Abstract:
A communication module is provided having a movable electrically conductive interface. This module comprises a printed circuit board with a first slidably receiving contact surface for providing electrical connectivity to the movable electrically-conductive interface, a non-metallic sealant disposed about at least a portion of the first slidably receiving contact surface about which the movable electrically-conductive interface is formed, the sealant imposing negligible resistance to the movable electrically-conductive interface, and a second slidably receiving contact surface for traveling across the sealant disposed about the first slidably receiving contact surface thereby forming the movable electrically conductive interface. Also a method is provided for overlaying the non-metallic sealing element over the first slidably receiving contact surface.

Description:
BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates to improved printed circuit boards, and more particularly, to non-metallic sealant elements covering contact surfaces on printed circuit boards. 
     2. The Relevant Technology 
     Since printed circuit boards replaced discrete wiring system, there has been a deluge of technology relating to printed circuit boards, and specifically, to the electrical features contained within circuit boards. Printed circuit boards integrated within PC cards provide the necessary interconnect for circuitry to perform its intended electrical functions. For example, in one type of PC card, the circuit board comprises electronics forming a modem that enables the host to receive and transmit information over telephone lines. In another PC card, the circuit board with its electronic components enables the host to receive and transmit information with a network system. 
     Printed circuit boards are comprised of conductive interconnections or traces that provide conductive “wiring” between components. These conductive interconnects or traces, usually made of copper, are etched from metallic planes on the printed circuit board using known techniques such as photographic and chemical processes. Because of the desire for low-resistance interconnections, these metallic interconnects are generally comprised of copper or related alloys which provide low-resistance at a reasonable cost. 
     Those familiar with conductive metals, such as copper, appreciate that some conductive metals, and in particular copper, tend to react forming oxidation in an ambient air environment. In fact, copper used on the contact surfaces of printed circuit boards tends to oxidize rapidly. If left unsealed from the ambient air, copper oxidizes forming a less conductive electrical interface for subsequent connector or contact mating, and the oxidation also results in easily detachable copper oxides that are undesirable debris throughout the printed circuit board and surrounding electronics. 
     While it is known that exposed conductive surfaces may be sealed using many insulative compounds, many surfaces must remain accessible and electrically conductive so that electrical communication between contact surfaces may be achieved and maintained. Thus, conductive sealants are essential for covering those conductive areas that require durable and reliable electrical interfaces. 
     In addition to the need that contact surface sealants be electrically conductive and thereby exhibit low resistance, sealants covering conductive surfaces that physically engage with other contacts such as connector terminals and the like must be further capable of withstanding repeated physical engagements. For example, physical conductive engagements occur when printed circuit boards having a card-edge connectors are inserted and removed from receiving connectors or jacks. This physical friction-based connector mating requires that any conductive sealant for conductive areas assume a sufficiently “hard” surface that is not easily marred and removed. If such degeneration of the sealed contact surface occurs, then oxidation resumes and conductive debris flakes-off and contaminates and may induce electrical shorts on the printed circuit board and surrounding electronics. 
     One prominent solution for sealing conductive surfaces involved in continuing physical interfacing has been to apply, usually in the form of plating, other non-oxidizable or less-oxidizable metals to the underlying conductive metal. For example, gold and other heavy metallic elements have been used to coat the copper contact surfaces while maintaining conductivity of the underlying copper contacts. Typically, the copper is plated with a layer of gold, which has an underlayer of nickel. After the gold is applied by plating, it is masked with tape or other physical barrier to prevent any contaminating solder reflow during the application of the electronic components to the printed wiring or electrically conductive traces on the printed circuit board. 
     Those familiar with plating processes appreciate the various undesirable side-effects of plating and particularly gold plating on small dimension electronic printed circuit boards. For instance, plating copper with gold is expensive because it is process-intensive and involves procedures that may be volatile and result in reduced quality. Gold is also not optimally environmentally sound because a number of toxic chemicals are used to process the gold and are left behind as dangerous by-products. 
     Furthermore, it is also difficult to plate contacts with metals such as gold and maintain alignment of the sliding contact on top of the etched contact surfaces of the printed circuit board as the plating process results in an additional layer of metal that exhibits sharp profile edges. The nature of copper etching leaves the copper with sharp vertical edges, and when gold is applied, this edge becomes even more pronounced. These edges can affect finely dimensioned interfaces that employ a sliding contact with the plated surface. 
     For example, a sliding contact interface generally results from a physical sliding of a contacting tab across the plated contact surface. When fine dimensions are involved, the contacting tab and the plated contact surface cannot be subjected to appreciable variations in tolerances otherwise the contacting tab “slips” off the sharp edge of the plated contact surface during the insertion of the connecting tab with the plated contact surface and cannot return to a centered orientation on the plated contact surface due to the steep conductive edge formed on the contact surface by the plating process. That is to say, if the sliding contact becomes misaligned, it is unable to surmount the sharp edges and realign itself. Thus, a need exists to adequately cover the contact surfaces with an element having a more gradually sloping edge. Additionally, if misalignment does occur, the sliding contact should more easily overcome the sloped edges and realign itself. 
     Others have attempted to solve the problem associated with copper sliding contact surfaces by varying etch widths of the copper, varying the printed circuit board thickness, altering the assembly process, re-configuring contact surfaces, and tightening tolerance controls. Unfortunately, these attempts have been to no avail. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     A non-metallic conductive structure, which covers the slidable contact surfaces on printed circuit boards and; (i) enables sufficient hardness, (ii) maintains adequate conductivity, (iii) maintains better alignment between sliding contact surfaces, (iv) reduces oxidation of the contact surfaces and brings about these benefits at a lower cost and with more environmentally-sound techniques than is provided by the available structures and processes. 
     Thus, in a preferred embodiment, the non-metallic conductive sealant coats the conductive printed circuit board trace, such as a copper contact surface of the printed circuit board. This non-metallic conductive sealant is comprised of a carbon-based ink composition that is preferably applied using a printing process such as a silk-screen process. 
     The second sliding contact surfaces comprise conductive pins or tabs that interface with the processed traces or contact surfaces on the printed wiring board. One such implementation of a sliding contact is present on a communication card employing a retractable/extendable communication jack such as an XJACK® or other electrical interface. When the extendable jack contact surfaces slide on top of and against the contact surfaces of the printed circuit board, an electrical communication is created. The carbon ink does not insulate the contact surfaces of the printed circuit board, but rather enables conductivity to pass from the underlying conductive copper contact surface to the sliding contact surface. 
     The use of carbon ink is also more cost-effective and environmentally sound than the use of gold. The application and cost of carbon ink is approximately one-fifth of the price of gold electroplating. The environmental benefits are also substantial. Carbon ink does not have the hazardous side products that are inherent with gold electroplating. Further, carbon ink is more easily applied to contact surfaces, which reduces or eliminates altogether the possibility of solder splash. 
     Additionally, carbon ink has desirable characteristics that make it well suited for its application onto copper contact surfaces. For instance, carbon ink has a greater hardness than gold. Also, carbon ink assumes more gradually sloping edges upon application, which make misalignment less probable and problematic. 
     These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to more fully understand the manner in which the above recited and other advantages and objects of the invention are obtained, a more particular description of the invention will be illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention in its presently understood best mode for making and using the same will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
     FIG. 1 depicts a perspective view of an environment within which the present invention may be practiced; 
     FIG. 2 depicts a top view of a printed circuit board having a sliding contact interface thereon, in accordance with a preferred embodiment of the present invention; 
     FIG. 3 depicts a sliding contact interface having a carbon ink sealant thereon, in accordance with a preferred embodiment of the present invention; 
     FIG. 4 is a side view of a portion of a sliding interface electrical connector depicting a pin block and electrical terminals having a non-metallic conductive sealant thereon for electrically contacting a media connector according to a preferred embodiment of the present invention; 
     FIG. 5 depicts a detailed view of the sliding contact interface having a sliding carbon ink sealant, in accordance with a preferred embodiment of the present invention; and 
     FIG. 6 is a cross-section profile of a conductive track of the slidable interface connector of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates primarily to a non-metallic conductive element, such as carbon ink, which is applied to slidable contact surfaces on printed circuit boards, and which enhances electrical communication when the contact surfaces are in sliding contact with one other. The term “non-metallic” as used herein, as relating to conductive elements, sealants, or coatings implies, a non-metal-based substance such as carbon used to formulate coating such as carbon ink for use in sealing electrically conductive contacts or traces, such as copper, from oxidation. Such non-metallic base compositions may be further comprised of metallic, such as silver, additives and still remain within the scope of “non-metallic” as sued herein. 
     Those of skill in the art appreciate that electrical continuity results when the contact surfaces of the printed circuit board slide against contact surfaces from other electrical connectors. The non-metallic conductive sealant may exhibit characteristics of increased hardness, improved conductivity, better maintenance of alignment and better accompanying cost and environmental benefits than other metallic plating prior solutions. 
     FIG. 1 depicts one environment in which the present invention may be practiced. In FIG. 1 a data device, depicted as computer  10 , incorporates various electronic components including electronic components resident on printed circuit boards. Those of skill in the art appreciate that printed circuit boards are manufactured through processes wherein various layers of metallic interconnect are created for providing the wiring of electronic components into circuits that perform specific functions. Those of skill in the art further appreciate that it is desirable to have interconnections between the various electrical components that exhibit very low resistances and therefore do not interfere with the electrical performance of the components comprising the various circuits. Therefore, as described above, metallic interconnects such as copper are highly desirable. 
     Furthermore, printed circuit boards and the circuitry associated therewith are designed to perform specific functions, and are frequently designed to interface with external devices such as network or other data devices. In order to facilitate the interfacing of these circuits with other devices, connector arrangements have been developed which facilitate coupling between devices. 
     FIG. 1 depicts computer  10  having an integrated form-factor such that a connecting interface, depicted as sliding interface electrical connector  12  extends therefrom for facilitating the interconnection of computer  10  with an external network or device via a media plug  14 . As depicted, sliding interface electrical connector  12  extends or protrudes from computer  10  for facilitating the coupling of the internal electronic circuitry within computer  10 , or alternatively within electronic modules directly coupled to slidable connector  12 . It should be apparent, that when computer  10  is not desirably coupled via media plug  14  to a network, sliding interface electrical connector  12  undesirably protrudes from computer  10 . It would be desirable, and is in accordance with the present invention, to form a slidable connector interface between sliding interface electrical connector  12  and internal printed circuit boards such that sliding interface electrical connector  12  may be received or recessed into a stowage position within a chassis or housing such as computer  10 . 
     FIG. 2 depicts a printed circuit board  16  having electronic components thereon which are interconnected through wiring tracks (not shown) which, as described above, perform the function of wiring various circuit components into specific desirable circuit functions. For illustration purposes, printed circuit board  16  is depicted as having a form-factor in accordance with the PCMCIA module standard. Such a depiction is illustrative and not limiting of the scope of the present invention. A portion of circuitry on printed circuit board  16  functions to provide an interface both physically and electrically through additional conductive tracks (FIG. 3) which couple both mechanically and electrically via sliding interface electrical connector  12  to media plug  14  (FIG. 1) and hence networks and other circuitry connected by media plug  14 . FIG. 2 depicts a portion of these interconnecting printed wires as conductive tracks  18 . A sliding interface electrical connector for ultimately providing electrical communication between a media connector and a computer is depicted generally as  12 . 
     With reference to FIG. 3, the sliding interface electrical connector  12  is defined by, for example, a communications card  20  having a retractable access portion  22  and a fixed portion  24 . The fixed portion  24  is in electrical communication with the computer by means of electronic circuitry connected on printed circuit board  16  housed internally within the communications card  20 . As used herein, fixed portion  24  shall refer to the generally stationary features internal to the communications card. Such features include, but are not limited to, the PCB including the interconnecting conductive traces, the electronic circuitry thereon, the mechanical spacers and connectors used to physically connect the PCB to the communications card. The retractable access portion  22  is in electrical communication with fixed portion  24  through the sliding interface electrical connector  12 , described in detail below. 
     During use, in means shown, the retractable access portion  22  slides in and out of a slot  26  formed within the fixed portion  24 . The retractable portion  22  is urged out of the slot  26  by a spring  28  biased to the fixed portion  24 . Although not shown, the computer housing is substantially parallel to an edge  31  of the communications card  20  during use. A biased mechanism  32  may be used to restrict the travel distance of the retractable access portion  22  to a predetermined distance when the retractable access portion is urged in a direction external to the computer housing by the spring  28 . After use, the biased mechanism  32  is used to retain the retractable access portion  22  within the housing of the computer and the housing of the communications card. 
     An aperture  36  having a plurality of walls  38  is formed within the retractable access portion  22 . The aperture  36  is so sized and shaped as to be capable of receiving a media connector. Formed within aperture  36  by means of walls  38  is a broad retention clip groove  40 , a narrow retention clip groove  42 , and a retention ridge  44 . These structures within aperture  36  provide for the retention of a connector pin block of a media connector. 
     When a user desires to connect a telephone line to the communications card, biased mechanism  32  is manipulated out of a limiting stop. As retractable access portion  22  is released from the grip of biased mechanism  32 , tension applied by spring  28  urges retractable access portion  22  out of slot  26 . The progress of retractable access portion  22  is guided by portions of the sliding interface electrical connector  12  and is halted when biased mechanism  32  engages another limiting stop. A user then inserts at least a portion of a media connector into aperture  36  to provide an electrical connection between communications card  20  and the telephone line or other network. When a user no longer desires to access the retractable access portion  22 , the user merely presses retractable access portion  22  back within the confines of the computer housing until the limiting stop is engaged by biased mechanism  32 . 
     However, it should be appreciated that even further biasing means, aperture embodiments for accepting a media connector during use and retention means for stabilizing the media connector, for example, are contemplated within the scope of the present invention and are more fully described in U.S. Pat. Nos. 5,183,404; 5,336,099; and 5,338,210. All three of these patents are expressly incorporated herein by reference. 
     The sliding interface electrical connector  12  comprises a pin block  46  for accommodating at least one conductive terminal or lead  48 . In FIG. 3, six conductive leads being in substantially parallel arrangement are illustrated. Each conductive lead  48  has a first end  50  and a second end  52 . It should be appreciated, however, that the conductive lead is preferably one singular conductive material and the first and second ends simply describe portions of the conductive lead  48  that extend beyond a boundary or support of pin block  46  on opposite sides thereof. Preferably, the conductive lead is inserted within and molded contiguously with the pin block  48  in a well known manufacturing technique often referred to as “insert molding.” 
     The first end  50  of the conductive lead  48  is for making electrical contact with the media connector during use when the media connector is inserted into aperture  36 . Preferably, the first end  50  extends at least partially into the aperture  36  for electrically contacting the necessary conductors of the media connector. The necessary conductors of an RJ-11 media connector usually include the “tip and ring” lines. 
     The second end  52  of the conductive lead  48  is for slidingly making electrical contact with a conductive track  18 . The conductive track  18  is elongated and of sufficient length that allows for a sliding electrical contact of the second end  56  throughout the range of motion as the retractable access portion is extended beyond the housing of the computer, communication card, or other boundary. 
     The profile of conductive track  18  is described in greater detail in FIG. 5, however, in general, conductive track  18  is comprised of a conductive trace  58  and a generally non-metallic electrically conductive trace sealant  104  (FIG.  5 ). Together, conductive trace  58  and non-metallic sealant  104  (FIG. 5) form an electrically conductive track onto which the also electrically conductive second end  52  of the conductive lead  48  slidably interfaces. The conductive trace  58  is preferably a metal, such as copper, silver, combinations thereof and similar other metals and metal combinations, but is not required. 
     The conductive track  18  is also of sufficient length to maintain electrical contact with the second end even when the retractable access portion  22  is inadvertently bumped during use and caused to slide in a direction generally towards the computer. When this inadvertent sliding occurs, the retractable access portion  22  is only able to travel towards the computer housing until the media connector, inserted in the aperture  36 , is prevented from further travel as it abuts against the computer housing. Thus, if the inadvertent sliding of the retractable access portion  22  remains as a possibility, the conductive tracks only need to be of a length sufficient to electrically contact the second end  52  when the retractable access portion is fully extended and when the media connector, during use, is pushed and abutted against the housing. 
     It should be appreciated that since the conductive track  18  is in electrical communication with the fixed portion  24 , the second end  52  is simultaneously in electrical communication with the fixed portion  24 . In turn, the first end  50  of the conductive lead  48  is also in electrical communication with the fixed portion  24 . Thus, during use, when conductive lines of the media connector electrically contact the first end  50 , the media connector is in electrical communication with the computer via the fixed portion  24 . 
     FIG. 4 depicts an exploded view of the sliding interface electrical connector  12 , in accordance with the present invention. The pin block  46  with included leads  48  including first ends  50  and second ends  52  are inserted into the retractable access portion frame  54  of retractable access portion  22 . In this embodiment, the pin block  46  operably mates with frame  54  and is retained by the interfacing of a ledge  74  on the pin block  46  with a ridge  80  on frame  54 . Also appreciated in this embodiment is a generally “J” shaped, curved terminal portion  70  of the second end  52 . In this manner, the curved terminal portion  70  more easily slides along the conductive tracks  18  of the fixed portion  24 . 
     Also depicted in FIG. 4 is the operative mating of fixed portion  24  with retractable access portion  22 . While the second ends  52  of the leads  48  provide the sliding electrical interface with the conductive tracks  18  of the fixed portion  24 , it should be apparent that the positive flexure of the second ends  52  on the conductive tracks  18  induce a natural deflection of the printed circuit board having the conductive tracks  18  thereon. In order to facilitate the sustained positive contact between the second ends  52  of the pin block  46  with the conductive tracks  18  of the fixed portion  24 , frame  54  is further includes a printed circuit board support shelf  100  integral thereto with a sliding surface  102  for supporting the portion of fixed portion  24  having the conductive tracks  18  thereon that comprise the sliding interface electrical connector of the present invention. 
     FIG. 5 is a perspective cross-section view of the sliding interface electrical connector, in accordance with a preferred embodiment of the present invention. The conductive track  18  is comprised of a conductive metal trace  58  which is fabricated onto the printed circuit board as part of the wiring or interconnection structure of the printed circuit board. Conductive trace  58  is preferably metallic, such as copper or aluminum or other metallic combinations similar thereto. Generally, conductive traces  58  are comprised of low resistance, and therefore highly conductive, metallic compounds, and in high production applications, are comprised of reasonably priced metallic compounds, most generally copper and related alloys. Those of skill in the art appreciate, however, the relative ease with which some metals, such as copper, oxidize when they are exposed to an ambient air environment such as when conductive traces are placed on the external sides of printed circuit board  16 . 
     As discussed above, prior implementations of slidable electrical interfaces incorporate plating, generally in the form of gold plating, onto the surfaces of conductive traces  58  to prevent oxidation of the conductive traces forming interconnections throughout the various circuit components. However, in the present invention, conductive traces  58  are sealed from ambient air oxidation by applying a carbon ink-based sealant  104  to conductive traces  58 . In the preferred embodiment, sealant  104  is applied over the conductive trace  58  using techniques, an example of which is screen-printing techniques, known by those of skill in the art. As depicted in FIG. 5, the sealant  104  encapsulates the exposed surfaces of the conductive trace  58  on the top surface as well as the side portions of the conductive trace  58 . Such encapsulation prevents oxides from forming on the conductive traces by providing a barrier for the conductive traces. 
     In the preferred embodiment, carbon ink is used for the sealant material and is applied according to the manufactures specification. While various carbon ink compositions may be employed, one preferred composition of carbon ink is Electra D&#39; or ™ED5601 which is manufactured by Polymers &amp; Chemicals AD of Roughway Mill, Tonbridge, Kent TN11 9SG, England. Other carbon ink compositions are also suitable for implementing the sliding interface electrical connector of the present invention and are contemplated to be within the scope of the present invention as claimed. The carbon ink sealant of the preferred embodiment exhibits an approximate resistance of 29-30 milliohms of resistance/square compared with gold plating which exhibits approximately 33 milliohms of resistance/square. Therefore, carbon ink sealant injects a series resistance, lower than gold plating, into the circuits, which in turn, lowers the negative effects on signal performance associated with increased series resistance. 
     Furthermore, the carbon ink of the preferred embodiment, exhibits a desirable improvement in hardness for the electrical sliding components of the sliding interface electrical connector of the present invention. In the preferred embodiment, the carbon ink sealant exhibits a hardness of 5H, on a pencil hardness scale, which is a significant improvement over gold plating which exhibits only a hardness of approximately 2H. The sliding interface electrical connector having carbon ink sealant also exhibits an improved friction coefficient as the carbon ink sealant is a self-lubricating finish as opposed to gold plating which exhibits scratching and marring after only a few hundred insertions. Additionally, the marring common to gold plating also results in an increase of series resistance and exposure to the underlying copper and or nickel prep layers. 
     FIG. 6 is a cross-sectional view of the conductive track used in the sliding interface electrical connector of the present invention. As shown, the conductive trace  58  assumes a largely rectangular profile needing sealing on both the top and sides of the conductive trace  58 . Traditional gold plating results in a nearly uniform thickness of gold on both the top and sides of the conductive trace. However, the carbon ink based sealant  104  exhibits a conformal profile which is more conducive to accommodating minor misalignment of the second end  52  of pin block  46  (see FIG.  5 ). That is to say, the more accommodating slope of carbon ink sealant  104  allows the second end  52  of pin block  46  to return to the top of the sealed conductive trace upon operation of the sliding contact should mechanical tolerances within the sliding interface electrical connector result in slight misalignment. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.