MOUNTING AND GROUNDING LENSES TO SOLID STATE IMAGE SENSOR

Cross-Reference to Related Applications

This is a continuation-in-part of commonly-owned, copending PCT Patent Application No. PCT/US92/03495, entitled ARRANGEMENT 5 FOR MOUNTING A LENS TO A SOLID STATE IMAGE SENSOR, filed on April 28, 1992 by Lynch and Gainey.

Technical Field of the Invention

The invention relates to mounting a lens in proximity to a solid state image-sensing semiconductor device (die) , or 10 integrated circuit (IC) , on a flexible substrate, such as a tape-automated bonding (TAB) tape.

Background Of The Invention

Modern charge-coupled devices and other photosensitive semiconductor devices (hereinafter "solid state image sensors") 15 are capable of providing signals representing images formed (focused) on a surface thereof. Generally, the surface of a solid state image sensor is provided with an array (for example, rows and columns) of discrete photosensitive semiconductor

elements (for example gates or junctions) , and particular array locations correspond to a particular "pixel" in the image. Modern video cameras, for example, use discrete lens systems (optics) to focus images onto such solid state image sensors. While excellent signal representations of images can be obtained with such systems, they tend to be both cumbersome and expensive. Generally, solid state image sensors used to provide image-quality resolution, pixel-based signals representing image information are referred to as "camera chips". Generally speaking, there are various techniques of packaging a semiconductor device (die) , in any case said package having leads, pins or the like exiting the package for electrically connecting the packaged die to other components, either by mounting directly to a printed circuit board or by plugging the packaged device into a socket which, in turn is mounted to a printed circuit board. These techniques generally include:

(a) plastic packaging, wherein plastic molding (moulding) compound is disposed about a semiconductor die connected to some form of lead frame;

(b) ceramic packaging, wherein a die is mounted within and connected to lead traces (fingers) formed as layers in a multilayer ceramic package;

(c) PCB substrate mounting, wherein a die is mounted to a printed circuit board (PCB) substrate; and

(d) flexible substrate packaging, wherein a die is mounted

to a flexible substrate having a conductive layer patterned to form lead traces (fingers) , which traces are supported by a plastic (for example, polyimide) layer. The die is bonded, such as with bond wires or using a tape-automated bonding (TAB) process to inner ends of the lead fingers.

In the main hereinafter, TAB bonding a die to a flexible (tape) substrate is discussed.

In tape-automated bonding (TAB) , "bumps" typically formed of gold, are located on either the die ("bumped die") or on the inner ends of the lead fingers ("bumped tape") . See, for example, U. S. Patent No. 4,842.662. Figures 5 and 6, respectively, incorporated by reference herein. In the main hereinafter, "bumped die" TAB bonding is discussed.

One attribute of a flexible substrate (e.g., tape) mounting for sericonductor dies is that the substrate is not very rigid. Such flexibility does not lend itself well to structural stability, and it is known to provide some additional structure to the substrate, once the die is mounted and connected thereto, to rigidize the substrate. This may simply include an overlying layer of "glob-top" epoxy, which also seals the die from the environment.

Disclosure Of The Invention

It is an object of the present invention to provide an improved solid state image sensor. It is a further object of the present invention to provide

an improved arrangement for mounting a lens to a solid state image sensor.

It is a further object of the present invention to provide an improved arrangement for mounting a lens to a solid state image sensor, in the environment of relatively-flexible, tape¬ like substrate mounting the solid state image sensor, especially with tape-automated bonding (TAB) techniques.

It is a further object of the present invention to provide an improved technique for mounting a lens and a semiconductor device to a flexible substrate.

It is further object to provide improved environmental characteristics for a solid state image sensor.

It is further object to alleviate buildup of static electricity on a lens of a solid state image sensor. It is a further object to provide an improved lens for a solid state image sensor.

It is a further object to provide solid state image sensors useful for color imaging.

According to the invention, a relatively-flexible, tape- like substrate for mounting a semiconductor device (die) has a patterned, conductive layer of fine-pitch leads (traces, fingers) extending into a central area in which a semiconductor die is connected to inner ends of the leads. The substrate includes an underlying insulating (for example, plastic film, particularly polyimide) layer (tape) supporting the leads, the plastic film layer having an opening larger than an area defined

by the die. For TAB processes, the opening in the plastic film layer is also larger than an area defined by the inner ends of the conductive leads so that inner end portions of the leads remain exposed past the opening in the plastic film layer for TAB connecting the leads to the semiconductor device. In the case of wire bonding (versus TAB) , it is not necessary that the leads extend past the opening.

Further according to the invention, the semiconductor device (die) is a solid state image sensor having a plurality of light-sensitive elements disposed in a "pixel" array across a planar front surface of the die, and the conductive traces are connected to bond pads (or bumps) on the front surface of the die, which bond pads are connected to the individual light- sensitive elements in the pixel array. Preferably, the conductive traces extend onto the front surface of the die from only two opposite edges thereof. Preferably, the inner ends of the conductive traces are TAB bonded to the semiconductor device. Preferably, a "bumped die" TAB process is used, wherein bumps for TAB bonding are formed on the die. Alternatively, a "bumped tape" TAB process can be used, wherein bumps for TAB bonding are formed directly on the lead fingers.

Further according to the invention, a lens element having a preferably round body portion is formed having an area corresponding to the area of the photosensitive element array and a bottom surface facing towards the array. The lens element is provided with at least two legs formed integrally with and

extending from the lens body towards the die. The front surface of the die is provided with corresponding at least two "landing pads", upon which portions of the two legs rest, to establish a fixed, predetermined vertical (z-axis) spacing between the lens and the die. These landing pads are preferably formed in the same process and manner as the TAB bumps on the front surface of the die.

According to a feature of the invention, other portions of the legs are provided with holes aligning with pins extending up from a printed circuit board (PCB) through the flexible substrate and through the holes in the legs, for establishing a fixed, predetermined planar location (x-axis and y-axis) and angular orientation (theta-axis) of the lens with respect to the die, and for biasing the lens legs onto the landing pads of the die.

In an alternate embodiment of the invention, the other portions of the legs are provided with pin structures extending through holes in the flexible substrate and through holes in the printed circuit board (PCB) for similarly establishing a fixed, predetermined planar location (x-axis and y-axis) and angular orientation (theta-axis) of the lens with respect tot he die, and for biasing the lens legs onto the landing pads of the die.

Further according to the invention, the lens is formed as a fresnel lens. Further according to the invention, three lenses are provided, three photosensitive arrays are provided, and three

suitable filters are provided so that each array receives one of three primary colors (e.g.. Red, Green, Blue) of a color image.

According to an aspect of the invention, the filters are formed integrally with the lenses.

According to another aspect of the invention, the three lenses are integrally molded with one another.

According to another aspect of the invention, the three photosensitive arrays are provided on a common semiconductor die.

Further according to the invention, the lens(es) is grounded to the die.

Further according to the invention, the photosensitive array(s) is coated with an optically clear coating. Further according to the invention, the photosensitive arrays may each be coated with a distinct, colored, optically- transmissive coating.

Other objects, features and advantages of the invention will become apparent in light of the following description thereof.

Brief Description Of The Drawings

Figure 1 is a top plan view of an arrangement for mounting a lens to a solid state image sensor, according to the present invention. Figure 2 is a side cross-sectional view of the arrangement of Figure 1, taken on a line 2-2 through Figure 1.

Figure 3 is a side cross-sectional view of the arrangement of Figure 1, taken on a line 3-3 through Figure 1, at ninety degrees to the side cross-sectional view of Figure 2. Figure 4 is a side cross-sectional view, similar to Figure 2, showing an alternate embodiment of the arrangement for mounting a lens to a solid state image sensor, according to the present invention.

Figure 5 is a side cross-sectional view, similar to Figure 4, showing additional features of the alternate embodiment of the invention.

Figure 6 is a cross-sectional view of a camera chip, according to the present invention, with an optically- transmissive coating applied to its front surface. Figure 7A is a cross-sectional view of an alternate embodiment of the lens of the present invention.

Figure 7B is a cross-sectional view of an alternate embodiment of the camera chip of the present invention.

Figure 7C is a cross-sectional view of an alternate embodiment of the lens of the present invention.

Figure 8 is a cross-sectional view of a semiconductor die

formed to ground the lens, according to the present invention. Figure 9 is a generalized illustration of the concept of color imaging, according to the present invention.

Figure 9A is top plan view of three lenses and three photosensitive arrays, according to the present invention.

Figure 9B is a top plan view of an alternate embodiment of three lenses and three photosensitive arrays, according to the present invention.

Figure 9C is a top plan view of a lens structure having three lens bodies, according to the present invention.

Figure 9D is a cross-sectional view of the apparatus of Figure 9C.

Figure 9E is a top view of an alternate embodiment of a lens having three lens bodies, according to the present invention.

Figure 10A is a side, partially-exploded view of an arrangement of a filter element fitting over a lens, according to the present invention.

Figure 10B is a side, partially-exploded view of an arrangement of a filter element fitting under a lens, according to the present invention.

Figure IOC is a side view of a colored lens, according to the present invention.

Detailed Description Of The Invention

FIRST EMBODIMENT Figures 1, 2 and 3 show an embodiment 100 of the present invention. As best viewed in Figure l, a semiconductor die 102 is mounted and connected to a substrate 104.

The die 102 is a solid state image sensor, having a plurality of photosensitive elements 106 arranged in an array (dashed lines) in a central area 108 on the front surface 110 of the die 102. The array 108 may include up to about 20,000 photosensitive elements 106, each photosensitive element having an array location (for example, column, row) corresponding to a "pixel" of image information. These photosensitive elements 106 are formed in any suitable manner, such as charge-coupled devices, photosensitive silicon gates, etc. The die 102 has four side edges 112, 114, 116 and 118. The edge 112 is opposite the edge 116, and the edge 114 is opposite the edge 118. A plurality of bond pads (sites) 120 are disposed on the front surface 110 of the die 102, just slightly within two opposite edges 114 and 118. There are shown eight such bond pads 120 on each of these two opposite edges 114 and 118.

Suitable circuitry (not shown) is disposed on the front surface of the die, outside the pixel array area 108, for providing image pixel signals out of the array of thousands (for example, 20,000) of individual photosensitive elements 106 by means of the relatively limited number (for example, sixteen)

of bond pads 120. This is according to well known techniques. The substrate 104 is a flexible substrate, comprising: (a) a metal foil layer 130 patterned into individual conductive lines (traces, fingers) 132; and (b) an underlying layer 134 of plastic, such as polyimide, film or tape.

Inner ends 136 of the lead traces 132 extend within an opening formed by an inner peripheral edge 138 of the plastic film layer 134, and the inner ends 136 of the lead fingers 132 extend slightly over the front surface of the die 102, over the bond pads 120, and are aligned with the bond pads 120.

As best viewed in Figure 3, in a "bumped die" TAB bonding technique, conductive bumps 140 are deposited onto the die bond pads (sites) 120. These bumps 140 are typically formed of gold, and are plated or otherwise deposited onto the die bond sites

120. The die 102 is brought into juxtaposition with the substrate 104, and the inner ends 136 of the conductive traces

132 are TAB bonded to the bumps 140 on the die bond sites 120.

This is according to known TAB techniques. Alternatively, the bumps (140) could be formed on the inner ends 136 of the conductive traces 132, again according to known TAB techniques

("bumped tape") .

As best viewed in Figure 3 (omitted from Figure 1) , a layer of glob-top epoxy 142, or the like, is applied over the inner ends of the leads 132, including an area extending outward partially over the plastic film layer 134, and including an area

extending inward partially over the die 102. This helps hermetically seal the connections between the lead traces 132 and the die 102, and also helps to support the die 102 with respect to the substrate 104. The "substrate" 104 includes the lead layer 130 and the plastic film layer 134.

According to the invention, a lens 150 is provided in close proximity to the die 102, for focusing an external image (see Figure 2, light rays "4-4-") onto the pixel area 108 on the front surface 110 of the die 102, particularly onto the array of photosensitive elements 106 on the front surface of the die.

Inasmuch as the die 102 is solid state image sensor, specifically intended to function as a "camera chip" (although not specifically in a video camera, per se) , it is essential that the external image be in focus on the front surface of the die. Hence, it is critical that the lens 150 be accurately located at a distance " " (see Figure 2) , representing the focal length of the lens, from the front surface of the die. In this example, the focal length of the lens is 2 millimeters (mm) .

As best viewed in Figure 2, the lens 150 has a round "body" 152 forming an optical element, and the bottom surface 154 of the lens body 152 is oriented towards the front surface 110 of the die 102. Two legs 154 and 156 are formed integrally with the lens body 152, and extend outward and downward (that is, towards the die, as best viewed in Figures 2 and 3) from diametrically-opposed locations on the lens body. This is termed a "C-mount", the legs 154 and 156 forming the two "legs"

of the "C". The legs 154 and 156 are parallel to each other, and spaced apart sufficiently to clear (not impede with) the array area 108.

More particularly, the leg 154 has a portion 158 extending radially from the lens body 152, thence a portion 160 extending at a right angle (to the portion 158) co-axially with respect to the lens body towards the die, thence a portion 162 extending at a right angle (to the portion 160) outward from the center of the die parallel to a plane defined by the front surface 110 of the die.

Similarly, the leg 156 has a portion 164 extending radially from the lens body 152, thence a portion 166 extending at a right angle (namely, ninety degrees) co-axially with respect to the lens body towards the die, thence a portion 168 extending at a right angle (to the portion 166) outward from the center of the die parallel to the plane of the die.

The leg portions 158 and 164 are collinear and extend in diametrically opposed directions outward from the lens body 152. The leg portions 160 and 166 are parallel to each other, and spaced apart from each other by a distance at lest as great as the diameter of the lens body 152. The leg portions 162 and 168 are collinear and extend in opposite directions with respect to the center of the die, and also with respect to the lens body. The leg portions 162 and 168 are parallel to the plane of the die, and extend from within the outer edges 116 and 112, respectively, of the die to beyond the outer edges of the die.

The lens 150 is positioned so that the legs 154 and 156 are disposed just within opposite side edges 116 and 112, respectively, of the die, and such that the leg portions 162 and 168, respectively, rest on the front surface of the die. The lens body 152 and legs 154 and 156 are formed integrally with one another, of clear plastic, such as acrylic. Hence, they are relatively hard and stiff. And, as we know, silicon dies (for example, 102) are especially brittle. Thus, if the lens were mounted directly to the die, it is likely that the die would crack. Hence, a "shock-absorber" is included for mounting the lens to the die.

"Landing pads" 170 and 172 are formed, outside the central area 108, at opposed locations on the front surface of the die for resiliently mounting the legs 154 and 156, respectively. The attributes of these "landing pads" 170 and 172, which function as "shock absorbers" for mounting the lens to the die, are that they are resilient (ductile) and are capable of being applied with a precise (known, fixed) thickness to the front surface of the die. According to the invention, the landing pads (or "spacers") 170 and 172 are formed in the same manner and of the same material as the bond bumps 140 (Figure 3) formed in the TAB process. TAB processes are well defined, and spacers (170, 172) having a thickness of 25 microns, plus/minus 3 microns, are readily achieved. The ability to deposit (or plate) the spacers 170 and 172 onto the front surface of the die with such

precision, allows for accurately positioning the lens with respect to the die, which is critical when dealing with a limited field of focus (depth of image field) for the lens. In this example, the depth of field for the lens is 30 microns, which is an order of magnitude larger than variations (3 microns) expected in the thickness of the spacers 170 and 172. With the lens resting on the die, via the intermediary of the spacers 170 and 172, it is possible to focus an external image onto the photosensitive element array of the die with image-quality resolution.

As best viewed in Figures 1 and 3, the landing pads 170 and 172 are wider than the respective leg portions 162 and 168. This is to ensure that the leg portion rests entirely on the respective landing pad. In this sense, the landing pads have a larger "footprint" than the respective leg portions.

It has been described how the lens rests upon the die, and how the legs 154 and 156 and landing pads 170 and 172, respectively, can establish a relatively precise vertical (z- axis) positioning of the lens with respect to the die. The position of the lens in the plane of the die (x-axis and y- axis) is also important, as is the rotational position (theta) of the lens with respect to the die. It is also important to securely mount the lens with respect to the die. There follows a description of establishing planar (x-axis, y-axis and theta) positioning of the lens, as well as means for holding the lens in place with respect to the die.

As best viewed in Figure 2, the die 102 and substrate 104 (only the plastic tape layer 134 of the substrate 104 is visible in Figure 2) are usually ultimately mounted to a printed circuit board (PCB) 180, or the like, for connecting the packaged (substrate-mounted) die to external system components (not shown) . This is readily accomplished with a layer 181 of suitable adhesive between the backside of the die and the front side of the PCB.

As best viewed in Figures 1 and 2, the leg portions 162 and 168 of the legs 154 and 156, respectively, extend substantially beyond the edges 116 and 112, respectively, of the die, and over the substrate 104. As best viewed in Figure 1, the top conductive layer 130 of the substrate is patterned to have conductive traces 132 only on two opposite sides 182 and 183 of the plastic layer 134 aligned with the two bumped edges 114 and 118 of the die, and is patterned not to have conductors (or any foil at all, for that matter) in areas 184 and 185 corresponding to the non-bumped edges 116 and 112 of the die where the leg portions 162 and 168 will rest upon the die and extend out over the substrate 104. In other words, the lens is oriented so that the leg portions 162 and 168 extend at ninety degrees to the conductive traces 132, so that they are over only the plastic layer portion 134 of the flexible substrate 104.

The leg portion 162 extending over the plastic substrate area 184 is provided with locating holes 202 and 204 aligned over the plastic substrate area 184. Two holes are preferred.

at least one is required. Similarly, the leg portion 168 extending over the plastic substrate area 185 is provided with two locating holes 206 and 208 aligned over the plastic substrate area 185. A pin 210 is provided extending "normally" (at ninety degrees) from the front surface of the PCB 180 towards the leg portion 162, through an aligned hole 203 in the plastic film layer 134 and through the hole 202 in the leg portion 162. A similar pin 212 is provided extending from the front surface of the PCB, through the plastic film layer, towards the leg portion 162 and through the hole 204, as best viewed in Figure 3.

Similarly, two pins are provided extending from the front surface of the PCB towards the leg portion 168 and through the two holes 206 and 208. In Figure 2, one of these pins 214 is shown extending through the an aligned hole 207 in the plastic film layer 134 and through the hole 206 in the leg portion 168.

The pins (210, 212, 214) are anchored with a suitable adhesive (not shown) into the PCB, and extend through the respective locating holes (202, 204, 206, 208) in the respective leg portions (162, 168). The leg portions 162 and 168 are then anchored down onto the PCB by suitable mechanical means, such as star washers 220 atop the respective leg portions, a suitable adhesive (not shown), or deformation (or "wedging", not shown) of the portions of the pins extending through the locating holes beyond the leg portions. The locating pins may extend suitable entirely through the PCB, and be retained by a head

(enlarged pin diameter) on the back side of the PCB.

Figure 2 is "nearsighted", in that it does not show the conductors 136, bond pads 120 or bond bumps 140 in the far background. As best viewed in Figure 2, the locating pins (210, 214) securely retain the substrate 104, die 102 and lens 150 onto the PCB 180, and there is a gap between the plastic layer 134 of the substrate 104 and the PCB 180. In some instances, this gap may be advantageously employed to resiliently bias the lens down onto the die, for example by how far the star washers (220) are positioned down the length of the locating pins. However, it may be more preferred to reduce the gap, while retaining some downward bias on the lens, while controllably limiting the downward bias, by interposing suitably-sized spacers 222 (see Figure 2) , somewhat smaller than the gap between the substrate and the PCB, around the respective locating pins between the PCB and the substrate.

The locating pins (210, 212, 214, etc.), locating holes (202, 204, 206 and 108), and corresponding aligned holes (203, 207) for the locating pins through the plastic film layer 134, establish the planar position (x-axis, y-axis, theta-axis) position of the lens 150 with respect to the die 102, hold the lens securely in position against the die, and bias the lens against the front surface of the die. Further, the landing pads 170 and 172 perform a shock absorbing function so that the legs of the lens do not damage the die.

It should be understood that the legs 154 and 156 can also be formed non-integrally with the lens body 152, as separate elements, although integral forming (as discussed above) is preferred. It should be understood that a "bumped tape" TAB process can be employed, although it would then be necessary to form the landing pads 170 and 172 in a separate process since the die is not being otherwise "bumped" for TAB bonding.

It should be understood that it is not necessary that the flexible substrate is a TAB substrate, and that the die can be wire bonded to the substrate. However, as with a "bumped tape"

TAB process, it would be necessary to separately form the landing pads (namely, separate from a "bumped die" step) .

It should also be understood that the locating pins (for example 210 and 214) could extend completely through the PCB

(180) , could have a head of increased diameter atop the substrate, and could be anchored (for example with star washers) on the lower side of the PCB.

These variations on the disclosed mounting technique will be evident to those of ordinary skill in the art to which this invention most nearly pertains, without further illustration, based on the disclosure contained herein.

SECOND EMBODIMENT Figures 4 and 5 show an alternate embodiment of the invention, and correspond generally to the view of Figure 2.

In this embodiment, the legs are formed differently than they were in the first embodiment (Figures 1-3) . To wit, the lens 450 has a body portion 452 (similar to the body portion

152 of Figures 1-3) with a lower surface 454 (154) facing the die 402 (102) .

In this embodiment, the lens is provided with two "vertical alignment legs" 454 and 456, again preferably formed integrally with the lens body. The vertical alignment legs 454 and 456 are parallel to each other and spaced apart, and extend from the bottom 454 of the lens, towards the die 402, and establish a predetermined vertical (Z-axis) spacing between the lens body 452 and the front surface 410 of the die. These legs 454 and 456 have a rectangular cross-section, and are flat at their lower ends 455 and 457, respectively. These ends 455 and 457 contact the landing pads 470 and 472, respectively, on the front surface of the die. As in the first embodiment (Figures 1-3) the landing pads 470 and 472 are preferably formed in the TAB process, and provide a resilient resting place for the lens, and are larger in area than the "footprint" of the vertical alignment legs.

The view of Figure 4 is not "nearsighted", in that TAB bumps 440 (140) , conductive traces 436 (136) and the plastic film layer 434 (134) can be seen in the distance, between the vertical alignment legs 454 and 456. Lateral alignment legs 462 and 468 extend from approximately midway along the vertical extent of the vertical

alignment legs 454 and 456, respectively, outward (parallel to the plane of the die) a suitable distance to be over the plastic film layer 434. At this point, the lateral alignment legs 462 and 468 turn (ninety degrees) downward and extend through respective holes in the plastic film layer. The downward- oriented portions 463 and 469 of the lateral alignment legs 462 and 468, respectively, are round in cross-section, similar to the alignment pins 210 and 214 of the first embodiment (Figures 1-3) . In this manner, the planar alignment (s-axis, y-axis, theta-axis of the lens is established with respect to the substrate-mounted die.

The pin-like portions 463 and 469 are sufficiently long to extend completely through the plastic film layer, and through respective holes 482 and 484 in an underlying printed circuit board 480 (PCB, compare 180) .

Turning now to securing the lens in place, and biasing the lens against the die, attention is directed to Figure 5.

A layer 490 of a compliant (resilient) material, such as elastomer, is interposed between the front of the PCB 480 and the back of the die 402. The layer 490 is at least as large (in area) as the die, but is preferably not much (such as less than ten percent) larger. This compliant layer 490 will establish a limited downward bias of the lens against the die .

As mentioned hereinabove, the pin-like portions 463 and 469 of the vertical alignment legs ("pegs") extend fully through the

PCB 480. On the lower side of the PCB, the pin-like portions

are secured against the bottom of the PCB in any suitable manner, such as with star washers 494, or by expanding their diameter (swaging) . It should be understood that each lateral alignment leg (462, 468) can be "forked", which is to say can have two pin-like portions extending outward and downward from the respective vertical alignment leg (454, 456) . Or, they can simply be flat. Similarly, there are readily provided two pin-like portions (463, 469) on each of the lateral alignment legs (462, 468), corresponding to the two pins per side (that is, per leg) of the first embodiment. Additional Comments

The landing pads (170, 172, 470, 472) are preferably formed of gold, in the same process and with the same material as the TAB-bumps are formed on the front surface of the die. However, the landing pads can be formed of copper, or of solder, or of other ductile material that will alleviate any tendency for the lens legs to crack the die, and that can be applied by electroplating or depositing onto the front surface of the die.

Inasmuch as the landing pads can be applied to the front surface of the die with relatively high precision (with respect to their thickness) , and the legs of the lens can be formed with reasonably good precision, it is possible to provide a known, critical spacing between the lens body and the front surface of the die. In other words, it is possible to "reference" off of the front surface of the die.

The invention advantageously employs the requirement for only a relatively small (for example, sixteen) bond sites on the front surface of the die, these bond sites conveniently disposed only along opposite edges of the die. While two diametrically-opposed legs have been disclosed, it should be understood that any suitable number of legs (namely, at least two) could be employed.

The invention is particularly well suited to focusing external images onto any optically-sensitive electronic device. It is of particular relevance to the situation where the alignment of the lens with respect to the sensitive surface of the device requires accurate alignment of the lens in both the vertical and lateral (planar) dimensions, such as for an image sensor. Given the situation where a lens must be positioned above an electronic device to within a tolerance of a few tens of microns in the vertical dimension, it is advantageous that the lens have integrally-formed vertical alignment legs formed to extend from the lens to the electronic device. The legs are formed to contact the electronic device only in areas where a controlled thickness of resilient material (landing pads) can be readily applied. Since the process of applying the landing pads to the electronic device is well controlled, the vertical spacing of the lens above the electronic device will be commensurately well controlled.

The discrete pins, or integrally-formed pin portions of the legs, establish the planar (lateral) position of the lens with respect to the electronic device, and also are used to bias the lens downward against the electronic device. The layer 490 of material shown (Figure 5) between a printed circuit board and the die is preferably an elastomeric spacer, or a gel dispensed onto either the back side of the die or onto the front side of the printed circuit board.

The portions of the discrete pins, or of the pin portions of the legs, extending through the leg portions or printed circuit board, respectively, can be fixed in place using any suitable technique, such as with star washers, with an adhesive, or by local deformation of the extending pin portions by application of heat via a hot tool or ultrasonic energy, or by soft swaging.

THIRD EMBODIMENT

A difficulty that may arise with the arrangement of mounting a lens, as disclosed in the first two embodiments, is contamination of the photosensitive array underlying the lens and it was assumed that the entire arrangement would be disposed in a relatively clean and dry environment (such as a camera housing) . In a dirty or humid environment, foreign matter may become deposited on the array, thereby adversely impacting the imaging capability of the array. Hence, it is an object of this embodiment to avoid the problems which may be associated with such contamination, thereby allowing the arrangement to be used

in a dirty or humid environment. Further, it may be desirable to protect the surface of the array from being scratched, which could adversely impact its imaging capability.

According to this embodiment of the invention, the photosensitive array (e.g., central area 108), is coated with a thin, reasonably uniform thickness, optically clear coating.

It is evident that the glob-top epoxy encapsulant 142, disposed over the leads 132 and bond pads 120 (bumps 140) is not suitable for use over the array, in that such encapsulants tend to be substantially opaque.

Figure 6 shows a side-cross-sectional view of a photosensitive array in an area 608 (comparable to 108) on a die 602 (comparable to 102) . The presence of a lens mounted atop the die is assumed, and is not shown (See, e.g.. Figures 1-5 for lens) . Bond pads and the like are not shown in Figure 6, for illustrative clarity.

Prior to mounting the lens, and as one of the final steps involved in the fabrication of the die itself, and/or as a final or penultimate step in the mounting of the die to a tape carrier, a thin layer 610 of an optically-transmissive, clear coating is applied over the die 602. Such a layer may also be deposited selectively only over the array area 608 (not shown) . Important characteristics of the layer 610 are that it is highly optically-transmissive, flat and relatively smooth over the array area 608, so that images focused by the lens onto the array will not be attenuated in intensity or distorted.

The optically-transmissive, clear coating material may, for example, be a two-part silicone, such as "Ql-4939" produced by Dow Corning, which provides excellent light transmission percentages in the visible spectrum (e.g., 75% light transmission at 4000 Angstroms to 80% light transmission at 8000 Angstroms) . A coating of such two-part silicone compound, on the order of 3 mils to 13 mils (0.33 mm) thick will "seal" the array. However, it has been observed that there is a propensity for the coating to dome (meniscus) if applied too thick, and a propensity for the coating to remain tacky after curing (which may attract airborne particles) .

Another coating material which is partially well suited to coating the die is siloxane polyimide, such as "TABCOAT 100" produced by Ablestik. However, this material tends to dry to a greenish-orange color.

Both of the aforementioned materials also exhibited a tendency to "wick" up the bumps (120) and spacers (170) , making accurate referencing (spacing) of the lens above the die difficult. Another, more viable technique of coating the die 602 is applying a layer of silicon dioxide, silicon nitride or silicon carbide, or combinations thereof, using a pulsed plasma deposition process. Pulsed plasma techniques are discussed, for example in Great Britain Patent No. 2,105,729. This can, and may preferably be performed after the die is mounted to the tape substrate, in which case the entire die and the bonds will

be sealed. A layer 610 applied by pulse plasma can be applied relatively uniformly, and relatively thinly (on the order of one micron, or less) . Thin layers, however, may reduce the transmissivity of the layer at certain wavelengths. This should be taken into account in light of the anticipated usage and desired sensitivity characteristics of the camera chip 602.

Certain advantages accrue to coating the entire die with an optically-transmissive layer 610, particularly ease of applying the layer. However, it should be understood that there may be additional circuitry on the surface of the die, outside of the central area 608 - for example circuitry for addressing and accessing the individual cells (pixels) of the photosensitive array. In this case, it is desirable to apply an opaque coating over such additional circuitry. Reference is made to the glob-top coating 142 shown in Figure 3, which is entirely suitable for covering such additional circuitry surrounding the photosensitive array, which preferably would be applied atop the layer 610.

For one or another of the above-described techniques of coating the die, it may be desirable to coat only the array area 608, in which case it would be necessary to "mask" the remaining area of the die surrounding the array area.

The particular environment in which the camera chip (100) is intended to operate will dictate the preferred choice of techniques for encapsulating the entire die or only the photosensitive array.

FOURTH EMBODIMENT A difficulty that may arise with the arrangement of mounting a lens disclosed in the first two embodiments is the overall vertical height of the lens structure atop the die. This is, of course, partially a result of the need to space the lens body at a distance equal to the lens focal length above the photosensitive array. Additional height is attributable to the thickness of the lens body itself.

According to this embodiment of the invention, the lens body is formed as a fresnel lens, having a focal distance commensurate with the lens body of the previous embodiments.

Figure 7A shows a cross-section of a lens body 752. Portions 758 and 764 of legs, similar to the legs 154 and 156 are shown extending radially from the lens body. The front surface 751 of the lens body is formed as a fresnel lens. The back (die-facing) surface 753 of the lens body is flat (compare 153) . In this manner, the vertical profile of the lens body can be minimized. Such a fresnel lens 750 is suitably mounted atop a die on a tape substrate in the same manner as the previous embodiments.

Figure 7B shows a variation of mounting a fresnel lens 750' above a die 702 having a photosensitive array 708. In this example, the die is mounted in an opening (cavity) 722 in a package body 720 (for example a ceramic package body) . Such cavities are known to eventually be closed by a lid, typically a metal lid. According to the invention, a lens 760 is used to

close over the cavity. To this end, the package body is preferably provided with a recessed step 724 on the inner top edge of the cavity, and the overall dimension of the lens is such that it will fit within the step. This will ensure reasonably accurate positioning of the lens. The lens body 762, preferably centrally located on the lens, can be of "traditional" shape (compare 152) , or can be formed as a fresnel lens body (as shown) . This packaging technique will provide lateral and vertical alignment of the lens commensurate with that provided by the legs (154,156) and pegs (210,214) of the previous embodiments, so long as the position of the die within the package body is also well known. The package body may be provided with any suitable external connections (not shown) , such as pins, leads or ball bumps. The "simple" lens bodies described above generally suffer from a degree of chromatic aberration. In other words, they tend to refract different wavelengths of incident light at slightly different angles.

Figure 7C shows a "compound" lens 770, generally similar to the "simple" lens 750 of Figure 7A. The lens has a body 772. Portions 778 and 784 of legs, similar to the legs 154 and 156 shown extending radially from the lens body (for resting on a die, not shown) . In this example, the front surface 771 of the lens body 772 is formed as a fresnel lens, and the back surface 773 of the lens body is formed as a spherical (non-fresnel) lens. Hence, the lens body 772 forms a "compound" lens. In

this manner, chromatic aberrations introduced by one of the lens surfaces (771, 773) can be offset the other lens surface (773, 771) . Although not shown, the back surface of the lens could be formed as the fresnel surface, and the front could be formed as a spherical surface. The particular application of the resulting camera chip will dictate the particular arrangement and curvatures of the front and back surfaces of the lens body.

The body 772 of the compound lens 770 of Figure 7C could be advantageously employed in a lens atop a package, as illustrated in Figure 7B.

FIFTH EMBODIMENT In use, electrostatic charges may accumulate on the lens (i.e., the lens or lenses of any of the above embodiments). This is of special concern when the lens is resting atop the die (as opposed to resting atop a package cavity) , and is capable of accumulating and dissipating large amounts of electrostatic charge. An emission of uncontrolled electrostatic discharge (ESD) can destroy semiconductor device. A lens made of a material (e.g., acrylic) capable of accumulating large amounts of electrostatic charge are very susceptible to this phenomenon. According to the invention, the lens is electrically grounded to the die. (The die, in turn, is typically grounded.) Returning momentarily to Figures 1-3, it is seen that the lens legs 154 and 156 (portions 162 and 168, respectively) rest atop landing pads 170 and 172, respectively, and that these landing pads are preferably formed in the same manner and of the same

(conductive) material as the bond pads 120 (bond bumps 140) . The conductive material is typically electrodeposited gold and, for the purpose of grounding the lens, these landing pads are grounded to the die. Since the lens is clamped to the landing pads (spacers) , this will provide an electrically conductive path from the lens, through the spacers, into the semiconductor device, and will eliminate the build-up of electrostatic charges on the lens, thereby protecting the semiconductor device from being damaged. Figure 8 shows a die 802 with a passivation layer 810 over the front surface. A central portion 808 of the front surface is a photosensitive array (compare 108) . A landing pad (spacer) 870 (comparable to 170) is shown atop the passivation layer. The landing pad 870 is typical of the pads required to support the lens (not shown) above the die (compare Figures 1- 3) . A conductive via 871 is provided from the pad 870, through the passivation layer 810, to an underlying metallization interconnect layer shown as dashed line 820. The line 820 is a patterned line in the metallization layer and is connected to a bond pad (not shown) that is grounded (VSS) in a normal manner. In this manner, the pad 870 is grounded, and provides a path for bleeding off static charges as they would otherwise tend to build up and accumulate on the lens, thereby avoiding a catastrophic discharge.

SIXTH EMBODIMENT The embodiments described above are generally limited to a monochromatic camera chip. In certain applications, it is desirable to have multi-chromatic, or "color" imaging capability.

According to the invention, three lenses are provided, three photosensitive arrays are provided (one for each lens) , and suitable filters are provided so that each photosensitive array is selectively sensitive to one of three "primary" colors (e.g.. Red, Green and Blue).

Figure 9 illustrates, schematically, an image 902 being focused by three lenses 904, 906 and 908, through three filters 910, 912 and 914 onto three camera chips 916, 918 and 920, respectively. The filters are each monochromatic. For example, the filter 910 is red, the filter 912 is green and the filter 914 is blue. This is a generalized description of a color camera using three camera chips of the type disclosed in the present invention. A common optic 922 may be employed to ensure that the image is properly distributed through the three lenses 904, 906 and 908.

Figure 9A shows an arrangement 900 having three discrete lenses 950a, 950b and 950c and three discrete dies 902a, 902b and 902c. Each die has its own photosensitive array 908a, 908b and 908c. The lenses are comparable to the lens 150 of Figures 1-3, or 450 of Figures 4-5, 750 of Figure 7A, or 770 of Figure 7C. Furthermore, the lens may be grounded as shown in Figure

3.3 8. Furthermore, there may be a coating on the die, as shown in Figure 6.

As shown, the three lenses are each mounted to a respective die (in the manner discussed above) . The dies (hence lenses) are maintained in a fixed positional relationship with each other, as indicated by the dashed lines 920 extending between the dies. This may be accomplished by means of a common tape carrier (compare 104) to which the dies are mounted, or by any other suitable means such as by mounting the dies to a printed circuit board.

Figure 9B shows an alternate arrangement 910 having three discrete lenses 960a, 960b and 960c, each disposed above and focusing on a corresponding one of three photosensitive arrays 918a, 918b and 918c on a single die 922. Figures 9C and 9D shows an alternate arrangement 920 of three lens bodies 952a, 952b and 952c, molded integrally with one another. Two leg porions 958 and 964 are shown, comparable to the leg portions 158 and 164 of the lens 150 of Figures 1- 3. The lens haying three lens bodies is positioned over three discrete dies (not shown, but compare Figure 9A) , or over a single die having three arrays (not shown, but see Figure 9B) .

Figure 9E shows an alternate embodiment of the arrangement of Figures C and 9D. In this embodiment, three lens bodies 932,

933 and 934 are formed in a single lens structure 930. Each lens body would be disposed over a corresponding photosensitive array (not shown) .

SEVENTH EMBODIMENT Figures 9A, 9B, 9C/9D and 9E illustrate various contemplated techniques for associating three lens bodies with three photosensitive arrays. What remains, for purposes of providing a color-capable arrangement, is providing each of the lens/array combinations (e.g., 960a/918a) with its own "filter", for example a red filter for one lens/array, a green filter for another lens/array, and a blue filter for the remaining lens/array. According to the invention, the "filter" is provided in one of many ways. Examples illustrating only one of the three lenses are shown, for illustrative clarity.

Figure 10A shows a single lens 1050 having a body 1052 comparable to any of the above lenses/bodies. For example, the lens is provided with two legs (one leg 1054 visible in this view) , comparable to the legs 154 and 156 of the lens 150 (Compare Figure 2) . In this example, a discrete filter element 1060 is disposed in front of the lens, and may, for example, simply be formed as a cap that snaps on over the lens body, said cap formed of a suitably colored (e.g., red, green or blue) plastic material. The cap is of uniform thickness, so that it does not alter the focusing properties of the lens, and has two diametrically-opposed legs 1062 and 1064 formed to snap (indicated by arrow " I" ) over the body portion 1052 of the lens, intermediate the lens legs (e.g, 1054/154 and 156) .

Figure 10B shows the lens 1050 with a discrete filter element 1060• disposed behind the lens. The element 1061 may, for example, simply be formed as a cap that snaps on under the lens body, said cap formed of a suitably colored (e.g., red, green or blue) plastic material. The cap is disc-like, and is of uniform thickness, so that it does not alter the focusing properties of the lens, and has two diametrically-opposed legs 1063 and 1065 formed to snap (indicated by arrow "t") around the body portion 1052 of the lens, intermediate the lens legs (e.g, 1054/154 and 156) .

Figure 10C shows a single lens 1051 having a body 1053 comparable to any of the above lenses/bodies. For example, the lens is provided with two legs (one leg 1055 visible in this view) , comparable to the legs 154 and 156 of the lens 150 (Compare Figure 2) . In this example, at least the body portion of the lens is formed of a colored plastic material (shown as shading) , and a discrete filter is not required (compare Figures 10A and 10B) .

Figures lOA and 10B show using discrete filter elements in front of or behind the lens body. Figure 10C shows that the lens body may itself be colored, to function as a filter. It is also possible that neither a discrete filter, not lens coloring is employed. To wit, as mentioned above, a coating may be applied directly to the array (108) , and certain coatings have a tendency to be colored (rather than clear) . According to this embodiment of the invention, each of three arrays

(whether on three dies or on a single die) are coated with a respective dissimilarly colored (e.g., red, blue, green) coating material -the coating material itself acting as a "surrogate" filter element. Hence, it has been shown that three lenses can be arranged with suitable three filters to provide for color imaging. The resulting color imaging chip (die or dies, and lens or lenses) can be employed in any video device requiring color capability, for example, in a color camera, in a color scanner, and the like. Evidently, the die/lens combinations discussed above would be housed in a suitable housing, and addition optics would be provided for focusing, and additional circuitry would be required for creating color image signals.