Low cost CCD packaging

Details Low cost CCD packaging Low cost CCD packaging

1999-10-14

2001-07-31

Potter, Roy (Department: 2822)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

C438S066000, C438S116000

Reexamination Certificate

active

06268231

ABSTRACT:

FIELD OF INVENTION
The invention relates generally to the field of electronic packaging, and more particularly, to packaging specific to charge coupled devices.
BACKGROUND OF THE INVENTION
Currently, most charge coupled devices (CCD) sensors are packaged in multilayer high temperature cofired ceramic dual-in-line packages. Multilayer ceramic packages have traditionally been used for the packaging of power devices or UV erasable memories. With the advent of Camcorders, and fax machines, the multilayer ceramic dual-in-line package has been extended to the packaging of low end charge coupled devices. The multilayer ceramic structure has many advantages when packaging CCDs. Multilayer ceramic dual-in-line (DIP) packages have the following desirable properties: 1) low moisture permeability; 2) high dimensional stability; 3) a temperature coefficient of expansion closely matching silicon; 4) good thermal conductivity; 5) infrastructure is in place for high volume manufacturing; and 6) testability;
The major disadvantages of the ceramic dual-in-line package is the cost, and to a lesser extent, the obsolescence issues surrounding the integrated circuit packaging industry moves away from dual-in-line package and toward surface mount technology.
Another key disadvantage concerns the alignment of the CCD to the imaging and viewfinder optics; as one finds in digital cameras. The alignment of the CCD to the lens system requires that the CCD be precisely positioned to the optical axis, and the focal plane of the lens. Unfortunately, the positional variability associated with the location of the dual-in-line package pins is so large that it is impractical to use these pins as mechanical reference to the CCD device. Consequently, other reference datums must be created. The dual-in-line package pins then become an additional mechanical constraint on the mechanical design. The pins while compliant are sufficiently rigid to require that additional compliance be added to the mechanical design of the system. Flexible circuits are often used to overcome the mechanical constraints imposed by the dual-in-line package pins. Typically, the flexible circuit is connected directly to the dual-in-line package. In other cases, the dual-in-line package is mounted to a circuit board, and the circuit board is then connected to the system electronics with a flexible interconnect.
Still another disadvantage of the dual-in-line package is the inability to automate the assembly of the CCD device into the product level assembly. The temperature sensitivity of the charge coupled device means that standard automated electronic assembly techniques; such as, solder reflow ovens, or wave-soldering can not be used when assembling the dual-in-line package to the system electronics. Often, a hand-soldering operation is required to interconnect the dual-in-line package to the system electronics. Elimination of the need to hand solder these connections increases the quality of the entire system.
As can be seen from the foregoing description, there remains a need within the art for a CCD packaging that can cure the previously discussed problems within the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a packaging structure for an image sensor is provided for comprising a flexible circuit board having a substrate with a plurality of conductors formed, thereon; a base structure fixedly attached to a first side of the flexible circuit board; a ring frame molded to having a cavity formed within the ring frame to house the image sensor, the ring frame being fixedly attached to a second side of the flexible circuit board such that electrical connectors on the image sensor can be juxtapositioned to make electrical contact with the electrical conductors on the flexible circuit board by placing the image sensor within the cavity in a predetermined position; and a cover glass fixedly attached to the ring frame.
The present invention addresses the packaging cost issue and offers the potential for a lower cost, automated assembly process. It is extendible not only to CCD devices, but would be useful in other opto-electronic applications. A moldable plastic material with low moisture permeability, and high dimensional stability; such as, a liquid crystal polymer, could be used to achieve performance similar to ceramic but at lower cost. While relatively high cost plastic materials may be used, the overall cost is expected to be substantially lower than a corresponding ceramic package. An interconnect circuit pattern could then be formed on the plastic using one of a variety of plating options known in the circuit board, and in the molded interconnect industry.
The present invention is employs a flexible circuit into the package. These conductors would likely consist of standard conductor materials well known in the circuit board industry; e.g., copper with selective nickel and gold plating. A non reflective substrate surface would be preferred. The CCD sensor would be mounted to this plastic substrate and connected to the conductive pattern using standard wire bonding processes.
In order to support a transparent cover glass which protects the CCD sensor, a supporting ring frame would be molded into the plastic. This support ring would surround the CCD sensor, and provide a means of supporting the cover glass. The plastic substrate would then be interconnected to the external world via the integral flexible circuit. Standard zero insertion flexible circuit connectors would be the preferred method of connecting the flexible circuit to the system electronics. The use of anisotropic adhesives or traditional butt joint soldering techniques might also be used depending upon the application.
The above and other objects of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.
ADVANTAGEOUS EFFECT OF THE INVENTION
The present invention has the following advantages: it eliminates the need for sockets used in mounting CCDs and image sensors in general; potentially lower manufacturing costs; ease of assembly because alignment to the optical system is simpler by usage of a flexible circuit board; the combination of flexible circuit board with a socketless mounting creates a mounting package that is smaller in size and more versatile in assembly; and it allows for a sub-assembly that can house additional components closer to the image sensing device resulting in higher frequency operation.


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