Abstract:
A surface mount poke in connector is disclosed for mounting upon a surface of a printed circuit board, and is particularly applicable for printed circuit boards supporting LEDs. The connector has a securing means for engaging an inserted wire lead without the use of solder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to co-pending application Ser. No. 11/063,065, filed Feb. 22, 2005 entitled “LOW PROFILE SURFACE MOUNT CONNECTOR” assigned to the assignee of the present invention and which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to a low profile surface mount electrical connector (SMEC) for connecting wire leads to an electrical device constructed using surface mount technology (SMT). The electrical device may be a printed circuit board (PCB), but is not limited thereto. The PCB may contain light emitting diodes (LEDs). The invention is particularly well suited for connecting multiple PCBs in series. 
       BACKGROUND OF THE INVENTION 
       [0003]    Electrical devices are often attached to printed circuit boards (PCBs) by soldering terminals of the electrical device to a surface of the PCB. Surface Mount Technology (SMT) is a particular method of soldering electrical terminals to a PCB. SMT has been developed to affix electrical devices upon PCBs in an automated manner, but the devices may also be placed manually. SMT has reduced cost, improved reliability, and reduced the overall physical size of the PCB in many applications. SMT allows for mounting electrical devices on both sides of a PCB, which was not possible using through hole mounting technology. 
         [0004]    SMT is a method for constructing electronic circuits in which the components are mounted directly onto the surface of a PCB or other suitable component surface. SMT is a proven technology for creating electronic assemblies with higher packaging density when compared with comparable through-hole technology methods of PCB assembly. The components are typically mounted on the board by an automated method such as robot assisted assembly line. Electrical points of contact between the components and the board may be treated with solder paste. Assembled PCBs may then be treated in a high temperature oven at temperatures of up to about 265° C. or higher to reflow the solder. The oven may be operated with an air atmosphere or under an inert atmosphere such as nitrogen. 
         [0005]    Electronic devices so made are called surface-mount devices (SMDs). SMT has largely replaced the previous construction method of fitting components with wire leads into holes in the circuit board, which is called through-hole technology. An SMT component is usually smaller than its leaded counterpart because it has no leads or smaller leads. It may have short pins or leads of various styles, flat contacts, a matrix of balls, or other terminations on the body of the component to assist with fixing the component to the board and/or establish an electrical connection between the board and the component. 
         [0006]    PCBs supporting light emitting diodes (LEDs) may be used to form light displays. Often, multiple LED lighting PCBs are coupled in series by two or more wires to form a string of PCBs. The string of PCBs provides for a flexible light source able to adapt to the contours of large letters used in signage. Current practice is to connect the wires to the PCBs by soldering the leads of the wires to the top surface of the PCB. The step of soldering the wire leads to the boards is time consuming and costly. 
         [0007]    Therefore, there is an unmet need to provide a connector for securely connecting a wire lead to a PCB that is capable of being attached to the PCB by a simple, reliable and cost effective process such as a SMT automated process. The connector must approach the small physical size envelope of the wires to be soldered so as not to shadow any neighboring components in a PCB supporting LEDs. 
       SUMMARY OF THE INVENTION 
       [0008]    This invention provides for a low profile surface mounted electrical connector (SMEC) for connecting a wire lead to a printed circuit board (PCB) or other suitable component surface. The low profile of the connector reduces shadowing by the connector when mounted on a PCB supporting LEDs. The SMEC is attached to the PCB by surface mount technology (SMT), a standardized automated process for placing and attaching electrical and electronic components to PCBs. Attachment may be by soldering, using a conductive adhesive, or other similar method. 
         [0009]    The SMEC is formed of a housing with an opening that allows for a stripped wire lead to be inserted and secured. Inside the opening in the housing is a contact to accept and secure the wire lead firmly in place, and thus establish an electrical path from the wire lead to the PCB. The securing mechanism may be in the form of a barrel, spring or other tensioning mechanism that provides for a strong, reliable electrical connection. The SMEC replaces a solder joint to connect wire leads to PCBs. 
         [0010]    The SMEC is formed of a housing and a contact. The SMEC may be attached to the PCB by conventional SMT techniques. The SMEC may be attached to the PCB by the soldering the contact to the PCB surface. Alternatively, the SMEC may be attached to the surface of the PCB by the use of a conductive adhesive or solder paste or similar attachment method. 
         [0011]    In a first embodiment, the SMEC is attached to the PCB by first attaching the housing to the contact to form the SMEC, and then attaching the SMEC to a surface of the PCB by known SMT techniques. The contact has attachment points for connection to the PCB surface. The attachment points may be attached to the PCB surface by soldering, using a conductive adhesive or solder paste, or by other known SMT techniques. 
         [0012]    In a second embodiment, the SMEC is attached to the PCB by first attaching the contact to the PCB by any known SMT technique including soldering. The contact is provided with attachment points to assist in the mounting to the PCB. Then the housing is attached to the contact. The housing may be attached to the contact by fabricating the housing with a structure that frictionally fits, or snaps into place over the contact. The housing may be manually attached to the contact or may be placed by other SMT techniques. 
         [0013]    In an alternative embodiment, the housing is omitted from the SMEC and the contact is left uncovered upon the PCB surface. This alternative embodiment may be used to reduce the cost of the connection. 
         [0014]    The housing may be formed of a high temperature material that is lightweight and high strength, and able to operate in a high temperature environment such as along the surface of a PCB that supports LEDs. The housing may be formed of a high temperature liquid crystalline polymer (LCP) such as Zenite 6330® by E.I. du Pont de Nemours and Company of Wilmington, Del. or a high temperature nylon such as Stanyl 46 HF® by DSM Engineering Plastics North America, Inc., based in Reading, Pa., or any other known industry acceptable non-conductive high temperature resin. The housing is designed with a low profile and small footprint so that it may be placed upon a PCB supporting lighting LEDs without shadowing or blocking the light emissions of the LEDs. The housing at least partially covers the contact. 
         [0015]    The contact may be cylindrical, square, rectangular or other geometry. The contact may be formed in part or in whole of a conductive material so as to provide an electrical connection from the wire lead to the PCB. For example, the contact may be formed of a phosphor bronze metal with a tin plating or other known industry acceptable conductive metal and plating. The contact may be formed by first forming a predetermined shape from a conductive sheet and then forming the predetermined shape into a cylindrical, rectangular, square or other geometry with extended attachment points. The first forming may be stamping. The conductive sheet may be formed of a phosphor bronze metal sheet with a tin plating. 
         [0016]    The first step in forming the contact is to stamp, cut or by other similar shaping methods form a predetermined shape from stock material. Then, a forming of the predetermined shape into the contact with extended attachment points may be performed by any material shaping method such as rolling and working to form the desired shape. The desired shape may be cylindrical, rectangular, square of other geometry. A combination of different shaping techniques may be used to complete the contact design. The extended attachment points of the contact may be provided with an edge bevel to assist in solder reflow during attachment to the PCB. Beveling of the attachment points is most important when pre-plated stock material is used, but the barrel may be plated at any point during the contact forming process. 
         [0017]    The contact is formed with an engaging mechanism such as a slot and lance, pin or other similar shape for firmly securing the wire lead within the barrel. The slot and lance may be formed into the contact during the forming of the predetermined shape. The lance may be shaped so as to provide for an edge to engage the wire lead within the barrel. The slot and lance may be placed at any radial location on the contact except for where forming seams prohibit the placement. The slot and lance are preferably placed on the side or bottom of the contact. Superior performance has been observed with the slot and lance placed on the bottom since the PCB acts as a stop to lance deformation. 
         [0018]    Further aspects of the method and system are disclosed herein. The features as discussed above, as well as other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  illustrates an arrangement of an embodiment of the surface mounted electrical connector. 
           [0020]      FIG. 2  illustrates a detailed view of a contact. 
           [0021]      FIG. 3  illustrates a sectional view of a contact. 
           [0022]      FIG. 4  illustrates a detailed view of an alternative embodiment of an attachment point of a contact. 
           [0023]      FIG. 5  illustrates a sectional view of the alternative embodiment of an attachment point of a contact. 
           [0024]      FIG. 6  illustrates an application of a surface mounted electrical connector upon a PCB containing LEDs. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    The present invention now will be described more fully hereinafter with reference to the accompanying drawing, in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. 
         [0026]    Referring to  FIG. 1 , an embodiment of the surface mounted electrical connector (SMEC)  10  is depicted. A SMEC  10  was formed of a housing  20  with at least one opening  30  and at least one contact  40 . The housing  20  was formed of Zenite 6330®, a high temperature liquid crystalline polyester by E.I. du Pont de Nemours and Company of Wilmington, Del. The heat resistance of the housing allows it to be attached at the temperatures used to reflow solder the connector to the PCB surface. 
         [0027]    The housing may be formed of a high temperature liquid crystalline polymer (LCP) such as Zenite 6330R or a high temperature nylon such as Stanyl 46 HF® or any other known industry acceptable non-conductive high temperature resin. 
         [0028]    The SMEC  10  allows for the electrical connection of wire leads to the PCB without having to solder the wire leads to the PCB. The housing  20  was designed with a low profile and small footprint so that it could be placed upon a PCB supporting lighting LEDs without shadowing or blocking the light emissions of the LEDs. 
         [0029]    The housing  20  contained at least one opening  30  that was initially formed into the housing  20 . The housing  20  was formed by injection molding, and the opening  20  was formed during this step. The opening  30  may be formed after the initial forming of the housing  20 . The housing  20  was designed to allow the contact  40  to be frictionally fit and retained by the housing  20  by a snap in feature. 
         [0030]    The contact  40  was formed with attachment points  50  to allow the contact  40  to be joined to a PCB by conventional SMT methods such as soldering. The contact  40  was formed with a slot  60  and a lance  70  to secure a wire lead upon insertion into the contact  40 . 
         [0031]      FIG. 2  shows a contact  40  with an attachment point  52  with a different geometry than attachment point  50  of  FIG. 1 . The shape of the attachment point  52  may vary depending upon the surface area desired to be in contact with the PCB surface. 
         [0032]    The contact  40  may be attached to a PCB by soldering the attachment point  50  to the PCB surface. The housing  20  may then be attached to the contact  40  to form the SMEC  10 . Alternatively, the contact  40  may be attached to the housing  20  to form the SMEC  10 , and the SMEC  10  may then be attached to the PCB at the attachment points  50  by a conventional SMT method such as soldering. 
         [0033]    As an alternative method of attachment, the attachment points  50  may be further formed to direct the attachment points  50  down 90 degrees so as to allow the attachment points to be inserted into through holes formed in a PCB surface. 
         [0034]      FIG. 3  illustrates a more detailed view of an embodiment of the contact  40  with a slot  60  and a lance  70  formed on the bottom side of the contact  40 . As shown in  FIG. 3 , the lance  70  is slightly depressed into the contact  40  so as to engage a wire lead when inserted into the contact  40 . The contact  40  was formed by first stamping out a flat pattern blank from a tin plated phosphor bronze sheet. The sheet was a phosphor bronze metal of about 320 microns thick with a tin plating of about 3.0 to about 4.0 microns. It should be noted that the invention is not limited to this sheet or plating thickness, and that thinner or thicker sheet and plating may be selected as determined by the wire gauge and application. The flat pattern blank was then partially rolled and worked to form the contact  40  as shown in  FIGS. 2 and 3  with a cylindrical portion  42  and an attachment point  52  for attaching the contact  40  to a substrate such as a PCB. 
         [0035]    The cylindrical portion  42  was formed with an orientation notch  41  to assist in SMT processing by assisting in mating with the housing  20  to assist in polarization and alignment of the contact  40  attachment points  50 , an expanded cylindrical portion  44  for receiving wire that has insulation thereupon, a wire lead portion  45  for receiving wire that has the insulation stripped therefrom. The contact  40  may be formed without the expanded cylindrical portion  44  to reduce the size of the contact  40 . The wire lead portion  45  may be formed to accept standard wire strip lengths of between about 4 mm and about 7 mm. The wire lead may be a solid wire, a fused stranded wire, a stranded wire, a stranded twisted wire, or any other suitable wire configuration. As shown in more detail in  FIG. 3 , a lance  70  was provided with a sharp edge  72  to assist in securely engaging an inserted wire lead. 
         [0036]    In an additional embodiment of the invention, the barrel may be used upon a PCB without a housing  20 . This additional embodiment may reduce manufacturing and materials cost in uses where it is less important to shield the barrel from unwanted contact. 
         [0037]    In an alternative embodiment of the attachment point as shown in  FIGS. 4 and 5 , the barrel  20  is provided with an alternative attachment point  55 . The attachment point  55  is shown with a beveled section  82  to assist in solder reflow during attachment to a PCB. As further illustrated in  FIG. 5 , the attachment point  55  is provided with a substantially horizontal bottom section  90  and a flat sidewall section  100 . A beveled section  82  with a thickness of about 50 to about 70 percent of the total thickness of the attachment point  55  has provided improved solder reflow properties. The beveled section  82 , which may be formed by hitting the edge of the attachment point  55  with a coining operation, the tin plating on the bottom surface is formed on an angle. The beveled section  82  allows for the solder to more easily wet the angled tin face, creating a fillet of solder that would not otherwise form. 
         [0038]      FIG. 6  illustrates an application of an SMEC  720  as a system and method for attaching wires to a PCB  730 . In this illustration, an SMEC  720  is attached to a surface of a PCB  730 . The SMEC  720  may be attached to the PCB  730  by a conductive adhesive or solder. The PCB  730  also supports resistors  740  and LEDs  750 . Wire leads  760  are attached to the PCB  730  via the SMEC  720 . In this method, several PCBs supporting LEDs may be wired in series to form lighted signs. 
         [0039]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.