High Throughput Microfluidic Rapid and Low Cost Prototyping Packaging Methods

Summary

In this article we describe different techniques for microfluidic rapid prototyping platforms. The proposed techniques are based on ultraviolet (UV) sensitive and temperature curing epoxies, polydimethylsiloxane (PDMS) based tubing, wire-bonding, and anisotropic adhesive films. The assembling procedures presented are developed for both one-time use devices as well as reusable microfluidic systems.

Abstract

In this work, 3 different packaging and assembly techniques are presented. They can be classified into two categories: one-time use and reusable packaging techniques.

The one-time use packaging technique employs UV-based and temperature curing epoxies to connect microtubes to access holes, wire-bonding for integrated circuit connections, and silver epoxy for electrical connections. This method is based on a robust assembly technique that can support relatively high pressure close to 1 psi and does not need any support to strengthen the microfluidic architecture.

Reusable packaging techniques consist of PDMS-based microtube interconnectors and anisotropic adhesive films for electrical connections. These devices are more sensitive and fragile. Consequently, Plexiglas support is added to the microfluidic structure to improve the electrical contact when anisotropic adhesive films are used, and also to strengthen the microfluidic architecture. In addition, a micromanipulator is needed to maintain tubes while using a thin PDMS layer to connect them to the access holes. Different PDMS layer thicknesses, ranging from 0.45-3 mm, are tested to compare the best adherence versus injection rates. Applied injection rates are varied from 50-300 μl/hr for 0.45-3 mm PDMS layers, respectively. These techniques are mainly applicable for low-pressure applications. However, they can be extended for high-pressure ones through plasma-oxygen process to permanently seal the PDMS to glass substrates. The main advantage of this technique, besides the fact that it is reusable, consists of keeping the device observable when the microchannel length is very short (in the range of 3 mm or lower).

Introduction

Recent progresses in microfabrication have led to more complex microfluidic devices including a large number of electrodes and different types of control algorithms. However, these advances highlighted new challenges in packaging. Furthermore, Lab-on-Chip (LoC) is a multidisciplinary concept where microfluidic devices, microelectromechanical systems (MEMS), microelectronic chips among other parts are connected together. Consequently it is impossible to develop a packaging process without considering different constraints of LoC components such as microelectronics circuitry sensitivity and protection, tubing, and mechanical aspects. In addition, packaging the component....

Protocol

1. Removable PDMS-based Interconnector for Low-pressure Microfluidic Applications^15-16

1. Preparation
   This section describes different steps to prepare the glass and PDMS in order to produce the interconnector.
   1. Prepare the PDMS: Mix the PDMS and curing agent with (10:1) ratio.
   2. Ensure that the oven temperature is stabilized at a constant temperature of 80 °C. Depending on the oven, use a measurement device to sense the temperature of the oven and then manually monitor it.
   3. Thoroughly clean the Petri dish with ethanol.
   4. Clean the surface of the microfluidic access holes where the....

Results

Figure 3 illustrates a detailed schematic of the proposed packaging technique. The packaging solution was tested with several PDMS thicknesses and sizes to characterize a transparent and efficient packaging process for hybrid microelectronics/microfluidic microsystems as shown in Figures 4 and 5. The dimensions of the designed PDMS interconnector layer are 6 mm x 6 mm and it is used to connect two access holes. However, with major commercially available connectors, it is.......

Discussion

The PDMS interconnector is intended for low-pressure applications, liquid leakage into the chip access hole when the PDMS interconnector is subsequently placed on the access hole must be prevented. Therefore, the recommended thickness of PDMS is less than 2 mm. A greater thickness can induce a weak adhesion of the PDMS to the microfluidic chip surface and is not recommended. An unsuccessful trial was made using a thickness of 4 mm. This work focuses on the adherence of the PDMS interconnector to the glass while syringe p.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Epoxy 731	Epotek	731
PDMS	Dow Corning	SYLGARD 184
UV Epoxy	Epotek	OG159
Micropump	Harvard Apparatus	PHD Ultra
PCB	Advanced Circuits
Plexiglass	Ecole Polytechnique
Adhesive conductive film	3M	9703