A Simple Bonding Process of SU-8 to Glass to Seal a Microfluidic Device

S. G. Serra(a), A. Schneider(a), K. Malecki(b), S. E. Huq(a), W. Brenner(b)
a: Science and Technology Facilities Council, Rutherford Appleton Laboratory,Technology – Central Microstructure Facility, Harwell Science and Innovation Campus, Didcot, OX11 0QX, UK
b: Institute of Sensor and Actuator Systems Vienna University of Technology, Floragasse Str./E366 MST, Vienna 1040, Austria

Abstract

This paper describes a simple process of adhesive bonding between a glass lid and a SU-8 microfluidic device. The bonding is made by applying pressure, between 1.24 MPa – 3.72 MPa, and heat, above the SU-8 glass transition temperature (Tg). The advantages of this process are low cost, simplicity and no need of extra adhesive material, which could block microchannels and inlets. The SU-8 microchannels are fabricated on a glass substrate by UV photolithography. The resist thickness is 30 μm and the smallest channels are 5 μm in width. The bonding process was performed using a simple uniaxial press, a torque wrench and a convection oven as an alternative to the complex and expensive bonding machines with a vacuum chamber and alignment tools. To identify a suitable bonding temperature, a Tg of 175°C for the patterned SU-8 was obtained by Dynamic Mechanical Analysis (DMA). The bonding strength was 1.15MPa, measured by a pull-out test, and a bonding area of 90% was achieved, which was observed by visual inspection. It was also investigated the effect of an O2 plasma cleaning process on the bonding quality.