Abstract:
A surface mount contact interposes between a mounted conductor and a pressing conductive member to make the mounted conductor conductive to the pressing conductive member when the mounted conductor and the pressing conductive member are proximate to each other. The surface mount contact includes: a base portion solderable to the mounted conductor; a movable portion elastically deformable according to a distance between the mounted conductor and the pressing conductive member, at least a part of the movable portion being closer to the base portion when the movable portion elastically deforms; and an insulating coating film provided in a region where the movable portion is closer to the base portion and inhibiting electric contact between the movable portion and the base portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Japanese Patent Applications No. 2008-236579 filed Sep. 16, 2008 in the Japan Patent Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    The present invention relates to a surface mount contact and particularly relates to a surface mount contact that interposes between a mounted conductor and a pressing conductive member. The surface mount contact makes the mounted conductor conductive to the pressing conductive member when the pressing conductive member and the mounted conductor are proximate to each other. 
         [0003]    Unexamined Japanese Patent Application Publication No. 2002-170615 discloses a terminal for electric connection, that is, a surface mount contact. The surface mount contact includes a base portion having a solder surface provided for soldering the surface mount contact and a movable portion having a contact region for contact conduction. This conventional surface mount contact is mounted on a mounted conductor so as to establish a conduction between the mounted conductor and a pressing conductive member that pressure-contacts with the contact region. The movable portion is elastically displaced in a direction of being proximate to the base portion when the contact region is pressed toward the base portion. 
         [0004]    The surface mount contact is made of a conductive metal plate formed into a generally U shape. The surface mount contact includes the movable portion having a longitudinal one end elastically bendable. The movable portion also has the other end portion formed by a pair of elastic pieces narrower than other portions. In case of this conventional surface mount contact, by pressure-contacting the pressing conductive member with the contact region of the movable portion, the movable portion is bent elastically downward and an electrical contact state between the pressing conductive member and the movable portion is kept. At that time, if the end portion of the movable portion abuts on the base portion of the surface mount contact, the elastic pieces forming the end portion are bent, thereby inhibiting a contact pressure between the pressing conductive member and the movable portion from excessively increasing. 
         [0005]    However, the conventional surface mount contact as stated above has the following problems. If the elastic pieces of the movable portion abut on the base portion of the surface mount contact, conductive paths via the respective elastic pieces are formed. As a result, an electric resistance, i.e., an impedance, of the surface mount contact slightly changes as a whole. If such a change occurs to the impedance, it is disadvantageously necessary to make adjustments in accordance with the impedance change when the surface mount contact is used to connect, for example, a printed circuit board for RFID (Radio Frequency Identification) with an antenna. 
       SUMMARY 
       [0006]    In a first aspect of the present invention, it is preferable that a surface mount contact is configured to prevent an impedance change by the formation of a new conductive path. 
         [0007]    In the first aspect of the invention, a surface mount contact interposes between a mounted conductor and a pressing conductive member to make the mounted conductor conductive to the pressing conductive member when the mounted conductor and the pressing conductive member are proximate to each other. The surface mount contact includes: a base portion solderable to the mounted conductor; a movable portion elastically deformable according to a distance between the mounted conductor and the pressing conductive member, at least a part of the movable portion being closer to the base portion when the movable portion elastically deforms; and an insulating coating film provided in a region where the movable portion is closer to the base portion and inhibiting electric contact between the movable portion and the base portion. 
         [0008]    The surface mount contact according to the first aspect of the invention includes the insulating coating film that is provided either entirely or partially in the region where the movable portion is proximate to the base portion when the movable portion is elastically displaced in a direction closer to the base portion. Due to this, in the region where the insulating coating film is provided, a new conductive path cannot be formed even if the movable portion contacts with any portion when being elastically displaced in the direction in which the movable portion contacts with the base portion. Therefore, occurrence of the following problem can be avoided: an electrical resistance, i.e., an impedance, of the movable portion, slightly changes as a whole due to formation of such a conductive path. Furthermore, occurrence of a failure resulting from the impedance change can be avoided. 
         [0009]    In what range in a region where the movable portion is closer to the base portion when the movable portion is elastically displaced in a direction closer to the base portion the insulating coating film is provided, that is, whether the insulating coating film is provided entirely or partially and on which part the insulating coating film is provided if the insulating coating film is provided partially are not decided uniquely by a structure, a shape and the like of the surface mount contact. However, these respects may be decided according to the structure, the shape and the like of the surface mount contact based on whether or not these respects are necessary and sufficient for preventing formation of the “new conductive path”. 
         [0010]    As the insulating coating film, available is an insulating coating film obtained by applying a plastic film using an adhesive material, a coating film provided by cold setting coating, a coating film provided by bake hardening coating or the like. Particularly if the insulating coating film provided by bake hardening coating is used for the surface mount contact, a thickness and a color of the coating film can be easily adjusted as compared with use of the plastic film. Moreover, a polymerization reaction occurs to the coating film by heating the coating film during baking. It is, therefore, possible to form a dense and strong coating film. 
         [0011]    Furthermore, if the surface mount contact is formed by pressing a sheet metal, it is particularly suitable to use the bake hardening coating so as not to cause separation of the coating film. 
         [0012]    If the insulating film is provided by bake hardening coating, the coating film is stable against heat since the coating film is already heated once. Due to this, it may be possible to avoid a problem resulting from heating even if the surface mount contact passes through a reflow furnace when attaching the contact to a printed circuit board. 
         [0013]    Moreover, in the surface mount contact, it is preferable that the base portion includes a base plate having the solder surface provided on a lower surface, one end of the movable portion is connected to the base plate via a folded spring portion and the other end of the movable portion is a free end, and that the insulating coating film is provided on each of or one of a surface of the other end that is the free end of the movable portion which surface faces the base plate and a portion of the base plate which portion is predicted to contact with the free end of the movable portion. 
         [0014]    By so configuring, a region where the insulating coating film is provided can be made relatively small. 
         [0015]    Furthermore, in the surface mount contact as stated above, a magnetic material may be dispersed either entirely or partially in the insulating coating film. 
         [0016]    By so configuring, the insulating coating film in which the magnetic material is dispersed functions as a noise filter since such film absorbs noise signal. 
         [0017]    Furthermore, in the surface mount contact, it is preferable that the movable portion has a vacuum-attraction surface that is in parallel to the solder surface in a state in which no external force acts on the surface mount contact, and that the insulating coating film is also provided on the vacuum-attraction surface. 
         [0018]    By so configuring, the insulating coating film provided on the vacuum-attraction surface makes an optical property (for example, reflectivity) of the vacuum-attraction surface differ from that of an adjacent portion (in which no insulating coating film is provided). It is, therefore, possible to improve detection accuracy when an optical detector detects a position of the vacuum-attraction surface. 
         [0019]    It is to be noted that “the vacuum-attraction surface that is in parallel to the solder surface” does not mean being a precisely parallel in a strict sense but means that soldered surface and the vacuum-attraction surface are designed to be parallel. In an actual product, the vacuum-attraction surface is “almost parallel to” the solder surface. 
         [0020]    It is further preferable that the insulating coating film is provided by bake hardening coating. In that case, a thickness and a color of the coating film can be easily adjusted as stated above. Moreover, a polymerization reaction occurs to the coating film by heating the coating film during baking. It is, therefore, possible to form a dense and strong coating film. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1A  is a plan view of a surface mount contact according to a first embodiment of the present invention;  FIG. 1B  is a front view of the surface mount contact according to the first embodiment;  FIG. 1C  is a bottom view of the surface mount contact according to the first embodiment;  FIG. 1D  is a left side view of the surface mount contact according to the first embodiment;  FIG. 1E  is a perspective view of the surface mount contact according to the first embodiment; 
           [0023]      FIGS. 2A ,  2 B and  2 C are explanatory views for use of the surface mount contact according to the first embodiment; 
           [0024]      FIGS. 3A and 3B  are explanatory views of an example of arranging an insulating coating film of the surface mount contact according to the first embodiment; 
           [0025]      FIG. 4A  is a front view of a surface mount contact according to a second embodiment of the present invention;  FIG. 4B  is a side view of the surface mount contact according to the second embodiment;  FIG. 4C  is a perspective view of the surface mount contact according to the second embodiment; and 
           [0026]      FIG. 5  is an explanatory view for use of the surface mount contact according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0027]    As shown in  FIGS. 1A to 1E , a surface mount contact  1  according to a first embodiment of the present invention is formed by pressing a sheet metal having a spring property (such as beryllium copper, phosphor bronze or stainless steel). The surface mount contact  1  has a generally U shape as a whole. The surface mount contact  1  includes a base portion  2 , a spring portion  6 , and a movable portion  7 . 
         [0028]    The base portion  2  includes a planar base plate  3  and a pair of guides  4 . 
         [0029]    A lower surface of the base plate  3  is almost flat and functions as a solder surface  5  used for soldering the surface mount contact  1 . 
         [0030]    Each of the paired guides  4  is raised from a side surface of an end of the base plate  3  to be perpendicular to the base plate  3 , and an upper end of each guide  4  is bent almost at 90 degrees toward the counterpart guide  4  and the bent upper end of the guide  4  serves as a restriction piece  4   a.    
         [0031]    The spring portion  6  is connected to an opposite end of the base plate  3  to the end on the guides  4 -side to be almost perpendicular to the base plate  3 , and an upper end of the spring portion  6  is connected to the movable portion  7 . The spring portion  6  functions as a spring while including up to a connecting portion  6   a  connected to the base plate  3  and a connecting portion  6   b  connected to the movable portion  7 , each of which connecting portions  6   a  and  6   b  is bent into a quarter circular arc (round) shape. 
         [0032]    The movable portion  7  includes a planar movable plate  8  adjacent to the spring portion  6  (connecting portion  6   b ) and a contact portion  10 . An upper surface of the movable plate  8  functions as a vacuum-attraction surface  9 . In a state in which no external force acts on the surface mount contact  1 , the movable plate  8  and the base plate  3  are parallel to each other (and designed to be parallel) and the vacuum-attraction surface  9  and the solder surface  5  are also parallel to each other. 
         [0033]    The contact portion  10  is connected to an opposite end of the movable plate  8  to the spring portion  6 -side end. The contact portion  10  is connected to the movable plate  8  at a foot  10   a  that is of a semicylindrical shape convex upward and that is bent into a quarter circular arc (round) shape. A top of the contact portion  10 , in particular, serve as a contact region. 
         [0034]    A restriction tongue  11  is connected to the contact portion  10  on an opposite side to the foot  10   a.  The restriction tongue  11  enters below the restriction pieces  4   a  and is stopped by lower surfaces of the restriction pieces  4   a,  thereby inhibiting the movable portion  7  from being displaced in a direction away from the base plate  3 . 
         [0035]    As shown in  FIGS. 2A to 2C , the surface mount contact  1  according to this embodiment is surface-mounted on a printed circuit board P (corresponding to a mounted conductor) by soldering the solder surface  5  of the base plate  3  onto a pattern of the printed circuit board P. The printed circuit board P and a pressing conductive member (such as an antenna A) arranged to face the printed circuit board P press the surface mount contact  1  so as to sandwich the surface mount contact  1  between the printed circuit board P and the antenna A ( FIG. 2B ). As a result, a lower surface of the antenna A presses the top of the contact portion  10  (contact region). Therefore, the movable portion  7  is elastically displaced in a direction close to the base plate  3  while using the spring portion  6  as a fulcrum. 
         [0036]    Action of the spring portion  6  to follow the elastic displacement generates an elastic bounce. Due to this, the lower surface of the antenna A pressure-contacts with and is electrically conductive to the top of the contact portion  10  (contact region). Accordingly, the antenna A and the pattern of the printed circuit board P are conductive to each other via the surface mount contact  1 . 
         [0037]    If a downward displacement of the movable portion  7  is large after the antenna A presses the contact region, the restriction tongue  11  possibly contacts with an upper surface of the base plate  3  as shown in  FIG. 2C . 
         [0038]    According to the conventional technique, if the restriction tongue  11  contacts with the base plate  3 , a new conductive path passing from the contact portion  10  through the restriction tongue  11  to the base plate  3  is formed as well as an existing conductive path passing from the contact portion  10  through the movable plate  8  and the spring portion  6  to the base plate  3 . 
         [0039]    However, an insulating coating film is provided on the surface mount contact  1  according to this embodiment so as to prevent formation of such a new conductive path. An example of providing the insulating coating film will next be described. 
       First Example of Providing Insulating Coating Film 
       [0040]    In an example shown in  FIG. 3A , a sequence of an insulating coating film Fa is provided on an inner surface (a surface opposite to the solder surface  5 ) of the base plate  3 , an inner surface of the spring portion  6  (including the connecting portions  6   a  and  6   b ) continuous to the inner surface of the base plate  3 , an inner surface (a surface opposite to the vacuum-attraction surface  9 ) of the movable plate  8  continuous to the inner surface of the spring portion  6  and inner surfaces of the guides  4 . Furthermore, an insulating coating film Fb is provided on the upper surface (vacuum-attraction surface  9 ) of the movable plate  8 . 
         [0041]    These insulating coating films Fa and Fb are formed out of epoxy resin, polyimide resin, PES (Poly Ether Sulphone), fluororesin or the like and obtained by subjecting such a material to bake hardening coating through a baking treatment at 200° C. to 300° C. for 30 to 100 seconds. Baking temperature and baking time differ according to the type, thickness and the like of the resin. As the insulating coating film Fb, a coating material obtained by dispersing a magnetic material (ferrite or metal magnetic material) in the above-stated resin is used. 
         [0042]    In the example shown in  FIG. 3A , the insulating coating film Fa is provided in the above-stated range. Due to this, in a region where the insulating coating film Fa is provided, even if the movable portion  7  contacts with the other portions when being elastically displaced in a direction closer to the base portion  2 , a new conductive path is not formed. Therefore, occurrence of the following problem can be avoided: the electric resistance, that is, impedance, slightly changes as a whole by formation of such a conductive path. In addition, occurrence of a failure resulting from the impedance change can be avoided. 
         [0043]    Since the insulating coating film Fb is formed by dispersing the magnetic material in the resin, the insulating coating film Fb functions as a noise filter since such film absorbs noise signal. Besides, the insulating coating film Fb provided on the vacuum-attraction surface  9  makes an optical property (reflectivity) of the vacuum-attraction surface  9  differ from that of an adjacent portion (the foot  10   a  and a part of the movable plate  8  continuous to the foot la) in which no insulating coating film is provided. It is, therefore, possible to improve detection accuracy during detection of a position of the vacuum-attraction surface  9  by an optical detector (not shown). 
         [0044]    In other words, if a suction nozzle of an automatic mounting device (not shown) vacuum-attracts the vacuum-attraction surface  9 , the optical detector detects the position of the vacuum-attraction surface  9 . Since the detection accuracy during the detection is improved, position accuracy with which the suction nozzle vacuum-attracts the vacuum-attraction surface is also improved. 
       Second Example of Providing Insulating Coating Film 
       [0045]    In an example shown in  FIG. 3B , a sequence of an insulating coating film Fc is provided on an inner surface of a tip end side (a portion to which the guides  4  are connected) of the base plate  3  and inner surfaces of the guides  4 . A sequence of an insulating coating film Fd is provided on an inner surface of a tip end side portion of the contact portion  10  and an inner surface of the restriction tongue  11  (a surface facing the base plate  3 ). That is, the insulating coating film Fd is provided on the surface of a free end (a portion including the tip end side portion of the contact portion  10  and the restriction tongue  11 ) of the movable portion  7  which surface faces the base plate  3 . In addition, the insulating coating film Fc is provided on the portion of the base plate  3  which portion is considered to contact with the free end of the movable portion  3 . It is to be noted that the insulating coating films Fc and Fd are formed out of the same material as that of the insulating coating film Fa and obtained by subjecting such a material to bake hardening coating similarly to the insulating coating film Fa. 
         [0046]    In the example shown in  FIG. 3B , the insulating coating films Fc and Fd are provided in the above-stated ranges. Due to this, in regions where the insulating coating films Fc and Fd are provided, even if the movable portion  7  contacts with the other portions when being elastically displaced in a direction closer to the base portion  2 , a new conductive path is not formed. Therefore, occurrence of the following problem can be avoided: the electric resistance, that is, impedance, slightly changes as a whole by formation of such a conductive path. In addition, occurrence of a failure resulting from the impedance change can be avoided. 
         [0047]    Moreover, as evident from comparison with  FIG. 3A , the regions where the insulating coating films Fc and Fd are provided can be made relatively small. 
       Second Embodiment 
       [0048]    A surface mount contact  21  according to a second embodiment of the present invention is formed by pressing a sheet metal having a spring property (such as beryllium copper, phosphor bronze or stainless steel). The surface mount contact  21  has a structure shown in  FIGS. 4A to 4C . 
         [0049]    The surface mount contact  21  includes a base portion  22 , a spring portion  26 , and a movable portion  27 . 
         [0050]    The base portion  22  includes a pair of legs  23  and a support plate  25  connected between these legs  23 . One end of each of the U-shaped legs  23  is connected to the support plate  25 . The other end of each of the U-shaped legs  23  is suspended downward and a lower end of each of the legs  23  is bent at  90  degrees to serve as a base plate  24 . A lower surface of the base plate  24  is almost flat and serves as a solder surface  24   a  for soldering the surface mount contact  21 . 
         [0051]    The support plate  25  is generally rectangular and the above-stated legs  23  (one end of the U-shaped portions) are connected to two opposing sides of the support plate  25 , respectively. One end of the spring portion  26  is connected to a side of the support plate  25  other than the two sides to which the legs  23  are connected, respectively. As preferably shown in  FIG. 4B , the spring portion  26  is a U-turn folded portion. The movable portion  27  is connected to the other end of the spring portion  26 . 
         [0052]    An elevating displacement plate  29  is connected to an upper end of the movable portion  27  via an obtuse corner portion  28 . The corner portion  28  and/or the elevating displacement plate  29  serves as a contact region. 
         [0053]    A steep sloping portion  31  is connected to an end of the elevating displacement plate  29  via an acute bent portion  30 . A lower end of the steep sloping portion  31  is bent, and the bent lower end is a bent end  32 . The bent end  32  has the same function as the restriction tongue  11  in the first embodiment. The bent end  32  enters below the support plate  25  and contacts with a lower surface of the support plate  25 . 
         [0054]    Because of the above-stated configuration, the elevating displacement plate  29  can be easily displaced downward toward the support plate  25 . However, a displacement (folded deformation) of the elevating displacement plate  29  in a direction of widening a distance between the elevating displacement plate  29  and the support plate  25  is inhibited since the bent end  32  is stopped by the lower surface of the support plate  25 . 
         [0055]    In the surface mount contact  21  according to this embodiment, an insulating coating film F similar to the insulating coating film Fb described in the first embodiment is provided on an upper surface of the elevating displacement plate  29 , an upper surface  27   a  and a lower surface  27   b  of the movable portion  27 , outer surfaces  23   a  and inner surfaces  23   b  of the legs  23  and a lower surface of the bent end  32  by bake hardening coating. 
         [0056]    As shown in  FIG. 5 , this surface mount contact  21  is surface-mounted on a printed circuit board P by soldering the base plate  24  (solder surface  24   a ) onto a pattern of the printed circuit board P by a solder S. Similarly to the first embodiment, the printed circuit board P and a pressing conductive member (such as an antenna) arranged to face the printed circuit board P press the surface mount contact  21  so as to sandwich the surface mount contact  21  between the printed circuit board P and the antenna and the pressing conductive member is contacted with the corner portion  28  (contact region). The pressing conductive member is thereby made conductive to the pattern of the printed circuit board P (corresponding to a mounted conductor) via the surface mount contact  21 . 
         [0057]    Even if the lower surface of the bent end  32  contacts with the base plate  24  due to a deformation, then the bent end  32  is not made conductive to the base plate  24  and impedance change can be inhibited since the insulating coating film F is provided on the lower surface of the bent end  32  by bake hardening coating. 
         [0058]    When the surface mount contact  21  is surface-mounted on the printed circuit board P, a suction nozzle of an automatic implementation device (not shown) vacuum-attracts an upper surface (a vacuum-attraction surface) of the elevating displacement plate  29 . A position of the vacuum-attraction surface at the time of vacuum-attraction is detected by an optical detector (not shown). The insulating coating film F provided on the vacuum-attraction surface makes an optical property (reflectivity) of the vacuum-attraction surface differ from that of an adjacent portion (the corner portion  28  and a bent portion  30 ) in which no insulating coating film is provided. It is, therefore, possible to improve detection accuracy during detection of the position of the vacuum-attraction surface by the optical detector. Accordingly, position accuracy with which the suction nozzle vacuum-attracts the vacuum-attraction surface is also improved. 
         [0059]    Moreover, as shown in  FIG. 5 , the insulating coating film F provided on the legs  23  inhibits the solder S from rising along surfaces of the legs  23 . That is, the insulating coating film F can inhibit excessive solder rising. 
         [0060]    Furthermore, since a magnetic material is dispersed in the insulating coating film F, the insulating coating film F functions as a noise filter since such film absorbs noise signal. 
         [0061]    Needless to say, the present invention is not limited to the embodiments stated so far and the like but can be carried out within a scope that does not depart from the spirit of the present invention.