Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
2000-11-28
2003-08-05
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S692000, C257S678000, C257S687000, C257S688000, C257S695000
Reexamination Certificate
active
06603199
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to integrated circuit packages. More specifically, the present invention relates to packaging of die having staggered bond pads into grid array-type integrated circuit packages.
BACKGROUND OF THE INVENTION
Current industry emphasis on decreased size and increased functionality of semiconductor dice has resulted in the continuing development of integrated circuit dice having a high density of active circuits. Conventionally, the logic circuitry of the die is formed on the interior portion of the die and a plurality of input/output (I/O) devices or cells are located around the periphery of the die. Each I/O cell, typically, is connected to at least one bond pad fabricated at the surface of the die that serves as the input/output (I/O) contact for that cell.
Placement of the bond pads along the edges of each side of the die allow for connection, for example, by bonding wires, of the bond pads to electrical contacts on another substrate, such as bonding rings or bond fingers on a package substrate. Bond pads are conventionally arranged in an in-line arrangement or in a staggered arrangement.
FIG. 1
is a diagrammatic illustration of a portion of a die having an in-line arrangement of bond pads. In an in-line arrangement, the bond pads
104
are located along the periphery of the die
102
in a single row. Spacing of the bond pads
104
may be described in terms of a pad pitch, or the center-to-center spacing of the pads. For example, pad pitch
106
of the bond pads
104
, may be, for example, 75 microns.
In some other dice, especially high-density dice, the bond pads may be arranged in a staggered arrangement resulting in multiple rows of bond pads located at the edges of the die. Staggering the bond pads permits more bond pads to be located on the die over that of an in-line arrangement. The location of a bond pad interior to the die, e.g., an inner bond pad, relative to the bond pads nearest the edge of the die, e.g., outer bond pads, may be described as being “perfectly” staggered or “non-perfectly” staggered.
FIG. 2
is a diagrammatic illustration of a portion of a die having staggered bond pads in a “perfect” staggered arrangement. As illustrated, the inner bond pads
204
are staggered relative to the outer bond pads
206
in that they are located interior to the die
202
from the outer bond pads
206
and are not “in-line” with the outer bond pads
206
. In this example, the inner bond pads
204
are arranged in a “perfect” staggered arrangement relative to the outer bond pads
206
as they are located interior to and directly between the outer bond pads
206
, i.e., in the spaces. Although the pad pitch
208
between the outer bond pads
206
may be the same as in the in-line arrangement earlier described with reference to
FIG. 1
, e.g., 75 microns, the stagger of the additional row of inner bond pads
204
may result in an smaller overall effective pad pitch, for example, 45 microns. Thus, a greater density of bond pads may be located on the same size die with a staggered arrangement of bond pads over that of a die having an in-line arrangement of bond pads.
FIG. 3
is a diagrammatic illustration of a portion of a die having staggered bond pads in a “non-perfect” staggered arrangement. In this example, the inner bond pads
304
of the die
302
are not located directly between the outer bond pads
306
, but are horizontally offset relative to the outer bond pads
306
so that, with increasing offset from the space between the outer bond pads
306
, portions of the inner bond pads
304
become located behind the outer bond pads
306
. The offset may be to such a large degree that an inner bond pad
304
is directly aligned behind an outer bond pad
306
.
As a staggered bond pad arrangement on a die provides greater bond pad density over that of most similarly sized die having in-line die arrangements, high-density dice are increasingly being designed with staggered bond pad arrangements. A design consideration, however, with the staggered arrangement is the possibility of wire crossing and shorting between bonding wires exiting from the inner bond pads with those bonding wires exiting from the outer bond pads when the die is attached to another substrate, such as a package substrate.
One type of packaging that is widely used in packaging a high-density die is a grid array-type package. There are many designs of grid array-type packages, for example, pin grid array packages and ball grid array packages. Generally, some packages mount the die on the surface of the package substrate, for example, a plastic ball grid array package; while, some others, mount the die in a die cavity formed in the substrate, for example, an enhanced ball grid array package.
When packaging a die, connections of the die to the conductive layers of the substrate are typically made by wire bonding the bond pad of the die to an associated bonding site, such as bond fingers or bonding rings, on the package substrate. With a die having an in-line arrangement of bond pads, there is usually a low risk of short circuits due to the bonding wires contacting each other as the bond pads are horizontally separated by the spacing between the bond pads and there is no crossing over of bonding wires from inner bond pads.
With a die having a staggered arrangement of bond pads, wire contact between bonding wires from inner bond pads which cross over bonding wires from outer pads is a concern. In some packages, the height of the wire loop of the bonding wire exiting the inner bond pad can be increased over that of the height of the wire loop of the bonding wire exiting the outer bond pad to provide vertical separation. However, in some other packages, this height adjustment can be constrained to such a degree that the particular package design cannot be used in packaging the die.
If the die is packaged in a surface mount package, such as a standard ball grid array package, there is little constraint on the height of the wire loop as the package encapsulant formed over the wire bonds and die can simply be adjusted.
FIG. 4
is diagrammatic illustration of a cross-sectional view of a portion of a ball grid array package having a die with bond pads wire bonded to the package substrate. Package
400
includes a substrate
402
having a die
404
mounted on the top surface. Bond pads
406
are connected to bond fingers (not shown) formed on the surface of the substrate
402
by bonding wires
408
. The bond fingers are typically interconnected to associated vias
410
formed through the substrate
402
to provide conductive interconnection of the die
404
to the external package contacts
412
. Typically, an encapsulant
416
, e.g., a plastic cap, is molded over the die
404
and the bonding wires
408
.
As illustrated, the height of the wire loop of the bonding wire
408
is maintained within the encapsulant
416
. When assembling a die having staggered bond pads, the wire loop heights may need to be adjusted to prevent the bonding wires from contacting each other. Encapsulation of the bonding wires can be maintained by adjusting the height of the encapsulant
416
.
Unfortunately, while this package presents little constraints on loop heights of the bonding wires, it has limited heat dissipation capability. Thus, for dice requiring higher heat dissipation or other package properties, especially high-density dice that utilize staggered bond pads, other package structures have been developed. Many of these designs mount the die within a cavity in the substrate so that the die is thermally connected to a heat dissipating layer of the substrate. The package may then be mounted on another substrate, such as a printed circuit board, so that the heat dissipating layer is facing out.
FIG. 5
is a diagrammatic illustration of a cross-sectional view of a portion of a single-tier thermally enhanced ball grid array-type package having a die mounted in a die cavity formed in the package substrate. Package
500
includes a substrate
502
having a die
504
located in
Berry Renee′ R
Beyer Weaver & Thomas LLP
National Semiconductor Corporation
Nelms David
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