Modular image sensor array

A modular image sensor array is disclosed which includes a plurality of tiles each of which has an image sensor mounted thereon. The tiles are mounted on a base plate such that the image sensors form a predetermined pattern. In order to precisely locate the tiles relative to each other and to provide for the replacement of defective tiles, the tiles are assembled in an interlocking pattern on the base plate. The top surface of the tiles is formed by ceramic plates, and electrical conductors for the image sensors are formed on one of the ceramic plates. A transparent cover is mounted over all of the image sensors in the array.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a modular image sensor array, and more 
particularly, to such an array in which a plurality of image sensors are 
assembled in a predetermined pattern on a substrate. 
2. Description of the Prior Art 
Image scanners are known for reading optical information in the form of 
text or graphics and converting the optical information into an analog 
electrical signal. The analog signal is then converted into digital 
information for image processing and image reproduction. In one 
arrangement of such a scanner, an image is projected onto a single image 
sensor by means of demagnification optics. Disadvantages of this 
arrangement are the necessity for a relatively long light path and the 
necessity for extreme accuracy in positioning the image sensor. In another 
type of scanner, as shown, for example in U.S. Pat. No. 4,775,895, an 
array of image sensors are used in order to overcome the problems 
associated with the demagnification optics in a scanner using a single 
sensor. 
U.S. Pat. No. 4,775,895, discloses a modular image sensor structure in 
which a plurality of drive modules are mounted on a substrate of ceramic 
or glass. Each of the drive modules contains a line of sensor elements. A 
disadvantage of the structure shown in the patent is that drive modules 
are spaced from each other on the substrate, and it is very difficult to 
precisely locate the drive modules relative to each other in order to form 
a desired pattern of sensor elements. A further disadvantage is that the 
glass or ceramic substrate is fragile and must be handled with care. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the problems disclosed 
in the prior art discussed above and to provide an improved modular image 
sensor array. 
In accordance with one aspect of the present invention, there is provided a 
modular image sensor array comprising: a plurality of tiles, each of the 
tiles including an image sensor on a surface thereof; and means for 
suppporting the tiles such that the image sensors form a predetermined 
pattern, each of the tiles being in abutment with an adjacent tile on the 
supporting means and each of the tiles being configured such that the 
tiles form an interlocking pattern on the supporting means. 
In one embodiment of the present invention, a modular image sensor array 
comprises a stainless steel base plate and four tiles mounted on the base 
plate. Each of the tiles supports a linear CCD image sensor. The tiles are 
generally T-shaped, and they are mounted on the base plate such that the 
image sensors form a predetermined pattern in which the image sensors 
overlap. Each of the image sensor is mounted along a central portion of 
the tile. Ceramic plates are mounted on a surface of each tile, and the 
plates are arranged on opposite sides of the image sensor. Electrical 
conductors are formed on one of the ceramic plates. An elongated 
transparent cover is mounted over the image sensors and is supported on 
the ceramic plates. 
A principal advantage of the present invention is that the image sensors in 
the array can be very accurately located relative to each other. Another 
advantage is that individual tiles can be replaced in the array without 
affecting the positions of the other tiles. A further advantage is that an 
image sensor can be fully tested after the sensor is mounted on a tile and 
before the tile is assembled in the array. Finally, the metal base plate 
provides a very flat and stable support for the image sensor array. 
Other features and advantages will become apparent upon reference to the 
following description of the preferred embodiment when read in light of 
the attached drawings.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIG. 1, there is shown a modular image sensor array 10 
which is constructed in accordance with the present invention. Array 10 
comprises four modules, or tiles, 12 which are mounted on a base plate 14. 
The number of tiles in array 10 will depend on the particular application 
and can be greater or less than four. Base plate 14 can be made from, for 
example, stainless steel. As shown in FIG. 1, tiles 12 are generally 
T-shaped, and the tiles 12 are mounted in an interlocking pattern on plate 
14. Other shapes could be used for tiles 12, for example, L-shaped or 
triangular-shaped tiles. 
The tiles 12 are located longitudinally on base plate 14 by means of 
L-shaped stops 16 and 18 disposed at opposite ends of plate 14. Each of 
the tiles 12 has an image sensor 20 mounted thereon, and the tiles are 
supported on base plate 14 such that the image sensors 20 overlap. It is 
known to overlap linear image sensors in this manner in order to insure 
that no information is lost in the area between adjacent sensors. Sensors 
20 can also be supported in an abutting arrangement for certain 
applications. Each of the image sensors 20 can be, for example, a linear 
CCD image sensor. A transparent cover 22 is mounted over the sensor 20. 
Each tile 12 includes a support 15 which is precisely machined from a plate 
of material, for example, stainless steel. One suitable machining 
technique is electrical discharge machining (EDM) which produces 
consistent results and can be used to machine a large number of tiles 
simultaneously. In one representative example, the tolerances on the 
supports 15 were held within 0.0001 inch (0.000254 cm), and the edge 
quality was acceptable for the vision system of an automated placement 
tool. 
Image sensors 20 are precisely located on the supports 15 relative to the 
support edges. The image sensors 20 are bonded to the supports 15 by, for 
example, a temperature-cured, silver-filled epoxy which can be a 84-1LMI 
epoxy, sold by Ablestik Laboratories. The silver-filled epoxy provides 
electrical conductance as well as a physical bond. 
A ceramic plate 30 is mounted on each support 15 adjacent the sensor 20. 
The plate 30 can be an alumina ceramic, obtainable from the Coors Co. Each 
plate 30 is about 0.025 inches (0.0635 cm) thick. As shown in FIG. 3, a 
dielectric layer 32 and a conductor layer 34 are screen-printed on a top 
surface of plate 30; after each layer is formed, the layer is fired. Layer 
34 is formed first on plate 30 and includes electrical conductors 33. As 
shown in FIG. 3, the electrical conductors 33 extend in a diverging 
pattern from the ends of the image sensor 20 to the edge connectors 36. 
The electrical conductors 33 in layer 34 can be made from a conductive 
paste, No. QS 170 or No. 9770, obtainable from the DuPont Co. Layer 32 is 
a dielectric layer which is formed over the layer 34 to insulate and 
protector the conductors 33 therein. A portion of layer 32 has been broken 
away in FIG. 3 in order to show the pattern of conductors 33. A dielectric 
paste, No. 5704, also obtainable from the DuPont Co., can be used for 
layer 32. 
The edge connectors 36 have a standard 0.1 inch (0.254 cm) pitch and are 
connected to the electrical conductors 33 on plate 30 prior to cementing 
the plate 30 to the support 15. The edge connectors 36 are connected to 
the electrical conductors 33 using, for example, a vapor phase solder 
reflow technique. Conventional ultrasonic wedge bonding is used for making 
the electrical bonds between wires 35 (FIG. 2) and the bond pads (not 
shown) on image sensor 20 and between wires 35 and the conductors 33. A 
silicon-doped aluminum wire having a diameter of 0.00125 inches (0.003175 
cm) is used for the wires 35. After the connections between the image 
sensor 20 and the electrical conductors 33 have been made, the sensor 20 
can be electrically tested. As noted above, there is a significant 
advantage in being able to fully test the sensor prior to assembling the 
tile 12 onto the base 14. An epoxy, for example, Ablebond epoxy 293-1, can 
be used to cement the plate 30 to support 15. Blank ceramic plates 40 are 
mounted on each support 15 opposite the plate 30. The ceramic plates 30 
and 40 provide a uniform surface for the mounting of the transparent cover 
22. 
Although tiles 12 have been described herein as having a metal support 15 
and ceramic plates 30 and 40 mounted thereon, it will be apparent to those 
skilled in the art that tile 12 could be made from a single piece of 
ceramic or other material. Further, plate 30 could be a metal plate with a 
ceramic coating, and plate 40 could be a metal plate or a metal plate 
having a ceramic coating. 
Tiles 12 are assembled onto the base plate 14 using stop 16 as a first 
reference point. The tiles 12 form an interlocking pattern, as shown in 
FIG. 1, and the overlap of the image sensors 20 is controlled by the 
position of the image sensor 20 on the tile 12 and by the outside 
dimensions of the tiles. Stop 18 serves as a second reference point for 
the tiles 12 in array 10. The tiles 12 are secured to base plate 14 by 
means of a soluble adhesive or a mechanical means (not shown). The edge 
connectors 36 are positioned away from the base plate 14 to provide easy 
access for mounting and dismounting the the array 10. As shown in FIG. 1, 
alternate tiles 12 are rotated 180.degree. in plane with respect to the 
remainder of the tiles, and as a result, the edge connectors 36 from 
adjacent tiles 12 extend from opposite sides of the array 10. 
Transparent cover 22 is mounted over the image sensors 20 to provide 
protection for the image sensors from dust and debris and to keep the 
delicate wire bonds from being damaged. Cover 22 can be made from glass, 
quartz, or other transparent material. The cover 22 is mounted on a 
supporting spacer 42. The spacer 42 is made from aluminum and has a black 
anodized surface which prevents the scattering of light and helps to 
electrically insulate the spacer 42. Spacer 42 is cemented to tiles 12 by 
a silicon resin, and the cover 22 is attached to the top of the spacer 42, 
using a u.v. curable resin. 
The present invention can be used for both monochrome and color arrays. In 
one exemplary device, the array is approximately 10 inches (25.4 cm) long 
and is used to scan a page-sized document without the use of 
demagnification optics. Array 10 can be made without exposing the image 
sensor 20 to temperatures in excess of 100.degree. C., and thus, the 
invention is particularly suitable for use in making color arrays which 
can be damaged by high process temperatures. 
The invention has been described in detail with particular reference to a 
preferred embodiment thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.