GB2152753A

GB2152753A - Decoupling capacitor for integrated circuits and relationship with a printed circuit board

Info

Publication number: GB2152753A
Application number: GB08430202A
Authority: GB
Inventors: Akihiko Matsumaru
Original assignee: Nippon Mektron KK
Current assignee: Nippon Mektron KK
Priority date: 1983-11-30
Filing date: 1984-11-29
Publication date: 1985-08-07
Also published as: IT1178640B; DE3443813A1; BR8406056A; GB8430202D0; FR2555801A1; JPS60117705A; IT8423807A0

Abstract

A bypass condensor or decoupling capacitor adapted to be mounted between an integrated circuit and a printed circuit board, includes a power supply electrode which is divided into a plurality of electrically separate electrode sections (13, 14) and dielectric material (12) which is sandwiched between the individual electrode sections (13, 14) and a common ground electrode (16). The capacitor is encapsulated (11). Alternatively, the dielectric material may also be divided into a plurality of separate or individual sections (17, 18) corresponding to the number of separate power supply electrode sections. In the alternative structure, each of the dielectric sections (17, 18) may have relatively different dielectric constant values. The decoupling capacitors of the present invention may be tailored to fit the power supply needs of an integrated circuit which is actuated by several kinds of power supplies. <IMAGE>

Description

SPECIFICATION Decoupling capacitor for integrated circuits and electronic subassembly comprising such a capacitor This invention relates generally to bypass condensors or decoupling capacitors for use in conjunction with integrated circuits. More particularly, this invention reiates to a decoupling capacitor of the type which is mounted on a circuit board and is disposed beneath an integrated circuit package.

Power supply bypass condensors or decoupling capacitors are known for providing a means of preventing noise in an integrated circuit mounted on a circuit board. In the prior art, such a bypass condensor was usually mounted on a printed circuit or wiring board using mounting holes which were different from those mounting holes used for an integrated circuit. The positioning of a decoupling capacitor in a location which is different than the location of the integrated circuit gives rise to many disadvantages. For example, circuit wiring patterns on the circuit board become complicated. Also, and of extreme importance, the mounting density of electronic components (i.e., integrated circuits) on the circuit board is greatly lowered.It will be appreciated that the mounting density of electronic components on a printed circuit board is of increasing concern to circuit board design engineers.

One attempt at eliminating the above discussed problems relating to conventional decoupling capacitors on printed circuit boards has been to provide a decoupling capacitor which is adapted to be mounted on a circuit board and which has an integrated circuit package superimposed thereover. A decoupling capacitor of this type will have its power supply and ground terminals inserted into common mounting holes with the power and ground connections pins of the integrated circuit. As a result, a decoupling capacitor of this type is mounted in very close proximity to the integrated circuit providing a mounting density on the circuit board which is vastly improved over the prior art. Also, the preparation of the circuit wiring pattern is less complicated. Finally, noise in the integrated circuit is prevented and adverse effects on the surrounding electrical circuits are reduced.It will be appreciated to those skilled in the art then, that decoupling capacitors of the type which are mounted underneath an integrated circuit has provided many advantages and features over prior art methods of mounting.

Decoupling capacitors of the type hereinabove discussed generally have a structure which comprises two electrode plates which sandwich a dielectric material therebetween. A ground terminal and a power supply terminal protrude from each respective plate while the entire package is covered with an insulating encapsulate material. While suitable for its intended purposes, this particular capacitor structure is not especially suitable for integrated circuit packages which are actuated by different types of, or a plurality of power supplies. Instead, the improved decoupling capacitors of the0 prior art are generally suitable only for integrated circuits which are actuated by only one type of power supply.

In accordance with the present invention there is provided a decoupling capacitor for use with an integrated circuit element which has a plurality of contact pins extending therefrom in a pair of spaced parallel rows, with at least a first pin in one row and at least a second pin in the other row being power supply pins, the capacitor including:: a flat dielectric body having a pair of opposed surfaces, a first electrode on one of said opposed surfaces of said dielectric body defining a ground electrode, a plurality of second electrodes on the other of said opposed surfaces of said dielectric body defining a plurality of power electrodes, each of said power electrodes being electrically insulated from the other, a first conductor in electrical contact with said ground electrode, and a second conductor in electrical contact with each of said power electrodes, said conductors extending outwardly and downwardly from points located adjacent opposite sides of said body, said conductors being shaped and positioned to be received in power supply sockets of a circuit board, and an insulating film encapsulating said dielectric body and electrodes, said conductors extending through said insulating film.

"The decoupling capacitor for use in conjunction with integrated circuits is specifically adapted to be used with those integrated circuits which are actuated by a plurality of power supplies. Unlike the prior art single power supply electrode, the power supply electrode of the present invention is divided into a plurality of sections so that a single decoupling capacitor can be used with a plural number of actuating power supplies required for a particular integrated circuit. In a first embodiment of the present invention, the dielectric member can be provided as a single piece or alternatively, in a second embodiment, the dielectric member may consist of a plurality of separate pieces corresponding to the number of actuating power supplies.In the second embodiment, wherein a plurality of dielectric members may be used, the individual values of the dielectric constant for each dielectric member may be different. In that case, the decoupling capacitor can be specifically tailored to the needs or properties of a particular integrated circuit.

The above discussed and other advantages of the present invention will be apparent to and understood by those skilled in the art from the following detailed description and drawings.

Referring now to the drawings, wherein like elements are numbered alike in the several Figures: Figure 1 is a perspective view of a decoupling capacitor in accordance with the prior art being mounted between a printed circuit board and an integrated circuit package, Figure 2 is a cross-sectional elevation view of the decoupling capacitor of Fig. 1 in accordance with the prior art, Figure 3 is a cross-sectional elevation view of a first embodiment of a decoupling capacitor in accordance with the present invention, Figure 4 is a cross-sectional elevation view of a second embodiment of a decoupling capacitor in accordance with the present invention.

Referring first to Figs. 1 and 2, a decoupling capacitor or bypass condensor in accordance with the prior art is shown generally at 7. Decoupling capacitor 7 is adapted to be mounted on a printed circuit board 4 with an integrated circuit 1 superimposed thereover.

The power supply pin 8 and ground pin 9 of capacitor 7 and the respective power and ground pins 2 and 3 of the integrated circuit 1 are each mounted in respective common mounting holes 5 and 6 as shown in Fig. 1.

As a result of decoupling capacitor 7 being mounted underneath integrated circuit 1, the mounting desnity of circuit board 4 is greatly improved over other prior art configurations wherein the capacitor was mounted adjacent the integrated circuit on the circuit board.

Moreover, the preparation of the circuit wiring pattern is less difficult when mounting the decoupling capacitor 7 underneath integrated circuit package 1. As is known to those skilled in the art, decoupling capacitor 7 reduces noise in integrated circuit 1 as well as reducing adverse effects on the surrounding electrical circuits.

In Fig. 2, the internal structure of the decoupling capacitor 7 of Fig. 1 is shown.

Decoupling capacitor 7 comprises two electrode plates 8,A and 9A having dielectric material 10 sandwiched therebetween. A ground terminal 8 and a power supply terminal 9 protrude from electrode plates 8A and 9A, respectively. The entire structure is then en capsulated with an insulating material 11 which covers the entire outer surface except for the protruding terminals 8 and 9. Note that ground and power supply terminals 8 and 9 protrude outwardly and then are bent downwardly at an angle of approximately 90 .

As discussed above, while the well known decoupling capacitor 7 of Figs. 1 and 2 is suitable for its intended purposes and solves many of the problems (i.e. such as increasing the mounting density on a printed circuit board) associated with other prior art decoupling capacitors, the internal structure of capacitor 7 is nevertheless not especially suited for those types of integrated circuits which are actuated by different kinds of, or a plurality of power supplies.

Referring now to Fig. 3, a decoupling capacitor or bypass condensor in accordance with the present invention is shown and comprises a first power supply electrode 1 3 and a second power supply electrode 14 separated by a gap 1 5 therebetween. Both electrodes 1 3 and 1 4 are disposed above a common ground electrode 1 6 while a flat dielectric body 12.

preferably of rectangular shape and comprised of a ceramic or other material having a high dielectric constant, is sandwiched between the first and second power supply electrodes 13, 14 and the ground electrode 16. Each of electrodes 1 3, 1 4 and 1 6 are provided with at least one terminal 1 3A, 1 4A and 1 6A respectively protruding therefrom. As shown in the drawings, terminals 1 3A, 1 4A and 1 6A are bent downwardly at an angle of about 90 degreees so that they can be inserted into the common mounting holes on a printed circuit board along with the connection pins of an integrated circuit as is shown in Fig. 1. As in the prior art configuration of Fig. 2, the entire structure, except for protruding terminal pins 1 3A, 1 4A and 1 6A are encapsulated with an insulating material 11.Note however, that unlike the prior art decoupling capacitor of Fig. 2, the capacitor of the present invention includes insulating material 11 which filis gap 1 5 between power electrodes 1 3 and 1 4 to establish electrical insulation therebetween.

As is clear from the above discussion, the bypass condensor or decoupling capacitor of the present invention is adapted to be mounted underneath an integrated circuit on a printed circuit board as shown in Fig. 1.

Unlike the prior art decoupling capacitor 7 however, the two electrodes 1 3 and 14 permit the decoupling capacitor of Fig. 3 to be used in conjunction with an integrated circuit which requires at least two different power supplies. The decoupling capacitor of the present invention solves this defficiency of the prior art while maintaining a relatively compact overall structure.

Referring now to Fig. 4, a second embodiment of a decoupling capacitor in accordance with the present invention is shown. In Fig. 4, the dielectric material 1 2 of Fig. 3 is replaced with a pair of flat dielectric bodies or members 1 7 and 1 8 corresponding to the pair of power supply electrodes 1 3 and 14. Insulating encapsulated material 11 is provided between the two dielectric members 1 7 and 1 8 in gap 1 SA to provide electrical insulation therebetween. In a preferred embodiment, the values of the dielectric constant of each die lectric member 1 7 and 1 8 are different from each other.As a result, the decoupling capaci tor of Fig. 4 can effect noise reduction for an integrated circuit having a plurality of different types of power supplies. Alternatively, each dielectric member 1 7 and 1 8 may have identical dielectric constants. It will be appreciated that the decoupling capacitor of Fig. 4 may be preferably over the decoupling capacitor of Fig. 3 as the physical and electrical properties of the Fig. 4 capacitor may be more easily tailored to suit the needs of a particular integrated circuit.

In accordance with the present invention, a bypass condensor or decoupling capacitor adapted to be mounted underneath an integrated circuit thus includes a power supply electrode which is divided into a plurality of electrically separate electrode sections, dielectric material which is sandwiched between the individual electrode sections and a common ground electrode. Alternatively, the dielectric member may also be divided into a plurality of separate or individual sections corresponding to the number of separate power supply electrode sections. The present invention therefore provides a single bypass condensor having a plurality of independent bypass condensors therein while maintaining an overall compact structure. The decoupling capacitors of the present invention may be tailored to fit the power supply needs of an integrated circuit which is actuated by several kinds of power supplies. The present invention is thus easily adaptable and may be designed for any particular integrated circuit having unique power supply requirements.

It will be appreciated that while Figs. 3 and 4 show decoupling capacitors having a pair of power supply electrodes 1 3 and 14, the present invention is not limited to this particular structure. In fact, more than two power supply electrodes as well as more than two corresponding dielectric members are encompassed by the decoupling capacitor of the present invention.

Claims

1. A capacitor for use with an integrated circuit element which has a plurality of contact pins extending therefrom in a pair of spaced parallel rows, with at least a first pin in one row and at least a second pin in the other row being power supply pins, the capacitor including: a flat dielectric body having a pair of opposed surfaces, a first electrode on one of said opposed surfaces of said dielectric body defining a ground electrode, a plurality of second electrodes on the other of said opposed surfaces of said dielectric body defining a plurality of power electrodes, each of said power electrodes being electrically insulated from the other, a first conductor in electrical contact with said ground electrode, and a second conductor in electical contact with each of said power electrodes, said conductors extending outwardly and downwardly from points located adjacent opposite sides of said body, said conductors being shaped and positioned to be received in power supply sockets of a circuit board, and an insulating film encapsulating said dielectric body and electrodes, said conductors extending through said insulating film.

2. A capacitor as claimed in Claim 1, wherein said dielectric body comprises a plurality of individual sections corresponding to the number of said power electrodes, each of said individual dielectric body sections being electrically insulated from the other.

3. A capacitor as claimed in Claim 2, wherein each of said individual dielectric body sections has about the same dielectric constant.

4. A capacitor as claimed in Claim 2, wherein each of said individual dielectric body sections have different dielectric constants.

5. A capacitor as claimed in Claim 1, wherein said dielectric body is ceramic.

6. A capacitor as claimed in Claim 1, wherein said ceramic body is of rectangular shape.

7. An electronic subassembly comprising: an integrated circuit package, said circuit package having a plurality of pins extending outwardly therefrom in the same direction, said pins and a first surface of said package defining a space, a circuit board having spaced holes receiving said circuit package pins, a plurality of specially displaced of said holes defining power supply sockets.

a decoupling capacitor, said decoupling capacitor being positioned in said space and thus being interposed between said first surface of said circuit package and said board, said capacitor comprising: a flat dielectric body having a pair of opposed surfaces, a first electrode on one of said opposed surfaces of said dielectric body defining a ground electrode, a plurality of second electrodes on the other of said opposed surfaces of said dielectric body defining a plurality of power electrodes, each of said power electrodes being electrically insulated from the other, a first conductor in electrical contact with said ground electrode, and a second conductor in electrical contact with each of said power electrodes, said conductors extending outwardly and downwardly from points located adjacent opposite sides of said body, said conductors being shaped and positioned to be received in power supply sockets of said circuit board, and an insulating film encapsulating said dielectric body and electrodes, said conductors extending through said insulating film.

8. An electronic subassembly as claimed in Claim 7, wherein said dielectric body comprieses a plurality of individual sections corresponding to the number of said power electrodes, each of said individual dielectric body sections being electrically insulated from the other.

9. An electronic subassembly as claimed in Claim 8, wherein each of said individual dielectric body sections has about the same dielectric constant.

10. An electronic subassembly as claimed in Claim 8, wherein each of said individual dielectric body sections have different dielectric constants.

11. An electronic subassembly as claimed in Claim 7, wherein said dielectric body is ceramic.

1 2. An electronic subassembly as claimed in Claim 7, wherein said ceramic body is of rectangular shape.

13. A capacitor for use with an integrated circuit element substantially as hereinbefore described and as illustrated in the accompanying drawings.

14. An electronic subassembly substantially as hereinbefore described and as illustrated in the accompanying drawings.