Abstract:
A compliant pin ( 10 ) is adapted to be pressed into a through-hole ( 12 ) of a printed circuit board ( 14 ) and have electrical contact with opposing surfaces of a side wall ( 16 ) of the through-hole. The compliant pin ( 10 ) includes a portion ( 30 ) insertable in the through-hole ( 12 ) that includes spaced deflectable beam portions ( 32 ) having outer surfaces ( 54  and  56 ) spaced apart a distance greater than the spacing of the opposing surfaces of the side wall ( 16 ). The beam portions ( 32 ) engage the side wall ( 16 ) and deflect toward each other when the portion ( 30 ) is inserted in the through-hole ( 12 ) and provide a frictional engagement between the beam portions and the side wall. The frictional engagement provides a retention force for retaining the portion ( 30 ) in the through-hole ( 12 ). The portion ( 30 ) includes an opening ( 50 ) that extends through the portion and defines inner surfaces ( 52 ) of said beam portions ( 32 ) opposite the outer surfaces ( 54  and  56 ). The inner surfaces ( 52 ) consist essentially of a plurality of blended cylindrical surfaces ( 60, 62, 64, 66, 68 ).

Description:
TECHNICAL FIELD 
   The present invention relates to an electrical contact. More particularly, the present invention relates to an electrical contact for being pressed into a through-hole of a printed circuit board. 
   BACKGROUND OF THE INVENTION 
   Electrical contacts for providing a variety of different electrical connections are widely known. One type of electrical contact provides an electrical connection between components mounted on a circuit board and electrically conductive traces on the circuit board. These electrical contacts may take the form of pins that are electrically connected to plated-through-holes of the circuit board or to electrically conductive pads of the circuit board. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a compliant pin that is adapted to be pressed into a through-hole of a printed circuit board and have electrical contact with opposing surfaces of a side wall of the through-hole. The compliant pin includes a portion insertable in the through-hole that includes spaced deflectable beam portions having outer surfaces spaced apart a distance greater than the spacing of the opposing surfaces of the side wall. The beam portions engage the side wall and deflect toward each other when the portion is inserted in the through-hole and provide a frictional engagement between the beam portions and the side wall. The frictional engagement provides a retention force for retaining the portion in the through-hole. The portion includes an opening that extends through the portion and defines inner surfaces of said beam portions opposite the outer surfaces. The inner surfaces consist essentially of a plurality of blended cylindrical surfaces. 
   The present invention also relates to a compliant pin adapted to be pressed into a through-hole of a printed circuit board and have electrical contact with opposing surfaces of a side wall of the through-hole. The compliant pin includes a portion insertable in the through-hole and engagable with the opposing surfaces of the side wall to provide a frictional engagement between the portion and the side wall. The frictional engagement provides a retention force of at least four pounds for retaining the portion in the through-hole and has a thickness no greater than 0.4 millimeters. 
   The present invention further relates to an electrical contact adapted to be pressed into a through-hole of a printed circuit board and have electrical contact with a surface defining the through-hole. The contact includes a portion for engaging the surface of the printed circuit board defining the through-hole and providing a frictional engagement with the surface. The frictional engagement provides a retention force for retaining the portion in the through-hole. The portion has an opening extending through the portion and intersecting opposite surfaces of the portion. The opening is defined by opposite beam portions of the portion that deflect when the contact is pressed into the through-hole. The beam portions have surfaces that define the opening. The surfaces consist essentially of a series of cylindrical surfaces on each of the beam portions and define the opening. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the invention will become more apparent to one skilled in the art upon consideration of the following description of the invention and the accompanying drawings in which: 
       FIG. 1  is a perspective view of an electrical contact according to the present invention; 
       FIG. 2  is a front elevation view of the electrical contact of  FIG. 1 ; and 
       FIGS. 3A–3C  are magnified elevation views illustrating the installation of electrical contact of  FIGS. 1 and 2 . 
   

   DESCRIPTION OF EMBODIMENTS 
   Referring to  FIG. 1 , an electrical contact  10  is connectable with a through-hole  12 . In the embodiment illustrated in  FIG. 1 , the through-hole  12  extends through a printed circuit board  14 . It will be appreciated, however, that the through-hole  12  could extend through or into any desired object with which a connection with the contact  10  is desired. 
   The contact  10  is press fit into the through-hole  12  and engages an electrically conductive side wall  16  of the through-hole. For the printed circuit board  14  of the embodiment illustrated in  FIG. 1 , the through-hole  12  is a plated-through-hole in which the side wall  16  is plated or otherwise coated with an electrically conductive material, such as copper, nickel, silver, gold, tin-lead, or a combination or alloy thereof. 
   Referring to  FIGS. 1 and 2 , the electrical contact  10  may include a portion  20  for interfacing with a component (not shown) with which an electrical connection is to be established with the through-hole  12  via the contact. The component may be any device or object with which an electrical connection may be desired, such as a switch, module, integrated circuit, solid state device, discrete device, wire or cable, etc. 
   The electrical contact  10  includes a pin portion  30  and a positioning portion  80  that are aligned with each other and centered on a longitudinal axis  24  of the contact. The interface portion  20  may also be aligned with the pin portion  30  and positioning portion  80  and centered on the axis  24 . 
   The pin portion  30  comprises what may be referred to as a compliant connector pin or a compliant pin. Compliant pins are given this name because they deflect, deform, or otherwise comply with a hole or aperture into which they are press fitted in order to form an interference fit. This interference fit helps connect the compliant pin to a member in which the hole or aperture extends. The pin portion  30  includes a pair of spaced beam portions  32 . As shown in  FIG. 2 , the beam portions  32  may be spaced symmetrically with respect to the axis  24 . The beam portions  32  each have first end portions  34  ( FIG. 2 ) that merge with each other at an interface end  36  of the pin portion  30 . The interface end  36  is located proximate the component interface portion  20  of the electrical contact  10 . The beam portions  32  each have second end portions  40 , opposite the first end portions  34 , that merge with each other at terminal insertion end  42  of the pin portion  30 . 
   The pin portion  30  includes an opening  50  that extends between and intersects opposite surfaces  54  and  56  of the pin portion  30 . The opening  50  is defined by opposing inner surfaces  52  of the beam portions  32 . Conversely, the inner surfaces  52  of the beam portions  32  may be considered as being defined by the opening  50 . The inner surfaces  52  consist of a series of cylindrical surfaces. More specifically, each inner surface  52  includes a first cylindrical surface  60 , a second cylindrical surface  62 , and a third cylindrical surface  64 . As shown in  FIG. 2 , the first cylindrical surfaces  60  are concave surfaces and presented facing each other. The second cylindrical surfaces  62  are convex surfaces presented facing each other. The third cylindrical surfaces  64  are concave surfaces presented facing each other. 
   The inner surfaces  52  share a fourth cylindrical surface  66  that extends between and interconnects the opposing first surfaces  60  of the beams  32 . The fourth cylindrical surface  66  helps define a terminal upper end portion  70  of the opening  50 . The inner surfaces  52  also share a fifth cylindrical surface  68  that extends between and interconnects the opposing third surfaces  64  of the beams  32 . The fifth cylindrical surface  68  helps define a terminal lower end portion  72  of the opening  50 . 
   Each of the cylindrical surfaces  60 ,  62 ,  64 ,  66 , and  68  has a radius and a length. According to the present invention, the radius and length of each cylindrical surface  60 ,  62 ,  64 ,  66 , and  68  selected so that each cylindrical surface is blended with its adjacent cylindrical surfaces. By blended, it is meant that the inner surfaces  52  are formed in their entirety by the cylindrical surfaces  60 ,  62 ,  64 ,  66 , and  68 . In other words, the inner surfaces  52  defining the opening  50  consist only of cylindrical surfaces. For example, the first cylindrical surfaces  60  are blended with their respective second cylindrical surfaces  62  and also with the fourth cylindrical surface  66 , which extends between them. 
   The beam portions  32  each include an outer surface  100  that are presented facing outward, that is, away from each other and away from the axis  24 . The outer surfaces  100  that help define an outer surface of the pin portion  30 . The outer surfaces  100  may include a combination of cylindrical, flat, or curved surfaces that are blended or intersect each other to form an outer contour of the pin portion  30 . Also, as viewed in  FIG. 1 , the outer surface of the pin portion  30  intersects the surfaces  54  and  56  at sharp corners. These intersections could, however, be rounded. As viewed in  FIG. 2 , the contour of the pin portion  30  is such that the interface end  36  and insertion end  42  have a narrowed or tapered configuration. The pin portion  30  tapers outward from the axis  24  or widens between the interface end  36  and insertion end  42 . 
   The pin portion  30  has an interface portion  102  that includes respective portions of the beam portions  32 . The interface portion  102  includes an interface surface  104  of each of the outer surfaces  100  of the beam portions  32 . The interface surfaces  104  include the widest portion of the pin portion  30  as measured along a lateral axis  110  of the pin portion, which extends perpendicular to the longitudinal axis  24 . The interface surfaces  104  are cylindrical in the region of the lateral axis  110  and merge with an insertion surface  106  that extends along the insertion end  42  of the pin portion  30 . The interface surfaces  104  also merge with respective surfaces  108  that extend tangentially between the interface surfaces and the curved cutouts  84 . 
   The interface surfaces  104  are positioned generally opposite the second cylindrical surfaces  62  of the beam portions  32 . The interface portion  102  of the pin portion  30  thus includes portions of each of the beam portions  32  that are widened in comparison with the remainder of the beam portions. 
   The positioning portion  80  is positioned adjacent the interface end  36  of the pin portion  30 . The positioning portion  80  may include a pair of leg portions  82  spaced from each other on opposite sides of the pin portion  30 . The leg portions  82  are partially defined by curved cutouts  84  positioned on opposite sides of the pin portion  30 . The cutouts  84  may also help define the interface end  36  of the pin portion  30 . Each leg portion  82  includes a flat base surface  86  that extends perpendicular to the axis  24 . 
   The contact  10  is constructed of an electrically conductive material, such as a metal alloy. The contact  10  may, for example, be stamped from a metal alloy sheet stock material using a die that is cut to form the desired configuration. The metal alloy sheet stock material may be heat treated or otherwise treated to provide a particular hardness and may be coated or otherwise treated to provide corrosion resistance. 
   One particular type of metal that may be used to construct the contact  10  is ASTM Specification No. B591, which is a tin-brass alloy having the following nominal composition: 89.5% copper, 8% zinc, 2.25% tin, 0.13% nickel, 0.13% iron, and 0.03% phosphorous. Such an alloy is commercially available from the Olin Corporation of Norwalk, Conn., which markets the alloy as Olin Alloy No. 4552. With a spring hardened temper, the ASTM B591 alloy has a tensile strength of 95–110 ksi, a nominal yield strength of 100 ksi, and a nominal elongation of 4%. 
   Another type of metal that may be used to construct the contact  10  is a phosphor-bronze alloy having the following nominal composition: 95.5% copper, 4.2% tin, 0.15% nickel, 0.10% iron, and 0.03% phosphorous. Such an alloy is commercially available from the Olin Corporation of Norwalk, Conn., which markets the alloy as Olin Alloy No. 5118. With a spring hardened temper, Olin Alloy No. 5118 has a tensile strength of 105–119 ksi, a nominal yield strength of 107 ksi, and a nominal elongation of 5%. 
   Another type of metal that may be used to construct the contact  10  is ASTM Specification No. B103, which is a phosphor-bronze alloy having the following nominal composition: 91.9% copper, 8% tin, and 0.1% phosphorous. Such an alloy is commercially available from the Olin Corporation of Norwalk, Conn., which markets the alloy as Olin Alloy No. 521. With a spring hardened temper, the ASTM B103 alloy has a tensile strength of 105–119 ksi, a nominal yield strength of 106 ksi, and a nominal elongation of 6%. 
   Other copper alloys, such as other tin-brass alloys and other phosphor-bronze alloys, as well as alloys of other metals, such as stainless steel, may also be used to construct the contact  10 . These metals may be tempered or otherwise treated to provide a desired hardness, tensile strength, yield strength, etc. 
   The contact  10  of the present invention may be installed in a quick and reliable manner without the use of solder or other materials, such as adhesives or fasteners. This is shown in  FIGS. 3A–3C . Referring to  FIG. 3A , the contact  10  is positioned with the pin portion  30  presented toward the printed circuit board  14 . The contact  10  is directed in a downward direction indicated generally by the arrow labeled  200  toward the through-hole  12  in the circuit board  14 . As described above and shown in  FIGS. 3A–3C , the side wall  16  of the through-hole  12  is formed with an electrically conductive material  202  (e.g., copper, silver, gold, nickel, tin-lead, or combinations or alloys thereof). 
   Referring to  FIG. 3B , as the contact  10  moves in the downward direction  200 , the interface surfaces  104  of the beams  32  engage the printed circuit board  14 . More specifically, the interface surfaces  104  of the beam portions  32  engage diametrically opposite locations on the side wall  16  of the through-hole  12  adjacent the intersection of the side wall and an upper surface  204  of the circuit board  14 . As shown in  FIG. 3B , the interface portions  102  of the pin portion  30  form an interference with the through-hole  12 . More specifically, an interference is formed between the interface surfaces  104  of the beam portions  32  and the side wall  16 . 
   Referring to  FIG. 3C , as the contact  10  moves farther in the downward direction  200 , the beams  32  are urged toward each other as a result of normal forces exerted on the interface portions  102  by the side wall  16  of the through-hole  12 . As the pin portion  30  enters the through-hole  12 , the beam portions  32  deflect toward each other in a direction generally along the lateral axis  110 . Also, as the contact  10  moves farther in the downward direction  200 , the interface surfaces  104  of the beam portions  32  slide past the intersection of the side wall  16  and the upper surface  204  of the printed circuit board  14 . Once the interface portions  102  enter the through-hole  12 , the interface surfaces  104  slide along the side wall  16 . 
   When the beam portions  32  deflect as a result of the pin portion  30  being inserted into the through-hole  12 , they exert a force on the side wall  16 . This force is caused by the resilience of the material used to construct the contact  10 . The material construction of the contact  10  causes the beam portions  32 , when deflated toward each other, to have a spring bias that urges the beam portions away from each other and toward the side wall  16 . Thus, when the contact  10  is inserted into the through-hole  12  and the beam portions  32  are urged toward each other, the beam portions are biased in an opposite direction into engagement with the side wall  16  of the through-hole  12 . This causes a frictional engagement between the interface surfaces  104  of the beam portions  32  and the side wall  16 . Since the side wall  16  may be plated or otherwise coated with an electrically conductive material, this engagement may also result in an electrically conductive connection between the contact  10  and the side wall and thereby between the circuit board  14  and any component connected with the contact. 
   As the pin portion  30  is urged into the through-hole  12 , the side wall  16  may also be deformed as the interfaces portions  102  cut into or gouge the electrically conductive material  202 . This deformation may help promote or enhance the frictional engagement between the interface portions  102  and the side wall  16 . It will be appreciated that the amount of frictional engagement between the beam portions  32  and the side wall  16  can be adjusted to desired levels by altering the material construction of the contact  10  and/or the side wall and also by altering the amount of interference between the interface portions  102  and the side wall. 
   As the contact  10  is moved in the downward direction  200  into the installed condition of  FIG. 3C , the lower surfaces  86  of the leg portions  82  engage the upper surface  204  of the circuit board  14 . This helps prevent over-insertion of the contact  10  into the through-hole  12 . This also helps ensure that the contact  10  is placed in a desired position relative to the circuit board  14  when in the installed condition. This may help place a component connected with the contact  10 , such as a switch, in a desired position relative to the circuit board  14 . 
   The positioning portion  80  helps determine and maintain the axial position of the pin portion  30  in the through-hole  12  when fully inserted. More specifically, the positioning portion  80  helps to limit insertion of the pin portion  30  in the through-hole  12  and thereby helps determine the axial position of the pin portion when fully inserted in the through-hole  12 . The frictional engagement between the pin portion  30  and the side wall  16  helps provide a retention force that helps retain the contact  10  in the installed condition. “Retention force” refers to the degree to which the frictional engagement between the pin portion  30  (i.e., the interface portions  102 ) and the side wall  16  prevents removal of the contact  10  once fully inserted in the through-hole  12 . To measure the retention force exhibited by the contact  10 , a measurement is made as to the amount of force, applied to the contact  10  in a direction generally parallel to the axis  24 , that is required to remove the contact from the through-hole  12  once the contact is fully inserted in the through-hole. 
   The contact  10  has a thickness that is measured perpendicular to the axes  24  and  110  and is indicated generally at T in  FIG. 1 . According to the present invention, the configuration of the contact  10 , combined with the material construction of the contact, allows the contact to be constructed from a relatively thin sheet of material (e.g., the materials listed above) while maintaining a desired retention force. For example, the configuration of the contact  10  may permit the use of a material that is as thin as 0.25–0.50 millimeters or less. This is because the opening, being formed by the blended cylindrical surfaces  60 ,  62 ,  64 ,  66 , and  68 , provides the interface portions  102  with a cross-sectional area that is large in comparison with the remainder of the beam portions  32 . 
   Because the interface portions  102  have this large cross-sectional area, the beam portions  32  are strengthened and stiffened in the area of the interface portions. This helps increase the resilience of the beam portions  32 , which increases the frictional engagement between the interface portions  102  and the side wall  16  and thus helps increase the retention force exhibited by the contact  10  when the contact  10  is fully inserted in the through-hole  12 . 
   When the pin portion  30  of the contact  10  is inserted in the through-hole  12 , the beam portions  32  are stressed as a result of being deflected toward each other. The interface portions  102 , making up the widest portion of the pin portion  30 , are deflected the greatest distance when the contact  10  is inserted in the through-hole  12 . The interface portions  102  may thus be subjected to higher stresses than the remainder of the beam portions  32 . The beam portions  32 , having the contoured configuration defined in part by the blended radiuses of the opening  50 , help spread out the stress uniformly over the interface portions  102 . Incorporation of the blended radiuses avoids having surfaces defining the opening  50  that have sharp corners or intersections that may act as stress risers in the beam portions  32 . This helps prevent overstressing the beam portions  32 , which could result in part failure, and also helps prevent plastic deformation of the beam portions, which could result in a reduced retention force. 
   The increase in retention force realized through the incorporation of the blended radius configuration of the opening  50 , which helps define the beam portions  32 . This, in turn, allows for providing a contact  10  that exhibits a desired retention force while having a relatively thin thickness. In one example embodiment using the contact  10  configuration of  FIGS. 1–3C , the contact has a thickness of 0.24–0.40 millimeters while providing a retention force of 4–6 pounds. In this configuration, an insertion force of about 10 pounds may be required to insert the contact  10  in the through-hole  12 . 
   Referring to  FIG. 2 , a datum line  112  extends parallel to the axis  112  and coplanar with the lower surfaces  86  of the leg portions  82 . In the example embodiment of the contact  10 , the pin portion  30  may have a length measured parallel to the axis  24  from the datum line  112  to the terminal tip of the insertion end  42  of about 3.22 millimeters. 
   The first cylindrical surfaces  60  may have respective radiuses of about 5.1 millimeters and respective axes positioned about 1.19 millimeters from the datum line  112  as measured parallel to the axis  24 . The second cylindrical surfaces  62  may have respective radiuses of about 0.83 millimeters and respective axes positioned about 0.36 millimeters from the datum line  112  as measured parallel to the axis  24 . The third cylindrical surfaces  64  may have respective radiuses of about 0.83 millimeters and respective axes positioned about 2.02 millimeters from the datum line  112  as measured parallel to the axis  24 . The fourth cylindrical surface  66  may have a radius of about 0.11 millimeters and respective axes positioned about 0.05 millimeters from the datum line  112  as measured parallel to the axis  24 . The fifth cylindrical surface  68  may have a radius of about 0.11 millimeters and respective axes positioned about 2.33 millimeters from the datum line  112  as measured parallel to the axis  24 . 
   The interface surfaces  104  may have respective radiuses of about 1.56 millimeters. The width of the pin portion  30 , measured parallel to the axis  110  between the respective apexes of the interface surfaces  104 , may be about 1.24 millimeters. The width of the pin portion  30 , measured parallel to the axis  110  at the insertion end  42  of the pin portion, may be about 0.40 millimeters. The spacing between the opposing first cylindrical surfaces  60 , measured parallel to the axis  110 , may be about 0.24 millimeters. 
   The interface surfaces  104  may have respective radiuses of about 1.56 millimeters and respective axes positioned about 0.97 millimeters from the datum line  112  as measured parallel to the axis  24 . The insertion surfaces  106  may have respective radiuses of about 1.71 millimeters and respective axes positioned about 2.24 millimeters from the datum line  112  as measured parallel to the axis  24 . 
   In the example embodiment, the through-hole  12  may have a diameter of about 1.0 millimeters. This results in an interference between the width of the pin portion  30  and the through-hole  12  of about 0.24 millimeters. Thus, when the contact  10  is inserted into the through-hole  12 , the deflection of the beam portions  32  combined with the extent to which the interface portions  102  dig or gouge into the side wall  16  absorbs this interference. 
   From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.