A reworkable adhesive-free interconnection technology for microfluidic systems

In this paper, we present a simple adhesive-free interconnect technology for microfluidic systems. Reliable connection between microfluidic devices and macroscopic world is a critical issue in many lab-on-a-chip applications. In such interconnections, it is particularly advantageous to avoid liquid adhesives (e.g., epoxy, silicone, etc.) since they can create reliability (blockage or leakage) and reproducibility problems. Our adhesive-free interconnection technology is based on a micromachined silicon flange which is connected to a medical-grade silastic tube using a heat shrink tubing sleeve. The silicon part was fabricated by consecutive anisotropic and isotropic etching processes resulting in a through-hole surrounded by a connection socket ring created using the well known lag effect of deep reactive ion etching. Biocompatible polyolefin heat shrink tubing (expansion ratio of 2:1 at its shrink temperature of 143°C) was used to connect and tightly seal the silicon flange to the silastic tube without application of any adhesive. A two-step heat treatment starting from the silicon flange and terminating at the silastic tubing was used to seal the connection. High temperature removability of the heat shrink tubing makes interconnects reworkable. Pull-out force was measured to test the mechanical strength of interconnects with different socket shapes (square, hexagon, octagon, and 32-side circle). Increasing the number of sides improves the mechanical strength with the circular interconnects having an average pull-out force of more than 3N. Leakage tests were also performed to characterize the seal quality. The circular connectors of two different flange sizes showed zero leakage up to the maximum test pressure of 200 kPa (29 psi).