Patent Application
20100309608
1. Field of the Invention
The present invention generally relates to a buried capacitor structure, and more particularly to a circuit board having a capacitor buried therein.
2. The Prior Arts
Buried passives are passive components disposed between layers of a multi-layer circuit board. The electronic components, such as capacitors or resistors are directly formed on an inner layer of the circuit board by etching or printing. Then, at least one outer layer of the circuit board is laminated onto the inner circuit board to bury the electronic component inside the multi-layer circuit board. The buried passives are adapted to replace those discrete passives soldered to the circuit board, so as to free up space on the circuit board to pack more circuitry and active components.
Buried resistor technologies are first proposed by Ohmega Technologies, Inc., a manufacturer of OHMEGA-PLY® resistor-conductor material. The buried resistor is a thin film of a phosphorous-nickel alloy serving as a resistive element plated onto a matt side of a copper foil of an inner layer. Then, they are compressed to configure a thin core, and later processed by photo-resist processing twice and etching processing thrice, so as to configure a desired thin film resistor at a specific position. Such a thin film resistor is disposed between the layers, and thus called buried resistor.
Generally, a conventional capacitor structure includes a parallel plate capacitor, which has a source electrode and a ground electrode divided by a dielectric layer. Various approaches have been used to increase capacitance of the capacitor. One of the solutions is to provide the dielectric layer with a higher permittivity. Capacitance of the capacitor increases with area and decreases with separation. Thus, another solution is to increase the area of the source electrode and ground electrode, and to decrease the distance between the source electrode and the ground electrode.
However, these solutions introduce other problems. On the one hand, the source electrode is disposed very close to the ground electrode to increase capacitance. Thus, when layers of the circuit board are laminated, the source electrode or the ground electrode is prone to be pressed into the dielectric layer. It even makes the source electrode to contact with the ground electrode, which causes short circuit. On the other hand, the large area of the source electrode and ground electrode increase the thickness of the entire capacitor structure.
To overcome the disadvantages mentioned above, a capacitor is embedded into a dielectric film by a pressing process. Moreover, the parallel plate capacitor is replaced by a comb-type capacitor, which has two comb shapes facing each other and interleaving their branches without touching. Therefore the distance between branches is narrower the distance between the electrodes.
In the above-described configuration, parts of the comb-shaped positive electrode plate and the comb-shaped negative electrode plate are exposed on the second surface of the dielectric film 20, and thus electrical property of the capacitor is affected by environmental factors. For example, high humidity can reduce breakdown voltage of the capacitor, and even damage the capacitor.
A primary objective of the present invention is to provide a buried capacitor structure, which overcomes the disadvantages of the conventional design. The buried capacitor structure according to the present invention is insulated from the environment and is not affected by environmental factors, and in the meanwhile has high capacitance.
The solution of the present invention is to provide a buried capacitor structure including a first conductive metal layer, a first dielectric film, a capacitor, a second dielectric film, and a second conductive metal layer, which are stacked in sequence. Wherein, the capacitor is buried between the first dielectric film and the second dielectric film. The first conductive metal layer and the second conductive metal layer are formed into a first circuit pattern and a second circuit pattern, respectively. The capacitor has a positive electrode end and a negative electrode end connected with the second conductive metal layer. The capacitor structure is provided with a through-hole to connect the first conductive metal layer with the second conductive metal layer, thereby increasing the reliability of the capacitor and reducing the area of the capacitor.
The capacitor according to the present invention may be a planar comb-shaped capacitor and has a positive electrode and a negative electrode. The positive electrode includes the positive electrode end and a plurality of positive comb branches, and the negative electrode includes the negative electrode end and a plurality of negative comb branches. The positive comb branches and the negative comb branches face each other and interleave without touching. The interleaving positive comb branches and the negative comb branches are disposed at the same plane, parallel to each other, and keep a same separation distance therebetween. Moreover, a capacitor paste is filled between the positive comb branches and the negative comb branches, thereby improving insulation and raising breaking voltage. Therefore, the capacitance of the buried capacitor structure is increased.
The buried capacitor structure according to the present invention includes a comb-type capacitor to increase capacitance. Further, the capacitor is buried in the dielectric films for being insulated from the environment, and thus is not affected by the environmental factors.
The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which:
The capacitor 10 has a positive electrode end 12 and a negative electrode end 14. A positive lead 11 electrically connects the positive electrode end 12 with the second conductive metal layer 32, and a negative lead 13 electrically connects the negative electrode end 14 with the second conductive metal layer 32. The positive lead 11 and the negative lead 13 are formed by filling conductive metal into a positive through-hole and a negative through-hole of the second dielectric film 22, respective.
The first insulating layer 41 is deposited to cover the patterned first conductive metal layer 31 and the exposed first dielectric film 21, and then a plurality of openings are formed therein to expose a portion of the first conductive metal layer 31. Similarly, the second insulating layer 42 is deposited to cover the patterned second conductive metal layer 32 and the exposed second dielectric film 22, and then several openings are formed therein to expose a portion of the second conductive metal layer 32. The first insulating layer 41 and the second insulating layer 42 provide electrical insulation, and may be made of conventional insulating green paint for printed circuit board. The third conductive metal layer 51 is deposited on the openings of the first insulating layer 41, and the fourth conductive metal layer 52 is deposited on the openings of the second insulating layer 42. The third conductive metal layer 51 and the fourth conductive metal layer 52 serves as soldering layers for soldering other electronic components, such as resistors, capacitors, inductors, etc.
Referring to
Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.
