Achieving high speed RFID die pick and place operation

Driven by the proliferation of smart cards and RFID tags, increasing throughput in the manufacturing line is critical to meeting market demands. Maintaining Unit-Per-Hour (UPH) rates in excess of 10,000 becomes a major challenge requiring that many different processes be tuned to work together. The fundamentals of materials surface properties - of the silicon wafer backside and of the wafer dicing film, and of their interaction - must be understood. The properties of the silicon chip backside and of the adhesive on the wafer film are critical to the manufacturer's ability to maintain high UPH for volume manufacturing, and are equally critical to achieving consistent release of the RFID tag from the support film. Achieving high pick and place throughput for RFID tags relies on processes prior to pick and place, particularly during the singulation, backgrind and dicing film mounting processes. In this paper, the release force of RFID tags from various wafer support films attached to the die backside is established. The support films are dicing tapes designed to provide extremely high adhesion strength during dicing and extremely low peel strength during pick and place. Ultraviolet light exposure allows the tape adhesive interface to the die backside to debond. The effect of wafer backside roughness and condition is measured in order to understand the critical properties necessary for consistent tag release under high UPH conditions. A simple peel testing sample is designed to measure peel forces of die on the Instron 5542 precision force measurement system. The peel test is comparable to the die release process and will provide pertinent data on the behavior of the silicon/adhesive interface. Samples of single RFID die on UV tape are prepared with different backside finishes including the 2000 grit finish, Poligrind
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and polished mirror finish. The exposure process and the shelf life before exposure of the samples are compared for peel strength. The temperature storage conditions of the samples and its impact on peel force are also compared. Results from this study will provide recommendations for optimal backside surface and optimal processing schedules of wafers at the end-user facility. These recommendations will help the end user achieve consistently high pick and place UPH.