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  Large area flat image sensor assemblyUSPTO Application #: 20080012082Title: Large area flat image sensor assembly Abstract: A low temperature method for producing a substantially flat large area image sensor assembly, the method includes the steps of providing a die attach substrate having a substantially planar surface; providing a lead frame having a bonding surface and a plurality of leads extending there from; adhering an imager die to the substantially planar surface of the die attach substrate with a low curing temperature first adhesive; and adhering the die attach substrate with adhered imager die to a bonding surface of the lead frame with a low curing temperature second adhesive for producing an image sensor assembly. (end of abstract) Agent: F-p, Patent Legal Staff Eastman Kodak Company - Rochester, NY, US Inventors: Jaime I. Waldman, Mario J. Ciminelli, Michael A. Marcus USPTO Applicaton #: 20080012082 - Class: 257431000 (USPTO) Related Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Responsive To Non-electrical Signal (e.g., Chemical, Stress, Light, Or Magnetic Field Sensors), Electromagnetic Or Particle Radiation, Light The Patent Description & Claims data below is from USPTO Patent Application 20080012082. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This is a divisional of U.S. Ser. No. 10022,529. which is a continuation-in-part of application Ser. No. 09/957,188, filed Sept. 20, 2001 entitled "A Method For Producing An Image Sensor Assembly" by Jaime I. Waldman et al, FIELD OF THE INVENTION [0002] The invention relates generally to the field of large image sensors and, more particularly, to such large image sensors that are assembled in a cavity package and are substantially flat over the entire active imager surface providing improved image capture capability. BACKGROUND OF THE INVENTION [0003] Large area imagers, CCDs and CMOS, are required to be flat to capture a quality image. For many applications, it is required that large area imagers be manufactured to form a substantially flat (with a deviation from flatness of less than 15 microns) active imaging surface over the entire active imaging area. A large area image sensor assembly is defined as a packaged imager having an active sensor area of 20 mm by 20 mm or larger. Currently, these CCD or CMOS imagers are composed of an imager die mounted on either a substrate or mounted in an electronic package. When an imager die is mounted on a substrate, there are several deficiencies that result. The die and bond wires are not protected from damage or debris. Additional potting of the wires or additional structural elements must be added to protect the die and wires. Without these additions, the imager remains unprotected. When currently available electronic cavity packages are used, the wires and imager are protected but the flatness of the imager is not sufficient to meet the needs of many applications including medical imaging sensors and large format digital cameras. Current electronic packages use high temperature methods to join the package components. These high temperatures approximately 400.degree. C. and higher are used to either melt glass, braze or co-fire a ceramic package as methods to join components together. These high temperatures and fastening techniques cause the critical die attach area to which the imager is attached to the electronic package to warp. The die attach area needs to be flat to create a flat imager. Since these are cavity packages, they impede post grinding of the die attach area to repair the warping or bowing of the imager plane created during the high temperature fabrication processes. [0004] Other methods of packaging an image sensor include mounting an imager into an injection molded thermoplastic resin package as disclosed by H. Yamanaka in U.S. Pat. No. 5,529,959. The assembly process includes injection molding of a base with an incorporated lead frame. This patent discloses that small imagers can be made flat by this process without quantifying a definition of flatness. Although injection molding is highly successful for the manufacturing of small imager packages, it is extremely difficult to achieve a base flatness of 10 .mu.m or less in larger areas in excess of 25 mm by 25 mm or larger. U.S. Pat. No. 5,382,310 by Ozimek et al. describe a method to make small conventional solid state image sensors by directly bonding an imager die to a conductive lead frame. The imager bonding pads are then wire bonded to the lead frame. The lead frame and imager are then encapsulated top and bottom with adhesive to provide structural strength. This approach is not amenable to making large area flat imagers. U.S. Pat. No. 6,121,675 by Fukamura et al. describes a method which utilizes silicone to cover the die and wirebonds thus preventing moisture and dirt egress. The flexible material prevents the wire bonds from breaking. [0005] Although the currently known and utilized methods for producing an image sensor assembly are satisfactory for many applications, they include drawbacks. The imagers produced by conventional packaging methods do not have sufficient flatness after the brazing or glass melting process to meet the requirements for large size medical imaging sensors and large format digital cameras. In addition, the flat substrates are not enclosed which obviously limits their ability to mount optical coverglass or protect the sensor and wire bonds. SUMMARY OF THE INVENTION [0006] The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, the invention embodies a low temperature process and method for producing a substantially flat image sensor assembly, the method comprising the steps of (a) providing a die attach substrate having a substantially planar surface; (b) providing a lead frame having a plurality of leads extending therefrom and a shelf on which a cover glass may be attached; (c) attaching an imager for collecting incident light to the substantially planar surface with a low temperature first adhesive substance; and (d) attaching the imager to a portion of the lead frame with a low curing temperature second adhesive substance for producing an image sensor assembly with a flat cavity package. [0007] These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. Advantageous Effect of the Invention [0008] The present invention has the following advantage of providing a substantially flat image sensor in a substantially flat cavity package while including a shelf on which a cover glass may be attached. The assembly provides a method to protect the bond wires, mount the cover glass and prevent contamination egress onto the sensor without additional structural components. BRIEF DESCRIPTION OF THE DRAWINGS [0009] FIG. 1 is a view in vertical cross section of the image assembly of the present invention; [0010] FIG. 2 is a view in vertical cross section of an alternative embodiment of FIG. 1; [0011] FIG. 3 is a view in vertical cross section of another alternative embodiment of FIG. 1; [0012] FIG. 4 is a top view of the first adhesive layer pattern; [0013] FIG. 5A is a view in vertical cross section of an imager die to substrate alignment fixture without the die and substrate; [0014] FIG. 5b is a view in vertical cross section of an imager die to substrate alignment fixture with the die and substrate mounted in place; and [0015] FIG. 6 is a leveled surface map of an imager mounted in a package using the inventive method and apparatus of this invention. DETAILED DESCRIPTION OF THE INVENTION [0016] Referring to FIG. 1, the present invention will be described showing only the right most portions of an image sensor assembly 10, and it is to be understood that an exact duplicate portion or mirror image of this portion is on the left portion. In other words, only a portion of the entire image sensor assembly 10 is shown for clarity of understanding. Furthermore, in the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "top," "bottom," "left," "right," "upwardly," "downwardly," and the like are words of convenience and are not to be constructed as limiting terms. [0017] The image sensor assembly 10 includes a lead frame 20, usually rectangular in shape, having a plurality of leads 30 (only one is shown) along its edge which can be electrically insulated from each other, and which extend from and are attached to a rectangular shaped lead frame portion 40, and in combination with the frame portion on the opposite side (not shown), forms a hollowed-out portion into which a suitable imager die 60 and suitable die attach substrate 50 is to be inserted. The lead frame portion 40 is a multi-tiered portion extending substantially perpendicular to the leads 30. The lead frame portion 40 of lead frame 20 is shown to have three tiers (or layers), although it is to be understood that more or less tiers could be used and each of these tiers may be made up of more than one layer. The top tier 40a or shelf provides a shelf for affixing a cover glass 45 to enclose the imager assembly. The middle tier 40b is slightly longer then the top tier 40a and it contains metallization such as lead traces 47 used to provide a means of electrically connecting the imager die 60 to the leads 30. Bond pads 46 are contiguous with the lead traces 47 and provide a surface to attach wire bonds 80 to the imager die 60. The bottom portion 40c is used to provide mechanical features for precisely locating the substrate 50 and imager die 60 within the lead frame 20. Continue reading... Full patent description for Large area flat image sensor assembly Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Large area flat image sensor assembly patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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