Abstract:
An electrical connector comprises a generally rectangular dielectric housing with a mating face and a mounting face. A plurality of terminal support posts extend in a direction from the mounting face towards the mating face and each support post has oppositely facing first and second sidewalls and a connecting surface. A plurality of terminal receiving cavities are spaced along a longitudinal axis of the housing for receiving terminals therein. A plurality of terminals are provided with each including a solder tail portion and a generally U-shaped contact portion. The solder tail portion is positioned along the mounting face and the contact portion includes a first, distal contact leg, a second, proximal contact leg spaced from and generally parallel to the first contact leg and a connecting portion extending between the first and second contact legs. The first contact leg extends along the first sidewall, the second contact leg extending along the second sidewall, and the connecting portion extending along the connecting surface.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to electrical connectors and, more specifically to low profile board-to-board electrical connectors. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Conventionally, a board-to-board connector pair is used to electrically connect two parallel circuit boards together (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2004-55463). Such a board-to-board connector pair includes two connectors which are respectively attached to mutually facing surfaces of two circuit boards and projects therefrom. Referring to  FIG. 1 , first connector  102  includes a plurality of first terminals  103  and is mounted on first circuit board  101 . A second, mating connector  112  includes a plurality of second terminals  113  and is mounted on second circuit board  111 . The first connector  102  and the second connector  112  are mated with and connected to each other, whereby the first circuit board  101  and the second circuit board  111  are connected together. 
         [0003]    Tail portions of the first terminals  103  and tail portions of the second terminals  113  are connected, through soldering, to wiring traces (not shown) formed on the surface of the first circuit board  101  and to wiring traces (not shown) formed on the surface of the second circuit board  101 , respectively. When the first connector  102  and the second connector  112  are mated, contact portions  104  of the first terminals  103  and recessed or concave portions  114  of the second terminals  113  come into mutual contact, whereby the first circuit board  101  and the second circuit board  111  are electrically connected. 
         [0004]    However, in the conventional board-to-board connector pair, since the second connector  112  is formed, by means of over-molding, such that the plastic housing of second connector  112  covers portions of the second terminals  113 , manufacturing costs are increased. Over-molding is often used because solder or flux may rise along the tail portions as indicated by arrow A, and contaminate the concave portions  114  if the second terminals  113  are press-fitted into the second connector  112 . Further, since each first terminal  103  comes into contact with the corresponding second terminal  113  via a single contact portion, if the contact portion is contaminated, contact failure may occur. 
         [0005]    Further, in order to increase the mating strength between the first connector  102  and the second connector  112 , the concave portions  114  are formed on the second terminals  113 , and distal end portions of the contact portions  104  of the first terminals  103  are received by the concave portions  114  for engagement therewith. This configuration may hinder the wiping effect of the contact portions  104 . That is, when the first connector  102  and the second connector  112  are mated, the distal end surfaces of the contact portions  104  move while engaging surfaces of the second terminals  113 , whereby dust or the like adhering the distal end surfaces of the contact portions  104  and the surfaces of the second terminals  113  is removed by the wiping operation. However, the wiping operation may be interrupted when the distal ends of the contact portions  104  enter the concave portions  114 , thereby impairing the wiping effect. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention is to solve the above-mentioned problems in the conventional board-to-board connector pair and to provide a board-to-board connector pair which ensures reliable mating of first and second connectors, prevents occurrence of contact failure, lowers production cost, and has excellent reliability. 
         [0007]    An electrical connector for interconnecting with a mating electrical connector comprises a generally rectangular dielectric housing with a mating face configured for engaging the mating electrical connector and a mounting face configured to be mounted adjacent a circuit member. A plurality of terminal support posts extend in a direction from the mounting face towards the mating face and each support post has oppositely facing first and second sidewalls and a connecting surface extending between the first and second sidewalls. The sidewalls are generally perpendicular to the mating face and the connecting surface is generally parallel to the mating face. A plurality of terminal receiving cavities are spaced along a longitudinal axis of the housing for receiving terminals therein. A plurality of terminals are provided with each including a solder tail portion and a generally U-shaped contact portion. The solder tail portion is positioned along the mounting face and the contact portion includes a first, distal contact leg, a second, proximal contact leg spaced from and generally parallel to the first contact leg and a connecting portion extending between the first and second contact legs. The first contact leg extends along the first sidewall, the second contact leg extending along the second sidewall, and the connecting portion extending along the connecting surface. Outer surfaces of the first and second contact legs are configured to operatively engage mating contact portions of the mating electrical connector. The electrical connector may also include a plurality of openings in the mounting face, with each terminal having a distal end adjacent the first, distal contact leg, and each terminal distal end being received in one of the openings. 
         [0008]    Each terminal may include first and second continuous surfaces, with the first continuous surface extending from the solder tail portion along the mating face and an inner surface of said U-shaped contact portion. The second continuous surface may extend along the outer surface of the first and second contact legs in order to reduce the likelihood of solder wicking from the solder tail to the outer surfaces of the first and second contact legs. In such embodiment, the first continuous surface extends along and engages an outer surface of said support post. 
         [0009]    If desired, each of the first contact legs may include a solder barrier on the outer surface thereof. The electrical connector may further include two rows of generally parallel support posts with terminals mounted thereon. The two rows of support posts generally defining a central cavity therebetween for receiving a portion of a mating electrical connector therein. 
         [0010]    Each solder tail portion may extends directly from the second contact leg at an angle thereto. In one embodiment, the angle would be 90 degrees. The U-shaped contact portion may substantially envelope the sidewalls and connecting surface of the support post in order to provide rigidity to the U-shaped contact portion. 
         [0011]    Through such structure, it becomes possible to ensure reliable mating of the first and second connectors, prevent occurrence of contact failure, lower production cost, and improve reliability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a sectional view of a conventional board-to-board connector pair; 
           [0013]      FIG. 2  is a sectional view of first and second connectors according to an embodiment of the present invention, taken along line B-B of  FIG. 3 ; 
           [0014]      FIG. 3  is a perspective view of the first and second connectors according to the embodiment of the present invention; 
           [0015]      FIG. 4  is a sectional view showing the first and second connectors mated together according to the embodiment of the present invention; and 
           [0016]      FIG. 5  is a fragmented perspective view showing the first and second connectors mated together according to the embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    An embodiment of the present invention will next be described in detail with reference to the drawings. 
         [0018]    Referring to  FIG. 2 , a first connector  10 , which is one of paired board-to-board connectors according to the present embodiment and which is a surface-mount-type connector to be mounted on the surface of one board, is shown with its mating, second electrical connector  30 , which is the other of the paired board-to-board connectors according to the present embodiment and which is also a surface-mount-type connector to be mounted on the surface of another board. The paired board-to-board connectors (i.e., a board-to-board connector pair) according to the present embodiment include the first connector  10  and the second connector  30  and electrically connect a pair of boards. Although the boards shown in  FIG. 1  are printed circuit boards (PCBs), the boards can be of any type such as flexible printed circuits (FPC). 
         [0019]    In the present embodiment, terms for expressing direction, such as up, down, left, right, front, and rear, are used for explaining the structure and action of respective portions of the board-to-board connectors; however, these terms represent respective directions for the case where the board-to-board connectors are used in an orientation shown in the drawings, and must be construed to represent corresponding different directions when the orientation of the board-to-board connectors is changed. 
         [0020]    The first connector  10  includes a first housing (connector main body)  11  integrally formed from an insulative material such as a synthetic resin or plastic. As shown in  FIG. 3 , the first housing  11  has a shape of a generally rectangular thick plate, and a generally rectangular concave portion or receptacle is formed on an upper surface of the first housing  11 . In one embodiment, the first connector  10  has a size of about 15 mm (length) by about  4  mm (width) by about 1.3 mm (thickness); however, the size can be changed freely. In the concave portion, a ridge portion or central projection  13  is formed integrally with the first housing  11 . Further, side wall portions  14  extending parallel to the ridge portion  13  are formed integrally with the first housing  11  such that the side wall portions  14  are located on the opposite sides of the ridge portion  13 . In this case, the ridge portion  13  and the side wall portions  14  project upward from the bottom or mounting surface of the concave portion and extend along the longitudinal direction of the first housing  11 . Thus, elongated groove portions  12  extending along the longitudinal direction of the first housing  11  are formed on both sides of the ridge portion  13  to be located between the ridge portion  13  and the corresponding side wall portion  14 . In the illustrated example, only one ridge portion  13  is provided; however, a plurality of ridge portions may be provided, and the number of the ridge portions is arbitrary. Although the ridge portion  13  has a width of about 0.8 mm, the width may be changed freely. 
         [0021]    First-terminal accommodation or receiving cavities or grooves  15  for accommodating first terminals  21  are formed such that they extend along the opposite side walls of the ridge portion  13  and the bottom walls surfaces of the groove portions  12 . In the embodiment shown, twenty first-terminal accommodation cavities  15  are formed on each of the side walls of the ridge portion  13  and on the bottom wall surface of the corresponding groove portion  12  at a pitch of about 1 mm. Thus, twenty first terminals  21 , which are accommodated within the twenty first-terminal accommodation cavities  15 , are disposed on each of the side walls of the ridge portion  13  and the bottom wall surface of the corresponding groove portion  12  at a pitch of about 1 mm. Further, first-terminal accommodation grooves or recesses  16  are formed on the upper surfaces of the side wall portions  14  at positions corresponding to those of the first-terminal accommodation cavities  15 . The first-terminal accommodation grooves  16  are identical in pitch and number with the first-terminal accommodation cavities  15 . At the middle of each first-terminal accommodation groove  16 , a first-terminal fixation or retention hole  17  is formed such that it vertically penetrates the corresponding side wall portion  14 . Notably, the pitches and numbers of the first-terminal accommodation cavities  15 , the first-terminal accommodation grooves  16 , and the first terminals  21  can be changed freely. 
         [0022]    As shown in  FIG. 2 , each of the first terminals  21  has a fixing or retention portion or leg  22 , a solder tail portion  23 , and a first connection or contact portion  24 , and is integrally formed from an electrically conductive metal sheet through punching or blanking. In the embodiment shown, terminals  21  are not significantly formed after the punching or blanking process and therefore remain in the plane of the sheet metal from which they were punched. Each of the first terminals  21  assumes a side shape obtained by combining the shape of the letter U and that of the letter F, wherein the first connection portion  24  is formed into a generally U-like shape, and the remaining portion is formed into a generally F-like shape. 
         [0023]    The first connection portion  24  has a front side wall portion  24   a  (a side wall portion located near the distal end), which is accommodated in the first-terminal accommodation cavity  15  formed on the corresponding side wall of the ridge portion  13 , and a rear side wall portion  24   c  (a side wall portion located near the solder tail portion), which extends in the vertical direction. A bottom portion between the front side wall portion  24   a  and the rear side wall portion  24   c;  i.e., a portion corresponding to the horizontal portion of the letter U, extends in the lateral direction and is accommodated in the first-terminal accommodation cavity  15  formed on the bottom surface of the corresponding groove portion  12 . A first projecting or contact portion  24   b  is formed in the vicinity of the upper end of the front side wall portion  24   a,  and a second projecting or contact portion  24   d  is formed in the vicinity of the upper end of the rear side wall portion  24   c.  The first and second projecting portions  24   b  and  24   d  project such that they face each other. The first projecting portion  24   b  projects from the first-terminal accommodation cavity  15  and is located within the groove portion  12 . An upper half of the rear side wall portion  24   c  including the second projecting portion  24   d  projects from the first-terminal accommodation cavity  15  and is located within the groove portion  12 . 
         [0024]    The first connection portion  24  has a spring property primarily due to elastic deformation of the front side wall portion  24   a  and the bottom portion  24   c.  Therefore, when the first connector  10  is mated with the second connector  30  and the first projecting portion  24   b  is thus pushed toward the ridge portion  13  by a front side wall portion  44   a  of a second terminal  41  (described below), the first connection portion  24  reacts by virtue of its spring property, so that the first projecting portion  24   b  and the second projecting portion  24   d  nip or engage the second terminal  24 . Thus, the reliability of the electrical connection between first terminal  21  and second terminal  41  can be extremely high. 
         [0025]    Further, the upper horizontal portion of the first terminal  21  extends in the lateral direction and is accommodated within the corresponding first-terminal accommodation groove  16 . The second projecting portion  24   d  is connected to an inner end (end located on the side toward the ridge portion  13 ) of the upper horizontal portion, and the upper end of the solder tail portion  23  is connected to an outer end (end located on the side opposite the ridge portion  13 ) of the upper horizontal portion. The solder tail portion  23  extends in the vertical direction downward, and the lower end surface of the solder tail portion  23  is soldered to a wiring land or pad (not shown) formed on the surface of a circuit board or member. In this case, a path along the first terminal  21  extending from the lower end surface of the solder tail portion  23  to the second projecting portion  24   d  of the first terminal  21  is long and generally travels in a complex manner. Therefore, the phenomenon of solder rising or wicking from solder tail portion  23  all of the way to second projecting portion  24   d  (as well as first projecting portion  24   b ) is less likely to occur. That is, there is little likelihood that solder ascends along the above-mentioned path and adheres to the second projecting portion  24   d,  let alone the possibility that solder adheres to the first projecting portion  24   b  which is separated further from the solder tail portion  23  as compared with the second projecting portion  24   d.    
         [0026]    Moreover, if necessary, a solder barrier (not shown) may be formed in the middle of the path extending from the solder tail portion  23  to the first projecting portion  24   b.  An example of the solder barrier portion is a nickel (Ni) coating layer formed through plating. However, a coating layer of any type may be used, so long as solder substantially does not adhere to the coating layer, and no limitation is imposed on the method of forming the coating layer. 
         [0027]    The upper end of the fixing portion  22  is connected to the middle of the upper horizontal portion. The fixing portion  22  extends in the vertical direction, and is accommodated within a first-terminal fixing hole  17  formed in the side wall portion  14 . As shown in  FIG. 1 , concave portions or recesses are formed on the opposite side surfaces of the fixing portion  22 , and projections corresponding to the concave portions are formed on the wall surface of the first-terminal fixing hole  17 . When the fixing portion  22  is press-fitted into the first-terminal fixing hole  17  from above, as shown in  FIG. 1 , the projections of the first-terminal fixing hole  17  enter the concave portions of the fixing portion  22 , so that the fixing portion  22  and the first-terminal fixing hole  17  are in a mated condition, and the fixing portion  22  is prevented from sliding out of the first-terminal fixing hole  17 . Thus, the first terminal  21  is fixed to the first connector  10 . 
         [0028]    In order to improve adhesion of solder, a gold (Au) coating layer is preferably formed on the lower end surface of the solder tail portion  23  through plating. Further, in order to reduce electrical contact resistance, a gold coating layer is preferably formed on at least the front surface of the first projecting portion  24   b  through plating. 
         [0029]    The second connector  30  includes a second housing (connector main body)  31  integrally formed from an insulative material such as a synthetic resin or plastic. As shown in  FIG. 3 , the second housing  31  has a shape of a generally rectangular thick plate. In one embodiment, the second housing  31  has a size of about 14 mm (length) by about 3 mm (width) by about 1.1 mm (thickness); however, the size can be changed freely. On the lower surface of the second housing  31  (as oriented in  FIG. 3 ), two ridge or rail portions  32  extending in the longitudinal direction are formed integrally with the second housing  31 . The ridge portions  32  are formed along the opposite lateral sides of the second housing  31 . Further, an elongated groove portion  33  extending in the longitudinal direction of the second housing  31  is formed between the two ridge portions  32 . Notably, in the illustrated example, the number of the ridge portions  32  is two; however, a single ridge portion or three or more ridge portions may be provided, and the number of the ridge portions is arbitrary. Although each of the ridge portions  33  has a width of about 0.8 mm, the width may be changed freely. When viewed in cross-section, the ridge portions appear to be a post projecting from the base of housing  31 . 
         [0030]    Second-terminal accommodation or receiving cavities (grooves)  34  for accommodating second terminals  41  are formed such that they extend along the opposite side walls of each ridge portion  32  and the lower surface thereof. In the embodiment shown, twenty second-terminal accommodation cavities  34  are formed on the opposite side walls and the lower surface of each ridge portion  32  at a pitch of about 1 mm. Thus, twenty second terminals  41 , which are accommodated within the twenty second-terminal accommodation cavities  34 , are disposed on the opposite side walls and the lower surface of each ridge portion  32  at a pitch of about 1 mm. Moreover, second-terminal end accommodation or receiving holes  35  are formed at the corners of the groove portion  33  at longitudinal positions corresponding to those of the second-terminal accommodation cavities  34 . The second-terminal end accommodation holes  35  are identical in pitch and number with the second-terminal accommodation cavities  34 . Notably, the pitches and numbers of the second-terminal accommodation cavities  34 , the second-terminal end accommodation holes  35 , and the second terminals  41  can be changed freely. 
         [0031]    As shown in  FIG. 2 , each of the second terminals  41  has a solder tail portion  43  and a second connection or contact portion  44 , and is integrally formed from an electrically conductive metal sheet through punching. Each of the second terminals  41  assumes a side shape obtained by combining the letter U and the letter I, wherein the second connection portion  44  is formed into a generally U-like shape, and the solder tail portion  43  is formed into a generally I-like shape. 
         [0032]    The second connection portion  44  has a vertically extending front side wall portion or contact leg  44   a  (a side wall portion located near the distal end), which is accommodated in the second-terminal accommodation cavity  34  formed on the inner side wall of the ridge portion  32 , and a vertically extending rear side wall portion or contact leg  44   b  (a side wall portion located near the solder tail), which is accommodated in the second-terminal accommodation cavity  34  formed on the outer side wall of the ridge portion  32 . A bottom connecting portion or bight between the front side wall portion  44   a  and the rear side wall portion  44   b;  i.e., a portion corresponding to the horizontal portion of the letter U, extends in the lateral direction and is accommodated in the second-terminal accommodation cavity  34  formed on the lower surface of the ridge portion  32 . The end portion of the front side wall portion  44   a  is received in the second-terminal end accommodation hole  35 . The second terminal  41  is fixed to the second connector  30  through press-fitting of the second connection portion  44  into the second-terminal accommodation cavity  34 . 
         [0033]    The inner end (end on the side toward the groove portion  33 ) of the solder tail portion  43  is connected to the rear side wall portion  44   b,  and extends in the lateral direction. The upper surface of the solder tail portion  43  is soldered to a wiring land or pad (not shown) formed on the surface of a circuit board or member. 
         [0034]    An engagement recess (engagement portion)  45  is formed on an outer side surface of the rear side wall portion  44   b  of the second connection portion  44  such that the engagement recess portion  45  engages the second projecting portion  24   d  of the corresponding first terminal  21  when first and second connectors  10  and  30  are mated. When the first connector  10  is mated with the second connector  30 , since the second projecting portion  24   d  enters and engages with the engagement recess portion  45 , the connection between the first terminal  21  and the second terminal  41  is reliably maintained, whereby the likelihood of disengagement of the first connector  10  and the second connector  30  is reduced. Notably, the first projecting portion  24   b  of the first terminal  21  comes into contact with the flat surface of the front side wall portion  44   a  of the second connection portion  44 . 
         [0035]    A solder barrier (barrier portion)  46  formed from a coating layer to which solder substantially does not adhere is provided so as to cover a portion of the rear side wall portion  44   b  of the second connection portion  44 . An example of the solder barrier  46  is a nickel (Ni) coating layer formed through plating. However, a coating layer of any type may be used, so long as solder substantially does not adhere to the coating layer, and no limitation is imposed on the method of forming the coating layer. The solder barrier  46  prevents occurrence of the phenomenon in which solder ascends along the second terminal  41  and adheres to the surface of the rear side wall portion  44   b  when the solder tail portion  43  is soldered to a wiring land of a board. Notably, the solder barrier  46  is desirably formed in an area including at least the engagement recess portion  45 . Thus, solder having ascended from the solder tail portion  43  is prevented from adhering and filling the engagement recess portion  45 . Notably, no solder adheres to the front side wall portion  44   a  due to rising of the solder, because the front side wall portion  44   a  is separated further from the solder tail portion  43  as compared with the rear side wall portion  44   b,  the path along the second terminal  41  is bent, and the solder barrier  46  is present in the middle of the path. 
         [0036]    In order to improve adhesion of solder, a gold coating layer is preferably formed on the upper surface of the solder tail  43  through plating. Further, in order to lower electrical contact resistance, a gold coating layer is preferably formed on at least the front surface of the front side wall portion  44   a  through plating. 
         [0037]    In operation, first connector  10  would be surface-mounted onto a circuit member or board (not shown) by means of soldering the solder tail portions  23  of the first terminals  21  to corresponding wiring lands or pads of the board. Similarly, the second connector  30  would be surface-mounted onto a second board (not shown) by means of soldering the solder tail portions  43  of the second terminals  41  to corresponding wiring lands or pads of the second board. 
         [0038]    Prior to mating, as shown in  FIG. 2 , the first connector  10  and the second connector  30  are positioned such that the upper surface of the first connector  10  and the lower surface of the second connector  30  face each other. In this state, the upper surface of the first connector  10  and the lower surface of the second connector  30  are generally parallel to each other, and the boards carrying the first connector  10  and the second connector  30 , respectively, are also generally parallel to each other. 
         [0039]    Subsequently, the first connector  10  and the second connector  30  are moved toward each other, or one of the first connector  10  and the second connector  30  is moved toward the other connector, whereby they are mated with each other as shown in  FIGS. 4 and 5 . Notably, in  FIGS. 4 and 5 , boards are omitted in order to simplify the illustration. In the state in which the first connector  10  and the second connector  30  are mated with each other, the ridge portion  13  of the first connector  10  is inserted into the groove portion  33  of the second connector  30 , and the ridge portions  32  of the second connector  30  are inserted into the corresponding groove portions  12  of the first connector  10 . As a result, the first projecting portion  24   b  of the first connection portion  24  of each first terminal  21  comes into contact with the flat front surface of the front side wall portion  44   a  of the second connection portion  44  of the corresponding second terminal  41 . Further, the second projecting portion  24   d  of the first connection portion  24  of each first terminal  21  engages the engagement recess portion  45  of the rear side wall portion  44   b  of the second connection portion  44  of the corresponding second terminal  41 . That is, each first terminal  21  and the corresponding second terminal  41  electrically communicate with each other via a first contact point (main contact portion) at which the first projecting portion  24   b  comes into contact with the front side wall portion  44   a , and a second contact portion (sub contact portion) at which the second projecting portion  24   d  comes into contact with the rear side wall portion  44   b.    
         [0040]    In the present embodiment, the distance between the facing surfaces of the first and second projecting portions  24   b  and  24   d  of the first connection portion  24  of each first terminal  21  is shorter than the distance between the outer surfaces (surfaces opposite the ridge portion  32 ) of the front side wall portion  44   a  and the rear side wall portion  44   b  of the second connection portion  44  of each second terminal  41 . The first connection portion  24  has a spring property. Therefore, when, as a result of mating of the first connector  10  and the second connector  30 , the ridge portions  32  of the second connector  30  are inserted into the corresponding groove portions  12  of the first connector  10  and the second connection portion  44  of each second terminal  41  is inserted into the first connecting portion  24  of the corresponding first terminal  21 , the distance between the facing surfaces of the first and second projecting portions  24   b  and  24   d  of the first connection portion  24  of the first terminal  21  increases, and mainly the front side wall portion  24   a  and the bottom portion elastically deform, whereby the first projecting portion  24   b  is pushed by the front side wall portion  44   a  of the second terminal  41  and moves toward the ridge portion  13 . In this case, by virtue of its spring property, the first connection portion  24  reacts to restore its original shape. Therefore, the second terminal  41  is nipped or engaged by the first projecting portion  24   b  of the front side wall portion  24   a  and the second projecting portion  24   d  of the rear side wall portion  24   c.    
         [0041]    As a result, the end of the first projecting portion  24   b  of each first terminal  21  is pressed against the front surface of the front side wall portion  44   a  of the corresponding second terminal  41 . Thus, reliable contact is established between the first projecting portion  24   b  and the front side wall portion  44   a,  and electrical continuity at the first contact portion is secured. Further, the end of the second projecting portion  24   d  of each first terminal  21  is forced to enter the engagement recess portion  45  of the corresponding second terminal  41 . Thus, reliable contact is established between the second projecting portion  24   d  and the engagement recess portion  45 , and electrical continuity at the second contact portion is secured. Further, reliable engagement is realized between the second projecting portion  24   d  and the engagement recess portion  45 , and the second connection portion  44  of each second terminal  41  is prevented from coming off the first connection portion  24  of the corresponding first terminal  21 , whereby the first connector  10  and the second connector  30  are mated with each other in a reliable manner. 
         [0042]    Further, when the second connection portion  44  of each second terminal  41  is inserted into the first connection portion  24  of the corresponding first terminal  21 , the tip portion of the first projecting portion  24   b  of the first terminal  21  moves while scrubbing or wiping the flat surface of the front side wall portion  44   a  in a state in which the tip portion is pushed against the front surface of the front side wall portion  44   a  of the second terminal  21 . Therefore, a scraping effect or wiping effect is produced, so that substances which hinder electrical continuity, such as dust, dirt or film adhering to the tip end of the first projection portion  24   b  and the front surface of the front side all portion  44   a,  are removed by means of wiping. Therefore, reliable electrical continuity is secured at the first contact portion. 
         [0043]    As described above, in the present embodiment, the first terminals  21  each having the generally U-shaped first connection portion  24  are attached to the first connector  10 , and the second terminals  41  each having the generally U-shaped second connection portion  44  to be fitted into the first connection portion  24  of the corresponding first terminal  21  are attached to the second connector  30 . When the first connector  10  and the second connector  30  are mated with each other, the first projecting portion  24   b  of the first terminal  21  comes into contact with the front side wall portion  44   a  of the second terminal  41  so that a first contact portion (main contact portion) is formed, and the second projecting portion  24   d  of the first terminal  21  engages with the engagement recess portion  45  of the rear side wall portion  44   b  of the second terminal  41  so that a second contact portion (sub contact portion) is formed. 
         [0044]    Therefore, it is possible to provide a board-to-board connector pair in which the first connector  10  and the second connector  30  are mated with each other with high reliability and performance which results in an electrical connector having lower production cost and excellent reliability. 
         [0045]    More specifically, each first terminal  21  assumes a side shape obtained by combining the shape of the letter U and that of the letter F, and the path extending along the first terminal  21  from the solder tail portion  23  to the first projecting portion  24   b  is long and travels in a relatively complicated pattern. Therefore, solder substantially does not adhere to the first projecting portion  24   b,  which adherence would otherwise occur because of the phenomenon of solder rising. Further, since the distance of the path is long, a solder barrier portion can be provided at the middle of the path so as to prevent adherence of solder to the first projecting portion  24   b  without fail. 
         [0046]    Further, each second terminal  41  assumes a generally U-like side shape, and the path extending along the second terminal  41  from the solder tail portion  43  to the front side wall portion  44   a  is long and is extends in a generally complicated pattern. Therefore, solder substantially does not adhere to the front side wall portion  44   a,  which adherence would otherwise occur because of solder rising. Further, since the distance of the path is long, the solder barrier  46  can be provided at the middle of the path so as to prevent adherence of solder to the front side wall portion  44   a  without fail. Accordingly, the second housing  31  is not required to be over-molded, such that the second housing  31  covers a portion of each second terminal  41 , and the second terminals  41  can be attached to the second housing  31  through press-fitting the second terminals  41  into the second housing  31 . Thus, production costs of the second connector  30  can be reduced. 
         [0047]    Moreover, since, as described above, rising of solder does not cause adhesion of solder to the first contact portion (main contact portion) at which the first projecting portion  24   b  and the front side wall portion  44   a  come into contact with each other, electrical continuity is not hindered by solder. Therefore, reliable electrical continuity can be established between the first terminals  21  and the second terminals  41 . 
         [0048]    Further, the greater portion of the U-shaped second connection portion  44  of each second terminal  41  is press-fitted into the corresponding second-terminal accommodation cavity  34  formed on the outer periphery of the ridge portion  32  of the second housing  31 . In other words, the U-shaped second connection portion  44  is supported by ridge portion  32 . Therefore, the second connection portion  44  is protected in that it is less likely to deform upon receipt of unexpected external force. Further, the distal end portion of the front side wall portion  44   a  of the second connection portion  44  is received within the second-terminal end accommodation hole  35 . Therefore, the distal end portion does not move apart from the wall surface of the ridge portion  32  and is retained therein for further stability. 
         [0049]    The first projecting portion  24   b  of each first terminal  21  comes into contact with the front side wall portion  44   a  of the corresponding second terminal  41 , whereby the first contact portion serving as the main contact portion is formed, and the second projecting portion  24   d  of each first terminal  21  engages the engagement recess portion  45  of the rear side wall portion  44   b  of the corresponding second terminal  41 , whereby the second contact portion serving as the sub contact portion is formed. Since electrical continuity is established between the first terminal  21  and the second terminal  41  at two contact portions, conduction failure does not occur, and reliability is improved. Further, since no recess is formed on the front side wall portion  44   a  of each second terminal  41 , the wiping operation of the first projecting portion  24   b  is not interrupted. Thus, a sufficient wiping effect is attained, and reliable electrical continuity can be established at the first contact portion serving as the main contact portion. 
         [0050]    Moreover, since the solder barrier  46  is formed in an area including at least the engagement recess portion  45 , solder having ascended from the solder tail portion  43  does not fill the engagement recess portion  45 . Therefore, the end of the second projecting portion  24   d  of each first terminal  21  is forced to enter the engagement recess portion  45  of the corresponding second terminal  41 . Thus, reliable engagement is more likely to be established between the second projecting portion  24   d  and the engagement recess portion  45 , and the second connection portion  44  of each second terminal  41  is less likely to come off the first connection portion  24  of the corresponding first terminal  21 . As a result, the first connector  10  and the second connector  30  are mated with each other in a reliable manner. Further, electrical continuity is secured at the second contact portion serving as the sub contact portion. 
         [0051]    In the present embodiment, from the viewpoint of wiping, the front side wall portion  44   a  of the second connection portion  44  is configured such that its contact portion for contact with the first projecting portion  24   b  of the first connection portion  24  is a flat surface. However, from the viewpoint of locking strength, a concave portion may be formed at the contact portion. Further, the entirety of the front side wall portion  44   a  may be formed such that its central portion projects frontward for engagement with the first projecting portion  24   b.    
         [0052]    In the present embodiment, the contact portion of the rear side wall portion  44   b  of the second connection portion  44  comprises the engagement recess portion  45  for engagement with the second projecting portion  24   d.  However, the contact portion may be configured to be flat without formation of the engagement recess portion  45  and to merely come into contact with the second projecting portion  24   d.    
         [0053]    The present invention is not limited to the above-described embodiments. Numerous modifications and variations of the present invention are possible in light of the spirit of the present invention, and they are not excluded from the scope of the present invention.