Patent Publication Number: US-6338632-B1

Title: Compliant, press fit electrical contact having improved retention

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electrical contact, and particularly to a compliant, press fit electrical contact having improved retention means. 
     BACKGROUND OF THE INVENTION 
     Referring to FIG. 7, an U.S. Pat. No. 4,775,326 discloses a press fit contact comprising a mounting portion (not labeled) for mounting the press fit contact in a hole  8  defined in a printed circuit board (not shown). The wall of such a hole is normally lined with copper or the like, which is electrically connected with one or more electrical circuits of the printed circuit board. The mounting portion comprises a pair of outer legs  3 ,  5  and a center leg  4  between the outer legs  3 ,  5  which deform and press against the wall of the hole  8  when the legs  3 ,  4 ,  5  are inserted into the hole  8 . The contact is retained in the hole  8  by friction between the legs  3 ,  4 ,  5  and the hole  8 . However, the legs  3 ,  4 ,  5  contact the wall of the hole  8  at a limited number of points, designated as  11  and  7 , which together have a limited contact area. A correspondingly large sheer stress exists at each interface between the legs  3 ,  4 ,  5  and the wall of the hole  8 . Thus, the press fit contact  1  may damage the copper lining of the hole  8  during insertion, thereby reducing the electrical conduction therebetween. Furthermore, the total area of engagement of the mounting portion and the wall of the hole  8  is so small that the friction force therebetween is unreliable for retaining the contact in the hole. Therefore, over a period of usage and a number of thermal cycles, the press fit contact will yield, shift in the hole  8  and lose electrical performance, thereby affecting reliability of signal transmission. 
     Hence, an improved press fit contact is required to overcome the disadvantages of the prior art. 
     BRIEF SUMMARY OF THE INVENTION 
     A first object of the present invention is to provide a compliant press fit contact which can be securely retained in a hole of a PCB; 
     A second object of the present invention is to provide a compliant press fit contact which will not damage a plated pad in a hole of a PCB during insertion into the hole. 
     A compliant press fit contact in accordance with the present invention comprises a retaining mounting portion for mounting the press fit contact into a metal-coated hole defined in a printed circuit board. The mounting portion is in the shape of a hollow cylinder and defines three slots extending a partial length of the mounting portion and a slit extending a full length of the mounting portion. The slots and the slit are spaced apart from each other in such fashion as to divide the mounting portion into four spring beams. Each beam has an arcuate outer surface bearing against the wall of the metal-coated hole, which elastically deforms, thereby frictionally retaining the press fit contact in the hole. 
     Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of the present embodiment when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a planar front view of a press fit contact of the present invention; 
     FIG. 2 a cross-sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a planar side view of FIG. 1; 
     FIG. 4 is a bottom view of FIG. 3; 
     FIG. 5 is a perspective view of the press fit contact of FIG. 1; 
     FIG. 6 is the press fit contact of FIG. 1 shown inserted into a hole of a printed circuit board which is taken in cross-section to particularly show the engagement of the contact with the wall of the hole; and 
     FIG. 7 is an end view of a prior art press fit contact inserted in a hole of a printed circuit board. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 through 6, a compliant press fit contact  1  in accordance with the present invention comprises a head portion  11 , a retaining mounting portion  12  and a link portion  13  between the head portion  11  and the mounting portion  12 . The head portion  11  mechanically and electrically connects to an electrical device (not shown) which is to be connected to a printed circuit board (PCB)  2 . The press fit contact  1  mounts into a hole  22  defined in the PCB  2 . The hole  22  has a nominal diameter that is less than a maximum outer diameter of the mounting portion  12 . As will be explained below, the mounting portion  12  comprises a spring system which, upon insertion into the hole  22 , produces a retaining force acting on a copper-coated wall  220  of the hole  22  to retain the contact  1  in the PCB  2  and to establish an electrical connection therebetween. The mounting portion  12  is designed in such a manner that, within the tolerance range of the hole diameter, it will generate a sufficient retaining force and still will not damage the coating of the hole upon insertion into the hole. The head portion  11  forms a pair of shoulders  112  for abutting against an edge of the PCB  2  around the hole  22 . 
     The mounting portion  12  of the press fit contact  1  is formed in the shape of a hollow cylinder and defines three longitudinal slots  121  extending a partial length of the mounting portion  12  and a slit  122  extending a full length of the mounting portion  12 . The slots  121  and the slit  122  are spaced apart from each other and thus divide the mounting portion  12  into four spring beams  120  each having an arc-shaped cross-section. Each spring beam  120  has an arced outer surface  124  for engaging the wall  220  of the hole  22 , elastically deforming upon insertion into the hole  22 . A lower end  125  of the mounting portion  12  is tapered for facilitating insertion of the press fit contact  1  into the hole  22 . Referring to FIG. 6, the four spring beams  120  flex evenly toward a center of the mounting portion  12  to an amount determined by the actual diameter of the hole  22  and the mounting portion  12 . By virtue of their resilient qualities, the spring beams  120  exert a force against the wall  220  of the hole  22 . Thus, the press fit contact  1  is securely retained in the hole  22  by the outer surfaces  124  of the four spring beams  120  elastically deforming to engage with the wall  220  of the hole  22 . 
     The mounting portion of the press fit contact of the present invention engages with the copper-coated hole by four arced outer surfaces thereof. Thus, the contacting area of the mounting portion and the hole is greater than that of the prior art contact, thereby enhancing the retaining force between the mounting portion and the hole. Furthermore, because of the increased engaging area and the corresponding lower stress force at the mounting portion-hole interface, the insertion/withdrawal of the mounting portion to/from the hole will not damage the copper coating of the hole. Moreover, the mounting portion elastically deforms when engaged in a hole and maintains its spring capability when it is inserted into the hole and after repeated thermal cycles, thereby ensuring the press fit contact in accordance with the present invention maintains a reliable electrical connection with the printed circuit board. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.