287 1 INTRODUCTION Since always the production of products and its components has been reduced in size in order to be lighter and allow the incorporation of more functions in a smaller space (Maluf & Williams 2004; Ho et al. 1998). Accelerometers are MEMS sensors with applica- tions in important fields such as automotive, medi- cal, consumer electronics among others (Yazdi et al. 1998). Accelerometers can work based on distinct transduction mechanisms such as piezoelectricity, piezoresistivity, capacitive sensing, resonant fre- quency shift and thermal sensing. This work will fo- cus in thermal accelerometers because their trans- duction mechanism is simple and presents no proof mass avoiding complex and expensive fabrication processes and mechanical failure typical from other types of accelerometers (Maillyet et al. 2003; Garraud et al. 2011; Park et al. 2008). Thermal accelerometers contain a hot bubble (gas or fluid), a heater and temperature sensors equally distant inside a sealed chamber. Once electrical cur- rent is applied to the system the heater temperature increases due to Joule effect. If the acceleration is zero the heat is equally distributed over the hot bub- ble being measured the same temperature value at the equally distant temperature sensors while if ac- celeration is different from zero the hot bubble shifts by free convection and different temperatures are measured by the temperature sensors. This tempera- ture difference can be correlated to the acceleration value (Leung et al. 1997; Luo et al. 2002). This paper presents an alternative fabrication method for thermal accelerometers based on the combining of microinjection moulding and MEMS technology. The use of polymeric materials with low thermal conductivity can overcome the thermal loss- es reducing this way the power consumption typical from silicon based technologies while the diverse design possibilities that polymeric technologies al- low can overcome the limited z-axis design (Garraud et al. 2011; Park 2008). Microinjection moulding technology allows the production of complex, small and low-weigh poly- meric parts. Polymeric materials are known for their wide range of thermal, mechanical and electrical properties and can be low cost processed for large scales (Huang & Chiu 2005; Sahli et al. 2009). This recent technology emerged due to new market re- quirements for smaller, complex, efficient and low- cost components (Vlack 1989; Varadan et al. 2006). Micromoulding builds on the idea of transferring the high potential of conventional injection moulding Mould redesign and analysis for the production of a micro-accelerometer C.S. Silva*, P. Pereira, J.C. Viana, L.A. Rocha, A.J. Pontes, Institute for Polymers and Composites /I3N, U. Minho, Guimarães, Portugal (*) catiasilva@visitor.inl.int ABSTRACT: In this paper we present an alternative fabrication method based on polymeric materials and technologies for three-axis thermal accelerometers. The device is composed by four microinjected parts form- ing an external structure responsible for the coupling and sealing of a polymeric membrane. The membrane contains and protects the heater and thermoresistors and is fabricated by microtechnologies. The fabrication process was successful although some issues were noticed in the mould during the microinjection process. Regarding the ejection side, a redesign was done to first assure the locking of the micro-parts on the movable side of the mould and second to improve the extraction of the parts avoiding its deformation. Overheating of the mould and polymer freezing on the injection nozzle were the main issues found on the injection side of the mould. Three different injection nozzle designs and two different fabrication materials were analyzed and simulated. The results show that an intermediate injection nozzle design using Ampcoloy 940® as construc- tion material can improve the maintenance of the established temperature values for both mould and injection nozzle.