Chip capacitor

Abstract

A chip capacitor which can be miniaturized with structural stability. In the chip capacitor, a capacitor device has a cathode layer formed on an outer surface thereof and an anode wire is protruded from a portion thereof. A cathode lead is electrically connected to the cathode layer. An anode lead is electrically connected to the anode wire through a weld reinforcement. A molding is configured to cover the capacitor device in such a way that the cathode and anode leads are only partially exposed. Protrusions are protruded from outer surfaces of the cathode and anode leads, respectively, thereby forming steps on the outer surfaces thereof. In the chip capacitor, the leads and molding are bonded with much greater strength, thus more structurally robust. Also, this prevents external moisture from penetrating inside the chip capacitor, thereby significantly enhancing moisture resistance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view illustrating a conventional chip capacitor, in which (a) is a side cross-sectional view and (b) is a cross-sectional view cut along the line A-A′;

FIG. 2 is a side cross-sectional view illustrating another example of a conventional chip capacitor;

FIG. 3 is a side cross-sectional view illustrating a chip capacitor according to the invention;

FIG. 4 is a cross-sectional view cut along the line B-B′ of FIG. 3;

FIG. 5 illustrates a conventional chip capacitor structure together with a chip capacitor structure of the invention to show that the chip capacitor of the invention is superior in bonding strength to the conventional structure, in which (a) illustrates the conventional structure and (b) illustrates the structure according to the invention;

FIG. 6 illustrates a conventional chip capacitor structure together with a chip capacitor structure of the invention to show that the chip capacitor of the invention is superior in moisture resistance to the conventional structure, in which (a) illustrates the conventional structure and (b) illustrates the structure according to the invention; and

FIG. 7 is a cross-sectional view illustrating a chip capacitor mounted on a PCB according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in FIGS. 3 and 4, a chip capacitor 1 according to the invention includes a capacitor device 10 having a cathode layer 12 formed on an outer surface thereof and an anode wire 14 protruding from a portion thereof.

The capacitor device 10 is a dielectric device obtained by compressing a tantalum oxide (Ta₂O₅) powder into a parallelepiped shape. But the invention is not limited to tantalum Ta, and optionally, other material such as Nibio (Nb) can be employed.

The capacitor device 10 as described above is rectangular box shaped. The capacitor device 10 has a front surface 10a from a portion of which the anode wire 14 is protruded and a rear surface 10b opposing the front surface 10a.

The capacitor device 10 has a cathode layer 12 formed on an outer surface thereof and a cathode lead 20 electrically connected to the cathode layer 12.

The cathode lead 20 is connected to the cathode layer 12 through an Ag paste as in the prior art. The cathode lead 20 has a protrusion 22 protruding from an outer surface thereof, thereby forming steps on the outer surface thereof. As shown in FIG. 3, the protrusion 22 has a step 24a extended along a length direction of the cathode lead 20, i.e., in a length direction of the capacitor device 10. Also, as shown in FIG. 4, the protrusion 22 has steps 24b extended along a width direction of the cathode lead 20, i.e., in a width direction of the capacitor device 10.

Moreover, the chip capacitor 1 of the invention includes an anode lead 30 electrically connected to the anode wire 14 protruding from the front surface thereof through a weld reinforcement 28.

The anode lead 30 is connected to the anode wire 14 through the weld reinforcement as in the prior art, preferably by laser welding.

The anode lead 30 has a protrusion 32 protruding from an outer surface thereof, thereby forming steps on the outer surface thereof.

As shown in FIG. 3, the protrusion 32 has a step 34a extended along a length direction of the anode lead 30, i.e., in a length direction of the capacitor device 10. Also, as shown in FIG. 4, the protrusion 32 has steps 34b extended along a width direction of the anode lead 30, i.e., in a width direction of the capacitor device 10.

Meanwhile, to form a molding in the chip capacitor 1 of the invention, the capacitor device 10 is molded to expose only some portions, i.e., underside surfaces of the cathode lead 20 and the anode lead 30.

The molding 40 carries electromagnetic compatibility (EMC) characteristics. That is, with these characteristics, the molding 40 emits a minimum amount of unnecessary electromagnetic waves outside the device, thereby not interfering electromagnetically with other devices. Also, the molding 40 operates normally even under the influence of external electromagnetic interference.

As described above, the molding 40 surrounds the capacitor device 10, the cathode lead 20, the anode wire 14, the weld reinforcement 28 and the anode lead 30, only exposing the underside surfaces of the cathode lead 20 and the anode lead 30, respectively. This forms a lead reinforcement area 42 around the steps of the cathode lead 20 and the anode lead 30, respectively.

Such a lead reinforcement area 42 is depicted in FIGS. 5 and 6.

As shown in FIG. 5, the lead reinforcement area 42 serves as a stopper which effectively prevents the anode and cathode leads 20 and 30 from being detached from the molding 40.

Therefore, the anode and cathode leads 20 and 30, even if pulled down from the molding 40, are not disengaged from the molding 40 due to the lead reinforcement area 42.

Furthermore, as shown in FIG. 6, external moisture can be more effectively deterred from penetrating into the capacitor device 10 due to a longer path. This significantly boosts moisture resistance.

The chip capacitor 1 configured as above is mounted on a PCB 50 as shown in FIG. 7.

Here, underside surfaces of anode and cathode leads 20 and 30 are mounted on the PCB 50 by soldering 52.

When it comes to bonding strength of the chip capacitor mounted as just described, it is experimentally found that the anode and cathode leads 20 and 30 are structurally robust without being detached from the molding 40 due to the lead reinforcement area 42.

Moreover, the protrusions 22 and 32 protruding from outer surfaces of the anode and cathode leads 20 and 30 allow the leads 20 and 30 to contact the molding 40 in a larger area. This ensures stable bonding between the leads 20 and 30 and the molding and also noticeably increases moisture resistance.

In addition, the protrusions 22 and 32 protruding from the outer surfaces of the anode and cathode leads 20 and 30, especially the protrusion 22 of the cathode lead, considerably enlarges the planar area, thereby greatly increasing an area of an Ag paste layer 46 which is bonded to the cathode layer 12 of the capacitor device 10. This assures structurally and electrically stable bonding.

As described above, when the Ag paste layer 46 is increased in its bonding area due to the protrusion 22 of the cathode lead 20, the capacitor device 10 can be securely mounted on the PCB. Especially, the Ag paste layer 46 is remarkably increased in its bonding area, thereby enhancing conduction between the capacitor device 10 and the cathode lead 20. In consequence, this greatly boosts impendence or equivalent series resistance (ESR) characteristics of the chip capacitor 1.

As set forth above, according to exemplary embodiments of the invention, steps are formed on outer surfaces of anode and cathode leads along length and width directions. These steps form a lead reinforcement area, thereby significantly enhancing bonding strength between a molding and the leads and ensuring structural stability.

Also, the steps allow the anode and cathode leads to contact the molding in a larger area. Thus, external moisture can be deterred from infiltrating into the capacitor device, thereby greatly improving moisture resistance.

In addition, the chip capacitor of the invention is compact, slim and highly reliable and is structurally and electrically stable when mounted on a PCB.

While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A chip capacitor comprising: a capacitor device having a cathode layer formed on an outer surface thereof and an anode wire protruding from a portion thereof;a cathode lead electrically connected to the cathode layer;an anode lead electrically connected to the anode wire through a weld reinforcement;a molding configured to cover the capacitor device in such a way that the cathode and anode leads are only partially exposed; andprotrusions protruding from outer surfaces of the cathode and anode leads, respectively, thereby forming steps on the outer surfaces thereof,whereby the chip capacitor is enabled to have a miniaturized structure with structural stability.

2. The chip capacitor according to claim 1, wherein the steps of the protrusions are extended along length and width directions of the cathode lead.

3. The chip capacitor according to claim 1, wherein the steps of the protrusions are extended along length and width directions of the anode lead.