Abstract:
An electrical contact is designed with a plurality of spiraling legs such that when compressed, the spiral legs create a rotation of the top of the contact resulting in a wiping action to the contacting device or pad. The resulting micro-spider contact may be used for a wide variety of non-permanent or permanent electrical connection purposes including use in construction of an interposer.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to the field of electrical contacts and more specifically to the field of electrical contacts incorporating a wiping action.  
         BACKGROUND OF THE INVENTION  
         [0002]    In designing electrical devices, modular structures are often used to allow nonpermanent attachment of modules. This allows for upgrading or repairing of devices without requiring expensive reworking of the circuit board. Non-permanent attachment of modules also allows field replacement of defective or out-of-date modules. Reusable non-permanent electrical contacts require the ability to make reliable electrical contacts with a module over repeated connection and disconnection of the contacts. The contacts also are required to withstand a large number of connection and disconnection cycles without sustaining damage. Also, as electrical designs shrink in size there is pressure to design reliable contacts as small as possible.  
           [0003]    One specific type of electrical contact is an interposer. Interposers are placed between two electrical devices. One of the devices may be a circuit such as a multi-chip module (MCM) and the other may be a printed circuit board. As electrical devices shrink in size, interposers must also allow for increased contact densities while still allowing repeated, reliable electrical contacts. Existing electrical contact designs include interposers constructed from elastomeric material and interposers constructed from balls of wire. Both of these solutions have limitations inherent in their design. Current elastomeric materials are unable to sustain adequate contact spring force over time and temperature and have a small range of working heights. Interposers constructed from balls of wire are fragile, often prone to unravel, require costly inspection, and provide a limited amount of contact travel.  
         SUMMARY OF THE INVENTION  
         [0004]    An electrical contact is designed with a plurality of spiraling legs such that when compressed, the spiral legs create a rotation of the top of the contact resulting in a wiping action to the contacting device or pad. The resulting micro-spider contact may be used for a wide variety of non-permanent or permanent electrical connection purposes including use in construction of an interposer.  
           [0005]    Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a perspective view of an embodiment of a micro-spider contact according to the present invention.  
         [0007]    [0007]FIG. 2A is a top view of an embodiment of a clockwise micro-spider contact according to the present invention.  
         [0008]    [0008]FIG. 2B is a top view of an embodiment of a counter-clockwise micro-spider contact according to the present invention.  
         [0009]    [0009]FIG. 3 is an oblique view of a plurality of micro-spider contacts according to an embodiment of the present invention.  
         [0010]    [0010]FIG. 4 is a cross-sectional view of an embodiment of the present invention illustrating micro-spiders constructed on opposite sides of a substrate.  
         [0011]    [0011]FIG. 5A is a cross-sectional view of an embodiment of the present invention illustrating a single pair of micro-spider contacts.  
         [0012]    [0012]FIG. 5B is a cross-sectional view of an embodiment of the present invention illustrating a single pair of micro-spider contacts.  
         [0013]    [0013]FIG. 6 is an oblique view of an embodiment of the present invention illustrating a single clockwise micro-spider and a single micro stop.  
         [0014]    [0014]FIG. 7 is a cross-sectional view of an embodiment of the present invention illustrating a single pair of micro-spiders and a single pair of micro stops.  
         [0015]    [0015]FIG. 8 is a perspective view of an embodiment of a three-legged counter-clockwise micro-spider according to the present invention.  
         [0016]    [0016]FIG. 9 is a perspective view of an embodiment of an array of three-legged counter-clockwise micro-spiders according to the present invention.  
         [0017]    [0017]FIG. 10 is a cross-sectional view of an embodiment of the present invention illustrating micro-spiders constructed on a first side of a substrate and ball grid array (BGA) balls constructed on a second side of a substrate. 
     
    
     DETAILED DESCRIPTION  
       [0018]    [0018]FIG. 1 is a perspective view of an embodiment of a specialized electrical contact created pursuant to the present invention referred herein to as a micro-spider contact, or simply as a micro-spider. In FIG. 1 the micro-spider  106 , is an example embodiment of the present invention with four spiraling legs  108  attached to an area of metal  104  surrounding a through-plated hole  102  in a substrate  100  material. The micro-spider  106  is preferably constructed from a thin sheet of metal, and may be fabricated by a variety of methods. One method for constructing micro-spiders is described further in a U.S. patent application, Ser. No. ______, “Method for the Fabrication of Electrical Contacts”, filed concurrently with the present application, and incorporated herein by reference. Another method for the fabrication of micro-spiders is described in a U.S. patent application, Ser. No. ______, “Method for the Fabrication of Electrical Contacts”, filed concurrently with the present application, and incorporated herein by reference. Note that other embodiments of the present invention may include micro-spiders with 3 legs  108 , or 5 or more spiraling legs  108 . In the example embodiment of the present invention shown in FIG. 1 the legs  108  of the micro-spider  106  spiral in a clockwise direction. Note that micro-spiders  106  may be constructed with legs  108  spiraling in either a clockwise or counter-clockwise direction within the scope of the present invention. In fact, in certain applications of the concepts of the present invention it may be desirable to include both clockwise and counter-clockwise micro-spiders  106  in the same device. By mixing the two types of micro-spiders in an approximately equal amount and approximately equal distribution, the slight rotational torque applied as each micro-spider  106  contact is compressed is approximately equalized between the clockwise and counter clockwise direction, resulting in a very small net rotational torque.  
         [0019]    [0019]FIG. 2A is a top view of an embodiment of a clockwise micro-spider contact according to the present invention. The micro-spider  106  shown in FIG. 2A is identical to the device of FIG. 1 as seen from the top. Again, micro-spider  106 , preferably includes four spiraling legs  108  attached to an area of metal  104  surrounding a through-plated hole  102  in a substrate  100  material. FIG. 2B is a top view of an embodiment of a counter-clockwise micro-spider contact according to the present invention. The micro-spider  106  shown in FIG. 2B is similar to the device of FIG. 2A except with counter-clockwise spiraling legs  108  instead of the clockwise spiraling legs  108  shown in FIG. 2A.  
         [0020]    [0020]FIG. 3 is a perspective view of a plurality of micro-spider contacts according to an embodiment of the present invention. The example illustrates an array of micro-spiders  106  on a substrate  100 . In this embodiment, all of the micro-spiders  106  shown are clockwise micro-spiders  106 . In other embodiments of the present invention, counter-clockwise micro-spiders  106  may be used, or a combination of clockwise and counter-clockwise micro-spiders  106  may be used.  
         [0021]    In a specific example embodiment of the present invention, micro-spiders  106  are preferably constructed on both sides of the substrate  100  creating an interposer for use in non-permanently attaching electronic devices such as a multi-chip module (MCM) to a circuit board. FIG. 4 is a cross-sectional view of such an embodiment. The example embodiment of the present invention shown in FIG. 4 illustrates a plurality of micro-spiders  106  constructed on opposite sides of a substrate  100 , connected together by through-plated holes  102  surrounded by areas of metal  104  contacting the legs  108  of the micro-spiders  106 . This example embodiment of the present invention may be employed as an interposer for use in non-permanently attaching electronic devices such as a MCM to a circuit board.  
         [0022]    [0022]FIG. 5A is a cross-sectional view of an embodiment of the present invention illustrating a single pair of micro-spider contacts. The device of FIG. 5A illustrates a counter-clockwise micro-spider  106  similar to the device shown in FIG. 2B on the top surface of the substrate  100 , and a clockwise micro-spider  106  similar to the device shown in FIG. 2A on the bottom surface of the substrate  100 . The two micro-spiders  106  are preferably electrically connected to each other by a through-plated hole  102  in the substrate  100  where each hole  102  is surrounded by an area of metal  104  electrically and mechanically contacting the legs  108  of the micro-spiders  106 .  
         [0023]    [0023]FIG. 5B is a cross-sectional view of another embodiment of the present invention illustrating a single pair of micro-spider contacts. The device of FIG. 5B illustrates a clockwise micro-spider  106  similar to the device shown in FIG. 2A on the top surface of the substrate  100 , and a counter-clockwise micro-spider  106  similar to the device shown in FIG. 2B on the bottom surface of the substrate  100 . The two micro-spiders  106  are preferably electrically connected to each other by a through-plated hole  102  in the substrate  100  where each hole  102  is surrounded by an area of metal  104  electrically and mechanically contacting the legs  108  of the micro-spiders  106 .  
         [0024]    In some example embodiment of the present invention, it may be preferable to add a micro stop to prevent over-compression of the micro-spiders when connecting to a device such as a printed circuit board (PCB) or MCM. FIG. 6 is a perspective view of an embodiment of a single clockwise micro-spider and a single micro stop according to the present invention. The addition of a micro stop  600  to a device comprising at least one micro-spider  106  allows the connection of, say, a MCM to the device without over-compressing the legs  108  of the micro-spiders  106 . The micro stop preferably halts further compression of the micro-spiders  106  when the devices are a predetermined distance apart, as set by the height of the micro stop  600 . The example embodiment of the present invention of FIG. 6 shows a clockwise micro-spider  106  electrically connected to the metal  104  surrounding a through-plated hole  102  in a substrate  100 .  
         [0025]    [0025]FIG. 7 is a cross-sectional view of an embodiment of a single pair of micro-spiders  106  and a single pair of micro stops  600  according to the present invention. A clockwise micro-spider  106  similar to that described in connection with FIG. 2A is shown on the top surface of the substrate  100 , and a counter-clockwise micro-spider  106  similar to that described in connection with FIG. 2B is shown on the bottom surface of the substrate  100 . The two micro-spiders  106  are electrically connected to each other by a through-plated hole  102  in the substrate  100  where each hole  102  is surrounded by an area of metal  104  electrically and mechanically contacting the legs  108  of the micro-spiders  106 . The two micro stops  600  may be constructed by a variety of methods within the scope of the present invention. The height of the micro stops  600  is determined by the structure and materials used in creating the micro-spiders  106 . The micro stops  600  are preferably short enough to allow enough compression of the micro-spiders  106  such that the spiraling legs  108  cause the top of the micro-spiders  106  to rotate slightly creating a wiping action on the device with which they are brought into contact. This wiping action may physically remove oxides or other contaminants from the device the micro-spiders  106  are contacting, thereby creating a more reliable electrical contact than would be obtained by a similar contact without any wiping action. The micro stops  600  are preferably tall enough to prevent the contacting device from over-compressing the legs  108  of the micro-spiders  106 . If the legs  108  are over-compressed, they may deform or break. If the legs  108  deform, their useful life as a re-usable contact may be shortened because they may not be able to create the wiping action, and they may become brittle due to strain hardening and may eventually break.  
         [0026]    Micro-spiders may be made with a variety of numbers of legs  108 . Note that any number of legs greater than one may be used in creating a micro-spider  106  within the scope of the present invention. FIG. 8 is a perspective view of an embodiment of a three-legged counter-clockwise micro-spider according to the present invention. It will be appreciated that a three-legged micro-spider  800  allows a different amount of wiping action and spring force than an equivalent four-legged micro-spider  106  previously described in connection with FIGS. 1 through 7. This three-legged micro-spider  800  embodiment of the present invention comprises spiraling legs  108  attached to an area of metal  104  surrounding a through-plated hole  102  in a substrate  100  material.  
         [0027]    [0027]FIG. 9 is a perspective view of an embodiment of an array of three-legged counter-clockwise micro-spiders according to the present invention. In this example embodiment, all of the micro-spiders  800  shown are counter-clockwise three-legged micro-spiders  800  on a substrate  100 . In other embodiments of the present invention, clockwise three-legged micro-spiders  800  may be used, or a combination of clockwise and counter-clockwise three-legged micro-spiders  800  may be used. In further embodiments of the present invention, three-legged micro-spiders  800  may be constructed on both sides of the substrate  100  creating an interposer for use in non-permanently or permanently attaching electronic devices such as a multi-chip module (MCM) to a circuit board.  
         [0028]    In a specific example embodiment of the present invention, micro-spiders  106  are preferably constructed on a first side of the substrate  100  and ball grid array balls  1000  are preferably constructed on a second side of the substrate  100 , creating an interposer for use in non-permanently attaching electronic devices such as a multi-chip module (MCM) to a circuit board. FIG. 10 is a cross-sectional view of such an embodiment. The example embodiment of the present invention shown in FIG. 10 illustrates a plurality of micro-spiders  106  constructed on a first side of a substrate  100 , and ball grid array (BGA) balls  1000  constructed on a second side of a substrate  100 , connected together by through-plated holes  102  surrounded by areas of metal  104  contacting the micro-spiders  106 . This example embodiment of the present invention may be employed as an interposer for use in non-permanently attaching electronic devices such as a MCM to a circuit board, while the interposer is attached to the circuit board by the BGA balls  1000 .