Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
1999-12-08
2002-09-24
Dinkins, Anthony (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C257S680000, C257S730000
Reexamination Certificate
active
06455774
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to an image sensor package.
BACKGROUND OF THE INVENTION
Image sensors and assemblies are well known to those of skill in the art. In these assemblies, an image sensor was located within a housing which supported a window. Radiation passed through the window and struck 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 positional tolerances.
Beaman et al., U.S. Pat. No. 5,821,532, hereinafter Beaman, which is herein incorporated by reference in its entirety, sets forth a printed circuit board which included a pair of apertures used as alignment features for mounting the image sensor and for mounting the optics which 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.
Formation of the assembly using the pair of apertures in the substrate as the alignment features resulted in at least three tolerance accumulations. First, a certain tolerance was associated with the formation, or patterning, of the metallic traces on the printed circuit board (see reference pads
14
and substrate
10
of Beaman FIG.
1
). Second, a certain tolerance was associated with the placement of the image sensor on the substrate (see images sensor
32
and substrate
10
of Beaman FIG.
3
). Third, a certain tolerance was associated the placement of the optics on the substrate (see Beaman FIG.
4
).
After the image sensor assembly was constructed, the lens assembly was placed over the image sensor assembly. The lens assembly was used to focus light on the image sensor. Typically, the lens assembly was attached directly to the substrate after the image sensor assembly was attached to the substrate. After attachment, the lens assembly was adjusted, for example with adjustment screws, to move the lens assembly until the proper focus was attained. This very rough adjustment was labor intensive. Further, a large tolerance was associated with this very rough adjustment.
Disadvantageously, the image sensor assembly had to accommodate the tolerances discussed above. However, as the art moves to smaller, lighter and less expensive devices, the acceptable tolerances for image sensor assemblies diminishes.
In conventional image sensor assemblies, a housing was used 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 which advantageously had excellent resistance to moisture transmission to protect the image sensor from the ambient environment. Further, the ceramic housing was formed with a shelf which held the window and facilitated proper height positioning of the window (see shelf
29
and window
25
of Beaman
FIG. 4
for example). However, ceramic is relatively expensive compared to other conventional packaging materials and it is important to form the image sensor assembly at a low cost.
In addition, mounting this housing at the printed circuit board level 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 factors, it was important to make repairs or replacement of the image sensor in a controlled environment such as a clean room. Otherwise, there was a risk of damaging or destroying the image sensor. Since neither of these alternatives are desirable and both are expensive, the art needs an image sensor assembly which is simple to manufacture and service so that costs associated with the image sensor assembly are minimized.
SUMMARY OF THE INVENTION
In accordance with the present invention, a plurality of image sensor packages are fabricated simultaneously to minimize the cost associated with each individual image sensor package. To fabricate the image sensor packages, a plurality of windows are placed in a mold. Molding compound is transferred to the mold to form a plurality of moldings, each of the moldings enclosing a corresponding window. The moldings are integrally connected together by bridge sections. After molding the windows in the molding compound, a molded window array, which includes the windows molded in corresponding moldings, is removed from the mold.
A substrate includes a plurality of individual substrates integrally connected together in an array format. Image sensors are attached to corresponding individual substrates. Bond pads of the image sensors are electrically connected to corresponding traces of the individual substrates.
The molded window array is aligned with the substrate such that each molding is precisely positioned with respect to the corresponding image sensor. After alignment, the molded window array is brought into abutting contact with an upper surface of the substrate such that an adhesive layer attaches the molded window array to the substrate. In one embodiment, the moldings are marked and a lower surface of the substrate is populated with interconnection balls. The substrate and attached molded window array are singulated into a plurality of individual image sensor packages.
By forming a plurality of image sensor packages simultaneously, several advantages are realized. One advantage is that it is less labor intensive to handle and process a plurality of image sensor packages simultaneously rather than to handle and process each image sensor package on an individual basis. Another advantage is that usage of materials is more efficient when a plurality of image sensor packages are fabricated simultaneously. By reducing labor and using less material, the cost associated with each image sensor package is minimized.
Of importance, the molding of the image sensor package is a low cost molded part. Advantageously, the molding is significantly less expensive than housings of the prior art which were typically ceramic. Accordingly, the image sensor package in accordance with the present invention is significantly less expensive to manufacture than image sensor assemblies of the prior art.
By forming the molding of the image sensor package as a molded part, a distance, sometimes called the Z height, between the window and the image sensor is precisely controlled to within tight tolerance.
Recall that in the prior art, the window was placed on a shelf of a housing after the housing was fabricated. Since a significant tolerance was associated with the window placement, the distance between the window and the image sensor had significant variations from assembly to assembly. However, to insure optimum operation of the image sensor, it is important that the distance between the window and the image sensor be precise. Since the tolerance in this distance is reduced in an image sensor package in accordance with the present invention, the performance of an image sensor package in accordance with the present invention is superior to that of the prior art.
In one embodiment, the molding of the image sensor package includes a plurality of alignment notches. These alignment notches are used to align a lens to the image sensor.
Use of the alignment notches facilitates alignment of the lens to the image sensor. As discussed above, the molding is precisely aligned to the image sensor. Advantageously, this allows the lens to be precisely aligned to the image sensor in a single operation by aligning the lens to the alignment notches. Accordingly, alignment of the lens to the image sensor in accordance with the present invention is relatively simple. This is in contrast to the prior art, which required a first alignment of the image sensor to the larger substrate and a second alignment of the optics to the larger substrate.
Enviro-hermetically sealing the image sensor in ac
Amkor Technology Inc.
Dinkins Anthony
Gunnison McKay & Hodgson, L.L.P.
Hodgson Serge J.
Ngo Hung V
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