LEAD FRAME ANTENNA

Abstract: RFID transponder comprising an integrated circuit (IC) connected to an antenna circuit. The antenna circuit is constituted of at least one lead frame (LF) layer. These lead frame layers are shaped and formed to be at same time the antenna, which can be three dimensional by using several lead frame layers, the mounting substrate for the ASIC (Application Specific Integrated Circuit) or integrated circuit (IC) and as support for the packaging.

Description: Lead frame antenna Field of the invention The present invention relates to a transponder and in particular to a RFID (Radio- Frequency Identification) transponder made essentially of an antenna circuit connected to an integrated circuit (IC). State of the art RFID transponders are generally used for identification purposes where wireless communication is needed. A passive RFID transponder 2 (see Fig. 1 ) is made by connecting an Application Specific Integrated Circuit (ASIC) 2b to an antenna circuit 2a. An external communication circuit 1, also called reader, supplies the transponder 2 with energy 3 as information 4 trough both antennas 1a, 2a. The supplied transponder 2 sends information 4 back to the reader using the same antenna 2a. US patent No 5,420,757 (INDALA) discloses a transponder comprising a lead frame, an antenna circuit and an integrated circuit connected to the antenna circuit. Summary of the invention The invention relates to a transponder comprising a lead frame, an antenna circuit and an integrated circuit directly or indirectly connected to the antenna circuit, characterized by the fact that said lead frame is conductive and is designed to be the antenna. In a preferred embodiment the lead frame is furthermore designed to be the mounting substrate for said integrated circuit. In another preferred embodiment the lead frame is furthermore designed to constitute the frame or electronic holder for the transponder packaging. In another preferred embodiment the antenna is made of several lead frames. One of the lead frames may be used as holder during the packaging process. In another embodiment the transponder comprises several antennas where at least one is made of at least one lead frame. The transponder according to the invention, in using a single lead frame (LF), offers in particular the advantage to manufacture simple antennas for transponders. Brief description of the drawings Figure 1 illustrates a state of the art communication system including a transponder. Figure 2 shows a first transponder according to the invention where the antenna is a coil. Figure 3 shows another transponder according to the invention where the antenna is a dipole. Figure 4 shows another transponder according to the invention where the antenna uses a ground plane. Figure 5 shows another transponder according to the invention where the antenna includes a flat surface for the chip mounting. Figure 6 shows a portion of the transponder of Fig. 5 where the wire bonding is displaced on the antenna extremities. Detailed description of the invention Fig 2 shows in a simplified manner a 13.56Mhz transponder using a high Q factor coil. In the similar way Fig 3 shows a higher frequency transponder, for example a 900MHz transponder, using a dipole antenna. For both figures, 5 represents the lead frame (LF), 6 the antenna, 7 the ASIC and 8 the wire bonding interconnection in-between the ASIC and the antenna ends 10a and 10b. On Fig. 3, the ASIC 7 is placed on a specific portion 11 of the lead frame 5. If several lead frames are assembled together, more complex and effective antennas can be obtained. Reflectors, ground planes, or even matching capacitors can be designed. Fig. 4 shows a one pole antenna with ground plane. In an other example, the lead frame can be formed into a parable reflector, the ASIC together with its antenna are placed at the parable home. Also by using several lead frames, a multi frequency transponder can be obtained. The lead frames of Fig. 2 and Fig. 3 can be combined and packaged together to form one single part which uses at least one ASIC. Once the lead frame and the ASIC are assembled, the system can be used for the packaging. The most efficient packaging methods to be used are: - the transfer moulding: the lead frame 5 on which the chip 7 is attached is placed in a lower mould cavity, the upper mould cavity is closed. An injection material pellet is then compressed by an injection piston. Under heat and pressure application the injection material flows through a gate to fill up the mould cavity. - the standard plastic injection: the lead frame 5 on which the chip 3 is attached is placed in-between an upper and a lower mould cavity. The injected material is compressed into the mould cavity by an injection snail through a gate to form the final part. - the potting packaging: the lead frame 5 on which the chip 7 is attached is placed on top of a mould in which is made a cavity in which is dispensed a potting material through a dispensing nozzle to form the final part. Once packaged, the part has to be cut or stamped out of the lead frame to form the final part. Lead frame shape The lead frame 5 can be a single part, a short stripe or even a complete roll of material comprising several parts. The antenna shape has to be adapted for each frequency band where the transponder will be used. This can be a coil 6 as shown in Fig. 2 where both ends 10a, 10b of the coil are prepared to accept a common wire bonding to connect coil to chip 7. Lead frame material The material used as lead frame has to be a conductive material, a very common material which could be used for the design of Fig. 2 is CuFe2. For high frequency applications, the material can be coated, e.g. with silver, to decrease the losses. In case of using conductive materials which do not allow a wire bonding process the interconnection areas (10a, 10b) can be gold plated. The lead frame shape should be designed so that the chip can be placed on a flat surface 11 as shown in Fig. 5. This avoids inducing stress into the ASIC during the manufacturing steps and even during its functional life. Lead frame thickness The thickness of the used lead frame layers, have to be chosen according to the needed performance of the antenna, as for the mechanical stability of the antenna to support the further packaging. For example, for 13.56MHz application, the thicker is the lead frame, the higher will be the Q factor of the transponder. ASIC interconnection The interconnection of the ASIC to the antenna, can be made by wire bonding, which is more interesting for 13.56MHz applications where the bond is used as bridge in-between both antenna ends. Other methods as used in flip-chip interconnection may also be used. By using wire bonding, as interconnection method in-between the ASIC and the antenna, the SRF (Self Resonant Frequency) of the transponder can be adjusted. Fig. 6 shows the effect of displacing the bonding place on the antenna extremity. A first position 8a corresponds to a high SFR. A second position 8b to a nominal SFR and a third position 8c to a low SFR. Lead frame interconnection By using a plurality of lead frames, some of them have to be mechanically and or electrically interconnected. This can be done by crimping, Ultrasonic welding, thermo-compression or even by using a third element a solder, non-conductive glue or conductive glue. It may be useful that an additional non-conductive layer is added in-between two conductive layer, this to form a needed matching capacitor.

Claims: Claims 1. Transponder comprising a lead frame (5), an antenna circuit (6) and an integrated circuit (7) directly or indirectly connected to the antenna circuit (6), characterized by the fact that said lead frame (5) is conductive and is designed to be the antenna (6). 2. Transponder according to claim 1 wherein said lead frame (5) is furthermore designed to be the mounting substrate for said integrated circuit (7). 3. Transponder according to claim 1 or 2 wherein said lead frame (5) is furthermore designed to be a support for the packaging. 4. Transponder according to any of the previous claim wherein the antenna (6) is three-dimensional. 5. Transponder according to any of the previous claims wherein the antenna (6) is made of several lead frames (5). 6. Transponder according to claim 5 wherein the antenna (6) is made of at least one non-conductive layer which may be mechanically and or electrically interconnected. 7. Transponder according to claim 5 or 6 wherein at least one lead frame (5) is used as holder during the packaging process. 8. Transponder according to any of the previous claims comprising several antennas (6), each antenna (6) being made of at least one lead frame (5).

Inventors: BATAILLARD LAURENT, FURTER URS, BATAILLARD, LAURENT, FURTER, URS
Applicants: BATAILLARD LAURENT, FURTER URS, SOKYMAT S A, BATAILLARD, LAURENT, FURTER, URS, SOKYMAT S.A.
Application year: 2001
Main classification: G06K19
IPC codes: G06K19, H01L23, H01Q1, H01Q7, H01Q9