Component assembly

A component assembly includes an electric component with a body and a carrier substrate on which the component is fixed by means of a conductive adhesive layer. External electrical contacts that have a planar surface are arranged on the lower side of the body. The conductive adhesive acts upon the body in at least one contact region that is devoid of the external electrical contacts.

BACKGROUND

A ceramic-based, multilayer component is known from the German patent publication DE 10132798 C1.

SUMMARY

A component assembly is specified that comprises an electrical component with a body and a carrier substrate, on which the component is fixed by means of a conductive adhesive layer. External electrical contacts having a flat surface are arranged on the underside of the body. The conductive adhesive contacts the body at least one contact area that is free of external electrical contacts.

The body preferably contains a sintered ceramic material. It was found that the conductive adhesive adheres well to ceramic surfaces. It is therefore advantageous if the body and the carrier substrate are additionally bonded to one another directly, i.e., outside the external electrical contacts situated between them.

Compared with external contacts that are produced in a dipping process and therefore have a curved surface, the external contacts with a flat surface are distinguished by a lower manufacturing tolerance, particularly with regard to their height. The distance between the carrier substrate and the body is then substantially constant.

The excess conductive adhesive can be guided through a gap between the carrier substrate and the body. How far the conductive adhesive penetrates into the gap depends on the wetting properties of the adhesive and the gap size. Therefore, a constant gap size is particularly advantageous for estimating the optimal amount of adhesive.

A well-defined amount of the conductive adhesive is applied to the respective external contact surface of the carrier substrate, preferably printed through a stencil. Alternatively, there is the possibility of printing the external contacts of the component with the conductive adhesive. The component is pressed against the carrier substrate, with a part of the conductive adhesive being pressed into the gap. The amount of conductive adhesive to be printed per external contact is dimensioned such that no short circuits result when excess conductive adhesive penetrates into the gap. The conductive adhesive should therefore penetrate less than half the distance between two external contacts. This can be precisely adjusted for external contacts with a planar surface.

The amount of conductive adhesive is calculated such that a tight bond between the carrier substrate and the body is created, due to the excess conductive adhesive that has penetrated into the gap.

The curing of the conductive adhesive takes place in one embodiment at approximately 150° C., e.g., at a temperature that lies below ordinary soldering temperatures.

The external electrical contacts are preferably not produced with a dipping method, but rather with a method in which a conductive paste is formed. They can be produced by printing, for example, in a screen printing process. The conductive paste is baked and galvanically reinforced by a Au or PdNi layer. The external contacts can be produced by applying the conductive paste with a roller, with subsequent baking.

By means of suitable printing methods such as screen printing, external contacts that have a largely planar surface can be produced. A small variation of the layer thickness can thus be maintained.

In a first embodiment, a AgPd layer is printed onto the underside of the body and baked to form external contacts.

In a second embodiment, a copper layer is printed on and baked. Then a Au or PdNi layer is produced on the layer with a galvanic method.

In a third embodiment, a sintered base, for example, a Ni layer, is produced by applying a Ni layer to the unsintered green body of the precursor component, preferably in a screen printing process, and the Ni is “sintered up” in the subsequent sintering of the component. Thereafter a Au or PdNi layer is produced in a galvanic method on this layer.

A stencil is preferably used for the shaping. Not only the footprint of the respective external contact, but also its height, is specified by the stencil.

The height of the external electrical contacts is preferably selected between 10 and 50 μm.

Preferably, all external contacts of the component are arranged on the underside of the body.

In one embodiment, the component is formed as a multilayer component, preferably a multilayer capacitor or MLCC. MLCC stands for multilayer ceramic capacitor.

The multilayer capacitor comprises alternately arranged first and second internal electrodes that are arranged in the body. The first internal electrodes are connected to the first external electrical contact, and the second internal electrodes are connected to the second external electrical contact. The first and second internal electrodes are insulated from one another. A capacitance is formed between areas of the first and second electrodes.

The internal electrodes are oriented parallel to the underside of the body in one embodiment and are connected by means of plated through-holes to the external electrical contacts.

In another embodiment, the internal electrodes are oriented perpendicular to the underside of the body. The internal electrodes can be oriented parallel to the longitudinal axis of the body. They can also be oriented perpendicular to the longitudinal axis of the body.

The body preferably has the shape of a cuboid. The corners of the cuboid are preferably rounded off. The respective external electrical contact extends in one embodiment up to at least one of the rounded corners.

The upper side and at least planar-shaped areas of the side faces of the body are free from external electrical contacts in one embodiment. In this case, all external electrical contacts of the component are arranged on the underside of the body. Thus material can be saved, which is advantageous particularly in the case of Pd-containing external contacts.

The conductive adhesive contains epoxy resin filled with conductive particles, preferably Ag and/or Cu.

The material of the external contacts is selected such that a good adhesion between conductive adhesive and external contact is assured. In an advantageous embodiment, the external electrical contacts have a layer that contains palladium, nickel-palladium, silver-palladium, or some other noble metal. Palladium favors the adhesion of the epoxy resin. The external electrical contacts may also comprise an additional layer, preferably containing copper. This layer, which was already mentioned above, is arranged between the body and the Pd-containing layer, and serves as an electrically conductive layer promoting adhesion.

The external contacts can each have at least one cutout or opening. Thereby a cavity is formed, which is filled with conductive adhesive. An additional contact surface is formed between the conductive adhesive and the body. In one embodiment, the cavity opens into the above-mentioned gap. In another embodiment, the cavity is isolated from the gap.

The following list of reference symbols may be used in conjunction with the drawings:1Component10Body11,12External electrical contacts of the component13Contact region14,15Internal electrodes2Carrier substrate21,22External contact areas of the carrier substrate23Contact region3Conductive adhesive4Gap5Recess

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Various views of a component assembly are shown inFIGS. 1A,1B. This assembly comprises an SMD-capable electrical component1that is mounted on a carrier substrate2. SMD stands for surface mounted device.

Component1comprises a body10, on the underside of which first and second external electrical contacts11,12are arranged. The height of the external contacts11,12is preferably selected to be between 10 and 50 μm. The external contacts11,12have a planar surface that faces the external contact areas of the carrier substrate2.

First and second external contact areas21,22are arranged on the upper side of carrier substrate2. Body10is fixedly connected to carrier substrate2in the area of external contacts11,12by a conductive adhesive3. The conductive adhesive3contacts body10in a contact region13and contacts carrier substrate2in a contact region23.

A narrow gap4, which is partially filled with conductive adhesive3, is formed between body10and carrier substrate2.

The conductive adhesive3forms a strong connection between body10and carrier substrate2, the cross section of which connection exceeds that of external contacts11,12and of external contact areas21,22. Thus, a particularly good adhesive strength of the component on the carrier can be guaranteed.

The contact region13is arranged between two external electrical contacts21,22on the underside of body10. An additional contact region13a, which is arranged on the side face of body10, is also present.

A stack of first internal electrodes14, each conductively connected to first external contact11, is arranged in body10. A stack of second internal electrodes15, each conductively connected to second external contact12, is arranged in body10.

A cross section AA of component1is shown inFIG. 1C, and a cross section BB, inFIG. 1D.

Various views of an electrical multilayer component, which, unlike the previous embodiment, has a body with rounded edges, are shown inFIGS. 2A,2B. The edges are rounded off by rubbing, for example.

The respective external electrical contacts11,12extend in the longitudinal direction toward the rounded edge formed between the underside and a first or second side face of the body. Although the shape of the external contacts is matched to the rounded edge, the lower surface of the external contacts is flat.

Various views of an additional electrical multilayer component are shown inFIGS. 3A,3B. In this case, the first internal electrodes14are connected to one another and to first external contact11of the component by means of a plated through-hole16arranged in body10. The second internal electrodes15are connected to one another and to second external contact12of the component by means of a plated through-hole17arranged in body10.

External contacts11,12with two recesses5are shown inFIG. 4A, and an external contact with a cutout in the form of an opening is shown inFIG. 4B. Several openings per external contact may also be considered.

FIG. 5shows an external contact11that has a first layer111and a second layer112. First layer111preferably contains silver-palladium. Second layer112, which is arranged between first layer111and body10, preferably contains metallic copper.

First layer111can contain metallic Pd, PdNi or Au, for example, which is preferably applied galvanically. Second layer112can contain metallic Cu, Ag or AgPd, which is applied by screen printing in one embodiment.

In one embodiment it is possible to forgo layer111if, for example, layer112contains AgPd. This layer is preferably applied by screen printing.