Abstract:
A connector terminal includes a metal socket defining a top opening and a bottom through hole, a probe head having a lower stoppage portion stoppable inside the metal socket and supported on a spring inside and an upper contact portion extending out of the top opening of the metal socket, and a plug tightly plugged into the bottom through hole of the metal socket.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to electrical signal connectors and more particularly to a connector terminal, which comprises a metal socket having a metal coating layer coated on inner and outer surface thereof, a probe head, an elastic member floatably supporting the probe head partially in the metal socket and a plug plugged into a bottom through hole of the metal socket, and which has the characteristic of low resistivity (high conductivity) and high level of signal transmission efficiency and stability. 
     2. Description of the Related Art 
     With the rapid development of electronic technology and multimedia revolution, cell phone, smart phone, GPS navigation device, PDA and many other mobile electronics are created and widely used in different fields. It is now the market tendency to create mobile devices having light, thin, short and small characteristics. In consequence, electronic components for installation in a circuit board for mobile device must be made smaller, more precise and stronger than ever before. 
     Further electrical connectors are intensively used to connect electronic devices to a circuit board. An electrical connector generally comprises a plurality of signal connector terminals and power connector terminals connected with respective conductors of a cable for transmitting signal or power supply to a control circuit. As electrical connectors get ever smaller, many new types of electrical connectors are created. For example, a pogo pin connector is a spring loaded connector used in an electronic device to establish a connection between two printed circuit boards. A pogo pin generally comprises a metal socket (cylinder), a probe head mounted in the metal socket, and a spring mounted inside the metal socket to support the probe head. When the probe head is forced toward the inside of the metal socket by an external pressure, the spring can be elastically deformed. Subject to contact between the probe head and the inside wall of the metal socket, the pogo pin achieves electrical connection between two printed circuit boards. For the advantages of small size, large current, strong contact point, high durability and connection stability, pogo pin connectors are widely used in cell phone battery, antenna connectors, GPS navigation device, tablet computer, handheld computer, wireless receiver or wireless communication device for conducting electric current or transmitting signals. 
     Further, when the probe head of a pogo pin is forced toward the inside of the metal socket to compress the spring, the elastic potential energy of the spring forces the probe head to stop against a part of the inside wall of the metal socket, achieving electric connection. To ensure connection stability, the inner and outer surface of a metal socket for pogo pin will be electroplated with a metal coating layer to enhance conductivity and to provide a better bonding surface. During electroplating, metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material. 
     However, as the metal socket of a pogo pin is a blind hole structure, gases (hydrogen and etc.) released during electroplating may be accumulated in the blind hole of the metal socket, causing cracks in the metal coating layer, or affecting even distribution of electric current to lower the speed of the deposition of metal ions on the surface of the metal socket. Due to low current efficiency (the ratio of the amount of electricity, in coulombs, theoretically required to yield a given quantity of material in an electrochemical process, to the amount actually consumed), it takes much plating time to reach the desired coating thickness. Because of slow deposition rate, it is difficult to coat the desired metal coating layer on the inner surface of the metal socket. In consequence, the manufacturing cost of the metal socket is high. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is therefore the main object of the present invention to provide a connector terminal, which has the characteristic of low resistivity (high conductivity) and high level of signal transmission efficiency and stability. 
     To achieve this and other objects of the present invention, a connector terminal comprises a metal socket comprising a base having a center through hole and a cylindrical body extended from the base, a probe head mounted in the metal socket and partially protruding out of the cylindrical body, an elastic member mounted in the metal socket to floatably support the probe head, and a plug plugged into the through hole of the metal socket. Further, the inner and outer surfaces of the base and cylindrical body of the metal socket are electroplated with a metal coating layer to enhance the mechanical properties of the metal socket. When depositing the metal coating layer on the inner and outer surfaces of the base and cylindrical body of the metal socket, the structural design of the through hole enables the applied electric current to be evenly distributed over the inner and outer surfaces of the metal socket and facilitates quick dissipation of released gases during electroplating. Thus, the finished connector terminal has the characteristic of low resistivity (high conductivity), enhancing signal transmission efficiency and stability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique elevational view of a connector terminal in accordance with the present invention. 
         FIG. 2  is an exploded view of the connector terminal in accordance with the present invention. 
         FIG. 3  corresponds to  FIG. 2  when viewed from another angle. 
         FIG. 4  is a sectional side view of the connector terminal in accordance with the present invention. 
         FIG. 5  is a schematic sectional view of the metal socket of the connector terminal in accordance with the present invention, illustrating the distribution of the deposited metal coating layer. 
         FIG. 6  is an exploded view of a part of the connector terminal in accordance with the present invention, illustrating the relationship between the metal socket and the plug. 
         FIG. 7  is a sectional view of  FIG. 6 . 
         FIG. 8  corresponds to  FIG. 7 , illustrating the plug plugged into the through hole of the metal socket. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1-4 , a connector terminal in accordance with the present invention is shown. The connector terminal comprises a metal socket  1 , a probe head  2 , an elastic member  3 , and a plug  4 . 
     The metal socket  1  comprises a base  11 , a cylindrical body  12  perpendicularly extended from one side of the base  11 , an accommodation chamber  10  surrounded by the base  11  and the cylindrical body  12  for accommodating the probe head  2  and the elastic member  3 , an opening  101  located on one end, namely, the top end of the cylindrical body  12  remote from the base  11  and disposed in communication with the accommodation chamber  10 , and a through hole  13  cut through the center of the base  11  in communication with the accommodation chamber  10 . The base  11  has an outer diameter equal to or slightly greater than the outer diameter of the cylindrical body  12 . 
     The probe head  2  is shaped like a stepped cylinder, comprising a lower stoppage portion  21  having a relatively larger diameter, an upper contact portion  22  having a relatively smaller diameter, a tapered propping portion  211  connected between the lower stoppage portion  21  and the upper contact portion  22 , and a leveled or sloping bottom surface  212  located on the bottom side of the lower stoppage portion  21 . Further, the tapered propping portion  211  has an outer diameter gradually reducing in direction from the lower stoppage portion  21  toward the upper contact portion  22 . 
     The elastic member  3  can be a spring, for example, coil spring, having two opposite ends thereof respectively terminating in a first bearing end piece  31  and a second bearing end piece  32 . 
     The plug  4  can be prepared from a flexible material or a rigid material, comprising a conical plug head  41  and a stub plug stem  42  perpendicularly extended from the center of the bottom side of the conical plug head  41 . The stub plug stem  42  has a relatively smaller outer diameter than the conical plug head  41  so that an annular space  421  is defined at the bottom side of the conical plug head  41  around the stub plug stem  42 . 
     Referring to  FIGS. 5-8 , the inner and outer surfaces of the base  11  and cylindrical body  12  of the metal socket  1  are electroplated with a metal coating layer  14  to enhance the mechanical properties of the metal socket  1 , such as conductivity, thermal resistance, wear resistance and corrosion resistance. Further, the structural design of the through hole  13  enables the applied electric current to be evenly distributed over the inner and outer surfaces of the metal socket  1  and facilitates quick dissipation of released gases during electroplating. Thus, after the metal socket  1 , the probe head  2 , the elastic member  3  and the plug are assembled, the finished connector terminal has the characteristic of low resistivity (high conductivity), enhancing signal transmission efficiency and stability. 
     When assembling the metal coating layer-coated metal socket  1  and the plug  4 , insert the conical plug head  41  of the plug  4  upwardly into the through hole  13  of the metal socket  1  with force to the state where the bottom edge of the stub plug stem  42  is kept in flush with the bottom wall of the base  11 . If the plug  4  is prepared from a flexible material (for example, rubber or silicon rubber), the outer diameter of the conical plug head  41  of the plug  4  must be slightly greater than the diameter of the through hole  13  of the metal socket  1  so that the conical plug head  41  of the plug  4  can be elastically deformed and tightly secured to the through hole  13  of the metal socket  1 . If the plug  4  is prepared from a rigid material (for example, rigid plastic material or metal), the outer diameter of the conical plug head  41  of the plug  4  can be equal to or slightly greater than the diameter of the through hole  13  of the metal socket  1  so that the conical plug head  41  of the plug  4  can be tightly secured to the through hole  13  of the metal socket  1  by means of friction. 
     Referring to  FIGS. 2 ,  4 ,  5  and  8  again, after installed the plug  4  in the through hole  13  of the metal socket  1 , put the probe head  2  and the elastic member  3  in the accommodation chamber  10  of the metal socket  1 , then employ a machining technique to reduce the diameter of the opening  101  of the metal socket  1  to the extent where the diameter of the opening  101  is smaller than the lower stoppage portion  21  but larger than the upper contact portion  22 . Thus, subject to the elastic potential energy of the elastic member  3 , the tapered propping portion  211  of the probe head  2  is forced into friction engagement with the perimeter of the opening  101  of the metal socket  1 , preventing the probe head  2  from being forced out of the metal socket  1  accidentally by an external force. Further, the diameter of the through hole  13  of the metal socket  1  is smaller than the outer diameter of the elastic member  3 , preventing escape of the elastic member  3 . After installation, the first bearing end piece  31  and second bearing end piece  32  of the elastic member  3  are respectively stopped against the base  11  of the metal socket  1  and the bottom surface  212  of the probe head  2 , and therefore the elastic member  3  elastically deformably supports the probe head  1  in the metal socket  1 . 
     Multiple pieces of connector terminals constructed in accordance with the present invention can be installed in an electrically insulative substrate (not shown) to form a pogo pin connector for use in a cell phone battery, antenna connector, GPS navigation device, tablet computer, handheld computer, wireless receiver or wireless communication device. After installation of multiple pieces of connector terminals in an electrically insulative substrate, the base  11  of the metal socket  1  of each connector terminal is exposed to the outside of the bottom wall of the electrically insulative substrate, the upper contact portion  22  of the probe head  22  and an upper part of the cylindrical body  12  of the metal socket  1  of each connector terminal around the opening  101  are exposed to the outside of the top wall of the electrically insulative substrate. Thus, the bases  11  of the metal sockets  1  of the connector terminals of the pogo pin connector can then be bonded to a circuit board (not shown). When bonding the base  11  of the metal socket  1  of each connector terminal of the pogo pin connector to the circuit board, the annular space  421  at the bottom side of the conical plug head  41  of the plug  4  around the stub plug stem  42  within the through hole  13  of the metal socket  1  can receive the applied solder paste, presenting insufficient solder coverage and enhancing solder joint strength. 
     Referring to  FIGS. 2 ,  4 ,  5  and  8  again, as stated above, a connector terminal in accordance with the present invention comprises a metal socket  1  comprising a base  11  having a center through hole  13  and a cylindrical body  12  extended from the base  11 , a probe head  2  mounted in the metal socket  1  and partially protruding out of the cylindrical body  12 , an elastic member  3  mounted in the metal socket  1  to floatably support the probe head  2 , and a plug  4  plugged into the through hole  13  of the metal socket  1 , wherein the inner and outer surfaces of the base  11  and cylindrical body  12  of the metal socket  1  are electroplated with a metal coating layer  14  to enhance the mechanical properties of the metal socket  1 . When depositing the metal coating layer  14  on the inner and outer surfaces of the base  11  and cylindrical body  12  of the metal socket  1 , the structural design of the through hole  13  enables the applied electric current to be evenly distributed over the inner and outer surfaces of the metal socket  1  and facilitates quick dissipation of released gases during electroplating. Thus, after the metal socket  1 , the probe head  2 , the elastic member  3  and the plug  4  are assembled, the finished connector terminal has the characteristic of low resistivity (high conductivity), enhancing signal transmission efficiency and stability. Further, the plug  4  can be either solid or hollow, having a cylindrical, conical, round or oval shape. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.