Abstract:
An electrical connector for connecting oppositely arranged first and second mating electrical devices includes a support member, a first circuit having a plurality of electric contact elements arranged on one surface of the support member to contact electric contacts of the first mating electrical device, a second circuit having a plurality of electric contact elements arranged on the other surface of the support member to contact electric contacts of the second mating electrical device, and conductors connecting the first and second circuits. The electric contact elements of the first and second circuits are formed in the most suitable manner to meet the shapes of the mating electric contacts, respectively. The support member is formed through its thickness with slits closely around the electric contact elements, respectively. As a result, when the electric contacts of the first mating electrical device urge the electric contact elements arranged on the support member to deform the support member, the electric contacts slide on the electric contact elements, thereby removing solders adhered on the electric contact elements. The slits are arranged at random to be directed substantially in different directions so that horizontal forces caused by the urging forces of the electric contacts of the first mating electrical device are canceled out each other, thereby maintaining the axial alignment of the first mating electrical device with the electrical connector.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to an electrical connector for connecting oppositely arranged first and second mating electrical means, comprising a support member, a first circuit having a plurality of electric contact elements arranged on one surface of the support member to contact electric contacts of the first mating electrical means, a second circuit having a plurality of electric contact elements arranged on the other surface of the support member to contact electric contacts of the second mating electrical means, and conductors connecting the first and second circuits, and more particularly to an electrical connector capable of removing solders adhered to electric contact elements from mating electric contacts, while limiting the sliding movement of the mating electric contacts. 
   In order to inspect the performance of a ball grid array connector having a plurality of electric contacts in the form of a hemispherical protrusion made of solder or the like, a socket connector has been used, which is detachably fitted with the ball grid array connector. In such inspections, the electrical contact between electric contacts of the two connectors amounts often to several thousand times or more. As a result, the solder forming the electric contacts of the ball grid array connector tends to adhere to the electric contact elements of the socket connector, causing defective or failed electrical connection therebetween. 
   Owing to such an adherence of the solder to the electric contact elements of the socket connector, removal of the adhered solder therefrom is needed by the use of a brush every several hundred times or thousand times of the contact between the electric contacts and the electric contact elements. However, the removal of the adhered solder by brushing is not an easy matter if not impossible. Earlier use of the brush would make it easy to remove the adhered solder. However, it would increase the number of time of the brushing operation, which would also increase the man-hour of the operation of the electrical connector, resulting in increased cost of operation. 
   There is disclosed in U.S. Pat. No. 5,984,691 an electric contact element of an electrical connector, having the dendritic structure at its surface. According to its explanation the dendritic structure serves only to enhance the electrical connection. The dendritic structure does not contribute to removal of adhered solder on the mating electric contacts. 
   In the U.S. Pat. No. 5,984,691, there is also disclosed the interposer comprising the support member, apertured members arranged on its upper and lower surfaces and the flexible circuitized substrates further arranged on the upper and lower surfaces of the apertured members and supporting the conductors or electric contact elements. With this construction, when a force is applied to the conductors or electric contact elements, the circuitized substrate is depressed within the aperture of the apertured member. In the preamble of the specification of the U.S. Pat. No. 5,984,691, there are described that when a force is applied to the conductive elastomer elements, the resistivity of such conductive elastomer elements will be varied, that when the flexible circuit is subjected to a cyclic stress, it will shorten the fatigue life of the circuit lines on the flexible circuit, thereby possibly resulting in a failed connection, and that if the various components in the system are poor in compressibility, they could not accommodate their manufacturing tolerances. In order to overcome these problems, the invention of the U.S. Pat. No. 5,984,691 proposed the elastic support member. It is clear, however, that this proposal does not have the purpose of removing adhered solder. 
   As can be seen from FIG. 1 of the U.S. Pat. No. 5,984,691, electric contacts arranged on the upper and lower surfaces of the support member are similar in shape to one another. However, there is need to change the shapes of the upper and lower contacts in the most suitable manner depending upon the shapes of mating contacts and their applications. 
   In manufacturing, moreover, it is needed to investigate microstrip lines in consideration of characteristics as transmission lines preferable for measurements. In reality, however, it is very difficult to investigate the microstrip lines. 
   As described above, there is a hitherto used electrical connector comprising a ball grid array connector (first connector) and a socket connector (second connector) which are brought into detachable abutment against one another to electrically connect a plurality of electric contacts made of solder in the form of a hemispherical protrusion provided on one surface of the first connector and a plurality of electric contact elements provided on one surface of the second connector. In such a construction, the electric contacts of the first connector arranged with an interval of 0.8 mm are as little as about 0.2 mm in diameter. The narrower the interval or pitch of the electric contacts, the narrower will become contacting areas with the mating contact elements. Therefore, a CCD (charge-coupled device) camera is commonly used to bring the electric contacts of the first connector and the electric contact elements of the second connector into alignment with one another. 
   As shown in  FIGS. 10 and 12 , the first connector  110  includes a connector plate  111  made of a ceramic or hard resin substrate or board having a rigidity, on one surface of which are provided a plurality of electric contacts  112  of solder (Pb and Sn) in the form of a hemispherical protrusion. These electric contacts  112  are formed by reflow-soldering of solder balls arranged on lands of a hard resin board. 
   The second connector  120  includes a plurality of electric contact elements  130  adapted to contact the electric contacts  112  of the first connector  110 . These electric contact elements  130  are provided on conductors  126  provided on one surface of a substrate  122  or flexible printed board or the like which is formed with slits  124  around the conductors  126 , thereby making flexible the parts of the substrate and the conductors surrounded by the slits  124 . With this construction, the elastic support of the electric contact elements accommodates any differences in height between the electric contacts  112  of the first connector  110 . The electric contact elements  112  are in general treated with a surface treatment such as nickel or gold plating because they are electrically contacting portions. 
     FIG. 11A  illustrates part of such a first connector  110  including four electric contacts, and  FIG. 11B  shows part of the second connector  120  in opposition to the part of the first connector  110 , whose slits  124  are directed in the same direction.  FIG. 11C  is a cross-sectional view of the part of the second connector  120  shown in  FIG. 11B .  FIG. 11D  schematically illustrates the electric contact elements  130  supported in the cantilevered manner before urged.  FIG. 11E  schematically illustrates the electric contact elements  130  urged downward by the electric contacts  112 . As shown in  FIG. 11E , in the case of the arrangement of the slits  124  directed in the same direction, the electric contacts  112  of the first connector  110  are subjected to horizontal direction shown by an arrow A owing to the horizontal components of the reaction forces caused by the parts of the substrate and the conductors surrounded by the slits  124  of the second connector  120 , as a result of which the first connector  110  is subjected to the horizontal force shown by the arrow A. Consequently, the distance of the sliding movement of the electric contacts  112  of the first connector  110  increases although the first connector  110  is guided to prevent it from wobbling in the direction A by a plug and socket mechanism. 
   In the case of 70% or more of the slits  124  directed in the same direction, it would be difficult to restrain the distance of sliding movement of the electric contacts  112  of the first connector  110 , so that contacting positions between the electric contacts  112  of the first connector  110  and the electric contact elements  130  of the second connector  120  would irregularly vary, resulting in unstable contact between the electric contacts  112  and the electric contact elements  130 . 
   With the slits  124  in excess of 70% directed in the same direction, the first connector  110  is further moved by the force shown by the arrow A in  FIG. 11E  in addition to the sliding movement of the electric contacts  112  although the first connector  110  is guided by the plug and socket mechanism. As described above, the range of contact between the electric contacts  112  and the electric contact elements  130  is very narrow, so that the contact therebetween comes out of the range, with the result of defective or failed electrical connection. 
   If the slits  124  are directed substantially in the same direction, the distance of the sliding movement of the electric contacts on the electric contact elements would excessively increase, causing excess wear of the contacting portions therebetween. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide an electrical connector which eliminates all the disadvantages of the prior art and which has electric contact elements on both sides different in shape in the most suitable manner depending upon applications and prevents solder of, for example, a ball grid array connector from adhering even in repeated contacts of several thousand times or more to ensure the stable electrical connection without requiring any investigation of microstrip lines in consideration of characteristics of transmission lines. 
   It is a further object of the invention to provide an electrical connector having first and second connectors, capable of maintaining the alignment of the two connectors in the connecting direction, with a resultant stable electrical connection therebetween. 
   In order to accomplish the first object, in an electrical connector for connecting oppositely arranged first and second electrical means, comprising a support member, a first circuit having a plurality of electric contact elements arranged on one surface of said support member to contact electric contacts of said first mating electrical means, a second circuit having a plurality of electric contact elements arranged on the other surface of the support member to contact electric contacts of said second mating electrical means, and conductors connecting said first and second circuits, according to the invention, said electric contact elements of the first and second circuits are formed in the most suitable manner to meet the shapes of the mating electric contacts, respectively. 
   The expression “the most suitable manner” used herein means that shapes of electric contact elements are most preferably adapted to contact respective electric contacts of the first and second electrical means depending upon the shapes of these electric contacts. For example, if the mating contacts are ball grid array, the electric contact elements are shaped to have at their surfaces ridges having triangular cross-sections, and if the mating contacts are flat pads, the electric contact elements are in the form of a hemispherical protrusion. 
   Preferably, when the first mating electrical means is a ball grid array connector and the second mating electrical means is a printed circuit board, the electric contact elements of the first circuit are each provided on its surface with at least one ridge having a triangular cross-section and the electric contact elements of the second circuit are hemispherical protrusions, thereby making the surfaces of the first and second circuits different in shape. It is preferable that each of the electric contact elements to contact the electric contacts of the first mating electrical means is formed by plating together with the at least one ridge. 
   In a preferred embodiment, the at least one ridge of each of the electric contact elements is formed to extend in a direction substantially parallel to the direction in which the electric contact of the first mating electrical means slides on the electric contact element upon being displaced in the urged direction by the electric contact when the electric contact contacts and urges the electric contact element in the urged direction. 
   Preferably, the support member is formed through its thickness with slits closely around the electric contact elements which contact the electric contacts of the first mating electrical means, respectively. As an alternative, the support member is made of a non-rigid resin capable of being elastically deformed. 
   In one embodiment, the support member is made of a composite body comprising an elastomeric resin material and a metal spring. Alternatively, the support member is composed of a plurality of support element members to form spaces therebetween, thereby more facilitating the deformation of the support member as a whole. In another embodiment, the support member is formed with at least one aperture parallel to or perpendicular to the surfaces of the support member provided with the first and second circuits, thereby more facilitating the deformation of the support member. 
   According to the invention, an electrically connecting length through a conductor between each of the electric contact elements of the first circuit on the surface of the support member and the corresponding electric contact element of the second circuit on the other surface of the support member is less than 5 mm. 
   In order to accomplish the second object, according to a preferred embodiment of the invention, the slits are arranged at random to be directed substantially in different directions. 
   With this arrangement, the first and second connectors maintain their initially contacting positions, while increasing their contacting distances in the connecting direction, thereby controlling the sliding movement of the electric contacts of the first connector. 
   The electrical connector according to the invention has the following significant effects. 
   (1) In the electrical connector according to the invention electric contacts on one surface are electric contact elements each having at least one ridge having the triangular cross-section, while electric contacts on the other surface are hemispherical protrusions different from the electric contact elements to accomplish the most suitable shapes of the electric contacts depending upon applications. 
   (2) According to the invention, at least one ridge having a triangular cross-section extending parallel to the sliding movement of the mating electric contact is provided on the electric contact element, so that in repeated electrical connection therebetween, a stable connection can be achieved without adherence of the solder of the mating electric contact to the electric contact element without causing any unstable electrical connection and any unstable measurement of contacting resistance therebetween. 
   (3) The electrical connector according to the invention is able to prevent the solder of the mating electric contacts from adhering to the electric contact elements, so that there is no need to remove adhered solder by a brush, thereby improving the operating efficiency without lowing the efficiency due to brushing operation. 
   (4) According to the invention an electrically connecting length through a conductor between each of the electric contact elements of the first circuit on the surface of the support member and the corresponding electric contact element of the second circuit on the other surface of the support member is less than 5 mm. Therefore, any particular caution is not required in measurement and inspection, with the result that there is no need to investigate microstrip lines in consideration of characteristics as transmission lines, thereby contributing to lower cost. 
   (5) With the slits arranged at random to be directed substantially in different directions according to the invention, when the contacting depths between the first and second connectors increase in the urging direction, the initially contacting positions or contact starting positions are maintained, thereby limiting the distance of the sliding movement of the electric contacts of the first connector to a certain value. 
   (6) With the slits arranged at random according to the invention in addition to the guiding of the plug and socket mechanism for the first and second connectors, the center axes of the two connectors are kept in alignment with each other without any lateral movement of the first connector relative to the second connector in spite of the sliding movement of the electric contacts of the first connector on the electric contact elements of the second connector. In other words, the sliding distance of the electric contacts on the electric contact elements is limited only to that corresponding to the urged distance of the electric contact elements. 
   (7) According to the invention when the first and second connectors are fitted with each other, the distance of the sliding movement of the electric contacts of the first connector on the electric contact elements of the second connector can be limited to a certain value, thereby obtaining stable electrical connection between two connectors. 
   (8) As the number of circuits increases, it becomes much easier to arrange the slits at random in a more suitable manner. 
   The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of the electrical connector with a connector to be inspected; 
       FIG. 2  is a schematic view for explaining the principle of removal of solder adhered to the electric contact element of the electrical connector according to the invention by means of the sliding movement of the mating electric contact on the electric contact element; 
       FIG. 3  is a plan view illustrating one step for forming elongated ridges on the electric contact element of the electrical connector according to the invention; 
       FIG. 4  is a sectional view of the electrical contact element of the electrical connector according to the invention; 
       FIG. 5  is a plan view of the electrical connector formed with slits around the electric contact elements formed with ridges according to the invention; 
       FIG. 6  is a sectional view of the alternatively modified support member of the electrical connector according to the invention; 
       FIG. 7  is a partly enlarged plan view of the substrate of the second connector according to the invention; 
       FIG. 8  is a partly enlarged sectional view of the electrical connector according to the invention; 
       FIG. 9A  is a partly enlarged sectional view of the first connector according to the invention; 
       FIG. 9B  is a partly enlarged plan view of the second connector according to the invention; 
       FIG. 9C  is a partly enlarged sectional view of the second connector shown in  FIG. 9B ; 
       FIG. 9D  is a schematic pictorial view of the electric contact elements in  FIG. 9C ; 
       FIG. 9E  is a schematic pictorial view illustrating deformed electric contact elements shown in  FIG. 9D  which have been moved downward by the electric contacts; 
       FIG. 10  is a partly enlarged plan view of the substrate of the second connector of the prior art; 
       FIG. 11A  is a partly enlarged sectional view of the first connector for explaining the force acting thereon; 
       FIG. 11B  is a partly enlarged plan view of the second connector of the prior art; 
       FIG. 11C  is a partly enlarged sectional view of the second connector shown in  FIG. 11B ; 
       FIG. 11D  is a schematic pictorial view of the electric contact elements in  FIG. 11C ; 
       FIG. 11E  is a schematic pictorial view illustrating electric contact elements shown in  FIG. 11D  which have been moved downward by the electric contacts; and 
       FIG. 12  is a partly enlarged longitudinal sectional view of the electrical connector of the prior art illustrating one electric contact urging and sliding on one electric contact element. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates an electrical connector  20  according to one embodiment of the invention. A connector  10  located above the electrical connector  20  viewed in the drawing is in this case first mating electrical means to be inspected for its performance and includes a plurality of electric contacts  14  of solder or the like in the form of hemispherical protrusions provided on one surface of a connector plate  12  of a ceramic or hard resin substrate having a rigidity. The solder of the electric contacts is superior for use in electric contacts, including silver, antimony and the like in addition to lead and tin as solder elements. 
   The electrical connector  20  according to the invention comprises a substrate or support member  21  having a first circuit  22  on its one surface facing to the connector  10 . In forming the first circuit  22 , for example, a metal layer such as a copper foil is previously provided on the surface of the support member  21  and then treated as by the printed circuit forming method which is one of the printed circuit board producing techniques to form the first circuit  22  having required conductors. Lead lines  24  to be connected to the first circuit  22  can also be formed by the printed circuit forming method. The material from which to form the first circuit  22  may be any material, insofar as it is highly conductive, preferably, brass, beryllium copper, phosphor bronze or the like. 
   Provided on the first circuit  22  are a plurality of electric contact elements  26  which are made of a material having a high conductivity and to be brought into contact with the electric contacts  14  of the connector  10 . The electrical connector  10  is to be subjected to the inspection for its performance. The electric contact elements  26  are provided on the first circuit  22  as by plating, whose construction will be explained later with reference to  FIGS. 3 and 4 . A protection covering layer  28  of a synthetic resin is provided on the surface of the support member  21  with the exception of the electric contact elements  26  for protecting the first circuit  22  and the lead lines  24 . 
   Provided on the surface of the support member on the side opposite to the first circuit  22  is a second circuit  30  of required conductors, whose material and the forming method are substantially similar to those of the first circuit  22 . The second circuit  30  is provided with a plurality of hemispherical electric contact elements  32  which are brought into contact with pads  42  provided on a substrate  40 . The electric contact elements  32  are made of an alloy of gold, nickel, copper or the like. As can be seen from the drawing, there are differences in shape between the electric contact elements  26  to contact the electric contacts  14  of the connector  10  and the electric contact elements  32  to contact the pads  42  on the substrate  40 , depending upon the applications. 
   Conductors  34  are provided for connecting the first and second circuits  22  and  30 . Usual lead wires, metal foils or the like may be used for the conductors  34 . According to the invention a continuity distance between the electric contact elements  26  and  32  of the electrical connector  20  is less than 5 mm. The term “continuity distance” used herein means an electrically connecting length through a conductor between one electric contact element  26  of the first circuit  22  on one surface of the support member  21  and the corresponding electric contact element  32  of the second circuit  30  on the other surface of the support member  21 . 
   Provided on the substrate  40  mating with the electrical connector  20  as second mating electrical means and located therebelow viewed in the drawing are the pads  42  plated with gold which the electric contact elements  32  contact. 
   When the electric contact elements  26  contact the electric contacts  14  of the connector  10  as first mating electrical means, a small amount of solder of the electric contacts  14  tends to adhere to the electric contact elements  26 . In order to remove the adhered solder therefrom, each of the electric contact elements is formed on its surface with at least one ridge  36  having a triangular cross-section, whose crest is preferably somewhat sharp ( FIG. 4 ). 
   The height of the ridges  36  is of the order of 0.1 mm to 0.2 mm which will sufficient to remove the adhered solder. The number of the ridges  36  is preferably plural in consideration of a positional deviation between the electric contact  14  of the connector  10  and the electric contact element  26  of the electrical connector  20 . With a plurality of ridges  36 , they form a wave-shaped surface. 
   When the connector  10  or first mating electrical means to be inspected is urged against the electrical connector  20  to bring the electric contacts  14  into contact with the electric contact elements  26  of the electrical connector  20 , the support member  21 , or at least parts individually supporting the electric contact elements  26  are elastically deformed downward viewed in  FIG. 1 . Such a deformation causes the electric contact  14  of the connector  10  to move slidably on the electric contact element  26  of the electrical connector  20 , thereby enabling the adhered solder to be removed from the surface of the electric contact element  26 . 
   The principle of removal of the adhered solder with the deformation will be explained with reference to  FIG. 2 . When the electric contact  14  of the connector  10  is urged with a constant force against the electric contact element  26  of the electrical connector  20 , the electric contact  14  contacts the electric contact element  26  at the position X in  FIG. 2 . The electric contact  14  is further urged with the constant force against the electric contact element  26  so that the electric contact element  26  is displaced about a fulcrum shown by O in  FIG. 2 , with the result that the contact point X on the electric contact element  26  moves to the point X. However, as the connector  10  is guided by a socket construction, the electric contact  14  could not move in the horizontal direction, so that the electric contact  14  moves only in the vertical direction. As a result, the electric contact  14  of the connector  10  contacts the electric contact element  26  of the electrical connector  20  at the point Y. Therefore, the electric contact  14  slidably moves on the electric contact element  26  from the point X to the point Y with the constant force so that the adhered solder on the electric contact element  26  can be removed. 
   A method for forming the electric contact element  26  having the elongated ridges  36  each having a triangular cross-section of the electrical connector  20  will be explained with reference to  FIGS. 3 and 4 . First, the protection covering layer  28  is provided all over the first circuit  22 . As shown in  FIG. 3 , at each of locations where the electric contact elements are to be formed, the protection covering layer  28  is formed with at least one slit  50 , preferably a plurality of slits  50  extending in parallel with the sliding movement of the electric contact  14  of the connector  10 . The slits  50  may be formed by, for example, the laser machining. 
   Thereafter, the formed slits  50  are progressively plated with the same material as that of the electric contact element  26  to an extent that the slits  50  are filled with the plating metal to form the electric contact element  26 . The plating with the plating metal is further carried out to form a plurality of ridges  36  which project higher than the surface of the protection covering layer  28  as shown in  FIG. 4 .  FIG. 4  is a sectional view taken along a plane perpendicular to the plane along which the sectional view of  FIG. 1  is taken. 
   The substrate or support member  21  of the electrical connector  20  will be explained. In order to cause the electric contacts  14  of the connector  10  to slide on the electric contact elements  26  of the electrical connector  20 , there is a need for the support member  21  of the electrical connector  20  to be elastically deformed. Therefore, the support member  21  is preferably made of a non-rigid plastic material having an appropriate rigidity such as an elastomeric resin material having a sufficient elasticity. However, without being limited to the resins, a composite body comprising an elastomeric resin material and a metal spring(s) may be used. 
   In another embodiment of the invention, as shown in  FIGS. 1 and 5  the substrate or support member  21  is formed with inverted U-shaped slits  52  closely around the electric contact elements  26  so that the electric contact elements  26  are supported by the respective U-shaped cantilevers. Therefore, when the electric contacts  14  of the connector  10  urge the electric contact elements  26 , they deform to cause the sliding movement of the electric contacts  14  on the electric contact elements  26 . 
   In a further embodiment of the invention shown in  FIG. 6 , a support member  21  may be composed of support element members  53 ,  54  and  55  of, for example, a resin to provide spaces  56  therebetween, thereby increasing the elasticity of the support member  21 . As an alternative, a unitary support member  21  may be formed with at least one aperture  56  to increase the elasticity of the support member  21 , or the upper and lower support element members  53  and  55  may be formed with at least one aperture  58  substantially perpendicular to the surfaces of the support member  21  to facilitate the deformation of the support member  21 . 
   A preferred method for providing the conductors  34  shown in  FIG. 1  will be explained. First, a required number of conductors are extended spaced apart from each other with a predetermined distance and a liquid silicone is poured into the space in which the conductors are extended and is allowed to solidify. The solidified silicone is then sliced in the direction perpendicular to the conductors, and the sliced surface of the silicone is etched by laser so as to permit ends of the conductors to extend from the sliced surface. The ends of the conductors are fitted in apertures provided in metal conductors extending from the electric contact elements of the first and second circuits. After pasty solder is applied to the metal conductors, the conductors extending from the silicon and the metal conductors are firmly connected and fixed to one another by reflow soldering. 
     FIGS. 7 to 9  illustrate an electrical connector  120  according to another embodiment of the invention. For the sake of convenience, the connector  120  is referred herein as a second connector and a mating connector  110  is a first connector. In the drawings, a first connector  110  includes a connector plate  111  made of a ceramic or hard resin and a plurality of electric contacts  112  of solder or the like in the form of a hemispherical protrusion provided on one surface of the connector plate  111 . A second connector  120  includes a connector plate or substrate or board  122  made of a soft resin or non-rigid plastic material having an appropriate rigidity, a plurality of electric conductors  126  of disc-shaped metal layers on one surface of the board  122  facing to the electric contacts  112  of the first connector  110 , electric contact elements  130  provided on the electric conductors  126 , and a protection covering layer  128  of an insulating material on the board  122  on the side of the conductors  126 . The board  122  together with the protection covering layer  128  is formed with inverted U-shaped slits  124  closely around the electric conductors  126 . 
   The first and second connectors  110  and  120  can be detachably fitted with each other with the aid of a plug and socket mechanism in the conventional manner. Needless to say, on the connector plate  122  on the opposite side of the electric contacts  112  there are provided required wiring such as printed circuits electrically connected to the electric contacts  112  of the first connector  110 . 
   The construction of the second connector  120  will be explained. With the second connector according to this embodiment, the required electric conductors  126  are provided on the one surface of the board  122 , for example, by treating a metal layer such as a copper foil previously provided thereon by means of the printed circuit forming method which is one of the board producing techniques as shown in  FIG. 8 . 
   The electric contact elements  130  made of a conductive material superior in electric conductivity are provided at locations where the electric conductors  126  electrically contact the electric contacts  112  of the first connector  110 . The electric conductors  126  are plated with such a conductive material to form the electric contact elements  130  of the conductive material on the electric conductors  126 . The material from which to form the electric conductors  126  may be any material, insofar as it is highly conductive, preferably, brass, beryllium copper, phosphor bronze and the like which have an elasticity. Flexible copper or copper foils may be used for this purpose. 
   In forming the electric contact element  130  by plating, which is to be in contact with the electric contact  112  of the first connector  110 , the electric conductor  126  is first plated with copper, then with nickel, and last with gold. 
   As described above the substrate  122  of the second connector  120  is formed with the U-shaped slits  124  to support the conductors  126  and the electric contact elements  130  elastically as shown in  FIGS. 7 and 8 . When the first connector  110  is brought into abutment against the second connector  120  so that the electric contacts  112  of the first connector  110  abut against the electric contact elements  130  of the second connector  120 , the electric contact elements  130  compliant in the direction toward and away from the first connector  110  will elastically contact them to keep the stable electrical connection therebetween even if there are some differences of the electric contacts  112  in height. In this manner, the electrical connection between the first and second connectors  110  and  120  is accomplished with high reliability. In this case, as the elasticity for the electric conductors  126  and the electric contact elements  130  depends upon the elasticity of the small tongue-shaped movable pieces  136  formed by the U-shaped slits  124  in the substrate  122 , it is required for the substrate  122  of the soft resin or non-rigid plastic material to have a rigidity to an extent such that a sufficient elasticity is given to the small tongue-shaped movable pieces  136 . 
   The arrangement of the slits  124  formed in the substrate  122  will be explained, which is the subject matter of the embodiment. As shown in  FIG. 7 , the slits  124  are arranged at random to be directed substantially in different directions. In other words, the slits  124  are arranged in a manner such that all the slits  124  are not directed in the same direction. Preferably, more than 70% of the slits  124  are not directed in the same direction. As an alternative, the slits  124  are alternately arranged in a manner that two adjacent slits are alternately directed in opposite directions, or in a manner that two adjacent slits are directed in the same direction and next two adjacent slits in the opposite direction. 
   With the arrangement of the slits  124  directed in different directions, when the first and second connectors  110  and  120  are being connected to each other, these connectors increase the contacting depths, maintaining the contact starting positions, thereby limiting the sliding distance of the electric contacts  112  of the first connector  110  to a certain distance. Such an effect will be explained in more detail by referring to  FIGS. 9A to 9E . 
     FIG. 9A  illustrates part of the first connector  110  including four electric contacts, and  FIG. 9B  shows part of the second connector  120  in opposition to the part of the first connector  110 , whose two electric contact elements  130  are directed in the same direction and the remaining two electric contact elements  130  are directed in the opposite direction.  FIG. 9C  is a cross-sectional view of the part of the second connector  120  shown in  FIG. 9B .  FIG. 9D  schematically illustrates the electric contact elements  130  supported in the cantilevered manner before being urged.  FIG. 9E  schematically illustrates the electric contact elements  130  urged downward by the electric contacts  112 . With the arrangement of the slits  124  directed in the different directions in addition to the guidance of the plug and socket mechanism, horizontal components of the urging forces of the electric contacts  112  of the first connector  110  are canceled out each other so that the center lines of the first and second connectors  110  and  120  are maintained in coincidence with each other without any unstable movement. Accordingly, the sliding distance of the electric contacts  112  on the electric contact elements  130  is limited only to that corresponding to the urged distance of the electric contact elements  130 . 
   While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details can be made therein without departing from the spirit and scope of the invention.