Reduced thickness packaged electronic device

Details Reduced thickness packaged electronic device Reduced thickness packaged electronic device

2001-07-26

2003-07-01

Thomas, Tom (Department: 2811)

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

Housing or package

With window means

C257S780000, C257S787000, C257S239000, C257S432000, C257S434000, C257S690000, C257S784000, C257S737000, C257S738000

Reexamination Certificate

active

06586824

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to packaged electronic components. More particularly, the resent invention relates to packaged electronic components with reduced thickness.
BACKGROUND OF THE INVENTION
Virtually every business in the world has become dependent, directly or indirectly, on electronic components such as integrated circuits. In addition, electronic components have permeated our personal lives through their use in systems that control or contribute to almost every aspect of our day from coffee making to network computing. This application of electronic components to what were once seemingly unrelated fields has created a huge demand for these components in increasingly diverse industries and locations. Consequently, there has been a corresponding increase in demand for better methods and structures to package electronic components and for smaller packaged electronic components. This demand has made electronic component packaging one of the most critical and competitive markets in the electronics industry.
To stay competitive, those of skill in the art of electronic component packaging are constantly seeking better ways to provide protection of the extremely fragile electronic components from environmental elements and contamination while, at the same time, providing a solution that does not significantly increase the size or the cost of the finished, packaged electronic component.
FIG. 1
is an enlarged cross-sectional view of an exemplary prior art packaged electronic component
10
. As shown in
FIG. 1
, a first surface
32
of an electronic component such as an integrated circuit (IC) chip
30
was typically mounted to a first surface
18
of prior art substrate
13
by a layer of adhesive
31
so that IC
15
chip
30
was positioned above prior art substrate
13
. IC chip
30
was typically mounted to prior art substrate
13
in a location central to metallizations
22
. Also shown are bonding pads
38
that were located on a second surface
36
of IC chip
30
. Bonding pads
38
were typically electrically connected to corresponding contacts
23
by bond wires
40
, made of gold or aluminum for example, using conventional wire bonding techniques. Contacts
23
were connected to metallizations
22
. Electrically conductive vias
14
electrically coupled metallizations
22
on first surface
18
of prior art substrate
13
to metallizations
26
on second surface
20
of prior art substrate
13
.
Also shown in
FIG. 1
, is layer of encapsulant
42
that was applied over the entire assembly. In particular, layer of encapsulant
42
covered IC chip
30
including bonding pads
38
, bond wires
40
, contacts
23
, metallizations
22
and the remaining exposed first surface
18
of prior art substrate
13
.
As also shown in
FIG. 1
, interconnection balls
28
, typically eutectic solder balls, were attached to contacts
27
using conventional techniques. Contacts
27
were, in turn coupled to metallizations
26
on second surface
20
of prior art substrate
13
. Interconnection balls
28
were often arranged in an array thus forming a ball grid array.
As can be seen in
FIG. 1
, the resulting prior art packed electronic device
10
had a thickness
60
extending from top surface
48
of encapsulant
42
to bottom surface
39
of prior art substrate
13
. In prior art packaged electronic devices, such as prior art packaged electronic device
10
, the value for thickness
60
was relatively large and typically on the order of 1.1 to 2.0 millimeters. This was highly disadvantageous because the relatively large thickness
60
meant larger and thicker systems. In a market that increasingly stresses small size and portability, this situation was far from ideal.
One major reason that prior art packaged electronic device
10
had a relatively large thickness
60
was the additional thickness
70
that prior art substrate
13
added to prior art packaged electronic device
10
. Prior art substrate
13
was necessary to allow electrical connections to be made between IC chip
30
and off chip locations by way of contacts
23
, metallizations
22
, electrically conductive vias
14
, metallizations
26
, and contacts
27
, as discussed above. Thickness
70
was added to prior art packaged electronic device
10
because, in the prior art, IC chip
30
was mounted on top of prior art substrate
13
, to first surface
18
of prior art substrate
13
. Consequently both the thickness of IC chip
30
and the thickness
70
of prior art substrate contributed to the thickness
60
prior art packaged electronic device
10
. This added thickness was considered a necessary evil in the prior art because it was thought that the IC chip
30
needed to be mounted on top of prior art substrate
13
to provide a strong and stable structure during die electrical connection and to stabilize IC chip
30
within the structure of prior art packaged electronic device
10
.
In addition to being relatively thick and cumbersome, prior art packages, such as that shown in
FIG. 1
, were particularly ill suited for newer electronic devices such as image sensor die and other optical devices, which not only require small size, i.e., minimal thickness, but also require mounting of optical elements such as glass plates or lenses. Image sensors and assemblies are well known to those of skill in the art. Image sensors typically include an active area, which is responsive to electromagnetic radiation.
In prior art image sensor assemblies, an image sensor was located within a housing that supported a window. Radiation passed through the window and struck the active area of the image sensor, which responded to the radiation. For the image sensor to function properly, the image sensor had to be positionally aligned with the window to within tight tolerances.
Since prior art packages, such as shown in
FIG. 1
, were not well suited to packaging image sensor dice, in the prior art, an image sensor assembly was formed by mounting the image sensor directly to a printed circuit motherboard. After the image sensor was mounted, a housing was mounted around the image sensor and to the printed circuit motherboard. This housing provided a seal around the image sensor, while at the same time, supported a window above the image sensor.
Beaman et al., U.S. Pat. No. 5,821,532, hereinafter Beaman, which is herein incorporated by reference in its entirety, is one example of a prior art image sensor assembly. Beaman sets forth a printed circuit board that included a pair of apertures used as alignment features for mounting the image sensor and for mounting the optics that included the window. More particularly, the pair of apertures were used as the mounting reference for the image sensor and then were used as the mounting reference for the optics.
As discussed in Beaman, prior art image sensor assemblies used a housing to support the window and to hermetically seal the image sensor (see housing
24
and window
25
of Beaman
FIG. 4
for example). This housing was typically formed of ceramic that advantageously had excellent resistance to moisture transmission to protect the image sensor from the ambient environment.
In addition, ceramic housings provided the strength and stability thought necessary in the prior art. However, ceramic is relatively expensive and heavy compared to other packaging materials and, in the current market, it is critical to form the image sensor assembly at minimal cost. In addition, and perhaps even more disadvantageous, was the fact that prior art image sensor assemblies were very large and bulky and further added to the thickness and overall size of subsystems employing these prior art image sensor assemblies.
In addition, mounting the housing at the printed circuit board level, as was done in the prior art, was inherently labor intensive and made repair or replacement of the image sensor difficult. In particular, removal of the housing exposed the image sensor to the ambient environment. Since the image sensor was sensitive to dust, as well as other environmental factor

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