Patent Publication Number: US-6984135-B2

Title: Press fit pin

Description:
FIELD OF THE INVENTION 
     The present invention relates to a press fit pin having a press-fitted region to be press-fitted to a conductive through hole of a printed circuit board or other circuit substrate. 
     BACKGROUND OF THE INVENTION 
     As a press fit pin (a terminal) having a press fitted region to be press-fitted and connected to a conductive through hole of a printed circuit board, one having the press fitted region, in which substantially parallel beam-like regions are connected by a deformable connection region, is known. 
     This press fit pin is designed so that, when the press-fitted region is press-fitted to the conductive through hole, outer corner portions of the outer surfaces of the beam-like regions are contacted (pressure-contacted) with the inner wall of the through hole while the connection region is deformed. As a typical example thereof, there is one in which the cross-sectional shape of the press fitted region is formed into an M-shape by the beam-like regions and the connection region (see Japanese Patent Examined Publication No. Sho 60-23471). 
     The press fit pin of this type is obtained by punching a thin metal plate with die and a punch into a predetermined pin shape, and at the same time molding it into a predetermined cross-sectional shape. In the case of the press fit pin having the press fitted region of M-shape in cross-section, sharpened portions must be provided both in the die and the punch, which correspond to a portion of a downwardly oriented V-shaped valley in the upper central portion thereof, and portions of upwardly oriented V-shaped valleys in the outer lower side thereof, but these shape portions are liable to be damaged during processing of the press fit pin, and thus the punch and die are lowered in durability. 
     Accordingly, the present inventors and so on of the present application have proposed a technique described in the Japanese Patent No. 2929176 as a press fit pin devised in view of this problem. In this technique, as shown in  FIG. 9 , a connection region  301  for two beam-like regions  300  and  300  is constructed by a central planar portion  302  extending in a direction substantially perpendicular to the beam-like regions  300  as viewed in a cross-section, and by oblique  303  and  303  extending obliquely outwardly from respective sides of the planar portion  302  and continuous to the respective beam-like regions  300 . The press fit pin of the related art as shown in  FIG. 9  is not so large in deformable capability of the beam-like regions  300 , and an adaptable through hole diameter is limited to a small range. 
     Additionally, other prior art press fit pins include those disclosed in U.S. Pat. No. 4,762,498 and DE 35 35 074 A1. 
     However, recently, such a press fit pin has been required that can be adapted to a through-hole of a wide diameter range of, for example, 0.65 mm to 0.8 mm (a range of 0.15 mm) as defined by IEC standards. 
     Assuming that the conventional press fit pin is applied to the individual conductive through holes having the through hole diameters defined by the IEC standards, a holding force is insufficient with respect to the through hole having the maximum hole diameter of 0.8 mm, and the press-fitted portion may be largely deformed with respect to the through hole of the minimum hole diameter of 0.65 mm to cause a stress concentration and increase in the required insertion force. 
     OBJECT AND SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a press fit pin, which can increase the holding force of the press fit pin with respect to a maximum hole diameter of a mating through hole to which the press fit pin is to be inserted, and at the same time that can suppress the stress concentration and the increase of the required insertion force with respect to a minimum hole diameter of the mating through hole, thereby being adaptable to the hole diameters of the conductive through holes in a wider range in comparison with the related art. 
     To solve these and other problems, a press fit pin of the present invention adopts the following structure. It has a press-fitted region to be press-fitted and connected to a conductive through hole of a printed circuit board. The press-fitted region is formed into substantially an M-shape in cross-section, which has two beam-like regions extending substantially in parallel, and a connection region connecting the beam-like regions in a deformable manner. The connection region is formed into such an arcuate shape in cross-section that an upper surface corresponding to a valley side of the M-shape is a concave surface and an opposite lower surface is a convex surface. A part of the upper surface is partially located in the lower surface side with respect to a straight line connecting left and right inner side continuous portions where the lower surface of the connection region and the inner surfaces of the two beam-like regions are continuous to each other. 
     According to the present invention, since a part of the upper surface of the M shape is located on the lower surface side with respect to the straight line connecting the left and right inner side continuous portions where the lower surface of the connection region and the inner surfaces of the two beam-like regions are continuous to each other, the connection region can be deformed easily. Therefore, a dimension between press-fitted portions on the outer surfaces of the two beam-like regions can be set sufficiently large. This makes it possible to increase the holding force of the press fit pin upon its insertion into a through hole with the maximum hole diameter, as well as to suppress the stress concentration on the press fit pin and the increase of the insertion force for the press fit pin in the case of its insertion into a through hole with the minimum hole diameter. 
     In the present invention, it is preferable that the most concaved portion at the center of the upper surface corresponding to the valley side of the M-shape is located in the lower surface side with respect to the straight line connecting the left and right inner side continuous portions. With this structure, the connection region can be easily and uniformly deformed elastically. 
     It is preferable that the two beam-like regions are reduced in thickness so that they can be elastically deformed when press-fitted to the conductive through hole. By reducing the thickness of the two beam-like regions in this manner, the beam-like regions can be elastically deformed more easily due to the reduced thickness of the beam-like regions. Accordingly, each of the beam-like regions is configured such that the stress concentration stemming from the large deformation of the press-fitted region can be dispersed, and that the increase of the insertion force can be suppressed at the same time. 
     It is preferable that the radius of curvature of the outer surface of each of the two beam-like regions is set larger than the radius of curvature of the inner wall surface of the conductive through hole. This makes it possible to effectively bring the outer surface of each beam-like region into tight contact with the inner wall surface of the conductive through hole. That is, by pressure-contacting the outer surfaces with the inner wall surface of the conductive through hole while elastically deforming the beam-like regions, the holding force of the press fit pin can be increased. 
     The outer surface of each of the two beam-like regions may be substantially equal in radius of curvature to the inner wall surface of the conductive through hole. By making the radius of curvature of the outer surface of each beam-like region substantially equal to the radius of curvature of the inner wall surface of the conductive through hole, the outer surface of the beam-like region can be tightly and substantially uniformly contacted with the inner wall surface of the conductive through hole. Therefore, the stress concentration stemming from large deformation can be effectively dispersed over the entire beam-like regions. 
     It is preferable that the two beam-like regions are formed such that, when the press-fitted region is press-fitted to the conductive through hole, the outer surfaces of the beam-like regions are pressure-contacted with the inner wall surface of the conductive through hole while the connection region is deformed. With this structure, by the deformation effect of the connection region and the beam-like regions, it is possible to further enhance the effects of increasing the holding force of the press fit pin, dispersing the stress, reducing the insertion force, etc. 
     It is preferable that both of the inner side continuous portions where the inner surfaces of the two beam-like regions and the lower surface of the connection region are continuous to each other is formed as a curved surface. With such a configuration, most part of the surface of the press-fitted region is formed by the curved surface. This makes it possible to elastically deform the entire press-fitted region substantially uniformly without any partial nonuniformity when the press-fitted region is elastically deformed. Accordingly, also in view of this point, it is possible to enhance the effects of increasing the holding force of the press fit pin, dispersing the stress, reducing the insertion force, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which: 
         FIG. 1  is a plane view of a press fit pin according to the present invention; 
         FIG. 2  is a front view of the press fit pin according to the present invention; 
         FIG. 3  an enlarged sectional view of a press-fitted region of the press fit pin according to the present invention; 
         FIG. 4  is an enlarged plane view of a base plate portion and a press-fitted region of the press fit pin according to the present invention; 
         FIG. 5  is a sectional view taken along a line V—V of  FIG. 4 ; 
         FIG. 6  is a partial sectional view showing a relationship between the press fit pin according to the present invention and a printed circuit board having conductive through hole; 
         FIG. 7  is a sectional view showing an elastically deformed state of the press-fitted region of the press fit pin according to the present invention with respect to a minimum hole diameter; 
         FIG. 8  is a sectional view showing an elastically deformed state of the press-fitted region of the press fit pin according to the present invention with respect to a maximum hole diameter; and 
         FIG. 9  is an enlarged sectional view of a press-fitted region of a press fit pin in a related art. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, a specific embodiment with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein. Hereafter, an embodiment of the present invention will be discussed with reference to the accompanying  FIGS. 1 to 8 . 
     A press fit pin  1  shown in these drawings is obtained by punching a thin metal plate with a punch and a die (not shown) and molding it. More specifically, a plurality of press fit pins  1  are manufactured such that they are arranged in parallel on one side of a carrier  2  at given intervals with interconnection bars  3  interposed between them, as shown in  FIGS. 1 and 2 . 
     The press fit pin  1  has such a structure that a first pin  5  straightly extends from one side of a rectangular base plate portion  4 , and a second pin  7  straightly extends, via a press-fitted region  6  to be press-fitted and connected to a conductive through hole  20  of a printed circuit board B, from the other side of the base plate portion  4 . Accordingly, the press fit pin  1  includes the first pin  5 , the base plate portion  4 , the press-fitted region  6  and the second pin  7  that are concentric to each another. 
     The cross-sectional shape of the press-fitted region  6  is shown in  FIG. 3 . That is, the press-fitted region  6  has such a shape that substantially parallel two beam-like regions  8  are made continuous to a deformable connection region  9 . By this shape, when the press-fitted region  6  is press-fitted to the conductive through hole  20  of the printed circuit board B, both of the outer surfaces  81  of the two beam-like regions  8  are pressure-contacted with an inner wall surface  21  of the conductive through hole  20 . 
     The press-fitted region  6  is designed such that, at this time, at least outer corner portions  8   a  of the respective outer surfaces  81  of the beam-like regions  8  are pressure-contacted with the inner wall surface  21 . Accordingly, each of the outer corner portions  8   a  is formed in an arcuate shape in cross-section. In the outer surface  81  of each beam-like region  8 , an outer surface portion between the outer corner portions  8   a  is formed as a planar surface. 
     A feature of this press fit pin  1  resides in the structure of the press-fitted region. As shown in  FIG. 3 , it is formed in an M-shape in cross-section by the two beam-like regions  8  and the connection region  9 . The connection region  9  is formed into an arcuate bent portion in cross-section, that has a concave upper surface  9   a  corresponding to a valley side of the M-shape, and a convex lower surface  9   b  opposite therefrom. Further, a part of the upper surface  9   a  is positioned on the lower surface  9   b  side with respect to a straight line L that connects left and right inner side continuous portions  12  where the lower surface  9   b  of the connection region  9  and inner surfaces  8   b  and  8   b  of the two beam-like regions  8  are continuous to each other. 
     In this embodiment, the most concaved portion  9   c  at the center of the upper surface corresponding to the valley side of the M-shape is set to be located on the lower surface  9   b  side with respect to the straight line L connecting the left and right inner side continuous portions  12 . With this structure, the connection region  9  can be easily and uniformly deformed elastically. 
     The two beam-like regions  8  are reduced in thickness so that they can be elastically deformed when press-fitted to the conductive through hole  20 . By reducing the thickness of the two beam-like regions  8 , the beam-like regions  8  can be elastically deformed more easily because of the reduced thickness of the beam-like regions  8 . Accordingly, each of the beam-like regions  8  is configured such that the stress concentration stemming from large deformation of the beam-like regions  8  can be dispersed, and that the increase of the required insertion force can be suppressed at the same time. 
     The radius of curvature of the outer surface  81  of each beam-like region  8  is larger than the radius of curvature of the inner wall surface  21  of the conductive through hole  20 . This is because the outer surface  81  of each beam-like region  8  can be thus effectively brought into tight contact with the inner wall surface  21  of the conductive through hole  20 . That is, by pressure-contacting the outer surfaces  81  with the inner wall surface  21  of the conductive through hole  20  while elastically deforming the beam-like regions  8 , the holding force of the press fit pin can be increased. To fully exhibit this holding force, a diagonal dimension among the outer corner portions  8   a  serving as the press-fitted portions must be set to be larger than a hole diameter (the maximum hole diameter) of the conductive through hole  20 . 
     The outer surface  81  of each beam-like region  8  may be substantially equal in radius of curvature to the inner wall surface  21  of the conductive through hole  20 . By making the radius of curvature of the outer surface  81  of each beam-like region  8  substantially equal to the radius of curvature of the inner wall surface  21  of the conductive through hole  20 , the outer surface  81  of the beam-like region  8  can be tightly contacted with the inner wall surface  21  of the conductive through hole  20  substantially uniformly. This can effectively disperse the stress concentration stemming from large deformation over the entire beam-like region. 
     In this embodiment, the two-beam-like regions  8  are so constructed that, when the press-fitted region  6  is press-fitted to the conductive through hole  20 , as shown in  FIGS. 7 and 8 , mainly the connection region  9  is deformed, while the bean-like regions  8  are also (slightly) deformed so that the outer surfaces  81  of the beam-like regions  8  are pressure-contacted with the inner wall surface  21  of the conductive through hole  20 . 
     That is, as shown in  FIG. 8 , in the case of a conductive through hole  20  having the maximum hole diameter (for example, 0.8 mm), mainly the connection region  9  is deformed, and the beam-like regions  8  are also deformed a little so that the outer surfaces  81  are pressure-contacted with the inner wall surface  21 , thereby providing a sufficient holding force. 
     On the other hand, as shown in  FIG. 7 , in case of a conductive through hole  20  having the minimum hole diameter (for example, 0.65 mm), the connection region  9  is largely deformed, and the entire beam-like regions  8  are also deformed slightly so that the outer surfaces  81  are pressure-contacted with the inner wall surface  21 . Therefore the stress is dispersed, while the increase of the required insertion force is suppressed. 
     Each of the inner side continuous portions  12  where the inner surfaces  8   b  of the two beam-like regions  8  and the lower surface  9   b  of the connection region  9  are continuous to each other is formed as a curved surface. Consequently, most part of the surface of the press-fitted region  6  is formed by the curved surface. This makes it possible to elastically deform the entire press-fitted region  9  substantially uniformly without any partial nonuniformity when the press-fitted region  6  is elastically deformed. Accordingly, also in view of this point, it is possible to enhance the effects of increasing the holding force of the press fit pin, dispersing the stress, reducing the insertion force required, etc. 
       FIGS. 4 and 5  show, in an enlarged manner, a portion of the press fit pin  1  from the base plate portion  4  to the press-fitted region  6 . The base plate portion  4  is formed with two dimples (protrusions)  4   a  protruded from the surface thereof. A plurality of lances  4   b  are formed in edge portions of the base plate  4 , which are, for example, to bite into terminal mounting holes of a housing of a connector to mount the press fit pin  1 . 
     To use this press fit pin  1 , an individual press fit pin  1  is cut off and separated from the carrier  2 . In a state in which the press fit pin  1  is mounted to the housing, the first pin  5  constitutes a pin contact. 
     Since the most concaved portion  9   c  of the upper surface  9   a  of the connection region  9  is disposed at a position corresponding in height to substantially center positions of the beam-like regions  8 , when the press fit pin  1  is press-fitted to the conductive through hole  20  of the printed circuit board, the contact pressures of the outer corner portions  8   a  (at four locations) of the beam-like regions  8  against the inner wall of the conductive through hole can be made substantially uniform. 
     An experiment was actually conducted to investigate a relationship between the through hole diameter and the insertion force or holding force of the press fit pin according to the present invention by inserting the press fit pin of the present invention which is gold-plated or solder plated into through holes having through hole diameters (0.65 mm to 0.8 mm) adopted by the IEC standards. It was found through the experiment that, as the through hole diameter becomes smaller, both the insertion force required and holding force of the press fit pin becomes greater. 
     Further, it was also found that even though the through hole diameter is in such a wide range of from 0.65 mm to 0.8 mm, the obtained insertion force and holding force both fully satisfy the respective target performances such that the insertion force in case of the minimum hole diameter, 0.65 mm, is smaller than a desired value, and the holding force in case of the maximum hole diameter, 0.8 mm, is larger than a desired value. 
     While a preferred embodiment of the present invention is shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.