Bond wire pressure sensor die package

Details Bond wire pressure sensor die package Bond wire pressure sensor die package

2001-01-03

2002-08-27

Clark, Sheila V. (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Encapsulated

C237S049000

Reexamination Certificate

active

06441503

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to methods for making bond wire pressure sensor die packages.
BACKGROUND OF THE INVENTION
FIG. 1A
illustrates a pressure sensor die
10
suitable for use with the present invention. In one embodiment, pressure sensor die
10
is a piezoresistive pressure sensor. Piezoresistive pressure sensors are discussed, and one method for making piezoresistive pressure sensors is disclosed, in U.S. Pat. No. 5,719,069, entitled “ONE-CHIP INTEGRATED SENSOR PROCESS”, issued Feb. 17, 1998 to Sparks, which is incorporated, in its entirety, by reference herein. Another type of pressure sensor is disclosed in U.S. Pat. No. 3,748,571, entitled “PRESSURE SENSITIVE TRANSDUCERS EMPLOYING CAPACITIVE AND RESISTIVE VARIATIONS”, issued Jul. 24, 1973 to Kurtz, which is also incorporated, in its entirety, by reference herein.
Pressure sensors and pressure sensor die assemblies are well known to those of skill in the art and come in a large variety of sizes and configurations. Consequently, while one embodiment of a pressure sensor die
10
is discussed below, it will be recognized by those of skill in the art that numerous other types of pressure sensors will work equally well with the present invention.
Referring back to
FIG. 1A
, pressure sensor die
10
includes a pressure sensitive micro-machine element
54
which is a pressure sensing membrane composed of a portion of the epitaxial silicon layer
16
. Pressure sensor die
10
also includes a plurality of piezoresistors
14
formed in epitaxial silicon layer
16
. Piezoresistors
14
serve as sensing elements for micro-machine element
54
.
Pressure sensor die
10
is formed by bonding a substrate
18
to a glass or silicon wafer
20
. Substrate
18
includes a cavity
22
such that when substrate
18
is bonded to wafer
20
, wafer
20
seals cavity
22
. Cavity
22
is positioned directly below micro-machine element
54
. In one embodiment, wafer
20
hermetically seals cavity
22
so that pressure sensor die
10
is an absolute pressure sensor.
FIG. 1B
shows another embodiment of a pressure sensor die
10
B, which includes a die hole
60
through wafer
20
to vent cavity
22
making pressure sensor die
10
B a differential pressure sensor. As discussed in more detail below, the method and structure of the present invention works equally well with both absolute pressure sensors, such as pressure sensor die
10
, and differential pressure sensors, such as pressure sensor die
10
B.
Pressure sensor die
10
or
10
B is typically used to monitor the pressure of an external fluid, i.e., a gas or liquid, by placing first or outer surface
56
of pressure sensor die
10
or pressure sensor die
10
B, including micro-machine element
54
, in contact with the external fluid. During normal operation of pressure sensor die
10
or
10
B, micro-machine element
54
flexes in response to pressure on first or outer surface
56
. This flex is sensed by piezoresistors
14
and processed to determine the pressure exerted on first or outer surface
56
by the external fluid, i.e., the pressure of the liquid or gas.
The structure and operation of pressure sensors, such as pressure sensor die
10
and pressure sensor die
10
B, is well known to those of skill in the art. Consequently, a more detailed discussion of the structure and operation of pressure sensor die
10
and pressure sensor die
10
B is omitted here to avoid detracting from the present invention. However, it is worth noting here that, as discussed above, in order for pressure sensor die
10
or pressure sensor die
10
B to function, first or outer surface
56
, including micro-machine element
54
must be flexibly coupled to the surrounding environment and cannot be shielded from that environment by interposing layers of packaging material such as plastics or epoxies.
FIG. 1C
is an enlarged cross-sectional view of a pressure sensor sub-assembly
100
including a pressure sensor die
110
mounted on a substrate
102
in die attach region
131
. Like pressure sensor die
10
of
FIG. 1A
, pressure sensor die
110
(
FIG. 1C
) includes a pressure sensitive micro-machine element
154
composed of a portion of the epitaxial silicon layer
116
. Like pressure sensor die
10
discussed above, pressure sensor die
110
is formed by bonding a substrate
118
to a glass or silicon wafer
120
. Substrate
118
includes a cavity
122
such that when substrate
118
is bonded to wafer
120
, wafer
120
seals cavity
122
. Cavity
122
is positioned directly below micro-machine element
154
.
Pressure sensor die
110
is attached to a first surface
111
(a die attach surface) of substrate
102
in die attach region
131
using any one of several well-known adhesives
104
. Substrate
102
is typically a printed circuit board (PCB). In one embodiment, electrically conductive contacts or pads
106
on first or outer surface
130
of pressure sensor die
110
are connected with electrically conductive bond wires
103
to electrically conductive traces
112
and/or electrically conductive regions (not shown) formed on first surface
111
of substrate
102
. Electrically conductive vias
114
are formed through substrate
102
, from traces
112
and/or regions on first surface
111
to a second surface (the mounting surface)
140
of substrate
102
which is opposite first surface
111
. Electrically conductive traces
113
formed on second surface
140
of substrate
102
extend to electrically conductive contact or pads
115
formed on second surface
140
of substrate
102
. Electrically conductive contacts
115
are used to connect substrate
102
and pressure sensor die
110
to a larger system, such as a mother board (not shown), using well known methods such as solder balls, pins, leadless carrier chip (LCC) contacts or other surface mounts.
SUMMARY OF THE INVENTION
In accordance with the present invention, a plurality of pressure sensor die packages are fabricated simultaneously, in an array, to minimize the cost associated with each individual pressure sensor die package.
In one embodiment of the invention, a plurality of pressure sensor dice are attached to an array of pressure sensor die sites located on a substrate. The pressure sensor dice are then electrically connected to the pressure sensor die sites using, in one embodiment, standard wire bond techniques.
The resulting array of pressure sensor die sub-assemblies is then molded, in one embodiment of the invention, using a mold tool that closes on three sides of the substrate so that a cavity is formed that is open on the fourth side. To this end, a first portion of the molding tool has a plurality of insert pins that close on the outer surface of each pressure sensor die.
As a result, using the method of the invention, a portion of the outer surface of the micro-machine element of each pressure sensor die is left exposed at the bottom of a cavity in the molding encapsulant. After molding, the exposed outer surface of the micro-machine element is covered with a pressure coupling gel that is applied in the shallow cavity. The coupling gel protects micro-machine elements from the environment, yet is compressible and is capable of coupling pressure from the external environment to the micro-machine elements.
The resulting array of packaged pressure sensor dice are then sigulated using well known sawing or laser techniques or by snapping a specially formed snap array.
In another embodiment of the invention, a hole is formed in the array substrate and the pressure sensor substrate to accommodate a differential pressure sensor die.
In another embodiment of the invention, a custom substrate is formed with a plurality of holes formed, one each, at pressure sensor die mounting sites. A plurality of pressure sensor dice are then attached to pressure sensor die mounting sites located on the substrate. The pressure sensor dice are then electrically connected to the pressure sensor sites using, in this embodim

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