Abstract:
The present invention relates to electrostatic dissipative alignment plates, sockets and socket assemblies comprising a base for providing an interface between an integrated circuit and an electrical system, and a frame for receiving the integrated circuit, where the base comprises an insulating material and the frame comprises a conducting material.

Description:
BACKGROUND OF INVENTION  
       [0001]     The present invention relates to alignment plates, sockets, and socket assemblies for interfacing integrated circuits (“ICs”) with electrical systems, and more particularly, to alignment plates, sockets, and socket assemblies having improved Electrostatic Discharge (“ESD”) dissipation characteristics.  
         [0002]     Alignment plates, sockets, and socket assemblies adapted to receive ICs are conventionally used to provide a mechanical and electrical interface between an IC and an electrical system. For example, the alignment plate, socket, or socket assembly may serve as an interface between: an IC and a system board (e.g. a motherboard or daughter board), an IC and a test system (e.g. an electrical test system), or an IC and a burn-in test system (system for stressing ICs at elevated operating conditions). The IC may comprise one or more semiconductor chips that may or may not be positioned on a module or printed circuit board.  
         [0003]     Various socket types are designed to hold a variety of IC products and are customized to accommodate the device leads of the IC, where the device leads refers to the electrical input/output connections (“I/O”) of the IC. Some examples of device lead types include: pin-grid-arrays (“PGA”), land-grid-arrays (“LGA”), ball-grid-arrays (“BGA”), column-grid-arrays (“CGA”) and the like.  
         [0004]     The socket houses a plurality of electrical contacts for providing an electrical interface between the device leads of the IC and the electrical contacts of the electrical system to which the IC is being interfaced. The socket must have an alignment feature for properly positioning the device leads in the socket. The socket must also have a portion for housing electrical contacts and receiving the device leads of the IC. This socket portion must be made from an insulating material to prevent current leakage among the various electrical contacts. Leakage currents can cause malfunction of the IC.  
         [0005]     Accumulation of electrostatic charge on the surface of the socket can occur during insertion or extraction of the IC from the socket. Electrostatic discharge (“ESD”) can cause damage to the IC and/or the electrical system to which the IC is being interfaced. The conventional approach for preventing ESD damage is to use electrostatic dissipative materials such as insulating plastics having conductive resin additives. However, the non-uniformity of such conductive resins can cause shorts or current leakage problems, especially inside the small holes which house the socket electrical contacts. Such an approach provides non-ideal ESD protection.  
         [0006]     Conventional sockets typically do not address ESD. They are entirely built from insulative materials (e.g. Polyamid-imide, Torlon 5530, etc.). In commercial sockets where ESD prevention is attempted the IC interface component (alignment plate) is built from dissipative materials (10 5  to 10 10  Ohms/sq) which can cause current leakage.  
         [0007]     Sockets typically comprise a guide plate for aligning the device leads of an IC with the electrical interface of an electrical system. Proper alignment is critical to assure that a particular IC is operated properly. Improper alignment can impact IC performance, reduce test and/or burn-in yields, or worse yet, can damage, often irreparably, the IC or the electrical system to which the IC is being interfaced. Conventional sockets typically comprise a single unit alignment formed from insulative material. The single unit alignment aligns the device leads of an IC with the electrical interface of an electrical system such as a system board, electrical tester or burn-in equipment. The single unit also has a second portion for housing the socket electrical contacts, which is also typically built from insulative material.  
         [0008]     Conventional single-unit sockets are typically constructed of a plastic material that is in the insulative range (10 12  ohms/sq or greater) of the material&#39;s resistivity properties and do not offer sufficient ESD protection. There are no known ideal materials that can be used to construct single-unit sockets that solve this ESD problem.  
       SUMMARY OF INVENTION  
       [0009]     The present invention relates to electrostatic dissipative alignment plates, sockets, and socket assemblies having a base for providing an interface between an integrated circuit and a plurality of electrical conductors, and a frame for receiving the integrated circuit, where the frame is formed from a conducting material that prevents electrostatic charge buildup that may occur when the integrated circuit is either inserted into or extracted from the socket and the base is formed from an insulating material that prevents current leakage between electrical conductors.  
         [0010]     The foregoing and other advantages and features of the invention will be apparent from the following more particular description of a preferred embodiment of the invention and as illustrated in the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]     The preferred exemplary embodiment of the present invention will hereinafter be described in conjunction with the appended drawings, where like designations denote like elements, and  
         [0012]      FIG. 1  is a perspective view of an electrostatic dissipative alignment plate.  
         [0013]      FIG. 2  is a bottom view of an electrostatic dissipative alignment plate as shown  FIG. 1 .  
         [0014]      FIG. 3  is a cross-sectional side view of an electrostatic dissipative alignment plate as shown  FIG. 1 .  
         [0015]      FIG. 4  is a perspective view of an electrostatic dissipative socket.  
         [0016]      FIG. 5  is a cross-sectional side view of an electrostatic dissipative socket as shown  FIG. 4 . 
     
    
     DETAILED DESCRIPTION  
       [0017]     The present invention thus provides an electrostatic dissipative alignment plate, socket, and socket assembly for use with electrical systems that overcomes many of the disadvantages of the prior art. Specifically, the electrostatic dissipative alignment plate, socket, and socket assembly minimizes electrostatic charge buildup on the surface of the alignment plate, socket, and socket assembly by dissipating electrostatic charge through the conductive frame.  
         [0018]     The invention will next be illustrated with reference to the figures in which the same numbers indicate the same elements in all figures. Such figures are intended to be illustrative, rather than limiting, and are included to facilitate the explanation of the process and device of the present invention.  
         [0019]     Turning now to  FIG. 1 , an exemplary electrostatic dissipative alignment plate  100  is illustrated in accordance with the present invention. The alignment plate  100  comprises base portion  110  and frame portion  120 . Base portion  110  and frame portion  120  are formed from different materials to prevent electrostatic charge buildup in sockets and electrical systems and to prevent current leakage. Base  110  receives electrical conductors and also aligns the device leads of IC  130  when the IC is positioned in alignment plate  100 . Base  110  has a plurality of openings for receiving electrical conductors which contact the device leads of IC  130 , thus aligning and electrically coupling the device leads of the IC to the electrical system. IC  130  may comprise one or more semiconductor chips that may or may not be positioned on a module or printed circuit board.  
         [0020]     Frame portion  120  is positioned on base  110  and receives IC  130 . For IC devices with protrusion type leads, frame  120  provides coarse alignment for IC  130  when it is placed in alignment plate  100 . Base  110  provides fine alignment for IC  130  as previously described. One or more pins may align frame  120  to base  110 . Because base  110  and frame  120  are separate components, the pins may be removable, thus enabling either the base and or frame portions to be interchanged as need be. For illustrative purposes only, pins may be inserted into openings  140  and  140 ″ to align frame  120  to base  110 . Additionally, fasteners such as screws may be inserted into multiple fastener openings  190  to attach frame  120  to base  110 .  
         [0021]     Base  110  is constructed from an insulating material and frame  120  is constructed from a conducting material. Because frame  120  is formed from a conducting material, it prevents electrostatic charge from building up on the mating surface of the alignment plate, thus preventing ESD from adversely effecting IC  130  or the electrical system to which the IC is coupled (e.g. a system board, test system, or burn-in equipment). Because base  110  physically contacts both the device leads of IC  130  and the electrical conductors inserted into the openings in the base, it is formed from an insulating material to avoid semiconductor device malfunction due to leakage currents.  
         [0022]     To prevent electrostatic charge build up, frame  120  of alignment plate  100  can be constructed from any suitable conducting material having a surface resistivity less than &lt;10 6  Ohms/sq. For illustrative purposes, the conducting material can be graphite or carbon filled thermoplastics such as: Polyetherimide (e.g. Semitron 410 commercially offered by Quadrant Engineering Plastic Products, or Hydel PC7 commercially offered by Boedeker Plastics, Inc.), Polycarbonate (e.g. Zelux CN-P commercially offered by Westlake Plastics Company), and Acetal Copolymer (e.g. Pomalux CN-SS commercially offered by Westlake Plastics Company).  
         [0023]     To prevent current leakage, base  110  can be constructed from any suitable insulating material having a surface resistivity of 10 12  Ohms/sq or greater. For illustrative purposes, the insulating material can be unfilled or glass-filled thermoplastics such as: Polyamide-imide (e.g. Torlon 5530 commercially offered by Quadrant Engineering Plastic Products), Polyimide (e.g. Vespel SP1 commercially offered by Dupont), Polyetheretherketone, Polyetherimide (e.g. Ultem commercially offered by GE), and Polyphenylenesulfide (e.g. Ryton commercially offered by Chevron Phillips Chemical Company LP, or Tecatron commercially offered by ENSINGER).  
         [0024]     Turning now to  FIG. 2 , a bottom view of an exemplary electrostatic dissipative alignment plate  200  is illustrated in accordance with the present invention. Alignment plate  200  comprises base portion  210  and frame portion  220 . Base  210  comprises openings  280 . Electrical conductors can be inserted into the bottom portion of openings  280 . Base  210  receives the electrical conductors via the bottom portion of openings  280  and also aligns the IC when the device leads of the IC are positioned in the upper portion of openings  280 . The upper portion of openings  280  in base  210 , which is not shown, align the IC by receiving the device leads of the IC when the IC is inserted into frame  220 . The lower portion of openings  280  in base  210 , which is shown, receive the electrical conductors, thus electrically coupling the IC to an electrical system when the IC is inserted into alignment plate  200 . For illustrative purposes, if the IC comprises BGA type device leads, the BGA leads would sit, or be counter-sunk, in the upper portion of openings  280  which are not shown. The electrical conductors are inserted into the bottom portion of openings  280  which are shown and contact the BGA device leads.  
         [0025]     Turning now to  FIG. 3 , a cross-section of an exemplary electrostatic dissipative alignment plate  300  is illustrated in accordance with the present invention. Alignment plate  300  comprises base portion  310  and frame portion  320 . Electrical conductors  350  can be inserted into the plurality of openings formed in base  310  as illustrated. Base  310  receives the electrical conductors and also aligns device leads  360  of IC  330  when the IC is positioned in alignment plate  300 . Electrical conductors  350  may be any suitable conductor for contacting device leads  360  such as a pin, pad, column, and the like. Device leads  360  may be any suitable lead type such as PGA, LGA, BGA, CGA, and the like. Base  310  has a plurality of openings for receiving electrical conductors  350  which contact device leads  360  of IC  330  when the IC is inserted into the alignment plate, thus aligning the IC and electrically coupling the IC to an electrical system. For illustrative purposes, if IC  330  comprises BGA type device leads as illustrated in  FIG. 3 , the BGA leads would sit, or be counter-sunk, in the openings of base  310  as illustrated. The electrical conductors are inserted into the opposite end of the openings in base  310  and contact BGA device leads  360 .  
         [0026]     Turning now to  FIG. 4 , an exemplary electrostatic dissipative socket  400  is illustrated in accordance with the present invention. The socket  400  comprises base portion  410 , frame portion  420 , and housing portion  470 . Base portion  410  and frame portion  420  are formed from different materials to prevent electrostatic charge buildup in sockets and electrical systems and to prevent leakage currents as previously described. Base  410  is interposed between housing portion  470  and frame portion  420 . Alignment pins  440  and  440 ″ may be inserted into openings in frame  420 , base  410  and housing  470  to align the frame and the base to the housing. Additionally, fasteners such as screws may be inserted into multiple fastener openings  490  to attach frame  420  and base  410  to housing  470 .  
         [0027]     Turning now to  FIG. 5 , a cross section of an exemplary electrostatic dissipative socket  500  is illustrated in accordance with the present invention. Socket  500  comprises base portion  510 , frame portion  520 , and housing portion  570 . Base portion  510  and frame portion  520  are formed from different materials to prevent electrostatic charge buildup in sockets and electrical systems and to prevent leakage currents as previously described. Base  510  is interposed between housing portion  570  and frame portion  520 . Electrical conductors  550  are inserted into the openings in base  510  when socket  500  is assembled. Base  510  receives electrical conductors  550  and also aligns device leads  560  of IC  530  when the IC is positioned in socket  500 . Base  510  has a plurality of openings for receiving electrical conductors  550  which contact device leads  560  of IC  530 . Housing  570  contains, or houses, electrical conductors  550 . When IC  530  is inserted into frame  520 , the IC is aligned by base  510  as previously described, and electrical conductors  550  make physical contact with device leads  560 , thus aligning the IC and electrically coupling the IC to an electrical system. Pins  540  and  540 ″ may align base  510  and frame  520  to housing  570 . Alternately, the alignment plate  100  illustrated in  FIG. 1  and the socket  400  illustrated in  FIG. 4  may be mounted on a printed circuit board to form a socket assembly.  
         [0028]     The embodiments and examples set forth herein were presented in order to best explain the present invention and its practical application and to thereby enable those of ordinary skill in the art to make and use the invention. However, those of ordinary skill in the art will recognize that the foregoing description and examples have been presented for the purposes of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the teachings above without departing from the spirit and scope of the forthcoming claims. Accordingly, unless otherwise specified, any components of the present invention indicated in the drawings or herein are given as an example of possible components and not as a limitation. Similarly, unless otherwise specified, any steps or sequence of steps of the method of the present invention indicated herein are given as examples of possible steps or sequence of steps and not as limitations.