DETAILED DESCRIPTION OF THE INVENTION

[0024] Referring in general to the accompanying drawings, various aspects of the present invention are illustrated to show exemplary image sensor package structures and methods for assembly of a package for housing an image sensor chip. Common elements of the illustrated embodiments are designated with like reference numerals. It should be understood that the figures presented are not meant to be illustrative of actual views of any particular portion of a particular image sensor package structure, but are merely idealized schematic representations which are employed to more clearly and fully depict the invention. It should further be understood that while depicted in terms of an image sensor, the package embodiments and methods presented herein would work equally well for housing other types of optically interactive electronic devices as described above.

[0025] Turning to FIGS. 1 through 13 , methods for simultaneously assembling a plurality of image sensor packages according to the present invention are illustrated. A carrier substrate 2 , shown in FIG. 1 , is provided with an array of image sensor chip attachment areas 4 formed on its top surface 6 . Broken section lines 100 are shown running in mutually perpendicular horizontal and vertical directions on top surface 6 to indicate the boundary between adjacent image sensor chip attachment areas 4 . Carrier substrate 2 may be a printed circuit board (PCB) having conductive traces 8 (see FIGS. 12 and 13 ) thereon, and may be formed using conventional PCB fabrication techniques. Carrier substrate 2 may be constructed with common PCB materials such as a BT resin or FR-4 or FR-5 laminate in order to reduce cost, but other materials such as silicon, ceramics or plastics may be used as well. Each image sensor chip attachment area 4 includes a chip adherence surface 9 bounded by a plurality of wire bonding locations 10 for wire bonding to conductive traces 8 , one of which is shown in broken lines in FIG. 1 , conductive traces 8 extending to locations for electrical connection of the completed image sensor package to higher-level packaging, such as a circuit board, for operation. The length, orientation and configuration of conductive traces 8 may be as desired, depending on the I/O format used to connect the completed image sensor package, and so will not be discussed further at this juncture.

[0026] A layer of barrier material 12 having apertures 14 therein coinciding with image sensor chip attachment areas 4 is then formed on, or secured to, the carrier substrate top surface 6 , as illustrated in FIG. 2 . In a currently preferred embodiment of the present invention, layer of barrier material 12 is formed from a mold compound 16 which is molded directly onto top surface 6 . This method is depicted in FIGS. 3A through 3C . As shown in FIG. 3A, a transfer molding tool or platen 18 including contiguous mold cavities 20 is placed in sealing relationship against top surface 6 of carrier substrate 2 with mold cavities 20 positioned over the perimeter of carrier substrate 2 and over areas coinciding with, and preferably bisected by, section lines 100 defining boundaries between adjacent image sensor chip attachment areas 4 . FIG. 3B shows that a liquified or otherwise molten mold compound 16 , such as a thermoplastic, silicon-filled polymer, is rapidly transferred under pressure from a reservoir 22 into mold cavities 20 via a plurality of runners 24 , the general process of transfer molding being well known in the art. The mold compound 16 then cures and hardens as it cools, and molding tool 18 is removed from the top surface 6 of carrier substrate 2 , leaving the structure as seen in FIG. 3C . The cured mold compound 16 comprises a contiguous matrix of raised walls 26 that surround each image sensor chip attachment area 4 to define apertures 14 , leaving the portion of image sensor chip attachment areas 4 containing chip adherence surface 9 and wire bonding locations 10 exposed, creating an array of chip cavities 28 sized and configured for receiving image sensor chips 52 , which are described in further detail below. FIG. 3D is a top view of carrier substrate 2 showing the arrangement of raised walls 26 surrounding chip attachment areas 4 .

[0027] As noted above, mold compound 16 may be a thermoplastic polymer or other suitable encapsulant material as known in the art. Further, a filler material such as fine silicon particles may be incorporated within the mold compound to reduce cost, also as known in the art. It should also be understood that while the present invention is described in terms of transfer molding, other molding techniques such as injection molding or pot molding could be used with an appropriately formulated mold compound. Other suitable materials for mold compounds as known in the art include, without limitation, thermoset polymers and epoxy compounds.

[0028] Another approach to forming a layer of barrier material 12 onto top surface 6 includes disposing a flowable material on top surface 6 in one or more sequentially cured layers to build the contiguous matrix of raised walls 26 . In one exemplary embodiment of this method shown in FIG. 4A, a high-viscosity liquid or gel 30 is dispensed from a nozzle 32 around the perimeter of carrier substrate 2 and along section lines 100 (not shown). The high-viscosity liquid or gel 30 is then cured to form a first hardened layer 34 . In FIG. 4 B, an additional layer of high-viscosity liquid or gel 30 is dispensed over first hardened layer 34 and cured to form second hardened layer 36 . Subsequent layers of liquid or gel 30 may be added, as desired, until the desired height for layer of barrier material 12 is reached. Liquid or gel 30 may comprise an activated epoxy or any other curable resin-type material that may be hardened by reaction of constituents thereof, application of heat thereto, or otherwise as known in the art.

[0029] Another exemplary embodiment of this layering approach exists in using a stereolithographic (STL) deposition process to form the contiguous matrix of raised walls 26 on top surface 6 . As defined in the art, STL involves the formation of solid structures by selectively curing portions of volumes of a liquid polymer or resin material contained within a tank or reservoir. Depending on the liquid material composition, curing may be accomplished by exposure to irradiation with selected wavelengths of light or other electromagnetic radiation, for instance, when curing a material susceptible to initiation of cross-linking by exposure to ultraviolet (UV) radiation, such as through use of a UV laser beam. By curing one or more successive layers of the liquid material, intricate solid structures of almost any shape may be formed. It is also possible to add elements to an existing structure using STL, as would be the case with the present invention. FIGS. 5A and 5B illustrate this technique. In FIG. 5 A, carrier substrate 2 is placed to a selected depth below the surface of a photocurable liquid 38 contained within a reservoir 40 . The use of a photocurable liquid 38 is only exemplary, and liquid materials cured by other activating agents could also be used. A focused beam of light such as a laser beam 42 is directed over the surface of photocurable liquid 38 in a pattern that coincides with the perimeter of carrier substrate 2 and section lines 100 between image sensor chip attachment areas 4 . The portions of the photocurable liquid 38 exposed to laser beam 42 cures to at least a semisolid state, forming a first layer of cured material 44 on top surface 6 . FIG. 5B shows that carrier substrate 2 may then be lowered another selected depth within reservoir 40 , and the beam of light 42 directed over the same pattern to form a second layer of cured material 46 on top of the first layer 44 . As with the previous dispensing embodiment, subsequent layers may be added until the desired height for layer of barrier material 12 is reached. Complete and accelerated curing of the photocurable material may be effected by devoted temperatures after cross-linking is initiated. Suitable equipment for forming a barrier layer as described is commercially available from 3D Systems, Inc. of Valencia, Calif. Suitable photocurable liquids which may be used with the 3D Systems, Inc. equipment is available from Ciba Specialty Chemicals Corporation.

[0030] In certain situations, it may be desirable to preform the layer of barrier material 12 defined by raised walls 26 and then secure it to carrier substrate 2 . FIG. 6 shows an exemplary preformed unitary frame 48 used for this purpose. Unitary frame 48 may be preformed by one of the previously described molding techniques, or may be formed from a sheet of solid material such as a plastic, silicon or green ceramic by removal of selected portions thereof. In the case of molding, the array of apertures 14 may be directly molded into unitary frame 48 . When formed from a solid material, apertures 14 may be cut, stamped, milled or etched into a sheet of material, the process employed being dictated by the material selected. Once completed, unitary frame 48 may be secured to top surface 6 of carrier substrate 2 with an adhesive material 50 , as illustrated in FIG. 7 . Adhesive material 50 may be in the form of an epoxy, a silicone, an acrylic or other liquid-type adhesive applied to top surface 6 and/or unitary frame 48 , or may comprise a double-sided adhesive-coated tape segment or film, such as a polyimide. Alternatively, a two-component resin may be employed, with one component applied in an appropriate pattern to top surface 6 of carrier substrate 2 and the other to a surface of frame 48 to be placed in contact with top surface 6 to prevent premature component reaction and adhesion.

[0031] After formation or attachment of the layer of barrier material 12 on top surface 6 , an image sensor chip 52 is mounted within each of the chip cavities 28 on chip adherence surface 9 . Image sensor chips 52 are secured to chip adherence surface 9 with a layer of adhesive material 54 , as shown in FIG. 8 . As with adhesive material 50 , the layer of adhesive material 54 may be an epoxy, a silicone, an acrylic or other liquid-type adhesive, a two-component resin, or a double-sided adhesive-coated tape segment or film. If required or desired, adhesive material 54 may comprise a conductive adhesive or bonding agent to ground or electrically bias the back side of image sensor chips 52 , in which instance a conductive or conductor-filled epoxy, a silver solder or a Z-axis anisotropic conductive adhesive may be employed. If a preformed frame 48 is used for layer of barrier material 12 and raised walls 26 , adhesive material 50 and the layer of adhesive material 54 may be applied to top surface 6 of carrier substrate 2 at the same time, in a single step, before preformed frame 48 is aligned with carrier substrate 2 and placed on top surface 6 . Once image sensor chips 52 are in place, bond pads 56 on the active surface 58 of each image sensor chip 52 are connected to wire bonding locations 10 on top surface 6 with gold or aluminum wire bonds 60 , as known in the art. It is contemplated that, if a preformed frame 48 is used for layer of barrier material 12 , image sensor chips 52 may be placed, wire bonds 60 formed, and then preformed frame 48 carrying adhesive on the surface thereof facing top surface 6 of carrier substrate 2 aligned and adhered to top surface 6 to provide enhanced clearance for a wire bonding capillary.

[0032] The resulting assembly is now ready to receive a unitary transparent cover 62 . Unitary transparent cover 62 is configured to substantially conform to the configuration of carrier substrate 2 , so that it covers the entire array of chip cavities 28 and extends over the peripherally outer portions of the contiguous matrix of raised walls 26 . Stated another way, unitary transparent cover 62 is dimensioned substantially the same as carrier substrate 2 , such term including both slightly smaller and slightly larger dimensions. In FIG. 9 , unitary transparent cover 62 is aligned with carrier substrate 2 , placed on the top of the layer of barrier material 12 and continuously sealed in place along the tops of the matrix of raised walls 26 . Unitary transparent cover 62 may be formed of an at least partially optically transparent material such as borosilicate glass (BSG). Of course, other types of glass, quartz or even plastic which allow the passage of a desired range of wavelengths of light or other forms of electromagnetic radiation may also be used. Furthermore, unitary transparent cover 62 may be formed to provide an optical function, for example, shaping its surface at locations corresponding to chip cavities 28 to act as focusing microlenses, as shown in broken lines 65 .

[0033] To secure unitary transparent cover 62 in place along the tops of raised walls 26 and hermetically seal the image sensor chips 52 within each respective chip cavity 28 , a bead of epoxy, silicone gel or other liquid or gel adhesive 64 may be applied to the tops of raised walls 26 of the layer of barrier material 12 , directly to unitary transparent cover 62 along selected lines, or both, prior to attachment. If desired, a two-component adhesive resin may be employed, with one component applied to the tops of raised walls 26 and the other to unitary transparent cover 62 so that a cure will not commence until the two components are in contact. Other sealing mechanisms, such as the previously described double-sided adhesive-coated tape, may be used as well, as long as they provide a suitable hermetic bond. It is desirable, so that the optical capabilities of image chip sensors 52 are not compromised, that any adhesive used be of a type which does not outgas volatiles or other compounds when curing, so as not to compromise the properties of the image sensor chips 52 . A snap-cure epoxy, as known in the art, may be suitable, as may an epoxy cured to a B-stage, or tacky state, prior to application of unitary transparent cover 62 . In some instances, the layer of barrier material 12 may be of a composition such that a thermal- or pressure-initiated bonding process may be used to adhere unitary transparent cover 62 directly to layer of barrier material 12 without the aid of an additional adhesive. As seen in FIG. 9, a vertical gap 63 exists between active surfaces 58 of image sensor chips 52 and unitary transparent cover 62 . For high-end image sensor chips 52 , it is often a requirement that active surface 58 be free of contact from any covering material to prevent interference with sensing circuitry and unwanted refraction of light. Accordingly, when one of these high-end image sensor chips is packaged using the present invention, gap 63 will be left free of any filler material. Gap 63 also maintains unitary transparent cover 62 above the tops of wire bonds 60 . If an image sensor chip 52 not having the requirement of a material-free gap is used, a transparent encapsulant material 67 may be used to fill chip cavities 28 . Such transparent encapsulant material 67 , which is indicated by a broken lead line extending into chip cavity 28 in FIG. 9 , may also be used to provide a transitional index of refraction between the image sensor and the index of refraction of the unitary transparent cover 62 , if desired. This approach would also secure and protect wire bonds 60 , and the transparent encapsulant material 67 may also be used as the adhesive mechanism for securing unitary transparent cover 62 . Example materials for transparent encapsulant material 67 may include clear epoxy, silicone, acrylic or other suitably transparent resin type materials.

[0034] In order to promote proper alignment of unitary transparent cover 62 , a raised lip 66 may be formed around the perimeter of the layer of barrier material 12 , as shown in FIG. 9 . Raised lip 66 may be formed integrally with, and at the same time as, forming the layer of barrier material 12 by any previously described technique. Unitary transparent cover 62 may then be aligned with the layer of barrier material 12 by placement within raised lip 66 .

[0035] Once unitary transparent cover 62 is sealed in place, the assembly essentially comprises an image sensor package array 68 . Image sensor package array 68 may now be cut or otherwise singulated to separate out individual image sensor packages. FIGS. 10 and 11 illustrate this process. FIG. 10 is a perspective view of image sensor package array 68 , having the location of section lines 100 indicated above the top surface thereof. Carrier substrate 2 , the layer of barrier material 12 and unitary transparent cover 62 are simultaneously cut along section lines 100 which run along the centers of raised walls 26 and divide image sensor package array 68 into individual image sensor packages 70 , as shown in FIG. 11 . This may be accomplished, for example, by cutting or scribing (followed by snapping image sensor packages 70 apart along the scribe lines) with a conventional wafer saw. Alternatively, the individual image sensor packages 70 may be singulated using a laser or other high energy beam.

[0036] For attachment of an image sensor package 70 to a higher-level packaging component such as an assembly substrate for communication with other components of an electronic device, metallized pads or other contact interfaces for electrical communication of image sensor chip 52 through conductive traces 8 are required. In one exemplary embodiment of the present invention shown in FIG. 12, a plurality of castellated solder pads 72 in respective communication with different traces 8 may be formed by techniques known in the art around the perimeter of a singulated image sensor package 70 to form a leadless chip-carrier (LCC) image sensor package. In another exemplary embodiment shown in FIG. 13 , discrete conductive elements 74 such as tin/lead solder balls, gold bumps or conductive or conductor-filled epoxy bumps, columns or pillars may be formed on or attached to the lower ends of vias 76 extending from conductive traces 8 in an array pattern on the bottom of singulated image sensor package 70 to form a ball-grid array (BGA)-type image sensor package, as illustrated by FIG. 13 . A redistribution layer (RDL) of conductive traces 78 may also be applied to or formed on the bottom surface 80 of carrier substrate 2 in communication with the lower ends of selected vias 76 to configure a suitable pad array for formation or disposition of discrete conductive elements 74 thereon. It is also contemplated, and currently preferred with a BGA-type arrangement, that discrete conductive elements 74 be attached to image sensor package array 68 prior to its singulation into individual image sensor packages 70 . This would be advantageous as discrete conductive elements 74 may thus be formed on or applied to all of the image sensor packages 70 of a given image sensor package array in a single step.

[0037] All of the above-illustrated embodiments and variations thereof of the present invention provide image sensor packages that are simultaneously fabricated to minimize assembly steps and reduce the cost associated with each individual package. Although the present invention has been depicted and described with respect to the illustrated embodiments, various additions, deletions and modifications are contemplated within its scope. For instance, if so desired, it is also contemplated that the layer of barrier material 12 may initially be formed on, or secured to, unitary transparent cover 62 rather than carrier substrate 2 . Barrier material would be similarly formed on unitary transparent cover 62 using one of the above described molding, deposited layering, or preform attach methods described above. The combination of unitary transparent cover 62 and barrier material 12 would then be secured to the top surface 6 of carrier substrate 2 after attachment and electrical connection of image sensor chips 52 to image sensor chip attachment areas 4 . In the same manner, securing and hermetic sealing of barrier material 12 to carrier substrate 2 may be accomplished with a bead of epoxy, silicone or other liquid or gel adhesive, double-sided adhesive-coated tape or thermal or pressure initiated bonding.

[0038] Furthermore, as previously discussed, the present invention would be suitable for packaging various other types of optically interactive electronic devices. The scope of the invention is, therefore, indicated by the appended claims rather than the foregoing description. Further, all changes which may fall within the meaning and range of equivalency of the claims and elements and features thereof are to be embraced within their scope.