The present invention relates to methods of manufacture of flexible circuits used in construction of Radio Frequency (RF) antennae.
Radio frequency antennae are typically made in a conductive coil pattern. The conductive coil pattern allows the antenna to receive and radiate energies in the radio frequency range. Typically, the antenna is optimized to transmit and receive energy in a relatively narrow portion of the radio frequency range.
Radio frequency antennae are used in a number of different areas including inventory control. Often the radio frequency antenna is connected to an integrated circuit. The integrated circuit receives energy from a detector unit, modulates the energy with an identification pattern stored in the integrated circuit, and then retransmits the modulated energy to the detector unit. Such inventory control units, including the radio frequency antennae, can be made quite inexpensively.
One way of forming a radio frequency antenna is to stamp out a conductive coil out of a sheet of metal. The downside of this method is that the production of the metal coil results in a large amount of scrap metal. Additionally, the radio frequency antennae produced by stamping from a sheet of metal may be stiffer than desired.
Another way of forming the radio frequency antenna is to use strip-back techniques common in printed circuit (PC) board fabrication. In PC board fabrication, a layer of the conductive material is formed on top of a substrate, and the areas not used for the antenna are stripped away. This method tends to be wasteful when used to produce the radio frequency antenna, because the radio frequency coil antenna tends to be about 10% of the surface area of the substrate. This compares to coverage areas of 70-80% common with typical PC board implementations.
Another way of forming a radio frequency antenna is to use conductive inks. Typically, the conductive ink is printed in a RF antenna coil pattern on top of the substrate. The conductive ink is then cured. The printed antennae may be used as is or electrodes are attached to the conductive ink pattern and a metal layer is electroplated on top of the conductive ink pattern.
One possible solution is to use the conductive ink with a thicker or wider pattern, thus reducing the resistance per length of the conductive ink strip. The downside of this solution is that the conductive ink is expensive compared to the much cheaper electroplated material.
For the above reasons, it is desired to have an improved method of forming a radio frequency antenna.
The method can further comprise removing at least a portion of the non-conductive layer and the printed short layer. The non-conductive layer can be a resist material.
The electrical short layer can be made of conductive ink that can be printed.
The electroless metallization catalyst layer can be formed by printing using an ink. The ink can be cured before the first metallic layer is deposited.
The ink can be treated to activate catalyst in the electroless metallization catalyst layer before the first metallic layer is deposited.
The first and second metallic layers can be copper layers.
The electroless metallization catalyst layer can be formed by removing some of the electroless metallization catalyst material.
A negative resist layer can be used to remove some of the electroless metallization catalyst material.
An electrical-short layer 46 can be formed over top of the antenna pattern, and a nonconductive plating resist can be formed over the short. The electrical-short layer 46 can ensure that points 48, 50 and 52 on the pattern 42 will have relatively similar voltages during the electroplating process. This means all locations on the conductive ink pattern 42 can be electroplated evenly. Thus the apparatus of the present invention allows for a conductive electroplate layer of sufficient thickness on all points of the radio frequency antenna.
The use of the electrical-short layer 46 allows for the use of a thinner and/or narrower pattern 42. The resistance of the pattern 42, during the electroplate process, is not as important of a factor because the electrical-short layer is used.
Typically it is desired to minimize the resistance of the radio frequency antenna. A desirable property of radio frequency antennae is to have a relatively high Q factor. The Q factor for an antenna is defined as the imaginary over the real part of the impedance. The imaginary part of the impedance is typically a function of the desired operating frequency and geometry and is typically fixed. Thus, to produce a high Q factor antenna, the resistance of the antenna should be kept as small as possible. This means that it is desired to have a relatively thick conductive metal layer forming the coils of the radio frequency antenna. The use of the electrical-short layer of the present invention aids in the construction of a uniformly thick electroplate layer, thus lowering the resistance and raising the Q factor.
In
In
The electroless metallization catalyst layer 54 can be printed upon the flexible substrate. In one embodiment, the electrical-short layer 54, and the insulating layer, 56 are differentially removable (for example soluble in a solvent that the initial seed layer is impervious to) from the conductive ink material.
In
In an alternate embodiment of the present invention, the electrical-short layer 54 is constructed of metallic foil, which could be attached to the RF antenna and then removed after the electroplating.
One embodiment of the present invention is a RFID antenna comprising of an electroless metallization catalyst layer in an RFID antenna pattern. A first metallic layer can be over the top of the electroless metallization catalyst layer, the first metallic layer formed by electroless deposition. A second metallic layer can be over the top of the first metallic layer. The second metallic layer can be formed by electroplating the electroplating using a removed electrical short layer.
The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.
This application claims priority to U.S. Provisional Application No. 60/988,655 entitled “ELECTROLESS/ELECTROLYTIC SEED LAYER PROCESS” filed Nov. 16, 2007, which is incorporated herein by reference (Atty. Docket No. RCDT-01020US0).
Number | Date | Country | |
---|---|---|---|
60988655 | Nov 2007 | US |