Patent Publication Number: US-9431737-B2

Title: Fitting type connecting terminal and method for producing same

Description:
TECHNICAL FIELD 
     The present invention relates generally to a fitting type connecting terminal (fitting type connector) and a method for producing the same. More specifically, the invention relates to a fitting type connecting terminal having a tin plating layer formed on a surface of each of male and female terminals, one of which is fitted into the other terminal, and a method for producing the same. 
     BACKGROUND ART 
     As conventional materials of fitting type connecting terminals wherein one of male and female terminals is fitted into the other terminal, there are used tin-plated products wherein a tin plating layer is formed as the outermost layer on a conductive material, such as copper or a copper alloy. In particular, tin-plated products have a small contact resistance, and are used as the materials of various connecting terminals for automotive vehicles, information and communication apparatuses, industrial apparatuses and so forth, from the standpoint of contact reliability, corrosion resistance, solderability, economical efficiency and so forth. 
     In recent years, connecting terminals for automotive vehicles and so forth are miniaturized, so that the thickness of spring portions thereof is decreased. In addition, it is not possible to sufficiently ensure spring displacement, so that the contact load at the contact point between male and female terminals is decreased. Particularly in fitting type connecting terminals of tin-plated products, if the contact load at the contact point between male and female terminals is decreased, there is a problem in that the contact reliability thereof is deteriorated by minute sliding abrasion due to minute sliding at the contact point. 
     In order to eliminate this problem, it is proposed to form an Ag—Sn alloy layer on the surface of a tin plating layer, which is formed on a base material of a small terminal, to suppress the rise of electric contact resistance due to the minute sliding abrasion of the small terminal to enhance the electric connection reliability thereof (see, e.g., Japanese Patent Laid-Open No. 2010-37629). 
     It is also proposed to provide a reinforcing member having a spring piece for reinforcing the contact pressure of a contact piece to obtain a strong contact pressure at which it is difficult to cause minute sliding abrasion due to vibration (see, e.g., Japanese Patent laid-Open No. 2006-134681), and to provide a holding portion for holding the tip portion of a tab of a mating terminal in a relative displacement regulated state to prevent the minute sliding abrasion between terminal fittings (see, e.g., Japanese Patent Laid-Open No. 2006-80004). 
     Moreover, it is proposed to provide prismatic protruding portions on an electric contact of one connector of an electric connector assembly to cause the electric contact of the other connector to slide thereon, so that it is difficult to allow impurities, such as solder, to adhere to the electric contact of the electric connector while it is difficult to cause contact failure (see, e.g., Japanese Patent Laid-Open No. 2001-266990). It is also proposed to cause the sliding distance producible between the male and female terminals in a state that a male connector is fitted into and fixed to a female connector to be less than the range of contact flaws in a contact range in which the contact portion of the male terminal contacts that of the female terminal, so that contact reliability is prevented from being deteriorated even under a high sliding environment (see, e.g., Japanese Patent Laid-Open No. 2005-141993). 
     However, as described in Japanese Patent Laid-Open No. 2010-37629 in which the Ag—Sn alloy layer is formed on the surface of the tin plating layer, if a conductive material is plated with an expensive noble metal, such as Au or Ag, as the outermost thereof or if a high strength material is used as a conductive material to increase contact load, the costs thereof are very high. 
     Also, even if the movement of the contact portion is prevented by the structure of the terminal so as to prevent sliding as described in Japanese Patent Laid-Open Nos. 2006-134682 and 2006-80004, if the contact load decreases in a fitting type connecting terminal of a tin-plated product, the contact point is easy to move, so that it is difficult to suppress the minute sliding abrasion due to minute sliding. 
     Moreover, if the prismatic protruding portions are provided on the electric contact of one connector of the electric connector assembly as described in Japanese Patent Laid-Open No. 2001-266990, or if the sliding distance producible between the male and female terminals while a male connector is fitted into and fixed to a female connector is caused to be less than the range of contact flaws in a contact range in which the contact portion of the male terminal contacts that of the female terminal as described in Japanese Patent Laid-Open No. 2005-141993, it is not possible to sufficiently prevent oxides of abrasion powder of Sn plating produced during minute sliding from being accumulated on the contact portion to restrain the minute sliding abrasion in a fitting type connecting terminal of a tin-plated product. 
     DISCLOSURE OF THE INVENTION 
     It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a fitting type connecting terminal, which can inexpensively and sufficiently restrain the rise of the value of electrical resistance due to minute sliding abrasion, the fitting type connecting terminal comprising male and female terminals, each of which has a tin plating layer formed on an electrically conductive base material. 
     In order to accomplish the aforementioned and other objects, the inventors have diligently studied and found that it is possible to produce a fitting type connecting terminal, which can inexpensively and sufficiently restrain the rise of the value of electrical resistance due to minute sliding abrasion, if the fitting type connecting terminal comprises a male terminal and a female terminal, each of the male and female terminals having a tin plating layer formed on an electrically conductive base material, wherein a surface of a contact portion of one of the male and female terminals with the other thereof has a plurality of grooves or recessed portions which are spaced from each other in longitudinal directions of the one thereof, and wherein the grooves or recessed portions are formed so as to satisfy d≦b, d≦a≦L and a+c≦L assuming that the width of each of the grooves or recessed portions is  a  (μm), the depth thereof being  b  (μm), the distance between two of the grooves or recessed portions adjacent to each other in the longitudinal directions being  c  (μm), the sliding distance producible between the male terminal and the female terminal in a state that the male terminal is fitted into and fixed to the female terminal being  L  (μm), and the maximum grain size of the oxide of abrasion powder producible due to sliding between the male terminal and the female terminal being  d  (μm). Thus, the inventors have made the present invention. 
     According to the present invention, there is provided a fitting type connecting terminal comprising a male terminal and a female terminal, each of the male and female terminals having a tin plating layer formed on an electrically conductive base material, wherein a surface of a contact portion of one of the male and female terminals with the other thereof has a plurality of grooves or recessed portions which are spaced from each other in longitudinal directions of the one thereof, and wherein the grooves or recessed portions are formed so as to satisfy d≦b, d≦a≦L and a+c≦L assuming that the width of each of the grooves or recessed portions is  a  (μm), the depth thereof being  b  (μm), the distance between two of the grooves or recessed portions adjacent to each other in the longitudinal directions being  c  (μm), the sliding distance producible between the male terminal and the female terminal in a state that the male terminal is fitted into and fixed to the female terminal being  L  (μm), and the maximum grain size of the oxide of abrasion powder producible due to sliding between the male terminal and the female terminal being  d  (μm). 
     In this fitting type connecting terminal, the plurality of grooves are preferably elongated grooves which are spaced from each other at substantially even intervals in longitudinal directions of the male terminal and which extend in width directions thereof, each of the grooves having a substantially rectangular planar shape. The plurality of recessed portions are preferably spaced from each other at substantially even intervals in longitudinal directions of the male terminal and spaced from each other at substantially even intervals in width directions thereof, the corner portions of each of the recessed portions being arranged so as to be adjacent to those of an adjacent one or more of the recessed portions, and each of the recessed portions having a substantially rectangular planar shape. The base material is preferably made of copper or a copper alloy, and the tin plating layer is preferably made of tin having a purity of 99.9 wt % or more. The fitting type connecting terminal is preferably a box-shaped connecting terminal having an elastic piece which is provided with the contact portion of the male terminal. The sliding distance  L  is preferably 1000 μm, and the maximum grain size  d  is preferably 10 μm. The sliding distance  L  is more preferably 250 μm, and the maximum grain size  d  is more preferably 30 μm. 
     According to the present invention, there is provided a method for producing a fitting type connecting terminal which comprises a male terminal and a female terminal, each of the male and female terminals having a tin plating layer formed on an electrically conductive base material, the method comprising the steps of: forming grooves or recessed portions, which are spaced from each other in longitudinal directions, in a portion of a surface of the electrically conductive base material of one of the male and female terminals corresponding to a contact portion of the one thereof with the other thereof so that d≦b, d≦a≦L and a+c≦L are satisfied assuming that the width of each of the grooves or the recessed portions is  a  (μm), the depth thereof being  b  (μm), the distance between two of the grooves or recessed portions adjacent to each other in the longitudinal directions being  c  (μm), the sliding distance producible between the male terminal and the female terminal in a state that the male terminal is fitted into and fixed to the female terminal being  L  (μm), and the maximum grain size of the oxide of abrasion powder producible due to sliding between the male terminal and the female terminal being  d  (μm); and thereafter, forming a tin plating layer on the electrically conductive base material of each of the male and female terminals. 
     Alternatively, according to the present invention, there is provided a method for producing a fitting type connecting terminal which comprises a male terminal and a female terminal, each of the male and female terminals having a tin plating layer formed on an electrically conductive base material, the method comprising the steps of: forming a tin plating layer on the electrically conductive base material of each of the male and female terminals; and thereafter, forming grooves or recessed portions, which are spaced from each other in longitudinal directions, in a surface of a contact portion of one of the male and female terminals with the other thereof so that d≦b, d≦a≦L and a+c≦L are satisfied assuming that the width of each of the grooves or the recessed portions is  a  (μm), the depth thereof being  b  (μm), the distance between two of the grooves or recessed portions adjacent to each other in the longitudinal directions being  c  (μm), the sliding distance producible between the male terminal and the female terminal in a state that the male terminal is fitted into and fixed to the female terminal being  L  (μm), and the maximum grain size of the oxide of abrasion powder producible due to sliding between the male terminal and the female terminal being  d  (μm). 
     In these methods for producing a fitting type connecting terminal, the plurality of grooves are preferably elongated grooves which are spaced from each other at substantially even intervals in longitudinal directions of the male terminal and which extend in width directions thereof, each of the grooves having a substantially rectangular planar shape. The plurality of recessed portions are preferably spaced from each other at substantially even intervals in longitudinal directions of the male terminal and spaced from each other at substantially even intervals in width directions thereof, the corner portions of each of the recessed portions being arranged so as to be adjacent to those of an adjacent one or more of the recessed portions, and each of the recessed portions having a substantially rectangular planar shape. The base material is preferably made of copper or a copper alloy, and the tin plating layer is preferably made of tin having a purity of 99.9 wt % or more. The fitting type connecting terminal is preferably a box-shaped connecting terminal having an elastic piece which is provided with the contact portion of the male terminal. The sliding distance  L  is preferably 1000 μm, and the maximum grain size  d  is preferably 10 μm. The sliding distance  L  is more preferably 250 μm, and the maximum grain size  d  is more preferably 30 μm. 
     According to the present invention, it is possible to inexpensively and sufficiently restrain the rise of the value of electrical resistance due to minute sliding abrasion, the fitting type connecting terminal comprising male and female terminals, each of which has a tin plating layer formed on an electrically conductive base material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view of a contact portion of a male terminal with a female terminal in a preferred embodiment of a fitting type connecting terminal according to the present invention; 
         FIG. 1B  is a sectional view taken along line IB-IB of  FIG. 1A ; 
         FIG. 1C  is a sectional view showing the contact portion of the male terminal of  FIG. 1A  with the female terminal in the preferred embodiment of a fitting type connecting terminal according to the present invention; 
         FIG. 2A  is a view showing a planar shape of a modified example of a contact portion of the male terminal of  FIG. 1A  with a female terminal; 
         FIG. 2B  is a sectional view taken along line IIB-IIB of  FIG. 2A ; 
         FIG. 3A  is a view showing a first modified example of a sectional shape of a contact portion of the male terminal of  FIGS. 1A and 2A  with a female terminal; 
         FIG. 3B  is a view showing a second modified example of a sectional shape of a contact portion of the male terminal of  FIGS. 1A and 2A  with a female terminal; 
         FIG. 3C  is a view showing a third modified example of a sectional shape of a contact portion of the male terminal of  FIGS. 1A and 2A  with a female terminal; and 
         FIG. 4  is a partially cross-sectioned side view of a box-shaped connecting terminal as an example of a fitting type connecting terminal according to the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring to the accompanying drawings, the preferred embodiment of a fitting type connecting terminal and a method for producing the same according to the present invention will be described below in detail. 
     As shown in  FIGS. 1A through 1C , the preferred embodiment of a fitting type connecting terminal according to the present invention comprises a male terminal  10  and a female terminal  12 , one of which is able to be fitted into the other thereof. On the surface of an electrically conductive base material of each of the male terminal  10  and female terminal  12 , there is formed a tin plating layer (of Sn preferably having a purity of 99.9 wt % or more). On the surface of a contact portion of the male terminal  10  with (the semi-spherical indent  12   a  of) the female terminal  12 , there are formed a large number of fine grooves  10   a  which are spaced from each other at substantially even intervals in longitudinal directions of the male terminal  10  and which extend in width directions (lateral directions) thereof, each of the grooves  10   a  substantially having elongated rectangular planar and sectional shapes. 
     The grooves  10   a  are formed so as to satisfy d≦b, d≦a≦L and a+c≦L, assuming that the width of each of the grooves  10   a  (the length thereof in longitudinal directions of the male terminal  10 ) is  a , the depth thereof being  b , the distance between two of the grooves  10   a  adjacent to each other in the longitudinal directions being  c , the sliding distance producible between the male terminal  10  and the female terminal  12  in a state (fitted/fixed state) that the male terminal  10  is fitted into and fixed to the female terminal  12  being  L , and the maximum grain size of the oxide of abrasion powder producible due to sliding between the male terminal  10  and the female terminal  12  being  d . 
     Specifically, the grooves  10   a  are formed so as to satisfy 10 (μm)≦b, 10 (μm)≦a≦1000 (μm) and a+c≦1000 (μm) where the sliding distance L producible between the male terminal  10  and the female terminal  12  in the state that the male terminal  10  is fitted into and fixed to the female terminal  12  is set to be 1000 (μm) and where the maximum grain size  d  of the oxide of abrasion powder producible due to sliding between the male terminal  10  and the female terminal  12  is set to be 10(μm). Preferably, the grooves  10   a  are formed so as to satisfy 30 (μm)≦b, 30 (μm)≦a≦250 (μm) and a+c≦250 (μm) where the sliding distance L is set to be 250 (μm) and where the maximum grain size  d  of the oxide of abrasion powder is set to be 30 (μm). 
     In place of the male terminal  10  having the grooves  10   a , as shown in  FIGS. 2A and 2B , there may be used a male terminal  110  having a large number of fine recessed portions  110   a  which are spaced from each other at substantially even intervals in longitudinal directions of the male terminal  110  and which are spaced from each other at substantially even intervals in width directions (lateral directions) thereof, the corner portions of each of the recessed portions  110   a  being arranged so as to be adjacent to (or substantially contact) those of an adjacent one or more of the recessed portions  110   a , and each of the recessed portions  110   a  having substantially rectangular planar and sectional shapes. 
     These recessed portions  110   a  are formed so as to satisfy d≦b, d≦a≦L and a+c≦L assuming that the width of each of the recessed portions  110   a  (the length thereof in longitudinal directions of the male terminal  110 ) is  a , the depth thereof being  b , the distance between two of the recessed portions  110   a  adjacent to each other in the longitudinal directions being  c , the sliding distance producible between the male terminal  110  and the female terminal  12  in a state that the male terminal  110  is fitted into and fixed to the female terminal  12  being  L , and the maximum grain size of the oxide of abrasion powder producible due to sliding between the male terminal  110  and the female terminal  12  being  d . 
     Specifically, the recessed portions  110   a  are formed so as to satisfy 10 (μm)≦b, 10 (μm)≦a≦1000 (μm) and a+c≦1000 (μm) where the sliding distance L producible between the male terminal  110  and the female terminal  12  in the state that the male terminal  110  is fitted into and fixed to the female terminal  12  is set to be 1000 (μm) and where the maximum grain size  d  of the oxide of abrasion powder producible due to sliding between the male terminal  110  and the female terminal  12  is set to be 10 (μm). Preferably, the recessed portions  110   a  are formed so as to satisfy 30 (μm)≦b, 30 (μm)≦a≦250 (μm) and a+c≦250 (μm) where the sliding distance L is set to be 250 (μm) and where the maximum grain size  d  of the oxide of abrasion powder is set to be 30 (μm). 
     The reason why the sliding distance L is set to be 1000 (μm), preferably 250 (μm), is that the sliding distance L producible between the male terminal  10  or  110  and the female terminal  12  in the state that the male terminal  10  or  110  is fitted into and fixed to the female terminal  12  (in the state that a minute load (of  3 N or less) is applied between the male terminal  10  or  110  and the female terminal  12 ) is in the range of from 30 μm to 1000 μm, usually in the range of from 50 μm to 250 μm. The reason why the maximum grain size  d  of the oxide of abrasion powder is set to be 10 (μm), preferably 30 (μm), is that it was found that the grain size of the oxide of abrasion powder is not greater than 10 μm and does not exceed 30 μm even if the oxide aggregates, although the maximum grain size  d  of the oxide of abrasion powder is usually about 3 μm. 
     If the grooves  10   a  or the recessed portions  110   a  are thus formed, the oxide of abrasion powder produced between the male terminal  10  or  110  and the female terminal  12  in the state that the male terminal  10  or  110  is fitted into and fixed to the female terminal  12  is designed to fall into the grooves  10   a  or recessed portions  110   a . Thus, it is possible to prevent the oxide of abrasion powder from being accumulated on the surface of the contact portion of the male terminal  10  or  110  with the female terminal  12 , so that it is possible to suppress the rise of the value of electrical resistance due to minute sliding abrasion to enhance electric connection reliability. 
     Between the tin plating layer and the surface of the electrically conductive base material of each of the male terminal  10  or  110  and female terminal  12  of the fitting type connecting terminal, Ni and Cu plating layers may be formed in that order, or Ni, Cu and CuSn plating layers may be formed in that order, from the side of the electrically conductive base material to the side of the tin plating layer. Alternatively, a CuSn or Ni plating layer may be formed. 
     The electrically conductive base material of each of the male terminal  10  or  110  and female terminal  12  of the fitting type connecting terminal is preferably made of copper or a copper alloy, and may be made of a Cu—Ni—Sn alloy (a copper alloy, such as NB-109 or NB-105 produced by DOWA METALTECH CO., LTD., for example), phosphor bronze, brass or the like. Although the electrically conductive base material of the male terminal  10  or  110  may be made of a high-strength copper alloy, such as a copper-beryllium alloy or a copper-titanium alloy, such a copper alloy is expensive. Therefore, the electrically conductive base material of the male terminal  10  or  110  is preferably made of a relatively inexpensive electrically conductive base material of a Cu—Ni—Si alloy (Corson alloy), a Cu—Ni—Sn alloy, phosphor bronze or the like. The electrically conductive base material of the female terminal  12  is preferably made of brass. Alternatively, the electrically conductive base material of each of the male terminal  10  or  110  and the female terminal  12  may be made of an iron material, such as stainless (SUS), an aluminum alloy or the like. 
     In the preferred embodiment of a method for producing a fitting type connecting terminal according to the present invention, in a portion of the surface of the electrically conductive base material of the male terminal  10  or  110  corresponding to the contact portion thereof with the female terminal  12 , there are formed the grooves  10   a , which are spaced from each other at substantially even intervals in longitudinal directions and which extend in width directions (lateral directions), each of the grooves  10   a  substantially having elongated rectangular planar and sectional shapes, or the recessed portions  110   a , which are spaced from each other at substantially even intervals in longitudinal directions and which are spaced from each other at substantially even intervals in width directions (lateral directions), the corner portions of each of the recessed portions  110   a  being arranged so as to be adjacent to (or substantially contact) those of an adjacent one of the recessed portions  110   a , and each of the recessed portions  110   a  having substantially rectangular planar and sectional shapes. The grooves  10   a  or the recessed portions  110   a  are formed so as to satisfy d≦b, d≦a≦L and a+c≦L assuming that the width of each of the grooves  10   a  or the recessed portions  110   a  is  a , the depth thereof being  b , the distance between two of the grooves  10   a  or recessed portions  110   a  adjacent to each other in the longitudinal directions being  c , the sliding distance producible between the male terminal  10  or  110  and the female terminal  12  in the state that the male terminal  10  or  110  is fitted into and fixed to the female terminal  12  being L, and the maximum grain size of the oxide of abrasion powder producible due to sliding between the male terminal  10  or  110  and the female terminal  12  being  d . Thereafter, a tin plating layer is formed on the electrically conductive base material of each of the male terminal  10  or  110  and the female terminal  12 . 
     Alternatively, a tin plating layer is formed on the electrically conductive base material of each of the male terminal  10  or  110  and the female terminal  12 . Thereafter, in a portion of the surface of the contact portion of the male terminal  10  or  110  with the female terminal  12 , there are formed the grooves  10   a , which are spaced from each other at substantially even intervals in longitudinal directions and which extend in width directions (lateral directions), each of the grooves  10   a  substantially having elongated rectangular planar and sectional shapes, or the recessed portions  110   a , which are spaced from each other at substantially even intervals in longitudinal directions and which are spaced from each other at substantially even intervals in width directions (lateral directions), the corner portions of each of the recessed portions  110   a  being arranged so as to be adjacent to (or substantially contact) those of an adjacent one of the recessed portions  110   a , and each of the recessed portions  110   a  having substantially rectangular planar and sectional shapes. The grooves  10   a  or the recessed portions  110   a  are formed so as to satisfy d≦b, d≦a≦L and a+c≦L assuming that the width of each of the grooves  10   a  or the recessed portions  110   a  is  a , the depth thereof being  b , the distance between two of the grooves  10   a  or recessed portions  110   a  adjacent to each other in the longitudinal directions being  c , the sliding distance producible between the male terminal  10  or  110  and the female terminal  12  in the state that the male terminal  10  or  110  is fitted into and fixed to the female terminal  12  being  L , and the maximum grain size of the oxide of abrasion powder producible due to sliding between the male terminal  10  or  110  and the female terminal  12  being  d . 
     In these methods for producing a fitting type connecting terminal, the grooves  10   a  are specifically formed so as to satisfy 10 (μm)≦b, 10 (μm)≦a≦1000 (μm) and a≦c≦1000 (μm) where the sliding distance L producible between the male terminal  10  and the female terminal  12  in the state that the male terminal  10  is fitted into and fixed to the female terminal  12  is set to be 1000 (μm) and where the maximum grain size  d  of the oxide of abrasion powder producible due to sliding between the male terminal  10  and the female terminal  12  is set to be 10 (μm). Preferably, the grooves  10   a  are formed so as to satisfy 30 (μm)≦b, 30 (μm)≦a≦250 (μm) and a+c≦250 (μm) where the sliding distance L is set to be 250 (μm) and where the maximum grain size  d  of the oxide of abrasion powder is set to be 30 (μm). The recessed portions  110   a  are specifically formed so as to satisfy 10 (μm)≦b, 10 (μm)≦a≦1000 (μm) and a+c≦1000 (μm) where the sliding distance L producible between the male terminal  110  and the female terminal  12  in the state that the male terminal  110  is fitted into and fixed to the female terminal  12  is set to be 1000 (μm) and where the maximum grain size  d  of the oxide of abrasion powder producible due to sliding between the male terminal  110  and the female terminal  12  is set to be 10 (μm). Preferably, the recessed portions  10   a  are formed so as to satisfy 30 (μm)≦b, 30 (μm)≦a≦250 (μm) and a+c≦250 (μm) where the sliding distance L is set to be 250 (μm) and where the maximum grain size  d  of the oxide of abrasion powder is set to be 30 (μm). 
     The grooves  10   a  or the recessed portions  110   a  may be formed by the press working, etching, electrical discharge machining, cutting or laser beam machining of a portion corresponding to the contact portion of the surface of the electrically conductive base material (the tin plating layer where the tin plating is carried out before forming the grooves  10   a  or the recessed portions  110   a ) of the male terminal  10  or  110  with the female terminal  12  after the male terminal  10  or  110  is formed in a terminal shape by press working. Alternatively, the grooves  10   a  or the recessed portions  110   a  may be formed when the tinplating is carried out. In this case, the tin plating is preferably carried out by electroplating from the standpoint of the costs thereof, and reflow may be carried out if necessary. 
     The sectional shape of the grooves  10   a  or recessed portions  110   a  of the male terminal  10  or  110  may be modified in any one of various shapes. It may have a wave form as shown in  FIG. 3A , or a substantially triangular form as shown in  FIG. 3B . Alternatively, it may have semi-spherical protruding portions between the grooves  10   a  or recessed portions  110   a  as shown in  FIG. 3C . Furthermore, in the modified examples shown in  FIGS. 3A through 3C , the distance c between two of the grooves  10   a  or recessed portions  110   a  adjacent to each other in the longitudinal directions of the male terminal  10  or  110  may be considered to be zero. 
     In place of the grooves  10   a  or recessed portions  110   a  formed in the male terminal  10  or  110 , grooves or recessed portions having a similar shape to that of the grooves  10   a  or recessed portions  110   a  may be formed on the surface of the contact portion of a female terminal with the male terminal  10  or  110  which is designed to be fitted into the female terminal. For example, as shown in  FIG. 4 , when the preferred embodiment of a fitting type connecting terminal according to the present invention is applied to a box-shaped connecting terminal, in place of the grooves  10   a  or recessed portions  110   a  formed in the male terminal  10  or  110 , grooves or recessed portions having a similar shape to that of the grooves  10   a  or recessed portions  110   a  may be formed on a semi-spherical indent (protruding contact portion)  112   b  provided on an elastic piece (spring portion)  112   a  of a female terminal  112  or may be formed on a raised portion (embossed portion)  112   c  of the female terminal  112  facing the elastic piece  112   a.    
     When the male terminal  10  or  110  and the female terminal  12  are prepared from a tin-plated product wherein a thin flat plate of an electrically conductive base material having a thickness of 0.15 to 0.25 mm is plated with tin, the depth b of the grooves  10   a  or recessed portions  110   a  is preferably 80 μm or less and more preferably 70 μm or less, in order to prevent the tin-plated product from being broken. 
     Examples of a fitting type connecting terminal and a method for producing the same according to the present invention will be described below in detail. 
     Example 1 
     First, there were prepared two tin-plated products wherein a tin plating film (of Sn having a purity of 99.9 wt % or more) having a thickness of 1 μm was formed on a flat plate of an electrically conductive base material of a Cu—Ni—Sn alloy (NB109-EH produced by DOWA METALTECH CO., LTD.) having a thickness of 0.25 mm. One of the tin-plated products was pressed by a die to form a plurality of grooves having a width  a  of 100 μm, a depth  b  of 50 μm and a space  c  of 100 μm on one side thereof as shown in  FIGS. 1A through 1C  to be used as a grooved flat plate test piece (a test piece as a male terminal). The other tin-plated product was indented (embossed in a semi-spherical shape of R=1 mm) to be used as an indented test piece (a test piece as a female terminal). 
     Then, the grooved flat plate test piece was fixed to the stage of an electric minute sliding abrasion testing machine, and the indent of the indented test piece was caused to contact the grooved flat plate test piece. Thereafter, there was carried out a sliding test wherein the stage, to which the grooved flat plate test piece was fixed, was reciprocated in horizontal directions by 30 strokes at a sliding speed of one reciprocation per one second in a range of 200 μm per one-way while the indented test piece was pressed onto the surface of the grooved flat plate test piece at a load of 0.7 N. After this sliding test, the value of electrical resistance at the contact portion of the grooved flat plate test piece with the indented test piece was continuously measured by the four terminal method. As a result, the maximum value of electrical resistance during the sliding test was 2 mΩ. Furthermore, the oxide of abrasion powder (tin oxide powder) smaller than the width of each of the grooves fell into the grooves of the grooved flat plate test piece. 
     Example 2 
     There were prepared the same test pieces as those in Example 1, except that one of the tin-plated products was pressed by a die to form a plurality of recessed portions having a width  a  of 100 μm, a depth  b  of 50 μm and a space  c  of 100 μm as shown in  FIGS. 2A and 2B . The test pieces thus prepared were used for measuring the value of electrical resistance at the contact portion by the same method as that in Example 1. As a result, the maximum value of electrical resistance during the sliding test was 2 mΩ. Furthermore, the oxide of abrasion powder (tin oxide powder) smaller than the width of each of the recessed portions fell into the recessed portions of the flat plate test piece having the recessed portions. 
     Comparative Example 
     There were prepared the same test pieces as those in Example 1, except that no grooves were formed in the one of the tin-plated products of Example 1. The test pieces thus prepared were used for measuring the value of electrical resistance at the contact portion by the same method as that in Example 1. As a result, the maximum value of electrical resistance during the sliding test was 248 mΩ. Furthermore, the oxide of abrasion powder (tin oxide powder) remaining on the flat plate test piece prevented the indent of the indented test piece from contacting the flat plate test piece. The size of abrasion powder aggregating on the flat plate test piece was 10 μm or less.