The Study On UHF RFID Tag Antenna Design And Packaging Technology

Radio frequency identification technology is a non-contact automatic identificationtechnology based on RF communication.Its principle is that the information is exchangedbetween the reader and the tag attached to items by inductive coupling or microwavebackscatter，to achieve automatic identification of tags.As a new type of automaticidentification technology, it has characters of non-contact, far distance, small size, largeinformation capacity, anti-interference, easy adapting ability, multi-target recognition,mobile identification, being reusable, long life, etc. The paper focuses on UHF tag antennadesign and ultrasonic flip-chip packaging process of the tag chips.First, a brief introduction of the RFID concept and principle is given, and then wedescribe its compositions and classifications, and explain UHF RFID systemcommunication link in detail. Based on the principle of microwave backscatter, weestablish the mathematical model of the system communication, make logic operations,and analysis important parameters of the tag antenna, including impedance, return loss,gain, etc. In addition, the mathematical formula of the tag’s farthest reading distance isestablished.Secondly, the common UHF tag chips are introduced, and the impedance of theselected chip is analysed. We mainly discuss the design principle and operatingcharacteristics of dipole tags, and explore characteristics of folded dipole and bendeddipole antennas. A folded dipole antenna with high gain and wide bandwidth is designedby simulations, and the laws of impedance matching and gain adjustment are summarized,then we finish the printing of the tag antenna.Again, the principle and methods of the anti-metal RFID tag are introduced,anti-metal tag antennas are discussed, and the properties of anti-metal tag antennas areanalysed, focusing on the design principle and structure features of the microstrip antenna.For the selected UHF tag chip, we design a ceramic base anti-metal tag antenna, andcomplete the simulation and optimization of the microstrip patch antenna. Later, the chipis bonded onto the ceramic base antenna by gold wire bonding, and the reading distancesof the sample tags in free space and on the metal surface are similar, which means theanti-metal performance of the sample tags is good. Finally, the tag packaging processes is introduced briefly, which are ACA conductiveadhesive connection and wire bonding, and their influences on impedance matchingbetween the tag chips and antennas are analysed. The former brings in large parasiticcapacitance, and the latter introduces small parasitic inductance. We mainly study thealternative process of ACA conductive adhesive connection–ultrasonic flip-chiptechnology. A introduction of ultrasonic flip-chip principle is given, and then the ultrasonicflip-chip experiment of the tag chips is completed. The experimental results are analysed,and the indicators meet requirements, which means ultrasonic flip-chip packaging processis entirely possiblely replaces ACA conductive adhesive connection.