Method of metallizing ferrite ceramics and component comprising a metallized ferrite ceramic

Abstract

The invention relates to a process for metallizing ferrite ceramics, which comprises the following steps: arrangement of a contact element composed of copper or a copper alloy on a surface of the ferrite ceramic, melting of the contact element at least in the region in which the contact element contacts the surface of the ferrite ceramic, and cooling of the contact element and the ferrite ceramic to below the melting point of copper or the copper alloy.

Claims

1. A process for metallizing ferrite ceramics, which comprises the following steps: arrangement of a contact element composed of copper or a copper alloy on a surface of the ferrite ceramic, melting of the contact element at least in the region in which the contact element contacts the surface of the ferrite ceramic, and cooling of the contact element and the ferrite ceramic to below the melting point of copper or the copper alloy, wherein the contact element is completely melted and rests in a droplet-like manner in the molten state on the surface of the ferrite ceramic.

2. The process as claimed in claim 1, wherein the ferrite ceramic is preheated to a temperature in a range from 300° C. to 600° C. before melting of the contact element.

3. The process as claimed in claim 2, wherein the ferrite ceramic is preheated at a heating rate in the range from 80 kelvin to 150 kelvin per minute.

4. The process as claimed in claim 1, wherein joining of a wire of a winding or connecting wire to the contact element occurs simultaneously with the melting of the contact element.

5. The process as claimed in claim 1, further including coating of an accessible surface of the contact element with a layer of tin after the contact element has been joined to the ferrite ceramic.

6. The process as claimed in claim 1, further including grinding of the contact element after the contact element has been joined to the ferrite ceramic.

7. The process as claimed in claim 1, wherein the cooling of the ferrite ceramic and of the contact element occurs by means of natural convection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention may be derived from the claims and the following description of preferred embodiments of the invention in combination with the drawings. Individual features of the various embodiments depicted and described can be combined with one another in any way without going outside the scope of the invention. The drawings show:

(2) FIG. 1 a view obliquely from below of a component according to the invention,

(3) FIG. 2 an optical micrograph of the cut joining region between a contact element and the ferrite ceramic of the component of FIG. 1, and

(4) FIG. 3 a BSE (backscattered electrons) image of the transition region between the ferrite ceramic and the contact element in FIG. 2.

DETAILED DESCRIPTION

(5) FIG. 1 shows a component 10 according to the invention which is configured as inductive component and has a core 12 composed of ferrite ceramic and two wire windings 14 located on the core 12. A lower section 16 of the component 10 in FIG. 1 is formed by an embedding composition and, as can be seen, accommodates sections of the core 12 and also sections of the windings 14.

(6) The core 12 has four projections at the free ends of which contact elements 18 are arranged in each case. The contact elements 18 consist of copper or a copper alloy and are intended to establish an electrically conductive connection to conductor tracks or solder pads of a circuit board when the component 10 is placed with its underside shown at the top in FIG. 1 on the circuit board.

(7) In addition, the ends 20 of the windings 14 are joined to the contact elements 18. The windings likewise consist, for example, of copper wire.

(8) During production of the component 10, the core 12 of ferrite ceramic is produced and the windings 14 are subsequently installed. In a further step, the free ends of the projections of the core 12 are metallized by applying the contact elements 18, which can occur either before or after installation of the windings. In the process of the invention, this is carried out by placing the contact elements, for example in the form of a piece of copper wire, on the free ends, shown at the top in FIG. 1, of the projections of the core 12 and then heating them until the contact elements, in other words the pieces of copper wire, melt and form molten beads on the ferrite ceramic of the core 12. The molten heads are kept on the upper side of the projections solely by the force of gravity on them.

(9) The end faces at the top of the projections of the core 12 are advantageously provided with a depression, see also FIG. 2, in order to keep the molten beads reliably in the intended position.

(10) In the molten state of the contact elements 18, a bond is formed between the copper or the copper alloy of the contact elements 18 and the ferrite ceramic of the core 12. In the cooled state, a transition layer composed of copper and copper oxide is present between the ferrite ceramic of the core 12 and the copper or the copper alloy of the contact element 18. A reliable mechanical bond between the contact elements 18 and the ferrite ceramic of the core 12 is established via this transition layer.

(11) In the process of the invention, a bond between the ends 20 of the windings and the contact elements 18 can also be formed simultaneously with the melting of the contact elements 18. For example, the ends 20 of the windings, which consist of copper wire, are simply brought into contact with the molten beads formed and thereby then form a mechanically stable and electrically conductive bond to the contact elements 18. In the same way, the subsequent soldering or welding of the ends 20 of the windings onto the contact elements 18 which have then cooled again is also possible, for example, according to the invention.

(12) After cooling of the contact elements 18, these can be additionally ground in order to produce a metallically pure surface and/or provided with a tin coating in order to make the component 10 storable for a long time and also to assist a soldered join between the contact elements 18 and conductor tracks or solder pads of a circuit board.

(13) The picture of FIG. 2 shows an optical micrograph of a section through the core 12 in the region of one of the contact elements.

(14) A sectional view through one of the upward-pointing projections of the core 12 composed of ferrite ceramic and one of the contact elements 18 is shown. It can be seen that depressions 22 are provided in the upper sides of the projections of the core 12; these depressions can then accommodate the molten beads formed by the contact elements and keep them reliably in position in the molten state thereof. It can be seen that the depression has a flat bottom and sides arranged obliquely to the bottom. Bonding between the contact element 18 and the surfaces of the depression 22 occurs both on the flat bottom and also in the region of the oblique side faces opening in the direction of the opening of the depression.

(15) The depiction in FIG. 2 shows the state of the contact element 18 after cooling from the molten state. The contact element 18 can be additionally ground starting from the state depicted in FIG. 2, for example in order to produce a flat contact surface.

(16) The depiction in FIG. 3 shows a more greatly enlarged depiction of the transition region between a contact element 18 and the ferrite ceramic of the core 12. The depiction of FIG. 3 is a BSE (backscattered electrons) image which has been produced by means of a scanning electron microscope and is also referred to as material contrast image. It can be seen that the ferrite ceramic of the core 12 is shown in black in FIG. 3. Going upward from the ferrite ceramic 12, there is a transition layer 24 which consists of copper and copper oxide. It can readily be seen that this transition layer 24 is also mechanically intermeshed with the ferrite ceramic of the core 12.

(17) The transition layer 24 is then followed by the somewhat lighter-colored material of the contact element 18, i.e. copper or a copper alloy. Mechanical intermeshing can also be seen between the transition layer 24 and the material of the contact element 18.

(18) The bond between the contact element 18 or the molten bead of the material of the contact element 18 and the ferrite ceramic of the core 12 is formed by reaction of the molten copper or the molten copper alloy in the molten bead with the ferrite ceramic of the core 12. After cooling, when the contact element is in the solid state, the contact element 18 is then reliably joined to the ferrite ceramic of the core 12.