Tham khảo tài liệu 'radio frequency identification fundamentals and applications, design methods and solutions part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fabrication and Encapsulation Processes for Flexible Smart RFID Tags 241 Fig. 3. FTM prototype including relative humidity temperature and light sensors and a flexible antenna. A credit card size was chosen for the tag. were considered as well. Details of the design and fabrication of the chips are given elsewhere Elmi et al. 2008 Abad et al. 2007 . To reach the extremely low power consumption necessary for flexible tag operation MOX sensors are designed to be used in discontinuous mode as reported in Sayhan et al. 2008 . The gas sensors based on MEMS structures need to be electrically connected to the rest of the tag electronics and subsequently mechanically encapsulated and protected from damaging. While for the electric connections the same strategies as for other dies can be adopted gas sensors have some mechanical peculiarities the sensing layer must be exposed to the air sample being analysed. Therefore assuming to have the sensing layer on the same side as the contact pads the typical flip-chip underfilling techniques cannot be applied since they would cover and damage the sensing layer. The suspended membrane and the sensing layer must be protected from damaging being generally very fragile they could brake if they get in contact with particulate or water drops. Considering the above issues two MOX sensor encapsulation strategies were followed in parallel aiming at an overall risk reduction of this activity. 242 Radio Frequency Identification Fundamentals and Applications Design Methods and Solutions ACA flip chip bonding Flip chip technology utilizing ACAs has been proved to be a possible solution for MEMS packaging Pai et al. 2005 and Johansson et al. 2006 . Using this technology a special procedure has been designed for the integration of the ULPHP involving the following main steps illustrated in Figure 4 a 1. Window opening by femtosecond laser ablation. 2. Patterning of the electrical contacts. 3. ACAs flip-chip for assembly. 4. Polymer casting and .
