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  Magnetic shield for integrated circuit packagingUSPTO Application #: 20060019422Title: Magnetic shield for integrated circuit packaging Abstract: Structures and methods for providing magnetic shielding for integrated circuits are disclosed. The shielding comprises a foil or sheet of magnetically permeable material applied to an outer surface of a molded (e.g., epoxy) integrated circuit package. The foil can be held in place by adhesive or by mechanical means. The thickness of the shielding can be tailored to a customer's specific needs, and can be applied after all high temperature processing, such that a degaussed shield can be provided despite use of strong magnetic fields during high temperature processing, which fields are employed to maintain pinned magnetic layers within the integrated circuit. (end of abstract)
Agent: Knobbe Martens Olson & Bear LLP - Irvine, CA, US Inventors: Mark E. Tuttle, James G. Deak USPTO Applicaton #: 20060019422 - Class: 438055000 (USPTO) Related Patent Categories: Semiconductor Device Manufacturing: Process, Making Device Or Circuit Responsive To Nonelectrical Signal, Thermally Responsive, Packaging (e.g., With Mounting, Encapsulating, Etc.) Or Treatment Of Packaged Semiconductor The Patent Description & Claims data below is from USPTO Patent Application 20060019422. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATION [0001] This application is a continuation application of U.S. application Ser. No. 10/719,419, filed Nov. 21, 2003, which is a divisional application of U.S. application Ser. No. 10/050,339, entitled "MAGNETIC SHIELD FOR INTEGRATED CIRCUIT PACKAGING," filed Jan. 15, 2002, now U.S. Pat. No. 6,906,396, the disclosures of which are hereby incorporated by reference in their entirety. FIELD OF THE INVENTION [0002] The present invention relates to magnetic shielding for integrated circuits and, more particularly, to magnetic shielding for integrated circuits having magnetic materials used therein for which protection from stray external magnetic fields is desired. BACKGROUND OF THE INVENTION [0003] Magnetic materials are used, for example, in magnetic cell memories and magnetic field sensors. In random access magnetoresistive memories, data is stored by applying magnetic fields and thereby causing a magnetic material in a cell to be magnetized into either of two possible memory states. The information stored in the memory is contained in the orientations of the magnetization vectors of the magnetic material layers used in each memory cell. Such memory cells exhibit a pronounced decrease in electrical resistance when an applied magnetic field brings the magnetization vectors in different layers into alignment. Recalling data is accomplished by sensing resistance changes in the cell. The cells can be written or erased by applying magnetic fields created by passing currents through conducting lines external to the magnetic structures, or through the magnetic structures themselves. [0004] There are often undesirable magnetic fields in and about the device, which are generated either as part of the device operation or from external sources. Such fields can have significant effects on the magnetization of the magnetic thin film. The field can contribute to a loss of information or to storage of erroneous information in the magnetic memory cells. Thus, magnetic memory cells function best when they are protected from external magnetic field disturbances. [0005] A metal with a relatively high magnetic permeability can be used to form a shield for protection from magnetic fields. Metals that are used widely in magnetic shielding include soft magnetic or high permeability materials, such as NiFe, NiFeMo and NiFeCu. Such magnetic shielding materials, are generally available from metal supply companies, such as Carpenter Technology Corporation of Wyomissing, Pa. [0006] U.S. Pat. No. 5,939,772 entitled "Shielded Package For Magnetic Devices," issued Aug. 17, 1999, describes the use of magnetically permeable metal shields attached to the outside of a hermetically sealed ceramic package. The shields are electrically connected to the package ground plane. Laminated magnetic shielding for ceramic packages is also described in U.S. Pat. No. 5,561,265, issued Oct. 1, 1996. [0007] Ceramic package technology can be expensive. Furthermore, as performance increases, the physical characteristics of ceramic packages may become limiting. Specifically, a ceramic material based on Al.sub.2O.sub.3 has a relatively high dielectric constant (.epsilon..sub.r.about.7-8). Additionally, because of the high-temperature processing, metallization is limited to refractory metals that are quite resistive, such as Mo and W. [0008] Other references include application of magnetic shielding within a plastic package. U.S. Pat. No. 4,953,002, issued Aug. 28, 1990, for example, teaches magnetic shielding internal to a plastic encapsulated package. [0009] Magnetic integrated circuit structures must also be housed in a way that minimizes cost if they are to be viable for the commercial memory market. Therefore, a shielding arrangement to protect magnetic films in magnetic integrated circuit structures from significant external adverse influences, including external magnetic fields, and which can be provided economically, would be desirable. Desirably, such a shielding arrangement should be flexible enough to meet the varied needs of integrated circuit users. SUMMARY OF THE INVENTION [0010] In accordance with one aspect of the invention, a housing is provided for protecting an integrated circuit device. The housing comprises a molded body that encapsulates the integrated circuit device. At least one magnetically permeable foil is applied to an outer surface of the molded body. [0011] In accordance with another aspect of the invention, a method is provided for magnetically shielding a semiconductor die. The method includes forming a molded unitary housing around the semiconductor die. A film of magnetic shield material is applied to at least one outer surface of the molded unitary housing. The film is applied in a manner that such that it is approximately parallel to a major surface of the semiconductor die. Advantageously, the shield material can be degaussed just prior to application, after the package is subjected to high temperature processing. [0012] In accordance with another aspect of the invention, an integrated circuit package is provided. The package includes an integrated circuit die, a molded body encapsulating the die, and a magnetic shield layer extending parallel to a major surface of the die over an outer surface of the molded body. [0013] In accordance with still another aspect of the present invention, a method is provided for packaging an integrated circuit chip. The method includes mounting the chip on a die carrier. Epoxy is molded over the chip to form an encapsulant. A magnetic shield layer is then selected for a particular integrated circuit environment. This selected magnetic shield is applied over the encapsulant. [0014] In accordance with still another aspect of the invention, an integrated circuit package is provided with an encapsulant surrounding an integrated circuit die. The encapsulant includes a recess on an outer surface thereof. The recess is configured for receiving and mechanically retaining a magnetic shield foil. In the illustrated embodiment, the recess includes overhanging tabs for removably trapping the foil within the recess. BRIEF DESCRIPTION OF THE DRAWINGS [0015] FIG. 1 is a schematic cross section of a packaged integrated circuit with magnetic shielding attached to outer surfaces of the package, according to an illustrated embodiment of the invention. [0016] FIG. 2 is a schematic cross section of an integrated circuit encapsulated in a ball-grid array package that has magnetic shielding attached to an outer surface of the package, according to an illustrated embodiment of the invention. [0017] FIG. 3 is a schematic cross section of a packaged integrated circuit with magnetic shielding set into recesses on outer surfaces of the package, according to an illustrated embodiment of the invention. [0018] FIG. 4 is a perspective view of a ball-grid array package showing a recess in the top surface in which a magnetic shield is held mechanically, according to an illustrated embodiment of the invention. [0019] FIGS. 5A and 5B are schematic cross sections cut along lines 5A-5A and 5B-5B, respectively, of FIG. 4. Continue reading... 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