Imager die package and methods of packaging an imager die on a temporary carrier

Methods for fabricating an imager die package and resulting die packages are disclosed. An imager die packaging process may include dicing through a fabrication substrate comprising a plurality of imager die. Thereafter, known good die (KGD) qualified from the imager die are repopulated, face down on a high temperature-compatible temporary carrier, the KGD on the temporary carrier are encapsulated and thereafter removed as a reconstructed wafer from the temporary carrier. Furthermore, a first plurality of discrete conductive elements on a back side of the reconstructed wafer may be partially exposed and, optionally, a second plurality of discrete conductive elements may be applied to the first plurality of discrete conductive elements. The encapsulated KGD are then singulated.

FIELD OF INVENTION

Embodiments of the present invention relate generally to packaging of optically interactive microelectronic devices. More specifically, embodiments of the present invention relate to an imager die package sealed within an encapsulant and to methods of packaging an imager die.

BACKGROUND

Microelectronic imagers are well known to those having skill in the electronics/photonics art, as they are used in digital cameras, wireless devices with picture capabilities, and many other applications. Cellular telephones and Personal Digital Assistants (PDAs), for example, are incorporating microelectronic imagers for capturing and sending pictures. The growth rate of microelectronic imagers has been steadily increasing as they become smaller and produce better images with higher pixel counts.

Microelectronic imagers include image sensors that use Charged Coupled Device (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS) systems, or other solid state systems. CCD image sensors have been widely used in digital cameras and other applications. CMOS image sensors are quickly becoming very popular because they have low production costs, high yields, and small sizes, CMOS image sensors, as well as CCD image sensors, are accordingly “packaged” to protect the delicate components and to provide external electrical contacts. Optically interactive microelectronic devices require packaging that provides protection from other environmental conditions while allowing light or other forms of radiation to pass through to a surface where sensing circuitry is located. One problem with conventional packaging techniques of microelectronic devices is that the final packages produced allow for the exposure of the image sensor to amounts of unwanted peripheral light.

Furthermore, the materials and structures involved in conventional semiconductor packaging techniques require fabrication processes that can be time consuming and require several precision assembly steps. Each assembly step increases the opportunity for contamination or damage to the imaging device itself, raising defect levels and slowing production time to avoid such damage and contamination. Additionally, if the package design or fabrication approach necessitates that all of the imager die located on a wafer be packaged regardless of whether a significant number of die are defective, a substantial waste of material results. Due to the extremely cost-competitive nature of the semiconductor industry, improvements in product yield and production time are of value, especially when considered in terms of the high volume of components being manufactured.

There is a need for methods to both improve the quality, and decrease the cost, of an imaging device. Specifically, there is a need for providing a method that enables low-cost, high volume encapsulated packaging of imager die while providing a high quality imaging device.

DETAILED DESCRIPTION

Embodiments of the invention include methods for packaging imager die and imager die packages. An imager die packaging method may utilize a temporary carrier during an encapsulation process. In a specific embodiment, the carrier may include a high temperature compatible film frame tape and an ultraviolet-releasable adhesive.

An embodiment of the invention includes a method of packaging an imager die. The method includes cutting through a thickness of a fabrication substrate between adjacent imager die carried by the fabrication substrate to form a plurality of individual imager die. The method further includes securing a plurality of known good die characterized from the plurality of individual imager die to a temporary carrier and at least partially encapsulating the plurality of known good die on the temporary carrier to reconstruct a wafer. The method also includes singulating the at least partially encapsulated plurality of known good die from the wafer. In a particular embodiment, a temporary carrier includes an ultraviolet-sensitive adhesive on a surface of a film formed from a material configured to withstand relatively high process temperatures. (e.g., temperatures of about 90° C. or greater).

Another embodiment of the invention includes an imager die package comprising a fabrication substrate having an active surface and a back side with an imager die having an image sensor formed on the active surface. The package further includes at least one conductive interconnect extending from the active surface to the back side of the fabrication substrate. Furthermore, the package may comprise an encapsulant formed at least partially around the fabrication substrate including the imager die.

According to yet another embodiment, the invention includes an electronic system comprising a processor-based device operably coupled to an imager die package according to an embodiment of the invention.

Another embodiment of the invention includes a known good die wafer comprising a plurality of known good imager die. Each known good die is fabricated on an active surface of one fabrication substrate of a plurality and a back side of each fabrication substrate includes circuit traces thereon. The known good die wafer further includes a first plurality of discrete conductive elements respectively formed on the circuit traces and an encapsulant at least partially formed around each known good imager die of the plurality.

Referring in general to the accompanying drawings, various aspects of the present invention are illustrated to show the structure and methods of packaging an imager die. Common elements of the illustrated embodiments are designated with like numerals. It should be understood that the figures presented are not meant to be illustrative of actual views of any particular portion of the actual device structure, but are merely schematic representations that are employed to more clearly and fully depict the invention. It should be further understood that while depicted and described in the context of an image sensor, the package embodiments and methods presented herein would work well for enclosing other types of optically interactive devices, such as, but not limited to, CCD and CMOS image sensors, electrically erasable programmable read-only memory (EPROM), and photodiodes, as well as light-emitting devices including semiconductor lasers and light-emitting diodes.

The fabrication of an imager die package according to an embodiment of the present invention is illustrated byFIGS. 1 through 8. Referring toFIG. 1, a semiconductor wafer110is illustrated at a preliminary processing stage. The wafer construction is subdivided into a plurality of die regions218, which are separated from one another, and bounded, by streets142. Each of the die regions218is, conventionally, processed identically to form a plurality of identical die. Each die region218includes an active surface111having an image sensitive area112, which comprises sensing circuitry reactive to light or other forms of radiation.

FIG. 2illustrates a cross-sectional view of a through wafer interconnect (TWI) wafer216taken along line2ofFIG. 1. The term “through wafer interconnect” may be used herein to describe a substrate having vias extending therethrough and lined or filled with conductive material for forming interconnects for connecting circuitry on one side of a portion of the substrate to circuitry on the other side thereof, or to external circuitry. TWI wafer216includes a first surface210and a second surface212. TWI wafer216may comprise a fabrication substrate232having a plurality of die regions218formed on an active surface thereof, and each die region218may comprise imager die226. Imager die226may each comprise an image sensor225, such as, but not limited to, a CMOS imager. By way of example only, fabrication substrate232may comprise a full or partial wafer of semiconductive material (e.g., silicon, gallium arsenide, indium phosphide, etc.), a silicon-on-insulator (SOI) type substrate (e.g., silicon-on-ceramic (SOC), silicon-on-glass (SOG), silicon-on-sapphire (SOS), etc.), or any other bulk or large-scale substrate upon which a plurality of semiconductor device components may be fabricated.

TWI wafer216may include a plurality of standoffs242secured to fabrication substrate232and comprising of, for example, a photopolymerized material. Standoffs242may be configured to provide spacing between imager die226and a subsequently attached layer, such as a cover glass or a lens. TWI wafer216may also comprise at least one conductive interconnect236located between adjacent die and extending from the active surface234to a back side235of fabrication substrate232and in contact with a redistribution layer (RDL). RDL may be in the form of conductive traces238formed at the second surface212of TWI wafer216. In addition, TWI wafer216may comprise a first plurality of discrete conductive elements240conventionally formed or disposed on and respectively in contact with conductive traces238. For example only, and not by way of limitation, first plurality of discrete conductive elements240may comprise solder balls, or bumps, studs, pillars or columns formed or covered with a conductive material, or formed of a conductor-filled material. The above description represents only one example of a TWI wafer and any other configurations known in the art are within the scope of the present invention.

FIG. 3(a) illustrates an embodiment of a TWI wafer216with a glass layer310or sheet of another suitable transparent material attached. Glass layer310may be of a size sufficient to cover the array of imager die active surfaces111(seeFIG. 1)and is attached to and peripherally supported about each die region218by the plurality of standoffs242. Glass layer310may be formed of an at least partially optically transparent material such as borosilicate glass (BSG). Other types of glass that allow the passage of a desired range of wavelengths of light or other forms of electromagnetic radiation may also be used. Glass layer310may comprise cuts312in the form of notches that may be formed before or after glass layer310is attached to TWI wafer216. As described in more detail below, cuts312are configured to minimize the peripheral light received by image sensor225and, therefore, increase the quality of image sensor225. Cuts312may be formed by a scoring blade (not shown) wherein the groove depth of cuts312may depend on the size of the scoring blade and the depth of penetration of the scoring blade into glass layer310. Additionally, the angle at which cuts312are formed in glass layer310may depend, in part, on the shape of the scoring blade. The shape of cuts312is not limited to a cut having angled or beveled edges, as depicted but, rather, cuts312may have a generally square or rectangular shape, as illustrated inFIG. 3(b). In the event the cuts312are formed after glass layer310has been attached to wafer110, standoffs242may be configured to withstand some compressive force as applied by the scoring blade.

In other embodiments, instead of a glass layer310, a substrate310′ formed from glass or another suitable transparent material that carries a plurality of lenses311′ or other optical elements may be positioned over TWI wafer216, as shown inFIG. 3(c). Each lens311′ is aligned over an image sensor225of a die region218. In embodiments where lenses311′ protrude from an outer surface of glass substrate310′, additional standoffs242′ may be formed or positioned around each lens311′ to facilitate further processing in accordance with teachings of the present invention (e.g., prevent encapsulant from contacting each lens311′.

Subsequent to attaching glass layer310(or lens311′, bearing glass substrate310′) to the plurality of standoffs242, glass layer310, standoffs242, and fabrication substrate232may be cut by way of a dicing operation carried out to form a plurality of individualized imager die regions218(SeeFIG. 4). Cutting of glass layer310may be accomplished, in some embodiments, using a resinoid blade saw. Cutting of fabrication substrate232may be accomplished, in a more specific embodiment, using a diamond plated nickel saw. In another embodiment of the present invention, fabrication substrate232, standoffs242and glass layer310may be cut by a “stealth” dicing process wherein the fabrication substrate232, standoffs242and glass layer310are weakened at an internal region by one or more lasers and thereafter the glass layer310, standoffs242and fabrication substrate232are stretched and broken at the weakened internal region. The stealth dicing process is developed by Hamamatsu Photonics K.K., Shizuoka, Japan. An alternative dicing process may be effected using a water-jet-guided laser available from Synova S. A., Lausanne, Switzerland. In other embodiments, the imager singulation process may be achieved by a jet singulation system wherein a jet stream of an abrasive slurry is used to singulate component parts. The jet singulation system may be made by Towa Intercon Technology, Inc., of Morgan Hill, Calif. Prior to or after the dicing operation is completed, individual imager die may be tested to ascertain which of the imager die are operational and meet qualitative performance standards and are thus deemed “good,” and which are defective. The imager die that are good can be considered to be “known good die” (KGD). Upon determining the KGD, the KGD may be placed on a temporary carrier410(SeeFIG. 5).

FIG. 5illustrates KGD510populated on a temporary carrier410. According to some embodiments, temporary carrier410comprises a film frame tape or a glass carrier. Temporary carrier410may comprise a high temperature compatible polyethylene terephthalate (PET) material that may withstand relatively high process temperatures (i.e., temperatures above about 90° C.). In addition, temporary carrier410may comprise a pressure sensitive adhesive. Furthermore, temporary carrier410may comprise an ultraviolet-sensitive adhesive, which loses adhesive strength when irradiated with a select wavelength of light, normally UV light. Use of an ultraviolet-type tape may be desirable since, when irradiated, it loses its adherent properties and thus reduces stress on the dice during a subsequent pick-and-place operation. Ultraviolet sensitive tapes are commercially available from Furukawa Electric Company, Ltd. of Japan.

As shown, KGD510are placed facedown on temporary carrier410, and, therefore,FIG. 5is shown inverted relative toFIGS. 2 through 4. KGD510may be positioned on temporary carrier410to provide for a desired gap width450and, thereafter, KGD510may be encapsulated with an encapsulant512to form wafer610. Encapsulant512may comprise any conventional compound known for use in encapsulating semiconductor chips that exhibits low moisture uptake and good dimensional stability. Encapsulant512may also be selected to have a coefficient of thermal expansion (CTE) that is compatible with those of substrate232and KGD510. For example only, and not by way of limitation, encapsulation of KGD510may be effected by a molding process or a dam and fill process. Molding processes known in the art may include injection molding, transfer molding, and compression molding. Injection molding is a process wherein an encapsulant is injected at high pressure into a mold cavity containing the device to be encapsulated. A compression molding process may include placing an encapsulant into a mold cavity containing the device to be encapsulated and thereafter applying pressure and heat. Transfer molding differs from compression molding in that instead of applying pressure to the pre-placed compound, the encapsulant material is preheated and then transferred into a molding cavity under pressure, containing the device to be encapsulated. Dam and fill is a two-step process wherein a dam is dispensed around a device within a cavity and, thereafter, the cavity may be filled with an encapsulant to encapsulate the device. Examples of encapsulant512contemplated for use in the present invention include, but are not limited to, thermoset and thermoplastic curable compounds such as silicon-filled polymers or liquid crystal polymers.

In embodiments where molding processes are used, a surface of a mold cavity may be configured to receive portions of discrete conductive elements240, which protrude from each KGD510to prevent encapsulant from completely covering the discrete conductive elements240. In one such embodiment, shown inFIG. 5(a), discrete conductive elements240may be partially received by a compressible, conformable element522(e.g., a polytetrafluoroethylene film, such as the material sold under the trademark TEFLON® by E.I. duPont Nemours & Co. of Wilmington, Del.) that lines at least a portion of a surface of a mold cavity550. Upon being confined within mold cavity550, portions of discrete conductive elements240, which protrude from each KGD510within mold cavity550, are received by compressible, conformable element552, shielding the received portions of discrete conductive elements240from encapsulant512as encapsulant512is introduced into mold cavity550. Therefore, upon completion of the mold process and removal of the resulting wafer610from mold cavity550, portions of discrete conductive elements240may protrude from an outer surface of encapsulant512. The distance that discrete conductive elements240protrude from the outer surface of the encapsulant may be defined by a depth that discrete conductive elements240are received and, thus, in embodiments where a compressible, conformable element552is used, by a thickness of compressible, conformable element552.

In embodiments where a mold cavity is not configured to receive discrete conductive elements240, as well as in embodiments where dam and fill or other encapsulation processes are used, it may be necessary to expose conductive elements240through encapsulant512. In such embodiments, wafer610may be subjected to appropriate processing to form a substantially planarized surface612extending across the first plurality of discrete conductive elements240and encapsulant512. The processing may further provide for the at least partial exposure of the first plurality of discrete conductive elements240. The formation of the substantially planarized surface612can be accomplished with any suitable method, and may be accomplished by backgrinding or another mechanical planarization process such as chemical mechanical planarization (CMP). Appropriate control of the planarization process may be required to prevent the smearing of any conductive material of the first plurality of discrete conductive elements240, which may result in shorting of one conductive element240to an adjacent one. After planarizing surface612, a second plurality of discrete conductive elements620(e.g., solder balls, pins, pillars, columns, etc.) may be formed or disposed on, and bonded to, the first plurality of discrete conductive elements240. The second plurality of discrete conductive elements620may provide for subsequent attachment to a carrier substrate or other higher-level circuit assembly, as shown inFIG. 6.

FIG. 6also depicts removal of wafer610from temporary carrier410. Cleaning of adhesive from wafer610may be required after separation of wafer610from temporary carrier410. Cleaning methods known in the art, such as, a plasma cleaning technique, may be effected.

As illustrated inFIG. 7, wafer610may then be placed on a dicing tape710and singulated by performing a dicing operation through encapsulant512and, therefore, resulting in a final packaged die810/810′, as shown inFIGS. 8(a) and8(b). Final packaged die810/810′ provide for, as a result of cuts312(seeFIGS. 3(a) and3(b)), regions822that extend laterally over non-imaging regions on the active surface of the final packaged die810/810′. These laterally extending regions822of encapsulant, or packaging material, prevent at least some unwanted, or stray, light from reaching the image sensor225and are, therefore, also referred to herein as “lateral light blocking elements.” Consequently, the accuracy of an image detected by image sensor225may be enhanced in embodiments of final packaged die810/810′ with laterally extending regions822.

Imager die packages, according to another embodiment of the present invention, may be formed in a manner similar to that described above, except the imager die are not covered with a glass layer. Instead, “known good lenses” (KGL) are identified or qualified, and are subsequently placed over known good imager die. KGD, comprising known good imagers with KGL assembled therewith may then be placed on a temporary carrier, with standoffs that completely circumscribe the periphery of each image sensor225contacting the temporary carrier. These assemblies may then be encapsulated by molding or dam and fill processes and, thereafter, singulated to form final die packages.

One variant of the second embodiment is shown inFIGS. 9 through 14.FIG. 9illustrates a plurality of lenses900A-E formed from a glass substrate904. Lenses900A-E may be individually qualified by methods known in the art to ascertain known good lenses. After testing, a dicing operation may be performed along dicing lines902resulting in a plurality of individual lenses. As shown inFIG. 10, a plurality of known good lenses900′ may thereafter be individually placed over a plurality of known good imager die910located on a TWI wafer960. As described above in reference toFIGS. 1 through 8and TWI wafer216, TWI wafer960, as illustrated inFIGS. 10 through 14may comprise a fabrication substrate908and at least one conductive interconnect236′ located between adjacent image die910and extending from active surface912to a hack side913of fabrication substrate908and in contact with an RDL. The RDL may be in the form of conductive traces238′ formed on the second surface212′ of TWI wafer960. TWI wafer960may also comprise a first plurality of discrete conductive elements240′ formed on and in contact with conductive traces238′.

The plurality of known good lenses900′ may be respectively peripherally supported on and attached to a plurality of standoffs242located on the active surface912of fabrication substrate908, wherein at least one known good lens900′ may be placed over one known good imager die910. Standoffs242/242′ may be configured to provide support for attached known good lenses900′ and to provide a selected vertical spacing between stacked known good lenses900′/900″ or between known good lenses900′ and TWI wafer960. Standoffs242′ may also be configured to seal against a temporary carrier410and to prevent encapsulant from contacting known good lenses900′/900″ Implementing the configuration described inFIGS. 9 and 10may improve the yield of an imager die package by ensuring bad lenses are not placed over good imagers and, therefore, decrease the amount of wasted material and component parts. Furthermore, this configuration may ensure that good lenses are not placed over bad imagers.

After placing known good lenses900′/900″ over known good imager die910, the imager die910with the known good lenses900′/900″ attached thereto may be singulated by a dicing operation resulting in a plurality of KGD510′. As described above, and illustrated inFIG. 11, KGD510′ may include at least one additional known good lens900″ and corresponding standoffs242″ (shown by dashed lines) stacked over known good lens900′ in order to achieve a desired focus onto imager die910.

Referring toFIG. 12, KGD510′ may be placed face-down on a temporary carrier410′, such as a film frame tape or glass carrier, with standoffs242′ positioned against and secured to temporary carrier410′ to prevent encapsulant from contacting known good lenses900′/900″. As the KGD510′ are placed face down on temporary carrier410′, KGD510′ are shown inverted relative toFIGS. 10 and 11. Once attached to temporary carrier410′, KGD510′ may be encapsulated with encapsulant512′, thus resulting in reconstructed wafer930, as illustrated inFIG. 13. As described above, encapsulant512′ may comprise any conventional compound known for use in encapsulating semiconductors. Encapsulation processes may include a molding or dam and fill process as known in the art.

Thereafter, reconstructed wafer930may be subjected to appropriate processing to form a substantially planarized surface950extending across first set of discrete conductive elements240′ and encapsulant512′. The processing may further provide for the at least partial exposure of the first plurality of discrete conductive elements240′. After planarizing surface950, a second plurality of discrete conductive elements620′, such as balls, bumps, columns, or pins of conductive material (e.g., solder, another metal, a conductor-filled polymer, etc.), may be bonded to the first plurality of discrete conductive elements240′. The second plurality of discrete conductive elements620′ provides for subsequent attachment to a carrier substrate or other higher-level circuit assembly. As shown inFIG. 14, one discrete element of the second plurality may be operably coupled to one discrete element of the first plurality. As described above, in an embodiment of the invention using a compression molding encapsulation process, at least a portion of the first plurality of discrete conductive elements240′ may remain exposed during a compression molding process and, therefore, neither a planarizing process nor a second plurality of discrete conductive elements may be required.

Subsequent to encapsulation, temporary carrier410′ may be removed and a dicing operation through encapsulation material512′ may be performed, resulting in a final packaged die810″ as shown inFIG. 14.

A processor based system1060that includes an imager die package810/810′/810″ in accordance with an embodiment of the present invention is illustrated inFIG. 15. Without being limiting, such a system1060may include a computer system, camera system, scanner, machine vision system, vehicle navigation system, video phone, surveillance system, auto focus system, star tracker system, motion detection system, image stabilization system, each of which may be configured to utilize an embodiment of the present invention.

A processor based system1060, such as a computer system, for example, generally comprises a central processing unit (CPU)962, for example, a microprocessor, which may communicate with and input/output (I/O) device964over a bus966. The imager die package810/810′/810″ may also communicate with the system1060over bus966. The system1060also includes random access memory (RAM)968, and, in the case of a computer system, may include peripheral devices such as a floppy disk drive970and a compact disk (CD) ROM drive972, which also communicate with CPU962over bus966. CPU962, imager die package810/810′/810″ and memory968may be integrated on a single IC chip.

Specific embodiments have been shown by way of example in the drawings and have been described in detail herein; however, the invention may be susceptible to various modifications and alternative forms. It should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.