Patent Publication Number: US-6213817-B1

Title: Compliant press-fit pin having compliant cantilever beam

Description:
FIELD OF THE INVENTION 
     The present invention relates to a compliant press-fit pin; and, more particularly, to the compliant press-fit pin having a compliant cantilever beam for the sake of electrically coupling a daughter plane to a backplane via a plated through hole formed in the backplane. 
     DESCRIPTION OF THE PRIOR ART 
     Generally, a one-piece connector has been employed as a connector for connecting a daughter plane to a backplane in a communication system. Further, a two-piece connector has been employed to improve signal processing, signal transmission speed and packaging density. 
     The two-piece connector includes a solder type of the two-piece connector and a solderless type of the two-piece connector. Because of a disadvantage of the solder type of the two-piece connector, the solderless type of the two-piece connector is preferred. 
     The solderless type of the two-piece connector includes a rigid body pin and a compliant press-fit pin. The compliant press-fit pin is press-fit into a plated through hole formed in the backplane. The compliant press-fit pin includes C, N, M, S and V types of compliant press-fit pins according to a sectional shaped configuration and an action pin as a division type of the compliant press-fit pin. 
     However, there is a problem that the conventional compliant press-fit pin is disadvantageous in commercialization where a size of the plated through hole is reduced according to high packing density of the communication system. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a compliant press-fit pin for electrically coupling a daughter board to a backplane via a plated through hole formed in the backplane that is capable of providing optimum insertion force and retention force. 
     In accordance with an aspect of the present invention, there is provided a compliant press-fit pin for electrically coupling a first board to a second board via a plated through hole formed in the second board, comprising: an upper part for electrically fixing the first board; a lower part for electrically coupling the first board to a third board via the plated through hole formed in the second board; and a press-fit part located between said upper part and said lower part and containing a fixed beam and a compliant cantilever beam, for electrically coupling the first board fixed to said press-fit part to the second board, wherein the fixed beam and the compliant cantilever beam provide a retention force against a wall of the plated through hole, thereby electrically press-fitting the compliant press-fit pin into the plated through hole, when said press-fit part is inserted into the plated through hole. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the instant invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which: 
     FIG. 1A shows a compliant press-fit pin having a compliant cantilever beam and a backplane in accordance with the present invention; 
     FIG. 1B depicts a sectional view of the backplane taken along a line A-A′ shown in FIG. 1A; 
     FIGS. 1C and 1D show sectional views of the compliant press-fit pin taken along a line B-B′ shown in FIG. 1A; 
     FIG. 2 shows a sectional view of a compliant press-fit pin press-fitted against a wall of the plated through hole shown in FIG. 1A; 
     FIGS. 3A to  3 C are graphs illustrating insertion and withdrawal force according to a front angle of the compliant press-fit pin shown in FIG. 1A; 
     FIGS. 4A and 4B are graphs describing insertion and withdrawal force according to a material of the compliant press-fit pin shown in FIG. 1A; and 
     FIG. 5 is a graph depicting insertion and withdrawal force according to displacement width of the compliant press-fit pin shown in FIG.  1 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1A, there is shown a compliant press-fit pin having a compliant cantilever beam and a backplane in accordance with the present invention. A compliant press-fit pin  100  electrically couples a daughter board (not shown) to a backplane  102  via a plated through hole  105  formed in the backplane  102 . The compliant press-fit pin  100  includes an upper part  101 , a press-fit part  107  and a lower part  108  as a wrap post. 
     The upper part  101  electrically fixes the daughter board. The press-fit part  107  electrically couples the daughter board fixed to the press-fit part  107  to the backplane  102 . The press-fit part  107  is located between the upper part  101  and the lower part  108 . The press-fit part  107  contains a fixed beam  104  and a compliant cantilever beam  103 . The fixed beam  104  and the compliant cantilever beam  103  provide a retention force against a wall of the plated through hole  105 , thereby electrically press-fitting the compliant press-fit pin  100  into the plated through hole  105 , when the press-fit part  107  is inserted into the plated through hole  105 . The lower part  108  electrically couples the daughter board to another daughter board via the plated through hole  105  formed in the backplane  102 . 
     Referring to FIG. 1B, there is shown a sectional view of the backplane taken along a line A-A′ shown in FIG.  1 A. Dimensions of the compliant press-fit pin  101  and the plated through hole  105  are determined by a standard of international electrotechnical commission (IEC). As shown, a diameter of the plated through hole  105  is 0.55 mm to 0.65 mm in a pitch of 2 mm, preferably. Further, a dimension of the press-fit part  107  may be defined by the standard of the IEC. Where the backplane  102  is drilled so that a through hole is formed in the backplane  102 , a diameter of the through hole is 0.68 mm to 0.72 mm. The through hole is plated with a material of Copper or a material of a compound metal made up of Copper and Tin/Lead (Sn/Pb) so that the plated through hole  105  is formed in the backplane  102 . 
     Referring to FIG. 1C, there is shown a sectional view of the compliant press-fit pin taken along a line B-B′ shown in FIG.  1 A. Referring to FIG. 1D, there is shown a sectional view of the compliant press-fit pin taken along a line B-B′ shown in FIG. 1A, when the compliant press-fit pin is press-fitted against a wall of the plated through hole  105 . 
     Referring to FIG. 2, there is shown a sectional view of a compliant press-fit pin press-fitted against a wall of the plated through hole  105  shown in FIG.  1 A. 
     The fixed beam  104  contained in the press-fit part  107  shown in FIG. 1A includes portions  301 ,  302  and  303 . 
     The portion  301  is connected to the upper part  101  shown in FIG. 1A at a rear angle  202 . The rear angle  202  is formed between the portion  301  and a line G running through a longitudinal axis of the upper part  101 . 
     The portion  302  is connected to the portion  301  and parallel to the line G running through the longitudinal axis of the upper part  101 . The portion  302  is in contact with the wall of the plated through hole  105  shown in FIG. 1A when the press-fit part  107  shown in FIG. 1A is inserted into the plated through hole  105 . 
     The portion  303  is connected between the portion  302  and the lower part  108  shown in FIG. 1A at a front angle  201 . The front angle  201  is formed between the portion  303  and the line G running through the longitudinal axis of the upper part  101 . 
     The compliant cantilever beam  103  contained in the press-fit part  107  includes portions  401  and  402 . 
     The portion  401  is connected to the portion  402  and parallel to the line G running through the longitudinal axis of the upper part  101 . The portion  401  is in contact with the wall of the plated through hole  105  when the press-fit part  107  is inserted into the plated through hole  105 . 
     The portion  402  is connected between the portion  401  and the lower part  108  at the front angle  201 . The front angle  201  is formed between the portion  402  and the line G running through the longitudinal axis of the upper part  101 . 
     The fixed beam  104  and the compliant cantilever beam  103  have a thickness of 0.25 mm, respectively. Maximum displacement width between the fixed beam  104  and the compliant cantilever beam  103  is 0.4 mm. The dimension of a reference numeral  204  affects an eccentric displacement. 
     Further, if the fixed beam  104  and the compliant cantilever beam  103  have a thickness of 0.275 mm, respectively, the displacement width between the fixed beam  104  and the compliant cantilever beam  103  is 0.1 to 0.45 mm. When the compliant press-fit pin  100  has the displacement width of 0.1 mm and the plated through hole  105  has a diameter of 0.6 mm, elastic force of the compliant press-fit pin  100  is 0 kgf. Accordingly, the elastic force of the compliant press-fit pin  100  should be more than 0 kgf. 
     When the compliant press-fit pin  100  is inserted into the plated through hole  105 , insertion force should be not beyond 25 kgf according to the standard of the IEC. When the compliant press-fit pin  100  is withdrawn from the plated through hole  105 , withdrawal force should be more than 2 kgf according to the standard of the IEC. 
     Referring to FIG. 3A, there is shown a graph illustrating insertion and withdrawal force according to a variation of the front angle  201  shown in FIG. 2 where the rear angle  202  shown in FIG. 2 is 150°. As shown, when the front angle  201  and the rear angle  202  are 150°, respectively, strongest insertion and withdrawal force are needed. Referring to FIG. 3B, there is shown a graph illustrating insertion and withdrawal force according to a variation of the front angle  201  shown in FIG. 2 where the rear angle  202  shown in FIG. 2 is 160°. Referring to FIG. 3C, there is shown a graph illustrating insertion and withdrawal force according to a variation of the front angle  201  shown in FIG. 2 where the rear angle  202  shown in FIG. 2 is 170°. The compliant press-fit pin  100  shown in FIG. 1A has the front angle  201  of 150° to 160° so that the compliant press-fit pin  100  is appropriate to the standard of the IEC. 
     Referring to FIGS. 4A and 4B, there is shown a graph describing insertion and withdrawal force according to a material of the compliant press-fit pin shown in FIG.  1 A. As shown, in an aspect of an elastic coefficient, Beryllium Copper as a material of the press-fit pin  100  shown in FIG. 1A is preferred. Referring to FIG. 5, there is a graph depicting insertion and withdrawal force according to displacement width of the compliant press-fit pin shown in FIG.  1 A. 
     Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.