Abstract:
The present invention provides an over-voltage surge protection device comprising a printed circuit board having a signal carrying conductive member having a plurality of nodes positioned therealong, and a conductive member running to ground also having a plurality of nodes positioned therealong. The nodes on the signal carrying member and ground member extend along a common path with corresponding ones of the signal carrying nodes positioned in adjacent, but spaced relation to the ground nodes. Preferably, the nodes are shaped in the form of triangles due to this particular geometry&#39;s favorable ability to accumulate and discharge voltage.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The present invention generally relates to electrical surge protection devices, and more particularly to spark gaps formed on printed circuit boards.  
           [0003]    2. Description of Prior Art  
           [0004]    Broadband coaxial cable communications networks, such as CATV networks, include various types of electronic equipment mounted to outdoor utility poles. This electronic equipment is subjected to all types of weather conditions including, for example, lightening storms. Due to the importance of these communications networks to society, it is important that they be able to withstand the harsh conditions under which they operate.  
           [0005]    On occasion, a high voltage surge may be transmitted through the coaxial cable to which the electronic components are interconnected, for instance, due to a lightning strike. If this high voltage surge is permitted to be picked up by the input or output pins of the interconnect device and transmitted to the electrical devices housed therein, the device would become inoperable due to the electrical components essentially melting or otherwise deteriorating as a consequence of the surge. A new connector would then need to be installed at the site of the surge.  
           [0006]    In order to improve the reliability of the electronic components in a communications network, the interconnect units are generally equipped with some type of over-voltage surge protection device. IEEE Standard C62.41-1991 sets forth a recommended practice on surge voltages in low voltage power circuits. The surge protectors incorporated into the interconnect may include, for instance, a single, conductive element positioned in adjacent, but spaced relation to the incoming signal. In the event of a transient, high voltage surge, the element will accumulate and discharge the over-voltage surge to ground prior to it passing through the electrical components. Incorporation of such surge protectors, however, add significantly to the complexity in manufacturing, and hence, the cost of an interconnect unit. In addition, if a voltage surge above what the protector is designed to handle is experienced by the connector unit, it will need to be replaced in any event.  
           [0007]    3. Objects and Advantages  
           [0008]    It is therefore a principal object and advantage of the present invention to provide an over-voltage surge protection device that is inexpensive to manufacture relative to the state of the art.  
           [0009]    It is a further object and advantage of the present invention to provide an over-voltage surge protection device that can withstand multiple surges, hence increasing the life of the coaxial cable interconnect device.  
           [0010]    Other objects and advantages of the present invention will in part be obvious, and in part appear hereinafter.  
         SUMMARY OF THE INVENTION  
         [0011]    In accordance with the foregoing objects and advantages, the present invention provides an over-voltage surge protection device comprising a printed circuit board having a signal carrying conductive member having a plurality of nodes positioned therealong, and a conductive member running to ground also having a plurality of nodes positioned therealong. The nodes on the signal carrying member and ground member extend along a common path with corresponding of the signal carrying nodes positioned in adjacent, but spaced relation to the ground nodes. Preferably, the nodes are shaped in the form of triangles due to this particular geometry&#39;s favorable ability to accumulate and discharge voltage.  
           [0012]    The over-voltage surge protection device may be fabricated directly into the board without mounting any additional structure thereto. A circuit board substrate that contains a layer of conductive material coated thereon may be fabricated by removing conductive material (e.g., by laser ablation, chemical or photolithographic etching, or other conventional fabrication process) in all areas on the board other than the signal carrying members and the conductive member leading to ground. The area of non-conductive material separating the signal carrying members from the ground member become the spark gaps.  
           [0013]    The spacing between the nodes (and their shape) determine the voltage level at which a spark will generate and shunt the circuit. The number of nodes present in the device will determine how many over-voltage surges it will be able to withstand.  
           [0014]    In operation, as the relative voltage potential between two corresponding nodes approaches a predetermined value, a spark will generate across the gap that separates them. This spark discharges the voltage from the signal carrying member to the grounded member, thereby shunting the circuit. Any particular spark may cause a deterioration of the particular node which discharges the surge. However, due to the circuit board having a plurality of corresponding sets of nodes, it will be able to withstand at least an equal number of over-voltage surges. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0015]    The present invention will be better understood and more fully appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, wherein:  
         [0016]    [0016]FIG. 1 is a plan view of a preferred embodiment of the present invention;  
         [0017]    [0017]FIG. 2 is a plan view of the present invention after it has been exposed to an over-voltage surge;  
         [0018]    [0018]FIG. 3 is an exploded perspective of an interconnect device in which the present invention is used;  
         [0019]    [0019]FIG. 4 is a longitudinal cross-sectional view of the interconnect device illustrated in FIG. 3;  
         [0020]    [0020]FIG. 5 is a plan view of a second alternate embodiment of the present invention;  
         [0021]    [0021]FIG. 6 is a plan view of a third alternate embodiment of the present invention;  
         [0022]    [0022]FIG. 7 is a plan view of a fourth alternate embodiment of the present invention; and  
         [0023]    [0023]FIG. 8 is a plan view of a fifth alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0024]    Referring now to the drawings, wherein like reference numerals refer to like parts throughout, there is seen in FIG. 1 a printed circuit board, designated generally by reference numeral  10 , for use in a coaxial cable interconnect device, shown generally by reference numeral  12 . Circuit board  10  is composed of a non-conductive substrate (e.g., a ceramic substrate of fiberglass) having a layer of conductive material, such as copper, coated on one planar surface  14  thereof. A series of electrical components, shown generally by reference numeral  16 , are mounted in a conventional manner to either planar surface of board  10 .  
         [0025]    Interconnect device  12  serves, for instance, as a trap with electrical components  16  comprising a filter having a narrow pass band response within a predetermined frequency range (e.g., 5-40 MHz) with a fixed level of attenuation across the return path frequency spectrum. Such devices are commonly used in CATV networks.  
         [0026]    Referring specifically to FIGS. 3 and 4, interconnect device  12  includes an elongated main body  18 ; a rear insulator  20  mounted concentrically within body  18  and positioned adjacent the terminal end thereof; a non-conductive (e.g., rubber) seal  22  positioned adjacent insulator  20 ; conductive female pin assembly  24  (which receives conductive pin  26  therein) concentrically extending through insulator  20  and seal  22 ; board  10  being electrically connected at one edge to pin assembly  24 ; a conductive, input pin  28  electrically connected to and extending outwardly from the opposing edge of board  10 ; a front insulator  30  positioned concentrically around pin  28 ; and a nut  32  threadingly engaging body  18  and housing insulator  30 . Conductive, input pin  28  receives a signal being transmitted through a coaxial cable (as part of a communications network), and conductive, output pin  26  sends the signal towards its destination after having been conditioned by electrical components  16  mounted on board  10 .  
         [0027]    Referring specifically to FIGS. 1, 2, and  5 , board  10  includes electrical components  16  mounted on surface  14 , a signal carrying, input member  34  electrically connected to pin  28 , and a signal carrying, output member  36  electrically connected to pin assembly  24  signal carrying members  34  and  36  are preferably mounted on the other side thereof (although these elements could be mounted on the same side as electrical components  16 , it is more space efficient to mount them on opposing sides and electrically interconnect there with vias). Signal carrying, input member  34  comprises electrically conductive material extending from pin  28  to a terminal node  38 , and includes a plurality of nodes  40  positioned between pin  28  and terminal node  38 . Output member  36  comprises an electrically conductive material extending from an terminal node  42  to pin assembly  24 , and a plurality of nodes  44  positioned between node  42  and pin assembly  24 . Nodes  40  and  44  are preferably triangular in shape (FIGS. 1 and 2), but may be shaped in other geometries, as well.  
         [0028]    Terminal node  38  is electrically connected to electrical components  16  which are, in turn, electrically connected to the output terminal node  42 . Thus, when the low voltage signal (e.g., device  12  generally operates on a circuit that passes 100 volts AC, with an RF level typically between +10 and −10 dBm) is received through pin  28 , the signal is transmitted through input member  34  to electrical components  16 . Electrical components  16  then appropriately condition (e.g. filter) the signal and send it through output member  36 . The signal is then sent towards its final destination via output pin  26 .  
         [0029]    An electrically conductive ground member  46  is also mounted on board  10 . Member  46  includes a first plurality of nodes  48  which correspond in shape and number to nodes  40 , and a second plurality of nodes  50  which correspond in shape and number to nodes  44 . Nodes  48  are positioned in adjacent, but spaced relation to corresponding ones of nodes  40 , thereby forming a first plurality of arc gaps  52  (each arc gap  52  defined by corresponding ones of nodes  40  and  48 ). Nodes  50  are positioned in adjacent, but spaced relation to corresponding ones of nodes  44 , thereby forming a second plurality of arc gaps  54  (each arc gap  54  defined by corresponding ones of nodes  44  and  50 ).  
         [0030]    The arc gaps  52  and  54  separating nodes  48  from nodes  40 , and nodes  50  from nodes  44 , respectively, are composed of non-conductive material and are of generally uniform thickness. If a transient surge of high voltage (e.g., as a consequence of a lightening strike) is received by either pin  28  or pin  26 , the voltage will travel to nodes  40  and  44 , respectively, at which point a spark will generate and arc across gaps  52  and  54 , respectively. The high voltage surge will then be grounded by member  46 , thereby shunting the circuit and protecting electrical components  16  therefrom. If the high voltage surge is not shunted, electrical components  16  will be destroyed through the heat generated by the surge. Consequently, it is essential to the long term reliability of interconnect device  12  that it contain the over-voltage surge protection capabilities embodied by spark gaps  52  and  54 .  
         [0031]    Spark gaps  52  and  54  are preferably between 1 and 10 mils thick. Obviously, the smaller the spark gap distance, the lower the voltage level that will generate a spark.  
         [0032]    If a transient high voltage surge does come through pins  28  or  26  and a spark does generate across nodes  40 ,  48  or  44 ,  50 , it is possible that a portion of the nodes  48 ,  50  will deteriorate and vaporize, as illustrated in FIG. 2 by reference letters V. However, even if portions of nodes  48 ,  50  do deteriorate, the remainder of the plurality of nodes  48 ,  50  remain intact. Accordingly, spark gaps  52  and  54  provide an over-voltage surge protection device that can withstand numerous over-voltage surges.  
         [0033]    Nodes  40 ,  48 ,  44  and  50  are preferably triangular in shape (as illustrated in FIGS. 1 and 2) as this geometry appears to most effectively accumulate and discharge voltages. However, these nodes could be shaped in other patterns so long as the spacing between corresponding nodes is small enough to maintain the efficiency spark gaps  52 ,  54  (e.g., the spacing can be variable, but preferably within the range of 1 to 10 Mils). For instance, corresponding nodes could be shaped sinusoidally rectangularly shaped (see FIG. 6), arbitrarily shaped (See FIG. 7), or rectangularly shaped with triangularly shaped corresponding nodes (see FIG. 8).  
         [0034]    In forming spark gaps  52 ,  54 , board  10  is provided with a coating of conductive material on one of its planar surfaces. Conductive material is then removed through any conventional process (e.g., laser ablation, photolithographic or chemical etching, or the like) from the areas of board  10  that are to be non-conductive, i.e., all areas other than input member  34 , output member  36 , and ground member  46 . Forming spark gaps  52 ,  54  in this manner causes them to be coplanar with board  10 , thereby using minimal space and not requiring the mounting of any additional structure to board  10 .