EP0200014B2 - Process for the break-proof contacting of varnish-insulated wires - Google Patents

Description

The invention relates to a contacting method of enamelled wire with a diameter of less than 100 microns on vertically aligned parts of plate-shaped terminal lugs in wire-wound ceramic, plastic or ferrite cores, which are designed as choke chips.

For electrical components such as in the case of relays, contactors and other components, the induction coils used are becoming smaller and smaller as the miniaturization progresses. This means that the winding wires used have an ever smaller diameter, which makes contacting the coil connections more difficult. For example, the enamel-insulated coil connections can have a diameter in the range from 30 to 100 µm (0.03 - 0.1 mm). In the older German patent application P 34 33 692.3, such a miniaturized HF choke in chip design is proposed, in which one or more layers of coated, insulated wire must be contacted on plate-shaped contact elements.

Until now, lacquer-insulated coil connections have been contacted by manual, mechanized or even fully automated soldering. Temperatures of approx. 500 ° C are necessary especially for soldering such high temperature resistant enamelled wires. The heat radiation can damage the materials in the immediate soldering area.

Ultrasonic welding can advantageously be used for contacting, the lacquer insulation layer being equally broken up and the welding effect being achieved due to the mechanical effect of the ultrasound. However, problems arise with diameters of enamelled wires less than 0.4 mm, since the wire weakens at the connection point due to the deformation. Since the mechanical requirements cannot generally be maintained, an additional cover plate has to be welded on to improve the mechanical strength. The latter is described specifically for laser welding in DE-OS 33 07 773. In the manufacture of RF choke coils, which are either manufactured with connecting wire or more recently with connecting lugs as so-called RF choke chips, this would mean an additional effort, since the cover plates have to be fed in before welding.

From DE-A-27 28 914 a so-called socket strip for electrical connectors of ribbon cables is known, in which the ends of the wires of the ribbon cable are connected to the respective contact springs by ultrasonic welding. The individual wires of the ribbon cable should be able to be brought to the contact springs without being stripped and welded through the insulation. Specifically, the insulated cable end is placed in a trough-shaped bed and the insulating material is squeezed away by the rubbing process caused by ultrasound. As an alternative to ultrasonic welding, DE-A-27 57 038 specifies the ultrasonic soldering of such lines, in which the wire end is provided beforehand with a metallic solder.

Furthermore, differently structured contacts of wires with electrical connection elements are known from DE-C-11 94 945, DE-A-19 03 006 and GB-A-21 02 632. Specific soldering methods are used throughout these contacts.

However, soldering methods are unsuitable for wires insulated with high-temperature resistant lacquer. Ultrasonic welding in particular becomes problematic when the wire to be contacted falls below a certain cross-section and there is no concavely curved receptacle. In US-A-38 22 465 it is stated that thin enamelled wires can only be successfully ultrasonically welded onto metallic substrates if the welding cycle consists of a pre-pulse to remove the insulation and the actual welding pulse to produce the metallic connection. There, it is worked in particular in partial steps with varying contact forces and ultrasonic amplitudes, which, however, cannot easily be used in an automatic production for the mass production of electronic components in particular. In practice, only a comparatively unspecific welding pulse can be given.

In contrast, the object of the invention is to create a contacting method suitable for microinductivities.

The object is achieved in a method of the type mentioned with the features a) to c) of the claim. This method makes it possible to contact microinductivities in an integrated manufacturing process.

In the invention, the advantages of ultrasonic welding of enamelled wires, such as reliable contacting and the low temperature load, are used and the previous disadvantage of low strength is also compensated for by the application of the adhesive. Such adhesives are easy to handle and can be applied as drops to the weld. After curing, the adhesive is mechanically strong and in particular also resistant to changes in temperature. The volume of the drop of adhesive can be selected so that the entire deformation site is enclosed. As a result, the strength of the contact is greater than the wire strength

When using the method for electro African components not only achieve the required improvement in mechanical stability while simplifying production; it is also achieved that the welding point of the component is protected against climatic and corrosive influences. The weld or the entire component can also be covered with mechanically strong coatings.

• FIG 1a) und b) das Prinzip des Kontaktierungsverfahrens.
• FIG 2 einen neuartigen HF-Drossel-Chip in perspektivischer Darstellung, bei dem die Erfindung verwendet ist und

Further details and advantages of the invention emerge from the following description of the figures of exemplary embodiments with reference to the drawing. Show it

• FIG 1a) and b) the principle of the contacting method.
• 2 shows a novel RF choke chip in perspective, in which the invention is used and

In FIG. 1, 1 means a metallic base, for example a contact element, on which a paint-insulated wire 2 is to be contacted. Ultrasound welding can advantageously be used for this purpose, for which an ultrasound sonotrode with 10 and associated ultrasound anvil with 11 are indicated. In the case of ultrasonic welding, the insulation layers are broken up by the mechanical effect and the metallic parts are contacted by friction welding with simultaneous deformation.

However, ultrasonic welding is problematic for wires of small diameter, in particular less than 0.4 mm, since the wire can shear due to the deformation. If, according to FIG. 1 b, a drop of a suitable adhesive is applied to the contact point after welding, the entire area at risk of shearing can be protected and a secure mechanical connection can thus be achieved.

In particular for the ultrasonic welding of wires with a diameter of less than 100 μm, it is important to deform the wire 1 beforehand by pressing the sonotrode 10 and then to allow the sound to act. For example, an ultrasound frequency of 40 kHz and pressure forces between 2 and 10 N are used, the powers usually being in the range up to a few watts.

For example, a one-component adhesive is used as the adhesive. It is important for the intended use that the adhesive substance is thixotropic, i.e. dimensionally stable, is and hardens quickly. In automated production, a drop of the adhesive can then be applied to the welding point directly after welding, which hardens after passing through UV light after a few seconds, so that a shape 4 results which surrounds the deformed area of the wire 1.

In FIG 2, an RF choke is designated 20. Such chokes usually consist of a core 21, which can be made of ceramic, plastic or ferrite, with a single-layer or multi-layer winding 24 made of enamelled, insulated round wire. In the context of miniaturization of such electronic components (for example 3.2 mm x 2.5 mm x 1.5 mm and 40 wm wire for nominal inductances of 0.068 - 8.2 µH at 2 MHz measuring frequency), one has started to do this instead of the previously usual Provide connecting wires with large-area contact elements. For this purpose, the core 21 has end faces 22 with recesses 23, into which connection tabs 25 with a platelet surface are introduced on the front and rear sides. The connecting lugs 25 are bent at their free part so that they can be plugged onto printed circuit boards or the like.

The connection lug 25 must be contacted with the winding wire 24: For this purpose, the winding wire 24 is placed diagonally around the connection lug 25 and the end 26 of the winding wire 24 is welded on using ultrasound in the manner described above. A drop of the specified adhesive is then applied to the surface of the connecting lug 25. An approximately wart-shaped area 27 is formed, which covers the entire deformation area of the ultrasonic welding. After the adhesive has hardened, a mechanically stable connection is achieved.

It has been shown that a combined weld and adhesive connection of thin enamel-insulated wires with the contact elements in the components according to FIG. 2 achieves a strength which is greater than the wire strength. Measurements of the contact resistance as well as temperature changes and other electrical tests gave sufficiently good values.

It is also advantageous in the examples described above that the weld is also protected against climatic and corrosive influences.

Claims (1)

1. A process for the break-proof bonding of lacquer- insulated winding wires (24) less than 100 µm in diameter to vertically aligned portions of small plate-shaped terminal lugs (25) of wire-wound ceramic, plastics or ferritic cores (21) that are formed into HF inductor chips (20), having the following features:

a) the non-stripped wire ends (26) are laid onto the terminal lugs (25),

b) by means of ultrasonic welding, each wire end (26) is welded onto the vertically aligned portion of the terminal lug (25) whilst breaking up the insulating layer and deforming its cross-section,

c) the joint area is enclosed by a drop (27) of a rapidly hardening organic or inorganic adhesive which has thixotropic properties.

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