Method of Mounting Filters on Image Sensors

The invention relates generally to the field of image sensors, and more specifically, the invention relates to mounting filters to image sensors.

There are numerous prior art references that detail methods for the mounting of various semiconductor components in a desirable manner. The prior art references typically detail methods and apparatus that employ epoxy type resins. Other prior art devices employ spherical beads as spacers. However, a problem exists in having the devices and methods providing a means to accurately space parts of these semiconductors to a high degree of accuracy. The prior art methods results in inefficient procedures that require too much time and expensive equipment. These references have not provided techniques that resolve the economic and manufacturing problems that are associated with the mounting of filters used with image sensors that require high tolerance spacing.

The present invention solves the above related problems, and others, in the prior art by creating a sandwich with a linear image sensor and a color filter that have spacing between them controlled to a very high tolerance by controlling the diameter of glass beads within the mixture applied between the sensor and the filter. The mixture provides a simple, quick and economical spacing device that can be cured in very short time periods by employing an ultraviolet sensitive epoxy and requires few tools and little time.

The method and apparatus for mounting the filter upon the sensor, comprises:

a) providing upon select predetermined areas of a sensor a mixture of an ultraviolet curable resin and glass beads, the glass beads having an essentially uniform diameter, and future providing a light filter upon the sensor and the mixture such that the filter remains at a fixed height above the sensor, the fixed height being determined by the essentially uniform diameters of the glass beads;

b) providing an ultraviolet light; and

c) curing the mixture between the sensor and the filter with the ultra violet light.

These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.

The present invention provides a method and apparatus that can accurately space filters used with image sensors:

that requires less time;

spaces filters accurately; and

requires few tools to implement.

FIG. 1a is an illustration of the mixing of the glass beads and resin;

FIG. 1b is an illustration of the method used to pick up the glass bead mixture;

FIG. 2a illustrates the placing of a mixture of glass beads and epoxy on an image sensor;

FIG. 2b illustrates the placing of a filter on the image sensor such that the spacing is controlled by the size of the beads; and

FIG. 3 shows the final image sensor device sandwich after curing;

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.

It has been discovered that highly accurate spacing in the mounting of color filters used in image sensors can be achieved in a timely and economical manner. The present invention describes a method of mounting dichroic filters on linear sensors, and the apparatus required to accomplish this method.

Referring to FIG. 1 in conjunction with FIG. 2, the mixture of glass beads 15 and UV resin 13 is mixed in dish 17. The mixture, generally referred to as 10, is then used to form a spacing material between a sensor and a color filter that requires a specific gap in relation to the sensor. Then by contacting the UV resin 13 adhesive with a plurality of glass beads 15 to form a mixture 10 that will allow the UV resin 13 adhesive to encapsulate the beads 15 but without allowing the beads 15 to flow freely within the mixture 10, it has been found that the spacing between the sensor and the filter can be accurately controlled.

Referring to FIGS. 2a and 2b the method envisioned by the present invention comprises the steps of providing an adhesive on the end of a pin vise 12 as shown in FIG. 1, which is an illustration of the preferred method used to pick up a glass bead 15, and bringing the pin vise 12 into contact with the mixture 10 to pick up the glass beads 15 that are covered in the UV resin 13 to form a viscous mixture 10. The beads 15 are brought into contact, along with the mixture 10, with selected regions 22, 23, of an image sensor 20. The image sensor 20 as illustrated by the preferred embodiment is a linear sensor. By placing the mixture 10 of glass beads 15 and UV curable resin 13 on the appropriate select regions 22, 23 of image sensor 25, the sensing elements 26 on sensor 25 will have consistent focal distances in relation to the color filter elements 28 of filter 27. The filter 27 used within the preferred embodiment is a dichroic filter which requires a fixed spacing distance in relation to the linear sensor 25. This spacing requires a high degree of tolerance. The sandwich 30 is then formed by placing the filter 27 upon sensor 25 aligning the filter 27 in accordance with alignment marks 32, 33. It should be understood to those skilled in the art that the selected region 22, 23 upon which mixture 10 is placed will not cover either the alignment marks 32, 33 or the sensing elements 26 of sensor 25.

By employing mixture 10 having glass beads 15 with identical diameters, it is envisioned that automated processes can be developed to complete the assembly of the image sensor with its corresponding color filter. Automating the mounting process is desirable because of the volume that can be produced by automation.

In either automated or more of a manual process, the final step is to cure the adhesive resin. An ultraviolet light source 40 is then used to cure the adhesive 13 within mixture 10 as placed in select region 22, 23. This will hold the filter 27 in placed of the silicon sensor 25. The height of the dichroic filter 27 above the silicon sensor 25 is determined by the diameter of beads 15 within mixture 10. The diameter of glass beads 15 can be one of several sizes, either 12 microns, 25 microns etc., depending on the focal length of the dichroic filter 27 used in conjunction with sensor 25. A typical UV curable resin 13 would be epoxy silicon acrylic.

The present invention envisions mixing an ultraviolet (UV) curable resin with glass beads. Norland 83H ultraviolet curable epoxy is the preferred resin envisioned by the inventor. This epoxy is preferred because its only partially UV curable. This allows a non-ultraviolet resin to be employed with the UV resin. A main reason for applying both UV and non-UV resins together is due to the yellowing characteristics of the UV type resins, the photosensitive areas are then covered with a non-UV resin. The UV resin is essentially used to provide spacing with the glass beads and for quick set up time. Norland 81H is also a desirable epoxy, however, it is completely UV curable and therefore does not bond as well with a non-UV resin. A non-UV resin that is preferred is the Dow Corning 93-500. It is also envisioned that spacers other than glass beads are usable, and that these are believed to be obvious variations of the preferred embodiment. Latex beads would be an alternative, especially if using a completely UV curable resin such as the Norland 81H . Cut silicon, or cut glass would also be usable alternatives but are less desirable than spherical elements such as beads.

The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.

Parts List:

10 mixture

12 pin vise

13 adhesive

15 glass beads

17 dish

22 selected region

23 selected region

25 image sensor

26 image sensing elements

27 filter

28 filter slits

30 sensor sandwich

32 alignment mark

33 alignment mark