Low-Pressure, Thermal Direct Bonding of PMMA-Dry Film Photoresist-PMMA for Microdevice Fabrication

• Published in: Lecture Notes in Mechanical Engineering
• Main Author: Yazid M.F.M.; Nawang F.M.; Nasir S.M.F.S.A.; Yusof A.M.
• Format: Conference paper
• Language: English
• Published: Springer Science and Business Media Deutschland GmbH 2024
• Online Access: https://www.scopus.com/inward/record.uri?eid=2-s2.0-85201525627&doi=10.1007%2f978-981-97-0169-8_35&partnerID=40&md5=7c12182e8fc136dbb65f9f6f2eb01add

In many microfluidic device fabrications, obtaining the hermetic sealing is a great challenge, especially for bonding between non-homogenous material pairs. This work presents the evaluations of non-homogeneous material bonding between dry film photoresist (DFR) and poly-methyl methacrylate (PMMA) substrates using low-pressure and low-temperature direct thermal bonding. DFR is a light-sensitive material and well adhered to the PMMA surface before UV exposure, but its chemical structures changed after being exposed to UV irradiation, which caused the DFR to crosslink permanently. Therefore, the low-pressure and low-temperature (below the glass transition temperature of PMMA, TG = 95 °C) bonding evaluation was made by first preparing the base substrate by laminating the DFR on PMMA (PMMA/DFR) and then exposing it under UV i-line irradiation (wavelength 365 nm) for 120 s. The base substrate was later bonded with another PMMA substrate, creating a substrate consisting of the PMMA/DFR + PMMA pairs. Three different surface conditions were evaluated: the PMMA substrate without surface treatment, the PMMA substrate surface treated with isopropanol, and PMMA substrate surface treated with ethanol. Different curing temperatures and times in the inductive oven were carried out. Results revealed that without sufficient clamping pressure, thermal direct bonding of an untreated PMMA substrate surface could not be obtained even after it was cured in an oven at a temperature close to TG. While surface treatment with ethanol revealed promising bonding between PMMA and DFR + PMMA, the bonding coverage area could attain only 50% at best with curing temperature of 90 °C for 25 min. Surface treatment with isopropanol revealed an interesting result whereby 90% coverage area of bonded surface obtained when cured in an oven at 90 °C for 20 min. Bonding shear stress evaluation produces 1.92 MPa at best. The results obtained in this work offer low-pressure and low-temperature thermal direct bonding which can be used as a guide for future microfluidics device fabrication. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.