PCB Design and Card Assembly for an Active RFID Tag in Credit Card Form Factor
An Active Radio Frequency Identification (RFID) transponder is used in conjunction with a customer relationship system to provide a variety of customer relationship management services within a retail establishment. The transponder includes a battery-powered integrated circuit and low-frequency antenna that detect a low-frequency activation signal from an activator when a customer enters a retail establishment. The transponder also includes a high frequency antenna and oscillating crystal for transmitting an identifier signal when activated. The battery, integrated circuit, high-frequency antenna, low-frequency antenna, and crystal are embodied in a card assembly substantially conforming to a form factor of a credit card or smaller that can be carried in, for example, a wallet, purse, or pocket of a customer.
1 . An Active Radio Frequency Identification (RFID) transponder for use in a customer relationship management system, the transponder comprising:
a card assembly having a form factor of a credit card or smaller;
an integrated circuit storing an identifier of the transponder, the integrated circuit configured to detect a low-frequency activation signal and responsive to the detection, generate a high-frequency identifier signal representing the identifier of the transponder;
a low-frequency antenna coupled to the integrated circuit for receiving the low-frequency activation signal;
a crystal coupled to the integrated circuit for generating high-frequency oscillations for generating the high-frequency identifier signal;
a high-frequency antenna coupled to the integrated circuit for transmitting the high-frequency signal representing the identifier; and
a battery for providing power to the integrated circuit;
wherein the integrated circuit, the low-frequency antenna, the high-frequency antenna, crystal, the antenna, and the battery are integrated into the card assembly.
2 . The transponder of claim 1 , further comprising:
passive components coupled to the integrated circuit and integrated in the card assembly.
3 . The transponder of claim 1 , wherein the card assembly has a form factor smaller than 85.47 mm×53.92 mm×0.8382 mm.
4 . The transponder of claim 1 , wherein the card assembly substantially conforms to bending stiffness standards specified in section 8.1 of ISO/IEC Standard 7810, Physical Characteristics of Identification Cards.
5 . The transponder of claim 1 , wherein the card assembly further comprises:
a magnetic strip on a surface of the card assembly, the magnetic strip readable by a magnetic card reader.
6 . The transponder of claim 1 , wherein a plurality of components of the card assembly are mounted on an FPCB (Flexible Printed Circuit Board) and combined into a FPCBA (Flexible Printed Circuit Board Assembly).
7 . The transponder of claim 6 , wherein the FPCBA includes the integrated circuit, the crystal, the high-frequency antenna and a plurality of passive components.
8 . The transponder in claim 7 , wherein the card assembly further comprises off-board components separate from the FPCBA, the off-board components including the low-frequency antenna and the battery embodied as a thin-film battery.
9 . The transponder of claim 6 , wherein the low-frequency antenna is positioned adjacent to the FPCBA in the card assembly.
10 . The transponder of claim 6 , wherein the low-frequency antenna is positioned away from conductive traces on the FPCB to avoid adverse inductive coupling.
11 . The transponder of claim 6 , wherein the FPCBA comprises a material tolerant to manufacturing processes including surface mount component attach and hot card lamination.
12 . The transponder of claim 6 , wherein the FPCB comprises an electrically non-conductive dielectric core having a thickness of 18 microns or less.
13 . The transponder of claim 12 , wherein the electrically non-conductive dielectric core comprises polymide (PI).
14 . The transponder of claim 12 , wherein the FPCB comprises very thin conductive traces formed on each side of the dielectric core, the thin conductive traces used to interconnect the components in the FPCBA.
15 . The transponder of claim 14 , wherein the FPCB further comprises electrical connections between the conductive traces on each side of the FPCB formed by using one or more plated-through via holes.
16 . The transponder of claim 15 , wherein at least one of the plated-through via holes is positioned to allow air trapped in solder paste under the integrated circuit to escape out a bottom side of the FPCB opposite the integrated circuit during a solder reflow assembly process, the at least one of the plated-through via holes further positioned to ensure that the integrated circuit is mounted substantially parallel to the FPCB, and the at least one of the plated-through via holes further positioned to act as a solder wick pulling the integrated circuit to the FPCB surface and reduce electrical resistance between top and bottom copper layers of the FPCB.
17 . The transponder of claim 12 , further comprising a solder mask covering a conductive layer on at least one side of the dielectric core for blocking flow of molten solder between adjacent conductive elements and preventing short circuits from forming when electronic components are soldered to the FPCB, the solder mask comprising a thin dielectric film.
18 . The transponder of claim 17 , wherein the FPCB further comprises openings in the solder mask to provide access for electrical probing.
19 . The transponder of claim 17 , wherein the FPCB further comprises nickel or gold plating in open areas of the solder mask for physically connecting between solder on the FPCB and electrical components.
20 . The transponder of claim 6 , wherein the FPCB is configured to temperatures and pressures associated with a lamination process without appreciable shifts in electrical characteristics.
21 . The transponder of claim 6 , wherein the FPCB further comprises holes of at least 3 millimeters in diameter, the holes configured to prevent air from being trapped during lamination of the card assembly.
22 . The transponder of claim 21 , wherein the large holes are further configured to stitch together top and bottom layers of plastic surfaces of the card assembly to prevent de-lamination of the card assembly.
23 . The transponder of claim 6 , wherein the FPCB comprises a thickness in a range of approximately 56 to 85 microns.
24 . The transponder of claim 1 , wherein the integrated circuit comprises:
a first chip for detecting the low-frequency activation signal; and
a second chip for transmitting the high-frequency identifier signal.
25 . The transponder of claim 24 , wherein the first chip and the second chip are positioned in a side-by-side assembly having a thickness less than or equal to 400 microns.
26 . The transponder of claim 25 , wherein the first and second chips of the integrated circuit are adhered to a die-attach pad of a lead frame with an adhesive.
27 . The transponder of claim 24 , wherein the integrated circuit further comprises:
wire bonds for electrically connecting the first and second chips to each other and to other components of the card assembly.
28 . The transponder of claim 1 , wherein the crystal comprises a cut, sized and metalized quartz crystal mounted within a precision surface mount ceramic package.
29 . The transponder of claim 28 , wherein the crystal has a thickness less than or equal to 500 microns.
30 . The transponder of claim 28 , wherein a portion of the crystal is sinked into a hole of the FPCB.
31 . The transponder of claim 28 , wherein the crystal is partially embedded into the FPCB using a stair-stepped ceramic package.
32 . The transponder of claim 28 , wherein the crystal is mounted directly to the FPCB using blanks and wherein a cover protects the blanks.
33 . The transponder of claim 1 , wherein the high-frequency antenna is configured to operate at approximately 433 MHz.
34 . The transponder of claim 1 , wherein the high-frequency antenna comprises a loop antenna.
35 . The transponder of claim 1 , wherein the high-frequency antenna comprises:
a first loop on a top portion of the card assembly; and
a second loop on a bottom portion of the card assembly, the second loop mirrored relative to the first loop.
36 . The transponder of claim 1 , wherein the high-frequency antenna is configured to be resistant to card lamination stresses and bending stresses of the card assembly.
37 . The transponder of claim 1 , wherein the low-frequency antenna and the battery are attached to the card assembly using a bed of nails fixture.
38 . The transponder of claim 1 , wherein the low frequency antenna is coupled to one or more capacitors to form a resonant circuit tuned to a frequency of the received activation signal.
39 . The transponder of claim 1 , wherein the low-frequency antenna comprises a plurality of turns of insulated wire wound on top of each other to form a thin flat air-core coil, and wherein the plurality of turns are bonded to each other to form a self-supporting coil.
40 . The transponder of claim 1 , wherein the low-frequency antenna is configured to operate at a frequency of that can permeate a human body without appreciable attenuation.
41 . The transponder of claim 1 , wherein the low-frequency antenna is configured to operate at approximately 125 kHz.
42 . The transponder of claim 1 , wherein the low-frequency antenna is tuned to maximize a Q factor of the low-frequency antenna.
43 . The transponder of claim 1 , wherein the battery comprises a thin film lithium metal battery meeting physical space limitations of the form factor of the transponder.
44 . The transponder of claim 1 , wherein the battery is configured to withstand temperature and pressure stresses associated with a card lamination process applied to the card assembly.
45 . The transponder of claim 1 , wherein the battery comprises battery terminals having metallurgy compatible with a bonding process and materials of the card assembly.
46 . The transponder of claim 45 , wherein the battery comprises battery terminals configured as flat metal tabs sized and spaced to match FPCBA pads.
47 . The transponder of claim 45 , wherein the battery terminals are suitable for thermo-compression bonding and soldering.
48 . The transponder of claim 45 , wherein the battery terminals are bonded to an FPCBA.
49 . The transponder in claim 1 , wherein the integrated circuit, the high-frequency antenna, the low-frequency antenna, the crystal, and the battery are embodied in a laminated plastic card substrate.
50 . A method for manufacturing a Radio Frequency Identification (RFID) transponder, comprising:
forming a Flexible Printed Circuit Board Assembly (FPCBA), the FPCBA comprising an integrated circuit, a high-frequency antenna coupled to the integrated circuit, and a crystal coupled to the integrated circuit; and
combining the FPCBA into a card assembly which further includes a low-frequency antenna coupled to the integrated circuit and a thin film battery for powering the integrated circuit, the card assembly substantially conforming to a form factor of 85.47 mm×53.92 mm×0.8382 mm or smaller.
51 . The method of claim 50 , wherein forming the FPCBA comprises:
fabricating a plurality of FPCBAs in a panel; and
separating individual FPCBAs from the panel.
52 . The method of claim 50 , further comprising:
positioning the FPCBA, the low-frequency antenna, and the thin film battery on a plastic card substrate; and
laminating the plastic card substrate to form a pre-laminate.
53 . The method of claim 52 , wherein laminating comprises:
positioning multiple card assemblies in a sheet; and
laminating the sheet of card assemblies.
54 . The method of claim 52 , wherein the laminating comprises:
adding a shielding layer with cut-outs to surround and shield the FPCBA, the low-frequency antenna, and the battery from the laminating.
55 . The method of claim 52 , wherein the laminating comprises applying heat and pressure to the plastic card substrate.
56 . The method of claim 52 , further comprising:
sandwiching the pre-laminate between additional plastic layers including text or graphics and providing a protective film to create an end-laminate.
57 . The method of claim 56 , wherein creating the end-laminate comprises:
adding a magnetic stripe to the card assembly for encoding information relating to a cardholder.