Patent Application
20050128677
1). Field of the Invention
The present invention generally relates to capacitors. More particularly, the invention relates to a capacitor having a reduced equivalent series resistance (ESR) and equivalent series inductance (ESL).
2). Discussion of Related Art
In the highly competitive personal computer (PC) industry, the difficult trade-off between cost and performance has been well documented. For example, in an effort to provide more features to the consumer at a lower cost, significant focus has been placed on streamlining motherboard systems and components. Most motherboards employ one or more voltage regulation circuits to ensure that the proper reference voltages are supplied to the motherboard processors, and it has been determined that such a circuit has a direct effect on the switching performance of the processor. The voltage regulation circuit typically has a voltage regulation module and a capacitor arrangement (among other components). The capacitor arrangement is critical because it provides decoupling between the voltage regulation module (VRM) and the processor. Conventional approaches to the capacitor arrangement involve the use of multiple high performance bulk-type capacitors, which can have very low temperature stability, wide frequency range, and long life. Low ESR reduces the unwanted parasitic impedance and heating effects that degrade capacitors, and is highly desirable in the computing industry. The cost of these performance capacitors, however, is relatively high with respect to other capacitors. It is therefore desirable to provide an alternative to conventional performance capacitors in voltage regulation circuits.
The alternative approach to the above design would be to use a combination of ceramic and conventional electrolytic capacitors, which would reduce the costs of the capacitor arrangement considerably. The trade-off to reduced cost, however, is reduced performance under conventional approaches.
Thus, the conventional capacitor arrangement provides a significant cost-saving opportunity, but certain difficulties remain. For example, the typical wound aluminum electrolytic capacitor is unable to meet the exacting ESR and ESL requirements of modem day high-speed processors.
It has been determined that the design of the dual lead configuration 16 can be quite challenging with regard to ESR and ESL. For example, limiting the lead configuration to two terminal assemblies has been found to contribute to a relatively high ESR in a capacitor of this type. The distance between terminal assemblies 18 and 20 has a significant impact on ESR and ESL.
It is also important to note that the weld 26 contributes to loop ESL and that the relatively long two-piece termination/lead design adds to both loop ESL and ESR. It is therefore desirable to provide a lead configuration that enables ESR to be reduced without sacrificing with respect to ESL.
It will also be appreciated that certain manufacturing and placement difficulties can also result from the conventional capacitor 10. For example, the typical solder connection that occurs at the leads 24 requires wave soldering, which prohibits the use of the capacitor 10 in dual-sided reflow PWBs. Furthermore, the traditional case 12 can be relatively tall, which limits the use of the capacitor 10 to applications having a great deal of clearance space. Tall body and long leads contribute to higher ESR/ESL as well. Redesign of the height could bring the ESR/ESL down.
The invention is described by way of example with reference to the accompanying drawings, wherein:
A capacitor and method of fabricating a capacitor in accordance with the principles of the present invention provide enhanced performance. The capacitor has a case and a wound foil disposed within the case. A ball-and-lead configuration is coupled to the foil and extends from the case. The use of ball-and-lead technology for the lead configuration provides substantial benefits with respect to ESR, ESL, manufacturability, and placement.
In another aspect of the invention, a ball-and-lead configuration of a capacitor includes a cathode termination having a first end coupled to a first surface of a foil. An anode termination has a first end coupled to a second surface of the foil. The ball-and-lead configuration further includes two conductive solder balls, of the kind used in ball grid array technology, coupled to second ends of the terminations, where the solder balls enable electrical connection of the lead configuration to a printed wiring board (PWB).
In another aspect of the invention, a method of fabricating a capacitor is provided. A case is provided, and a ball-and-lead configuration is coupled to a foil. The method further provides for disposing the foil within the case such that the ball-and-lead configuration extends from the case.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.
It can generally be seen that the capacitor 30 has a case 32 and a wound foil 34 disposed within the case 32. A ball-and-lead configuration 36 is coupled to the foil 34 and extends from the case 32. The ball-and-lead configuration 36 includes one elongate flat cathode termination 38 having a first end coupled to a first surface of the foil 34. The ball-and-lead configuration 36 includes one elongate flat anode termination 40 having a first end coupled to a second surface of the foil 34. In another embodiment, the ball-and-lead configuration 36 may have a total of three, four, or five terminations. The ball-and-lead configuration 36 may have an equal number of cathode and anode terminations or may have one more of one than the other.
As will be discussed in greater detail below, the foil 34 can be an aluminum foil of the type that is commercially available and widely used in the industry. U.S. Pat. No. 6,110,233 to O'Phelan, et al. describes one such foil, but other techniques may be used without parting from the nature and scope of the invention. It can further be seen that the ball-and-lead configuration 36 includes two solder balls 42 coupled to second ends of the terminations 38, 40, where the solder balls 42 enable electrical connection of the lead configuration to a printed wiring board 28 as best shown in
Turning now to
With continuing reference to
Additionally, by using solder balls 42, the physical height of the capacitor is reduced, which enables the component to fit into height-constrained locations. Furthermore, the solder balls 42 enable surface mount connection of the lead configuration 36 to the PWB 28. As best shown in
Turning now to
It will be appreciated that the order in which the processing blocks are performed may vary without departing from the nature and scope of the invention. For example, the solder balls may be coupled to the terminations before the terminations are coupled to the foil. It should also be noted that the solder balls enable surface mount connection of the lead configuration to the PWB.
Turning now to
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and following claims.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described since modifications may occur to those ordinarily skilled in the art.
