Radiant energy – Photocells; circuits and apparatus – Housings
Reexamination Certificate
2001-06-28
2004-05-11
Luu, Thanh (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Housings
C250S208100, C174S050510, C257S666000, C257S684000
Reexamination Certificate
active
06734419
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to method for forming an image sensor assembly.
BACKGROUND OF THE INVENTION
Methods for forming image sensors and assemblies are well known to those of skill in the art. Prior art image sensors typically included an active area, which was 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.
In the prior art, an image sensor assembly was formed by mounting the image sensor 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. However, ceramic is relatively expensive compared to other packaging materials and, in the current market, it is critical to form the image sensor assembly at minimal cost.
In addition to using relatively expensive ceramics, the prior art ceramic image sensor assemblies were also very labor intensive and expensive to produce. For instance, after the prior-art ceramic image sensor assembly was constructed, the lens assembly was placed over the image sensor assembly. 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 rough adjustment was very labor intensive. Further, a large tolerance was associated with this very rough adjustment.
In addition, mounting the housing at the printed circuit board level, as was done in the prior art, was itself 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, mounting the housing at the printed circuit board level made it mandatory to make repairs, or to replace, the image sensor in a controlled environment such as a clean room, otherwise there was a risk of damaging or destroying the image sensor. Thus, using the prior art method of mounting the housing at the printed circuit board level often meant transporting the entire motherboard into the clean room.
To overcome the problems with prior art ceramic image sensor assemblies discussed above, image sensor packages have recently been introduced that include a molding with an interior locking feature and an exterior locking feature. One example of a prior art molded image sensor assembly is set forth in the commonly assigned U.S. patent application Ser. No. 09/457,505 entitled “MOLDED IMAGE SENSOR PACKAGE”, listing Steven Webster as inventor, filed on Dec. 8, 1999, hereinafter referred to as the Webster reference, which is incorporated herein for all purposes, and in its entirety, by reference.
The interior locking feature and the exterior locking feature of prior art molded image sensor assemblies allowed the package to be made of a molding, typically plastic, that was a low cost part. The Webster image sensor package further included a window having an interior surface and an exterior surface. The exterior locking feature of the molding contacted a periphery of the exterior surface of the window and the interior locking feature of the molding -contacted a periphery of the interior surface of the window. In this manner, the window was supported by the molding both top and bottom. In addition, the distance which moisture had to travel along the interface between the molding and window to reach the image sensor was maximized, thus essentially eliminating moisture ingress into the image sensor package.
As a result, the prior art molded image sensor assemblies, such as the Webster image sensor package, did not suffer from the high costs associated with ceramic assemblies nor were they labor intensive or require large tolerances. In addition, the prior art molded image sensor assemblies, such as the Webster image sensor package, did not involve mounting the housing at the printed circuit board level. Consequently, these prior art molded image sensor assemblies were a marked improvement over the prior art ceramic image sensor assemblies.
While prior art molded image sensor assemblies represented a significant improvement over the ceramic prior art assemblies, the prior art molded image sensor assemblies were typically relatively large. This was because, in prior art molded image sensor assemblies, the image sensor chip was typically electrically connected to the motherboard using a support substrate and bond wires connecting bond pads on the image sensor chip to bonding locations on the substrate. The substrate was then, in turn, electrically connected to the motherboard. Consequently, extra structure, i.e., an extra substrate, and bond wires, both of which added significantly to the cost and the size of prior art molded image sensor assemblies, were required. In addition, the bond wires themselves were susceptible to breaking and the image sensor assembly therefore suffered from decreased reliability.
As the electronics industry has moved to smaller and lighter weight electronic devices, it has become increasingly important that the size of the image sensor assembly used within these electronic devices be minimized. However, as discussed above, the prior art molded image sensor assemblies used bond wire connections, which were inherently bulky and expensive. As a result, the prior art molded image sensor assemblies were relatively large and expensive to produce.
In the prior art it was well known that, theoretically, a more ideal method of connecting an image sensor assembly to a motherboard would be to connect the image sensor chip to a lead frame or a Land Grid Array (LGA) directly in a flip-chip configuration. Then the lead frame and sensor could be packaged in an assembly and electrically connected to the motherboard. If this structure were possible, then the extra substrate and bond wires of the prior art molded image sensor assemblies could be eliminated while, at the same time, the image sensor assembly cost, image sensor assembly reliability and image sensor assembly size could be improved.
FIG. 1
shows a top plan view of a lead frame
10
including: frame
11
; internal connection leads
12
; and external connection leads
13
. While the flip-chip structure discussed above sounded advantageous in theory, in practice, it was found that connecting an image sensor die to internal connection leads
12
of lead frame
10
in a flip-chip configuration was prohibitively difficult, and often impossible. This was because internal connection leads
12
,
Glenn Thomas P.
Hollaway Roy Dale
Webster Steven
Amkor Technology Inc.
Gunnison McKay & Hodgson, L.L.P.
Luu Thanh
McKay Philip J.
Yam Stephen
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