding. The demonstrated laser process can be applied to produce a new class of glass devices with reliability in a high pressure environment, which cannot be achieved by PDMS devices or ultraviolet (UV) glued glass devices.

Advances in femtosecond laser processing of optical material for device applications

“…Automated production of complex 3D glass parts for applications such as connectors, nested nozzles, and a cell‐sorting structures was demonstrated . Shown in Figure , a combination of femtosecond laser assisted selective etching and direct welding for local melting was used to demonstrate a rapid and robust new process for microfluidic device creation . The glass device exhibited increased bonding strength as it was able to endure up pressure up to 1.4 MPa without breaking or leaking, this pressure is even higher than that observed for polydimethylsiloxane (PDMS)–glass or PDMS–PDMS bonding.…”

“…The glass device exhibited increased bonding strength as it was able to endure up pressure up to 1.4 MPa without breaking or leaking, this pressure is even higher than that observed for polydimethylsiloxane (PDMS)–glass or PDMS–PDMS bonding. This shows a route to devices that can be used in high‐pressure environments where other devices created from other material fail . A new phenomenon was reported by Li et al where by chirping the Fourier‐transform‐limited femtosecond laser pulses to picosecond pulses, the etch rate dependence on polarization is eliminated.…”

“…E, Droplets collected at the reservoir. [Reprinted/Adapted] with permission from reference [66] © CC BY [Color figure can be viewed at wileyonlinelibrary.com]…”

Optimization of selective laser-induced etching (SLE) for fabrication of 3D glass microfluidic device with multi-layer micro channels

“…However, in the fabrication of glass microfluidic devices, various microelectromechanical systems (MEMS) process steps such as masking, etching, drilling, and bonding are required and thus it takes more time and cost than soft lithography [8]. To overcome these disadvantages, we have studied a rapid fabrication process that can make an all-glass microfluidic device within an hour using ultrafast laser 3D direct writing [9,10]. Ultrafast laser technology has been widely used in the microfabrication of various materials by taking the benefit of ultrashort laser pulses to minimize heat-affected zone (HAZ) which is critical for high precision, high speed, and high-quality manufacturing.…”

“…In particular, its' direct writing nature offers any freeform patterns programmed in computer-aided design (CAD) without a mask, and the structure formed inside glass has high durability because of no bonding process [28]. It also provides the good surface quality below 1 μm surface roughness after wet etching [10,15,29].…”