Patent Publication Number: US-7591666-B2

Title: Surface mount crimp terminal and method of crimping an insulated conductor therein

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention generally relates to a electrical connectors and, more specifically, to surface mount crimp terminals and method of crimping insulated conductor therein. 
   2. Description of the Prior Art 
   Typically, to terminate a wire to a surface mount printed circuit board a two-piece connection system is used. Usually, a receptacle is crimped onto the wire and the mating tab or pin is surface mounted on the printed circuit board (“PCB”). A less expensive solution is a one terminal system like the insulation displacement connector (“IDC”). Most surface mount IDC&#39;s are fairly large, require substantial amount of real estate on the board because of their large footprints and do not provide good strain relief on the wire. 
   SUMMARY OF INVENTION 
   Accordingly, it is an object of the present to provide a surface mount crimp terminal that does not have the disadvantages inherent in such prior terminals or contacts. 
   It is another object of the invention to provide a surface mount terminal that is simple in construction and economical to manufacture. 
   It is still another object of the invention to provide a terminal of the type suggested in the previous objects which requires a small footprint on the printed circuit board. 
   It is yet another object of the present invention to provide a terminal of the type under discussion which provides excellent strain relief for the wire. 
   It is a further object of the invention to provide a terminal of the type under discussion that can be readily and efficiently used with automatic pick and place equipment. 
   It is still a further object of the invention to provide a terminal as in the aforementioned objects which provides fast, reliable and efficient mounting on printed circuit boards and termination of insulated conductors therein which may have the insulation pre-stripped or pierced by the terminal during crimping. 
   In order to achieve the above objects, as well as other which will become apparent hereinafter, a surface mount crimp terminal in accordance with the present invention for connection to an insulated conductor having a predetermined substantially uniform external cross-sectional dimension comprises a generally flat deformable conductive member configures to have a generally uniform U-shaped cross-section to define a wire-receiving channel having a bottom wall, suitable for attachment by surface mounting (SM) to a land or pad on a printed circuit board and providing a generally central flat surface area suitable for cooperation with a vacuum nozzle of a pick-and-place machine. A pair of spaced substantially parallel side walls are provide for receiving a length of an insulated conductor between said side walls through an open side opposite to said bottom wall. Said side walls are spaced from each other a distance substantially equal to the external cross-sectional dimension of the insulated conductor. A conductor may have its end pre-stripped and the exposed conductor wires placed within the receiving channel prior to the crimping. Alternatively, insulation piercing means may be provided within said channel for piercing insulation on an insulated conductor upon application of a force applied urging the insulated conductor into said channel towards said bottom wall. Said side walls are capable of being crimped or bent inwardly toward each other and toward said bottom wall to at least partially close or reduce the dimensions of said open side to urge and maintain the pre-stripped conductor or the pierced insulated conductor within said channel. 
   A method of securing an insulated conductor to a printed circuit board using the surface mount insulation terminal in accordance with the invention includes positioning said bottom wall on a land or pad of a printed circuit board. The terminal is mechanically attached to the land or pad, such as by soldering. A length of the insulated conductor is at least partially inserted into said channel. The terminal is then crimped by deforming said side walls towards each other and towards said bottom wall to urge the insulated conductor further into said channel for either making electrical contact with the exposed wires of a pre-stripped conductor or piercing the insulation with insulation piercing means and at least partially closing or reducing the dimensions of said open side to prevent the crimped insulated conductor from moving out from within said channel. A crimping tool in accordance with the invention, for crimping a terminal as aforementioned, comprises a movable block capable of being aligned with and applying a pressure on said side walls. Said block has a recess having a width substantially equal to the spacing between said side walls for initially receiving said side walls within said recess when the crimping tool is positioned at a predetermined height above said bottom wall. Said recess exhibits gradually decreasing width interacting with said side walls as said height is gradually decreased below said predetermined height. Pressure applying pressure means is provided for selectively applying on such crimping tool to deform and crimp said side walls to secure the conductor in place. 
   The surface mount insulation terminals in accordance with the invention may be formed from a blank which includes coined triangular-shaped members formed in said bottom wall capable of being bent to an orientation substantially normal to said bottom wall. Such blanks may be produced in a continuous strip and selectively severed from each other prior to being formed into the final U-shaped configuration of the terminal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be better understood from the following specification when read in conjunction with the accompanying drawings. 
       FIG. 1  is a perspective view of a surface mount insulation piercing crimp terminal in accordance a presently preferred embodiment of the present invention, shown with a vacuum nozzle of a pick-and-place machine for cooperating with a flat surface of the terminal to pick up or deposit the terminal on a printed circuit board; 
       FIG. 2  is a perspective view of the terminal shown in  FIG. 1 , after being mounted or attached to a printed circuit board, such as by soldering, and further showing a crimping tool in the form of a press prior to engagement and crimping of the terminal to pierce the insulation of the insulated conductor and secure the termination; 
       FIG. 3  is an end elevational view of the terminal shown in  FIG. 2 , after the terminal has been crimped, indicating the manner in which the insulated conductor has been pierced to provide contact between the terminal and the internal conductors and the manner in which the side or lateral walls of the terminal secure and maintain the insulated conductor within the terminal; 
       FIG. 4  is a top plan view of two blanks of a continuous strip of blanks that can be used to form the terminals in accordance with the present invention; 
       FIG. 5  is an end elevational view of the crimp terminal in accordance with the invention, illustrating the piercing spikes in their operational positions; and 
       FIG. 6  is a side elevational cross-section of the crimp terminal shown in  FIG. 5  taken along line  6 - 6 . 
   

   DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENT 
   Referring now specifically to the Figures, in which the identical or similar parts are designated by the same reference numerals throughout, and first referring to  FIG. 1 , a surface mount (SM) insulation piercing crimp terminal in accordance with the present invention is generally designated by the reference numeral  10 . 
   While the presently preferred embodiment to be described is for a surface mount insulation displacement connector (IDC) the invention also contemplates to use of such SM crimp connectors or terminals that have ends pre-stripped of insulation that can be similarly crimped. 
   The terminal  10  is useful for connection to an insulated conductor C having a predetermined substantial uniform external cross-sectional dimension. In  FIG. 2 , the insulated conductor is shown to have a substantially uniform circular cross-sectional dimension having a diameter of D. The conductor C includes an sheath of electrical insulation C′ and central conductors or wires C″ imbedded centrally along the axis of the conductor. 
   The crimp IDC terminal  10  is formed of a generally flat deformable conductive member  12  configured to have a generally uniform U-shaped cross-section as shown in the figures, and best exemplified in  FIG. 5 . The conductive member  12  defines a wire-receiving channel  20  having a bottom wall  14  defining an interior surface  14 ′, suitable for attachment to a land or pad  42  on a printed circuit board  40  as shown in  Fig. 2 . 
   A pair of spaced substantially parallel side walls  16 ,  18  are substantially normal to the bottom wall  14 . The walls  14 ,  16  and  18  form the channel  20  for receiving a length of an insulated conductor between the side walls through an open side or top opening  22  opposite the bottom wall  14 . The side walls  16 ,  18  are spaced from each other a distance substantially equal to the external cross-sectional dimension of the insulated conductor C, the diameter D in the example shown in  FIG. 2 . 
   Insulation piercing means is provided within the channel  20  for piercing the insulation C′ on the insulated conductor C positioned between the side walls  16 ,  18  upon application of a force applied to the conductor urging the conductor into the channel  20  towards the bottom wall  14 . In accordance with a presently preferred embodiment, the insulation piercing means are in the form of a plurality of insulation piercing spikes  24  that project form the bottom wall  14  towards the open side or open end  22 . While a single spike may be provided a plurality of spikes are advantageously used to optimize the electrical contact between the terminal  10  and the central conductors C″. 
   To optimize termination and increase the efficiency of attaching a conductor to the terminal, there is preferably provided holding means for holding the conductor C within the channel  20  prior to crimping. In accordance with the presently preferred embodiment, protuberance means in the form of ribs  26 ,  28  or other projections that project into the channel  20  to create an interference fit with the conductor C when at least partially inserted into the channel. While a single rib  26 ,  28  may be provided, in the presently preferred embodiment, a plurality of ribs  26  are provided on the side wall  16  and a plurality of ribs  28  are provided on the side wall  18 . It will be evident that because the insulation C′ is deformable the conductor C can be urged into the channel  20 , where the insulation deforms to conform to accommodate the ribs  26 ,  28 . Such deformation and forceful insertion of the conductor into the channel  20  creates a friction fit which retains the conductor in place, as shown in  FIG. 2 . Preferably, the conductor C is urged inwardly or downwardly as shown in the Figures, from the open end or top opening  22  towards the bottom wall  14  to force at least the tips of the piercing spikes to penetrate into the insulation C′. The degree of initial insertion of the conductor into the channel and initial penetration of the piercing spikes into the insulation is not critical as long as the conductor is substantially received within the channel  20  as shown in  FIG. 2 , where the upper surface of the conductor is substantially coextensive with or slightly below the edges E 1 , E 2  of the side walls  16 ,  18 . 
   While the insulation piercing spike  24  may be created in any desired manner, in the presently preferred embodiment, the spikes  24  are die-cut or coined and bent from a plane of the bottom wall  14  to the orientations shown in which the spikes are substantially normal to the bottom wall  14  and to point upwardly towards the open end or top opening  22 . The piercing spikes  24  are preferably provided proximate to the ribs  26 ,  28 , and away from a central region of the bottom wall  14  which defines a flat pick up area  14 ″ which is suitable for pick up by a vacuum nozzle  32  at a lower peripheral edge or surface  32 ′. The vacuum nozzle  32  can be used in a well known manner to pick up and position the terminal  10  such that the bottom wall  14  is appropriately aligned on a land or pad  42  of a printed circuit board (PCB)  40 . The terminal may then be attached to the land or pad in a conventional manner, such as by solder  44  when the terminal  10  becomes mechanically connected to a land or pad of a PCB  40 . 
   Once the terminal is mechanically attached to the PCB  40 , a length of insulated conductor C is at least partially inserted into the channel  20  as shown in  FIG. 2 . A crimping tool  46  in the form of a block-press  48  may then be used to crimp the terminal as to be described. 
   The crimping tool  46  includes a downwardly open U-shaped channel  50  to provide skirt portions  52  and an interior surface  54 . In order to provide desired crimping action, the spacing W between the skirt portions  52  ( FIG. 2 ) is selected to be substantially equal or slightly larger then the spacing W 1  between the outer edges E 1 , E 2  of the side walls  16 ,  18 . Referring to  FIG. 5 , the spacing W 1  between the outer edges E 1 , E 2  is selected to be slightly smaller then the initial width W of the open channel  50 . The dimension w 2  is the dimension between the inner opposing surfaces of the side walls  16 ,  18 , while the dimension w 3  is the width between opposing ribs  26 ,  28 . To facilitate alignment between the side walls  26 ,  28  and the initial up right surfaces  54   a  of the interior surface  54 , lead-in or guide surfaces  56  are provided in the form of inclined edges or bevels as shown. If there is a slight horizontal misalignment between the crimping tool  46  and the terminal  10  the lead-in or guide surfaces  56  will engage the edges E 1 , E 2  and horizontally shift the terminal or the block press  48  to align them and provide the desired alignment. It will be evident that the movable block  48  is capable of being aligned with an applied pressure on the side walls once the block is moved to engage the upright side walls within the open channel or recess  50 . Initially, the upper edges of the side walls are received within the recess  50  when the crimping tool is position at a predetermined height above the bottom wall  14 . Because of the arcuate shape or configuration  54   b  of the interior surface  54  the side walls are forced inwardly as the height of the block  48  is further decreased below the predetermined height. Continue application of pressure on the press-block selectively applies pressure on the crimping tool to crimp the side walls as suggested in  FIG. 3  by forcing the upper edges E 1 , E 2  of the side walls to move inwardly towards each other and downwardly towards the bottom wall. This applies additional downward pressure on the conductor to enhance piercing action by the spikes  24 . 
   As will be noted, the recess or open channel  50  is elongated and comprises a substantial uniform cross-section. When fully lowered, the press-block  48  will deform or crimp the side walls to conform with the arcuate shape of the interior surface  54  of the U-shaped channel. It is clear, however, that other crimping configurations may be used and any press components may be utilized as long the side walls become crimped with the effect of urging the conductor to a desired depth within the channel and the conductor is retained and prevented from inadvertently leaving the channel. It will be appreciated, therefore, that once the terminal is mounted on a PCB  40 , a simple application of pressure by the press-block  48  simultaneously produces the desired piercing as well as crimping action to secure the position of the conductor. 
   Referring to  FIGS. 4 and 6 , a blank for forming the terminal in accordance with the present invention is illustrated. It will be clear that the terminals  10  may be formed from a continuous strip  60  die-cut to produce individual blanks  62  connected to each other by means of connecting tabs  64 . The connecting tabs are severed along center line  66  prior to forming of the flat strip into the U-shaped terminal. Once severed, resulting tabs  68  may remain at the end of each terminal, as shown in  FIGS. 4 and 6 . However, the extensions  68  may also be severed and removed if desired. 
   The die-cut openings  30  resulting from the bending of the spikes upwardly as shown in  FIG. 6 , creates regions where solder can wick upwardly to fill the openings  30  to provide a better or stronger bond with the PCB  40 . The length l, shown in  FIG. 6 , may be selected to suit a given application. When the side walls are collapsed as suggested in  FIG. 3 , clearly the longer the terminal the more surface area for crimping interaction between the terminal and the conductor and, therefore, the stronger the termination and the more difficult to remove the conductor. Removal of the conductor by pulling it along the length of the channel  20  is also rendered almost impossible by the piercing action of the spikes  24  which have entered into the insulation and make contact with the central conductors or wires C″. 
   The stiffening ribs  26 ,  28  have another function which is to temporarily hold the wire in place into crimping. They are sized in such a way that there is a slight interference fit with the wire insulation. Interference will hold the wire until crimping. The crimping tool is attached to a small pneumatic air hammer. It is placed over the terminal, perpendicular to the PCB, in such a way that the two crimp ears line up with the lead-in surfaces of the tool. When the tool  46  is lowered, the impact will curl the crimp ears forcing the wire all the way down so the insulation piercing spikes to penetrate inside the conductive core of the wire making electrical contact. 
   While the invention has been shown and described in connection with a preferred form of an embodiment it will be understood that modifications may be made without the departure from the scope or spirit of the invention.