3D packaging of a microfluidic system with sensory applications

Among the main benefits of microsystem technology are its contributions to cost reduction, reliability and improved performance. However, the packaging of microsystems, and particularly microsensors, has proven to be one of the biggest limitations to their commercialistion and the packaging of silicon sensor devices can be the most costly part of their fabrication. This paper describes the integration of 3D packaging of a microsystem. Central to the operation of the 3D demonstrator is a micromachined silicon membrane pump to supply fluids to a sensing chamber constructed about the active area of a sensor chip. This chip carries ISFET (Ion-Selective Field Effect Transistors) based chemical sensors, pressure sensors and thermal sensors. The electronics required for controlling and regulating the activity of the various sensors are also available on this chip and as other chips in the 3D assembly. The demonstrator also contains a power supply module with optical fibre interconnections. All of these modules are integrated into a single plastic-encapsulated 3D vertical multichip module (MCM-V). The reliability of such a structure, initially proposed by Val [1] was demonstrated by Barrett et al [2]. An additional module available for inclusion in some of our assemblies is a test chip capable of measuring the packaging-induced stress experienced during and after assembly. The packaging process described produces a module with very high density and utilises standard off-the-shelf components to minimise costs. As the sensor chip and micropump include micromachined silicon membranes and microvalves, the packaging of such structures has to allow consideration for the minimisation of the packaging-induced stresses. With this in mind, low stress techniques, including the use of soft glob-top materials, were employed.