Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2000-12-19
2002-11-19
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S309000, C361S306300
Reexamination Certificate
active
06483692
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to discrete capacitors, and more particularly, to surface lands on the surfaces of discrete capacitors, and methods of capacitor fabrication.
BACKGROUND OF THE INVENTION
Electronic circuits, and particularly computer and instrumentation circuits, have in recent years become increasingly powerful and fast. As circuit frequencies continue to escalate, with their associated high frequency transients, noise in the power and ground lines increasingly becomes a problem. To reduce such noise, capacitors known as decoupling capacitors are often used to provide a stable signal or stable supply of power to the circuitry. Capacitors are farther utilized to dampen voltage overshoot when an electronic device (e.g., a processor) is powered down, and to dampen voltage droop when the device powers up.
Decoupling capacitors and capacitors for dampening voltage overshoot or droop are generally placed as close as practical to a die load in order to increase the capacitors' effectiveness. Often, the capacitors are surface mounted to the die side or land side of the package upon which the die is mounted.
FIG. 1
illustrates a cross-section of an integrated circuit package
102
having die side capacitors
106
and land side capacitors
108
in accordance with the prior art. Die side capacitors
106
are mounted on the same side of the package as the integrated circuit die
104
. In contrast, land side capacitors
108
are mounted on the opposite side of the package
102
as the die
104
.
FIG. 2
illustrates an electrical circuit that simulates the electrical characteristics of the capacitors illustrated in FIG.
1
. The circuit shows a die load
202
, which may require capacitance or noise dampening in order to function properly. Some of the capacitance can be supplied by capacitance, as modeled by capacitor
204
, located on the die. Other capacitance, however, must be provided off chip, as indicated by off-chip capacitor
206
. The off-chip capacitor
206
could be, for example, the die side capacitors
106
and/or land side capacitors
108
illustrated in FIG.
1
.
Naturally, off-chip capacitor
206
would be located some distance, however small, from die load
202
, due to manufacturing constraints. Accordingly, some inductance, as modeled by inductor
208
, exists between the die load and the off-chip capacitor
206
. The value of the inductor
208
is related to the “loop area,” which is the electrical distance from die load
202
, through capacitor
206
, and back to die load
202
. Because inductor
208
tends to slow the response time of off-chip capacitor
206
, it is desirable to minimize the loop area, thus reducing the value of inductor
208
.
Referring back to
FIG. 1
, die side capacitors
106
are typically mounted around the perimeter of die
104
, and provide capacitance to various points on the die through traces, vias, and planes (not shown) in the package
102
. Because die side capacitors
106
are mounted around the perimeter, the path length between a die load and capacitor
106
may result in a relatively high inductance feature between the die load and capacitor
106
.
In contrast, land side capacitors
108
can be mounted directly below die
104
, and thus directly below some die loads. However, the package also includes land side connectors (not shown), such as pins or lands. In some cases, placement of capacitors
108
on the package's land side would interfere with these connectors. Thus, the use of land side capacitors
108
is not always an acceptable solution to the inductance problem.
FIG. 3
illustrates a top view of an eight contact discrete capacitor
300
, which can be used as a decoupling capacitor or to dampen voltage overshoot or droop, in accordance with the prior art. Contacts
302
provide electrical connections to electrodes of an internal capacitor structure within capacitor
300
. Going clockwise from the upper left contact
302
, the polarities of contacts
302
alternate between positive and negative. This results in opposing contacts (i.e., contacts directly opposite each other) having opposite polarities. Each contact
302
includes surface lands
304
on the top surface
308
and bottom surface of capacitor
300
.
Referring also to
FIG. 4
, which illustrates a side view of a discrete capacitor in accordance with the prior art, each top and bottom land pair is electrically connected through a side termination
402
on the side surface
404
of the capacitor. Inner electrodes (not shown) electrically connect with the side terminations
402
, and thus with the surface lands
304
.
The length of lands
304
is indicated by dimension
312
. Generally, the land length is designed to be a length that allows a reliable, surface mount solder attachment. A ratio of the length
312
of surface lands
304
to the width
310
of capacitor
300
is typically about the same for most devices. For example, a capacitor having a width
310
of 1.3 millimeters (mm) would typically have lands
304
with lengths
312
of about 0.3 mm, which is approximately 23% of the width
310
of capacitor
300
.
Capacitors sometimes have more or fewer contacts, as well. For example,
FIG. 5
illustrates a top view of a ten contact discrete capacitor
500
in accordance with the prior art. Eight of contacts
502
contact the sides of capacitor
500
, and are referred to herein as “side contacts.” Two of contacts
504
contact the ends of capacitor
500
, and are referred to herein as “end contacts.” Going clockwise from the upper left contact
502
, the polarities of contacts
502
,
504
alternate between positive and negative. Unlike the capacitor illustrated in
FIG. 3
, this results in opposing side contacts
502
having the same polarities, while end contacts
504
have opposite polarities.
The lengths of the side and end contact surface lands are represented by dimensions
512
and
514
, respectively. As with the capacitor
300
illustrated in
FIG. 3
, the ratio of the length
512
of the side contact surface lands to the width
510
of capacitor
500
is typically about the same (e.g., about 23%) for most capacitors. In addition, the ratio of the length
514
of the end contact surface lands to the length
516
of capacitor
500
is also typically about the same. For example, a capacitor having a length
516
of 2.0 mm would typically have end contact lands with lengths
514
of about 0.3 mm, which is approximately 15% of the length
516
of capacitor
500
.
As electronic devices continue to advance, an increasing need exists for higher capacitance with reduced inductance for decoupling, voltage dampening, and supplying charge. In addition, a need exists for capacitance solutions that do not interfere with package connectors, and which do not limit the industry to certain device sizes and packing densities. Accordingly, there is a need in the art for alternative capacitance solutions in the fabrication and operation of electronic devices and their packages.
REFERENCES:
patent: 4590537 (1986-05-01), Sakamoto
patent: 5345361 (1994-09-01), Billotte et al.
patent: 5347423 (1994-09-01), deNeuf et al.
patent: 5817543 (1998-10-01), McAllister et al.
patent: 5895966 (1999-04-01), Penchuk
patent: 6191932 (2001-02-01), Kuroda et al.
patent: 0335358 (1989-10-01), None
patent: 2622346 (1989-04-01), None
patent: 06-349678 (1994-12-01), None
Do Huong T.
Figueroa David G.
Rodriguez Jorge Pedro
Walk Michael
Dinkins Anthony
Intel Corporation
Schwegman Lundberg Woessner & Kluth P.A.
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