Integration and Packaging of Microsystems by Polymer Overmoulding

Individual microsystems and devices are made by, broadly speaking, lithographic techniques with inorganic materials such as silicon, and techniques such as embossing and injection moulding with polymers. Typically, devices made from inorganic materials are active, relatively high cost and have a so called "21/2D " structure, while devices made from polymers are passive, low cost, and can have truly 3D structures. It is proposed that through overmoulding, polymers can also be used for the 3D packaging and integration of microsystems, for example to interconnect and combine the functionality of different types of device at reduced cost. This paper reports results of a preliminary investigation into this concept. Glass and silicon inserts 25 mm times 20 mm in size, used in this case to represent microfluidic devices, were overmoulded in an injection moulding process with a range of polymers. The inserts were found to survive the moulding process intact. The adhesion between overmould and insert was investigated by subjecting the interface between the overmould and insert surface to hydrostatic pressure of up to 100 psi (6.9 bar). The durability of the interfacial adhesion to hydrolysis was investigated by immersion in water at 50degC for 24 hours before testing. Direct measurements of adhesion strength between polymer and glass were also attempted by tensile tests on lap joint samples. The best and most durable adhesion for glass and silicon inserts was found for PA12, a low hygroscopicity polyamide. Post-packaging by overmoulding with ABS of a commercial silicon pressure sensor module was also demonstrated. The results have potential for the development of a mass-manufacture friendly process for the packaging and fluidic interconnection of microsystems