Electric heating – Microwave heating – With diverse device
Patent
1999-04-14
2000-08-08
Walberg, Teresa
Electric heating
Microwave heating
With diverse device
219680, 219 58, 219 8518, 2281791, H05B 664
Patent
active
061005118
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method of producing an electrically-conductive connection between enamelled wires, and a device for executing the method, as defined in the independent claims.
To produce identification systems, particularly transponders, transmitter/receiver units having logic circuits are coupled into integrated circuits (chips). The system is connected to the outside world by coils that operate in the radio-frequency range and are wound from thin copper wires insulated with a polyurethane-enamel covering. Typical wire diameters are about 10-50 .mu.m. Methods such as thermocompression welding are used to connect electronic components of this type to semiconductor chips, in which case the ends of the copper wire are connected to the metallized chip contact surfaces. The wire is severely deformed in this method, however, so there is a risk of breakage. Prior to the electrical connection, an enamelled wire is first stripped, particularly by means of micro-mills or overheated soldering baths, then tin-coated and bonded to the chip contact surfaces. Conventional chip contact surfaces often comprise thin aluminum films, which undergo a so-called gold-bump method in an additional processing step for contacting the copper wires; this renders the aluminum surface solderable, and permits an adhesion between the different materials.
Transponders of this type are known from, for example, WO-A-93 09551. This publication discloses the connection of enamelled wires and chip contact surfaces in a laser-welding method. In this instance, the wire ends are heated with a laser beam prior to the connection, and the enamel is melted and vaporized. For reliable contacting, it is necessary to gold-plate and/or tin-coat the chip contact surfaces. It has also proven advantageous to tin-coat the wire ends as well. The wire is deformed only slightly or not at all, which can avoid breakage of the wire; however, the contact surface is consequently not utilized optimally. In addition, this method necessitates a number of complicated process steps. Finally, the electrical connection can be worsened by melted residual enamel remaining at the wire end, or vaporized residual enamel that contaminates the wire end.
A method of connecting enamelled wires through ultrasonic bonding is known from JP-A-2-112249. First, the wire end is stripped and bonded to the connecting surface with simultaneous ultrasound and heating. Stripping takes place on a surface that is adjacent to the connection surface and has a surface structure resembling a washboard. There, with ultrasound, the wire end is stripped as with a grater until the metal wire is visible, and is subsequently drawn across the actual connection surface. A similar method, from the same Applicant, is disclosed in JP-A-2-54947. While the disadvantage of contamination of the connection surface by carbonized residual enamel is avoided, the production of the frictional surfaces at each connection surface is technically highly complicated. Furthermore, the heat effect required in the method to produce a permanent electrical connection represents an undesirable stress on the component. The conventional methods consist of a series of technically-complicated, time-consuming and costly process steps that increase production costs.
JP-A-6-61313 discloses a bonding tool that is especially Supplemental Page 2a (insert between lines 23 and 24 of p. 2)
DE-A-21 61 023 discloses a bonding method in which wires are bonded to contact surfaces with ultrasound. In the process, the wire is first fixed to the contact surface with an ultrasonic prepulse, and then welded to the contact surface with a more intense pulse. At this point, the wire is severely deformed; its thickness in the processed region is only about 30% of the original diameter. An arbitrary oxide layer or an insulating coating of the wire is broken open on both the top side and the contact side. The top side of the wire is unprotected, and insulation residue can remain on the contact surface. The enamel layer
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AEG Identifikationssysteme GmbH
Daimler-Benz Aktiengesellschaft
Kinberg Robert
Pwu Jeffrey C
Walberg Teresa
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