Radio frequency identification is creating big changes in the way companies handle product tracking, security, authentication, and more. Find out how the technology works and why screen-printing shops are in a great position to stake claims in RFID manufacturing.
By Wim Zoomer
1. Direct printing using a silver conductive ink A conductive silver solvent-based ink is used to print the antenna on a plastic or paper substrate. For this application, screen printing is a popular manufacturing technique. Depending on the antenna type and frequency, different ink-deposit thicknesses are required. The deposit thickness can be modified by adjusting stencil parameters. After the silver ink is dry, the silver particles create the electric circuit that forms the antenna.
2. Subtractive process In this situation, the substrate is a laminate instead of paper or plastic. The laminate consists of 20-25 microns of copper or aluminum laminated on a plastic carrier film. On the metal side, a mask is screen printed using an etch resist. The etch resist is an ink that protects any areas that it covers from the effects of an etching agent used later in the process. When the aggressive etching agent is applied, it dissolves any uncovered metal. Then the mask is removed from the metal with chemical stripping solution, leaving only the metal antenna on the carrier material (Figure 1). Although this is an effective method of antenna production, the complexity of the process and the environmental impact (due to chemical waste) are factors that must be weighed.
3. Additive process Instead of removing material, the additive process adds substance. This process begins by screen printing a special conductive ink onto a plastic substrate, such as PET, to a thickness of several microns. After the ink is dried, the printed material undergoes a galvanizing process in which copper is electroplated onto the conductive ink until the entire antenna has a thickness of 5-15 microns, which gives the an-tenna its required performance characteristics. Unlike the subtractive process, this manufacturing method theoretically does not generate chemical waste.
To complete the antenna, the beginning and the end of the antenna coil must be connected. So a resistor is screen printed to create a bridge that crosses the windings of the antenna. Then both ends of the coil are connected by screen printing a silver conductive strip between them (Figure 2).
Rotary screen printing
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