Electric heating – Inductive heating – Metal working
Reexamination Certificate
1999-10-08
2001-08-07
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
Metal working
C219S661000, C219S635000, C219S647000, C219S659000, C219S670000, C219S676000
Reexamination Certificate
active
06271507
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to the art of electrical conductors and, particularly, to an apparatus and method for conductively bonding at least two conductors by induction heating.
BACKGROUND OF THE INVENTION
In the art of electrical transmission, conductors are repeatedly coupled so that electrical current flows from one conductor to another through some type of electrical interface. An electrical wire, for instance, often is connected to another electrical wire, to a conductor on a flat circuit such as a flat flexible circuit, to a circuit trace on a printed circuit board or in all kinds of combinations of such conductors. Often, two respective conductors are interconnected or electrically coupled by a soldering material. The solder is heated to its melting point and, when solidified, the solder mechanically and electrically or conductively joins the two conductors.
For example, a flat flexible circuit typically includes a plurality of flexible conductors which often are generally parallel to each other similar to the electrical wires of a hard-wired electrical cable. The flexible conductors are in a plane and are adhered to a flexible insulating substrate, such as an elongated substrate. Most often, the conductors are sandwiched between a pair of flexible insulating layers or films. The films and conductors are held in their flat configuration by an appropriate adhesive. When it is required to connect the conductors of a flat flexible circuit to the conductors of another circuit or other conducting member, the insulating substrate (i.e., the insulating layer) on one side of the flat circuit is removed to expose the embedded conductors. In some instances, one of the insulating layers on one side of the circuit is left shorter than the insulating layer on the opposite side of the circuit to expose distal ends of the conductors for connection to whatever connecting device(s) the circuit is to be electrically coupled.
Problems have been encountered in coupling such conductors as the flexible conductors of a flat circuit, particularly when the conductors are soldered and which requires the application of heat. In essence, the solder must be melted without melting the thin insulating films. Additionally, the parallel flexible conductors often are of varying widths in the same flat circuit and the resulting varying densities cause heat distribution problems. For instance, the heat required for soldering may be so intense in one area as to melt the insulating substrate or film and yet be insufficient in another area that a conductor or conductors are not adequately electrically coupled.
Various prior art methods have been used to electrically bond the conductors of flat circuits by soldering techniques. Such methods have included diode laser soldering and pulsed hot bar soldering. Laser soldering requires that several spot solder joints be made and scanned across the joint and this is a relatively time consuming process. Laser soldering requires expensive automation to focus the energy. Laser soldering also requires that the insulating substrate or film of the flat circuit to be transparent, and this is a problem with flame retardant material films that have opaque fillers as well as with opaque adhesives used in fabricating flat flexible circuits. Finally, laser soldering may require expensive stencils for soldering flat circuits.
Pulsed hot bar soldering processes also have had limited success in bonding the conductors of flat circuits. This process is not capable of heating relatively large conductors without melting the insulating substrates or films. Like laser soldering, the hot bar makes it difficult to focus energy to selective areas. The hot bar method relies on conduction and convection rather than a more desirable induction technique. Finally, heating heads for hot bar soldering apparatus are quite expensive.
The invention is directed to solving the above myriad of problems in an induction soldering process which uses unique magnetic concentrators. As is known, inductive coils create magnetic lines which pass through metal and cause eddy currents which, in turn, create friction and heat. The invention utilizes very simple and inexpensive magnetic concentrator blocks to selectively concentrate this heat wherever desired to melt the solder very quickly and evenly and bond the conductors without melting or damaging the insulating substrates or films.
SUMMARY OF THE INVENTION
An object, therefore, of the invention is to provide a new and improved apparatus and method for conductively bonding at least two conductors together. Although the invention is disclosed herein for soldering the conductors of flat circuits together, the invention should not be limited to such applications.
In the exemplary embodiment of the invention, the apparatus includes an inductive coil for generating a magnetic field when electrical current is run therethrough. A magnetic concentrator is disposed near the inductive coil and adjacent which a pair of conductors can be positioned for concentrating the magnetic field on the conductors. The magnetic concentrator is independent of the conductors. An applicator applies pressure to the two conductors. Therefore, the concentrator concentrates the magnetic field generated by the inductive coil on the conductors and thereby heats the conductors under pressure to electrically bond the conductors together.
As disclosed herein, the pressure applicator includes a movable ram having the inductive coil thereon. The ram moves toward and away from an anvil which includes the magnetic concentrator, preferably in the form of a ferrite block.
The invention is exemplified by using a plurality of the magnetic concentrators arranged in a row and adjacent which a planar array of conductors can be positioned, such as the conductors of a flat circuit. The concentrators are of varying masses or sizes for accommodating various sizes of conductors.
The invention also contemplates a method of conductively bonding the conductors and includes the steps of juxtaposing the conductors near the inductive coil and generating a magnetic field about the conductors in response to current run through the coil. A magnetic concentrator is located adjacent the conductors to concentrate the magnetic field on the conductors to heat the conductors. Pressure is applied to the conductors to facilitate electrically bonding the conductors together. Solder is applied to at least one of the conductors which, when heated, liquifies to facilitate the electrical bond between the conductors.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.
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Leung Philip H.
Molex Incorporated
Paschall James C.
Tirva A. A.
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