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Electronic assembly with detachable componentsElectronic assembly with detachable components description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070187844, Electronic assembly with detachable components. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001]This application is a continuation-in-part of U.S. patent application Ser. No. 11/351,418 entitled "Apparatus and Method for Predetermined Component Placement to a Target Platform," filed Feb. 10, 2006, which is hereby incorporated by reference. BACKGROUND [0002]1. Field of the Invention [0003]The present invention relates generally to electronic assemblies, and more particularly to assembly techniques on the use of anisotropic conducting material as a component interconnect and the use of substrate embossed with placement cavities or the use of positional fixtures to facilitate the placement of component on the substrate in an electronic assembly. [0004]2. Related Art [0005]Electronic assemblies are typically assembled by using surface mount technology (SMT), or more recently, the chip-on-board (COB) technology. Using SMT, packaged electronic components are soldered on a substrate, such as a printed circuit board (PCB), by printing a thin layer of solder paste on the substrate and following a thermal reflow process to solder the component to the substrate. Using COB technology, thin metal wires are attached or bonded to a bare die on a substrate to create a wire-bonded assembly. A layer of resin may then be applied to the surface of wire-bonded component to protect the bonded wires from being damaged in the assembly. [0006]One problem with both the SMT and the COB technique is that a soldered or wire-bonded component is typically difficult to remove for repair or reuse once it is attached to the substrate. At motherboards, sockets are often used for the installation of CPU chips to simplify its replacement or upgrade. The sockets are rather expensive. Therefore, there is a need for assembly techniques that allow components to be easily detached from the substrate for rework, reuse, or even replacement. SUMMARY [0007]The present invention addresses the above problems with an assembly technique, which uses anisotropic conducting membrane (ACM) at a component interconnect interface and uses a substrate with embossed cavities or with an aligning fixture to facilitate the assembly of components on substrate in an electronic assembly. The aligning fixture comprises openings at predetermined spatial regions in the fixture. The embossed cavity on the substrate or the opening at the fixture is chosen in such a way that it enables a contact array of a component to match a designated land pattern on a substrate when the component is placed at the cavity or opening. The embossed cavities on the substrate or the openings in the fixture can also hold ACM interfaced components in place on the substrate after the components are placed. The ACM layer electrically connects component to the substrate and enables component to be readily detached for reuse or replacement. An ACM layer may be directly laminated at a component surface. Alternatively, the ACM layer may be placed at the substrate surface during the assembly process. [0008]An alignment chain can monitor the positional and contact integrity for a group of components on a substrate in an electronic assembly. By incorporating conductive pads as alignment marks at predetermined regions in a component and incorporating conductive pads as reference marks at designated regions on the substrate to match the positions of alignment marks at the component to be placed on the substrate, an alignment chain can be built. The alignment chain is formed by linking the alignment marks at a group of components with the matching reference marks on the substrate over an ACM interconnect layer from component to component to create a serial, continuous conduction path among the group of components to be monitored. Depending upon the complexity of the electronic assembly, the alignment chain may be divided into multiple smaller alignment chains to detect the positional and contact integrity for a smaller group of components linked in a chain by monitoring its conduction status. The technique allows components to be detached for reuse. [0009]In different embodiments of the invention, an electronic assembly may stack multiple substrates into a more compact three-dimensional structure. Interconnection elements can be used to facilitate the interconnection between neighboring substrates in a stacked assembly. The interconnection element comprises a pre-fabricated conductive path or routing trace in a planar structure or package for insertion into a fixture opening or an embossed cavity on the substrate to interconnect neighboring substrates across ACM layers. The interconnection elements can replace expensive socket, mechanical connector, or flexible ribbon circuit with minimal positional constraint on the substrate to simplify the design of an electronic assembly. [0010]The electronic assembly may be sealed in a housing, such as a plastic housing in a flash card, to hold the ACM interfaced components in place. The inner surface of the housing may be molded to match a height profile of the components. The housing may be in a form that can be open for component access, such as a heat spreader used in a memory module. The housing may comprise contacts or openings allowing an alignment chain to be monitored from the housing. [0011]Some exemplary methods of using anisotropic conductive material in an electronic assembly are illustrated. One exemplary method uses a substrate comprising embossed cavities to facilitate the placement of components and an anisotropic conducting membrane at the embossed cavity as a component interconnect layer to the substrate. The ACM may be directly laminated at the component interconnect surface to eliminate the ACM insertion step in manufacturing the electronic assembly. An alternative exemplary method is the use of an aligning fixture in the electronic assembly. The aligning fixture can be aligned to a substrate by using a placement equipment and bonded to the substrate by using anisotropic conductive paste or solder paste, if the fixture also contains an interconnect circuitry. Alternatively, a sheet of ACM may be placed on the substrate surface prior to the placement of the fixture. Both the embossed cavities on the substrate and the openings at the fixture can hold components on the target land patterns at the substrate with accuracy. Alignment marks or alignment mechanism may be incorporated in the fixture to align with matching reference marks or reference mechanisms at the substrate, although an optical pattern recognition technique may be used to align fixture to substrate. [0012]Benefits of exemplary implementations of the invention include the use of the ACM layer to replace solder paste or wire-bonding in a conventional component assembly. By using ACM as a component interconnect layer and using a fixture or embossed cavity at the substrate, components can be readily removed and reattached to an electronic assembly. Components that are expensive or in short supply can be readily detached and reused in different electronic assemblies. Defective components may be easily removed at rework. Furthermore, components can be detached and replaced in a system upgrade. This flexibility results because the ACM layer allows components to be readily detached and reattached in an electronic assembly without necessitating desoldering or cutting wire-bond that may damage the component or other parts of the assembly. BRIEF DESCRIPTION OF THE DRAWINGS [0013]FIG. 1 illustrate a set of alignment marks at a component coupled to a set of reference marks on a substrate with auxiliary conduction pathways, in an exemplary implementation; [0014]FIG. 2 depicts an exemplary implementation of an alignment chain linking two components on a substrate using anisotropic conducting membrane as an interconnect layer; [0015]FIG. 3 is depicts an enclosed electronic assembly comprising an alignment chain, in an exemplary implementation of the invention; [0016]FIG. 4A depicts a profile of an exemplary electronic assembly using a fixture to assemble components on a substrate enclosed in a housing; [0017]FIG. 4B depicts a top view of an exemplary fixture comprising interconnection traces and coupled to a substrate underneath; [0018]FIG. 5 depicts an exemplary electronic assembly of a memory module, where a fixture is attached to a substrate to hold the ACM interfaced components in place enclosed in a housing; [0019]FIG. 6 depicts a top view of a memory module including a fixture, components, an alignment chain, and an external interface enclosed in a clamshell according to an exemplary implementation of the invention; [0020]FIG. 7 depicts a flowchart of an exemplary method for assembling ACM laminated components on a substrate embossed with placement cavities in an exemplary assembly enclosed in a housing; Continue reading about Electronic assembly with detachable components... 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