Abstract:
A method for the fabrication of electrical contacts using metal forming, masking etching, and soldering techniques is presented. The method produces a plurality of specialized electrical contacts, capable of use in an interposer, or other device, including non-permanent or permanent electrical connections providing contact wipe, soft spring rates, durability, and significant amounts of travel.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to the field of electrical contacts and more specifically to methods for the fabrication of electrical contacts.  
         BACKGROUND OF THE INVENTION  
         [0002]    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, prone to unravel, often require costly inspection, and provide a limited amount of contact travel.  
         SUMMARY OF THE INVENTION  
         [0003]    A method for the fabrication of electrical contacts using metal forming, masking etching, and soldering techniques is presented. The method produces a plurality of specialized electrical contacts, capable of use in an interposer, or other device, including non-permanent or permanent electrical connections providing contact wipe, soft spring rates, durability, and significant amounts of travel.  
           [0004]    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  
       [0005]    [0005]FIG. 1 is a perspective view of an embodiment of a substrate including an array of holes according to the present invention.  
         [0006]    [0006]FIG. 2 is a close-up perspective view of an embodiment of one of the substrate holes from FIG. 1 according to the present invention.  
         [0007]    [0007]FIG. 3 is a perspective view of an embodiment of the structure of FIG. 2 after through plating and etching according to the present invention.  
         [0008]    [0008]FIG. 4 is a perspective view of an embodiment of the structure of FIG. 3 with the addition of a molded dome according to the present invention.  
         [0009]    [0009]FIG. 5 is a perspective view of an embodiment of the structure of FIG. 4 after the dome has been metal plated according to the present invention.  
         [0010]    [0010]FIG. 6 is a perspective view of an embodiment of the structure of FIG. 5 after the addition of a mask layer according to the present invention.  
         [0011]    [0011]FIG. 7 is a perspective view of an embodiment of the structure of FIG. 6 after the metal layer has been etched away in all areas not covered by the mask layer according to the present invention.  
         [0012]    [0012]FIG. 8 is a perspective view of an embodiment of the structure of FIG. 7 after the mask layer has been removed according to the present invention.  
         [0013]    [0013]FIG. 9 is a perspective view of an embodiment of the structure of FIG. 8 after the dome has been dissolved according to the present invention.  
         [0014]    [0014]FIG. 10 is a top view of an embodiment of the final micro-spider contact structure from FIG. 9 according to the present invention.  
         [0015]    [0015]FIG. 11 is a perspective view of an embodiment of an array of clockwise micro-spiders according to the present invention.  
         [0016]    [0016]FIG. 12 is a cross-section view of an embodiment of a micro-spider interposer according to the present invention.  
         [0017]    [0017]FIGS. 13A and 13B are cross-section views of embodiments of single micro-spider interposer pairs according to the present invention.  
         [0018]    [0018]FIG. 14 is a view of an embodiment of a single clockwise micro-spider and a single micro stop according to the present invention.  
         [0019]    [0019]FIG. 15 is a cross-section view of an embodiment of the structure from FIG. 14 according to the present invention.  
         [0020]    [0020]FIG. 16 is a flowchart of a method of creating micro-spider contacts according to the present invention.  
         [0021]    [0021]FIG. 17 is a perspective view of an embodiment of a three-legged micro-spider.  
         [0022]    [0022]FIG. 18 is a perspective view of an embodiment of a plurality of three-legged micro-spiders on a substrate according to the present invention.  
         [0023]    [0023]FIG. 19 is a cross-section view of an embodiment of a micro-spider/ball grid array interposer according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0024]    [0024]FIG. 1 is a perspective view of an embodiment of a substrate including an array of holes according to the present invention. A quantity of holes or vias  102  is created in a substrate  100 . In an example embodiment of the present invention the holes may be drilled into a printed circuit board (PCB) substrate. In an example embodiment of the present invention using a PCB substrate, metal pads may be placed on the substrate surrounding the planned locations of the holes before the holes are drilled. Other methods of creating the holes, such as etching, and other substrate materials, such as ceramics, may be used within the scope of the present invention. The quantity of holes  102  does not need to form a regular array shown in FIG. 1. In other embodiments of the present invention, the holes may be irregularly spaced as desired for any particular design. The PCB substrate material is commonly fiberglass, however other materials may be used within the scope of the present invention.  
         [0025]    [0025]FIG. 2 is a close-up perspective view of an embodiment of one of the substrate holes from FIG. 1 according to the present invention. A hole  102  in a substrate  100  is shown here.  
         [0026]    [0026]FIG. 3 is a perspective view of an embodiment of the structure of FIG. 2 after through-plating and etching according to the present invention. After through-plating, the hole  102  has a ring of metal plating  300  surrounding the hole  102  and through the hole  102  to the opposite side of the substrate  100 . While the areas of metal plating  300  in this embodiment are circular in shape, other shapes of the areas of metal  300  will work equally well within the scope of the present invention. For example, in some embodiments of the present invention, the area of metal  300  may be elliptical, square, rectangular, or other, more complex shapes. While copper is a preferred metal for the metal plating, other example embodiments of the present invention may use other materials for the plating.  
         [0027]    [0027]FIG. 4 is a perspective view of an embodiment of the structure of FIG. 3 with the addition of a molded dome according to the present invention. A molded dome  400  is added to at least some of the through-plated holes  102 . Molded domes  400  may be added to none, some, or all of the through-plated holes  102  on each side of the substrate  100 . In an example embodiment of the present invention, molded domes  400  are added to both sides of the substrate  100  to create a dual micro-spider interposer. A specialized electrical contact created pursuant to the present invention is referred herein to as a micro-spider contact, or simply as a micro-spider. In an alternate embodiment of the present invention, molded domes  400  are added to only one side of the substrate  100  to create a micro-spider/ball grid array (BGA) ball interposer.  
         [0028]    [0028]FIG. 5 is a perspective view of an embodiment of the structure of FIG. 4 after the dome has been metal plated according to the present invention. The metal plated dome  500  of FIG. 5 may include copper or other metal elements or compositions according to design requirements.  
         [0029]    [0029]FIG. 6 is a perspective view of an embodiment of the structure of FIG. 5 after the addition of a mask layer according to the present invention. A mask layer  600  in the shape of a clockwise micro-spider has now been added over the metal plated dome  500 . The mask layer may comprise photoresist and be applied by any number of methods. The photoresist may be exposed and developed to produce the mask layer  600  in the shape of micro-spiders.  
         [0030]    [0030]FIG. 7 is a perspective view of an embodiment of the structure of FIG. 6 after the metal layer has been etched away in all areas not covered by the mask layer according to the present invention. An etched micro-spider  700 , covered with the mask layer  600 , is seen in place over the molded dome  400  on the substrate  100 .  
         [0031]    [0031]FIG. 8 is a perspective view of an embodiment of the structure of FIG. 7 after the mask layer  600  has been removed from the micro-spider  700 .  
         [0032]    [0032]FIG. 9 is a perspective view of an embodiment of the structure of FIG. 8 after the dome has been dissolved according to the present invention. The molded dome  400  may be preferably dissolved by any chemicals (or other etching method) capable of completely removing the dome material without damaging the micro-spider  700 , plating  300 , hole  102 , or substrate  100 .  
         [0033]    [0033]FIG. 10 is a top view of an embodiment of the micro-spider contact structure from FIG. 9 according to the present invention. A single clockwise micro-spider  700  is shown over a through-hole  102  surrounded by metal plating  300  on a substrate  100 . At this point the micro-spider may undergo further processing such as additional metal plating if desired. Also note that in other embodiments of the present invention counter-clockwise micro-spiders may be produced as desired. For example, it may be advantageous to design a large array of micro-spiders such that substantially equal numbers of clockwise and counter-clockwise micro-spiders are created. Such a design may reduce the rotational torque that would occur in an array of only clockwise or only counter-clockwise micro-spiders. Since the micro-spiders each rotate slightly, creating a wiping action on the contact during use, each micro-spider causes a small amount of torque on the device as it is connected.  
         [0034]    The resulting micro-spiders are described further in a U.S. patent application, Ser. No. ______, “Electrical Contact”, filed concurrently with the present application, and incorporated herein by reference. Another method for the fabrication of 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.  
         [0035]    [0035]FIG. 11 is a perspective view of an embodiment of an array of clockwise micro-spiders  700  shown over a substrate  100  according to the present invention. As disclosed above, in some embodiments of the present invention, it may be desired to alternate clockwise and counter-clockwise micro-spiders, for example in a checkerboard pattern.  
         [0036]    [0036]FIG. 12 is a cross-section view of an embodiment of a micro-spider interposer according to the present invention. In this example embodiment of the present invention micro-spiders are constructed on both sides of the substrate  100 . Connecting each pair of micro-spiders  700  is a through-plated hole  102 . The metal  300  surrounding each hole may be seen connecting to individual micro-spiders. While this example embodiment comprises clockwise micro-spiders  700  on the top of the substrate  100 , and counterclockwise micro-spiders  700  on the bottom of the substrate  100  other configurations are possible within the scope of the present invention.  
         [0037]    [0037]FIGS. 13A and 13B are cross-section views of embodiments of single micro-spider interposer pairs according to the present invention. In FIG. 13A a counterclockwise micro-spider  700  is shown on the top of the substrate  100 , and a clockwise micro-spider  700  is shown on the bottom of the substrate  100 . The pair of micro-spiders  700  are electrically connected by a through-plated hole  102  and the metal  300  surrounding the hole. In FIG. 13B a clockwise micro-spider  700  is shown on the top of the substrate  100 , and a counter-clockwise micro-spider  700  is shown on the bottom of the substrate  100 . The pair of micro-spiders  700  are electrically connected by a through-plated hole  102  and the metal  300  surrounding the hole.  
         [0038]    [0038]FIG. 14 is a perspective view of an embodiment of a single clockwise micro-spider  700  electrically connected to the metal  300  surrounding a hole  102  in the substrate  100  next to a micro stop  1400  in accordance to the present invention. The micro stop  1400  may be constructed using processes similar to standard printed circuit board processes, to create an elevated stop configured to prevent over-compression of the micro-spiders  700  during use. The height of the micro stop  1400  preferably enables compression and contact wiping action of the micro-spiders  700  while preventing over-compression that would physically damage the micro-spiders  700 .  
         [0039]    [0039]FIG. 15 is a cross-section view of an embodiment of the structure from FIG. 14 according to the present invention. In this example embodiment of the present invention a micro-spider interposer including a pair of micro stops  1400  is shown in cross-section view. The clockwise micro-spider  700  on top of the substrate  100  is electrically connected to the counter-clockwise micro-spider  700  on the bottom of the substrate through the metal  300  surrounding the through-plated hole  102  in the substrate  100 .  
         [0040]    [0040]FIG. 16 is a flowchart of a method of creating micro-spider contacts according to the present invention. In a step  1602 , a plurality of holes  102  are created in a substrate  100 . In a step  1604 , the holes  102  are through-plated and etched. In a step  1606 , molded domes are created over the through-plated holes  102 . In a step  1608 , the substrate  100  with the holes  102  covered by molded domes is metal-plated. In a step  1610 , a mask layer in the configuration of micro-spiders is created over the metal-plated domes. In a step  1612 , the metal-plating is etched away in all the places not covered by the mask layer. In a step  1614 , the mask layer is removed. In a step  1616 , the domes are dissolved or etched away leaving the finished micro-spiders. If desired, the micro-spiders may be metal-plated again with one or more additional metals, such as nickel or gold, at this point in the process. In an optional step  1618 , ball grid array (BGA) balls are placed on the through-plated holes  102  on a side of the substrate  100  opposite to the micro-spiders  700 . In such an embodiment of the present invention, micro-spiders  700  are placed on one side of the substrate  100  and BGA balls  1900  are placed on the other side of the substrate  100  producing a micro-spider/BGA interposer.  
         [0041]    [0041]FIG. 17 is a perspective view of an embodiment of a three-legged micro-spider according to the present invention. A three-legged micro-spider  1700  is shown connected to the metal  300  surrounding a through-plated hole  102  in a substrate  100 . Micro-spiders may be constructed with any number of legs (greater than one) as desired by an intended use, within the scope of the present invention.  
         [0042]    [0042]FIG. 18 is a perspective view of an embodiment of a plurality of three-legged micro-spiders on a substrate according to the present invention. FIG. 18 shows an array of three-legged micro-spiders  1700  on a substrate  100 . While this figure shows a regular array of micro-spiders  1700 , other embodiments of the present invention may use an irregular array of micro-spiders  1700  as desired by the intended use of the plurality of micro-spiders  1700 .  
         [0043]    In a specific example embodiment of the present invention, micro-spiders  700  are preferably constructed on a first side of the substrate  100  and ball grid array balls  1900  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. 19 is a cross-sectional view of such an embodiment. The example embodiment of the present invention shown in FIG. 19 illustrates a plurality of micro-spiders  700  constructed on a first side of a substrate and ball grid array (BGA) balls  1900  placed 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  300 . 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  1900 . This example embodiment of the present invention may be fabricated using the process described in connection with FIG. 16 including optional step  1618 .