Bumped integrated circuits for optical applications

Details Bumped integrated circuits for optical applications Bumped integrated circuits for optical applications

2002-05-21

2004-03-16

Cuneo, Kamand (Department: 2827)

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

Housing or package

Insulating material

C257S749000, C257S432000

Reexamination Certificate

active

06707148

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to integrated circuits, and more specifically to integrated circuits for optically related applications.
BACKGROUND OF THE INVENTION
Integrated circuits can be used in optically related applications such as sensor and optoelectronic signal transmission applications. Such integrated circuits contain devices for sensing and detecting light. As in most integrated circuit applications, the integrated circuit chips are packaged in a protective casing that allows the chip to be connected with an electrical system. For exanple, chips are commonly packaged in casings that have conductive leads that connect the chips to external systems such as printed circuit boards. With optical applications however, the packaging needs to allow light to reach the light sensing and/or detecting devices on an integrated circuit chip. One technique for allowing light to reach a chip is to mount the chip within a cavity of a package and then enclose the chip within the cavity with a plate of glass or clear plastic. This type of packaging is shown in
FIGS. 1 and 2
.
FIG. 1
is a top plan view an optical device package
100
as is currently known, which includes a case
102
having a cavity and a transparent plate
104
.
FIG. 2
is a side-plan cross-sectional view of optical device package
100
of
FIG. 1
along line
2
—
2
. An integrated circuit chip
106
is mounted inside the cavity
108
of case
102
and is electrically connected to case
102
through interconnecting wires
110
. Transparent plate
104
allows light to enter package
100
and reach the optical devices formed on the surface of chip
106
. Electrical vias embedded within case
102
connect interconnecting wires
110
to electrical contacts on the external surfaces of case
102
so that contact with an external system can be made. An example of package
100
of
FIGS. 1 and 2
is a ceramic cavity package where case
102
is made of a ceramic material. Unfortunately, packages resembling package
100
have certain drawbacks. First of all, the transparent plate and case are expensive, especially when the case is formed of ceramic. Secondly, it is also expensive to implement the specialized manufacturing processes related to placing the transparent plate onto the case. Finally, this packaging configuration usually is relatively large in size and therefore is less amenable for use in small-scale applications.
A second technique for packaging optical integrated circuit chips is to encase the chips in typical packaging form factors using clear molding material. Such typical form factors include QFP, TSSOP, DIP, etc. In many of these packaging form factors, the chip is wire bonded to the contact leads. Unfortunately, clear molding material has a higher coefficient of thermal expansion (CTE) than that of typical opaque molding material. Therefore, during heating and cooling processes, the large CTE causes the clear molding material to tear apart the connections made between the interconnecting wires and the bond pads on the chip or the contact leads. This leads to defective optical components that cannot be utilized.
In view of the foregoing, a technique for packaging optical integrated circuits within a structurally sound, cost-effective package having a small form factor would be desirable.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to an optical integrated circuit application where the integrated circuit is packaged in a clear molding material and is attached to a printed circuit board having an aperture. The integrated circuit senses and/or emits light through the clear molding material and the aperture in the printed circuit board. The present invention can be utilized in various electronic and optical applications that include optical sensor, optical signal transmission, and digital camera applications.
As an apparatus, the present invention includes at least a packaged integrated circuit and an electrical substrate. The packaged integrated circuit includes an integrated circuit having a set of light emitting or sensing devices and a plurality of bond pads formed thereupon, a conductive bump formed on each of the respective bond pads, and a clear molding material that encapsulates the integrated circuit and a portion of each conductive bump. Light can pass through the clear molding material and reach the set of light emitting or sensing devices. The electrical substrate has a plurality of electrical contact points and an aperture wherein the packaged integrated circuit is positioned on the electrical substrate wherein the aperture is located above the set of light emitting or sensing devices. In another embodiment of the invention, the integrated circuit contains more than one set of light emitting or sensing devices and the electrical substrate has a corresponding aperture for each set of devices.


REFERENCES:
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patent: 6034429 (2000-03-01), Glenn et al.
patent: 6163866 (2000-12-01), Ansari
patent: 6191359 (2001-02-01), Sengupta et al.
patent: 6204556 (2001-03-01), Hakamata
patent: 6396116 (2002-05-01), Kelly et al.
patent: 6441481 (2002-08-01), Karpman
patent: 6489675 (2002-12-01), Greber et al.

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