The present invention relates to a method and apparatus for batch testing of RFID straps arranged on a carrier web in a closely spaced relationship.
RFID tags consist of a chip (integrated circuit) and a planar antenna. The chip is carried on a strap for attachment on an antenna. As used herein, an RFID strap is an arrangement of two or more terminal pads on a foil such as a PET foil or paper and an RFID chip mounted on the foil and having contact bumps each in electrical contact with one of the terminal pads. In mass production of these tags, the straps are assembled with the antennas in a final bonding step. Prior to the final bonding step, the chips must be tested. In the case of RFID tags operating in the UHF frequency range, the antennas and the terminal pads of the straps are very small. Conventionally, the terminal pads of each strap are contacted with a pair of needle electrodes of a test probe. For high volume production, the handling of test fixtures with contacting test electrodes such as needles is a severe throughput limitation. Contact-less testing by RF radiation is possible, but simultaneous batch testing of multiple tags would require complex shielding techniques due to the crosstalk between the units under test.
An aspect of the present invention provides a method and apparatus for contactless testing of RFID straps and, in particular, RFID chips for the UHF frequency range. The basic idea of the invention is to use capacitive coupling between each test probe and a strap under test. This approach avoids crosstalk between the chips under test and permits batch testing, i.e. simultaneous testing of multiple chips. With the inventive method and apparatus, multiple straps can be tested in a very short period of time. For example, in a practical implementation of the invention, each batch may comprise 32 straps, and each batch is tested in about 50 ms including an indexing step of the carrier web. Even larger batches and shorter test times are envisioned.
An aspect of the invention provides a method of batch testing RFID straps arranged on a carrier web in a closely spaced relationship, where each strap includes a circuit part with two terminal pads exposed on the carrier web and an RFID chip mounted on the web so as to have its contact bumps in electrical contact with the terminal pads. The carrier web is moved so as to align all straps in a batch with corresponding test probes of a test equipment. Each test probe is moved transversely to the moving direction of the carrier web into close proximity with a corresponding strap. A capacitive coupling is established between test electrodes on each test probe and the terminal pads of a corresponding strap. Test signals are then transmitted from each test probe to a corresponding strap, and response signals are received at each test probe from a corresponding strap for evaluation by the test equipment.
An aspect of the invention also provides an apparatus for batch testing RFID straps arranged on a carrier web in a closely spaced relationship, each strap including a circuit part with a pair of terminal pads exposed on the carrier web and an RFID chip with contact bumps connected to the terminal pads. The apparatus includes a test equipment with a test head that has a plurality of test probes arranged in an array corresponding to an array of straps in a batch on the carrier web. Each test probe has a pair of test electrodes adapted to be aligned with the terminal pads of a corresponding strap. The apparatus further includes means for indexing the carrier web so as to successively expose batches of straps to the test head, and means for moving the test head transversely to the moving direction of the carrier web into close proximity with the straps on the carrier web so as to establish a capacitive coupling between each pair of test electrodes in a test probe and a pair of terminal pads of a corresponding strap.
Further details of the invention appear from the dependent claims and from the following description with reference to the appending drawings.
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In operation, a batch of RFID straps 12, for example 32 straps in the four parallel rows on web 10, are presented simultaneously to the test head 14, and each test probe 16 is capacitively coupled with the aligned terminal pads 12b, 12c of a strap 12. Test signals are simultaneously sent from each test probe 16 to a corresponding strap 12, and response signals are received in the test probes from the straps for evaluation by the common test equipment. Any RFID strap that has not passed the test would be marked, such as by applying an ink spot with an inking device 18 or by punching. After a batch test is completed, the web 10 is indexed to present a next batch of tags to test head 14. The testing process is preferably incorporated on-line in the RFID tag production line since testing with the inventive method is fast enough.
To avoid or at least reduce any crosstalk effects, units not under test are disabled by short-connecting the corresponding terminals 16a and 16b of test head 14. The strap will not respond, and no energy is injected. In addition, an interlaced test structure is preferably used to increase the distance between the units under test.
While the invention has been particularly shown and described with reference to preferred embodiments thereof it is well understood by those skilled in the art that various changes and modifications can be made in the invention without departing from the spirit and scope of the invention as defined by the appended claims.
Number | Date | Country | Kind |
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10 2004 061918.2 | Dec 2004 | DE | national |
Number | Date | Country | |
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Parent | PCT/EP05/13912 | Dec 2005 | US |
Child | 11766978 | Jun 2007 | US |