Abstract:
An electric connector of the present invention is directed to alleviating a stress in housings of an electric connector. In the housings  16  of the electric connector, slots  44, 46  are formed to receive associated terminals. Projections  48   a   , 48   b  are formed in a staggered fashion on the oppose wall portions of the slot. The terminal  24  has a retaining section  28  against which the projections  48   a   , 48   b  abut and a projection  29  abutting against one wall surface. By the projection  29  and projection  48   a  on the wall surface against which the projection  29  abuts, a projection  48   b  on the other wall surf ace supports a force urging the terminal  24 , so that the terminal  24  is retained in place in the slot  44.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a high-density electric connector called as a BGA connector to be connected to a board through solder balls arranged in a grid-like array. 
     With a recent advance of an electronic apparatus, such as a computer, toward a high-density and miniaturization unit, a surface-mounting high-density connector called a BGA connector ha been developed in which solder balls are arranged at the connection sections of respective terminals to be connected to a board and such solder balls are a ranged as a grid-like array on the connector housing. The BGA connector is placed on contact pads arranged on a board surface and each solder ball is partially melted by heating and bonded to the corresponding contact pad on the board. The distance between th mutually adjacent solder balls is very narrow and a larger number of solder balls can be provided on the board in a limited range. 
     In the BGA connector, a large number of slots extend through the bottom wall of an insulating housing and a terminal is received in each lot. Normally, respective projections are provided in a coaxially opposed state, on an opposite wall of each slot. The respective terminal has its retaining section forced into the slot at an area between the opposite projections and is held in the slot, while the retaining section is pushed by the opposed projections from both sides. A contact section contacting with the terminal of the associated connector is projected from a mating surface mated to the associated connector and a connection section is placed in the corresponding opening on an attaching surface side attached to a printed circuit board and a solder ball is attached to the connection section. By simply pressing the respective terminal into the slot at an area between the opposite projections, the terminal can be readily attached to the housing. 
     In the case where a compact and high-density connector is formed for use in an IC package, such as a CPU, the dimensions of the housing, such as the wall thickness and height, are restricted to very small values and a force by which such a terminal is retained in the housing produces a greater stress in the housing. Such a greater stress acting upon the housing provides a cause for a crack. In particular where the connector is soldered to a printed circuit board, etc., by a reflow soldering, there is produced a cause for thermal deformation. 
     BRIEF DESCRIPTION OF THE INVENTION 
     It is accordingly the object of the present invention is to provide a very simple and inexpensive electric connector which can positively retain respective terminals in associated slots in the housing and prevent any deformation of the housing. 
     In order to achieve the above-mentioned object of the present invention, there is provided an electric connector having an insulating housing and a plurality of terminals in the insulating housing, the housing receiving respective terminals and having a plurality of slots with a plurality of projections formed in a staggered fashion on mutually opposed surfaces, the terminal having a retaining section against which these projections abut and a projection abutting against one of the opposed wall surfaces, in which the projection on the other surface supports a terminal urging force to retain the terminal in place in the slot. 
     According to the electric connector, projections are projected in an offset fashion from the opposed surfaces in the slot and, when being abutted against the retaining section of the terminal, these projections impart no greater stress to the housing and, further, a projection on the terminal together with the above-mentioned projections in the slot, positively supports the terminal relative to the housing. 
     The housing has a mating surface mated to an associated connector and housing a terminal insertion inlet opened at the respective slot, the projection on the terminal is formed on the retaining section and a distance from a forward end of the retaining section to the projection of the terminal is preferably so formed as to be made longer than a distance between the mating plane and the projection on a side spaced apart from the mating plane. When, in this case, the forward end of the terminal engages the projection on a side spaced apart from the mating surface, since the projection is arranged outside the slot, the projection on the terminal is smoothly inserted without any intervention when the retaining section of the terminal is inserted between the opposed projections in the slot. Further the terminal preferably has a connection section externally exposed from the slot and on which the solder ball is mounted. 
     The projection can provide a contact making contact with the plate-like terminal when it is inserted in the slot. In this case, it is possible to provide a terminal of a simple structure which positively engages the plate-like terminal of a mating connector through the rotation moment of the two projection. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a perspective view diagrammatically showing an electric connector according to a preferred embodiment of the present invention; 
     FIG. 2 is a cross-sectional view showing the internal structures of a receptacle housing and plug housing in an electric connector in FIG. 1; 
     FIG. 3 is an explanatory view showing a slot as seen along line III—III in FIG. 2; 
     FIG. 4 is a perspective view showing a male terminal and female terminal in FIG. 2; 
     FIGS.  5 (A) to (E) explanatory views showing sequential steps of inserting the terminal into the slot; and 
     FIGS.  6 (A) to (C) are explanatory views showing male and female terminals in another embodiment, FIG.  6 (A) being cross-sectional views showing the male and female terminals before they are mated to each other; FIG.  6 (B) cross-sectional views showing the male and female terminals mated to each other; and FIG.  6 (C) explanatory views showing the side surface shapes of the terminals. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 to  4  show an electric connector according to a preferred embodiment of the present embodiment. The embodiment is formed as a board-to-board electric connector for connecting a daughter board D to a mother board M. 
     The electric connector  10  of the present embodiment has a receptacle connector  12  attached to the mother board M and a plug connector  14  attached to the daughter board D. The receptacle connector  12  and plug connector  14  have solder balls arranged in a grid array on their attaching surfaces attached to the mother board M and daughter board D, respectively. In FIG. 1, in order to reveal the solder ball array, the plug connector  14  are illustrated as being detached from the daughter board D. 
     In the electric connector  10  of the present embodiment, a pair of polarity tabs  18  of different size are formed on a receptacle housing  16  and a pair of cutouts  22  are formed in a plug housing  20  in those places corresponding to the polarity tabs  18 . The receptacle connector  12  and plug connector  14  can be prevented from being wrongly inserted into each other by arranging their mating surfaces in an opposed relation and aligning/mating the polarity tabs of different size with/to the corresponding cutouts  22 . These housings  16 ,  20  are formed of a proper insulating material such as a liquid crystal polymer. 
     As shown in FIGS. 2 to  4 , female terminals  24  are attached to the receptacle connector  12  and male terminals  26  are attached to the plug connector  14 . 
     The female terminals  24  has their retaining section  28  retained by the receptacle housing  16  and solder balls  34  are attached to connection sections  30  of the female terminals which are situated near the attaching surface  16   a  of the receptacle housing  16 . A contact section  32  of the female terminal  24  has a pair of contact arms  32   a ,  32   b  and is projected from the mating surface  16   b . Similarly, the male terminals  26  have their retaining sections  36  retained by the plug housing  20 . Solder balls  42  are attached to connection sections  38  of the male terminals which are situated near the attaching surface  20   a . A sheet-like contact section  40  is projected from the mating surface  20   b . When the plug connector  14  is mated to the receptacle connector  12 , the contact section  40  of the male terminal  26  is held between the contact arms  32   a ,  32   b  of the contact section  32  of the female terminal and these terminals  24  and  26  can be electrically connected to each other. The female terminal  24  and male terminal  26  are made of a proper material, such as phosphor bronze or beryllium copper and their portions contacting the contact sections  32 ,  40  are preferably gold-plated. 
     In order to retain such female terminals  24  and male terminals  26 , a large number of slots  44  and  46  are provided at a required interval in the receptacle housing  16  and plug housing  20 . These slots  44  and  46  are opened at the mating surfaces  16   b  and  20   b  and attaching surfaces  16   a  and  20   a , respectively, in the housings  16  and housing  20 , that is, opened at both surfaces of the housing  16  and housing  20 . In order for the solder balls  34  and  42  to be mounted in the openings of the attaching surfaces  16   a  and  20   a , these openings allow the connection sections  30  and  38  of the female terminal  24  and male terminal  26  to be externally exposed. On the other hand, those openings of the mating surface ( 16   b ,  20   b ) sides are so formed as to be enlarged and to ensure the easiness with which the mating terminals are inserted. In order to prevent the terminals  24  and  26  from being slipped out of the attaching surface ( 16   a ,  20   a ) sides, shoulder portions, not shown, are provided at these slots  44  and  46  to latch the retaining sections  28  and  36 . 
     A pair of projections  48   a ,  48   b  are provided in the slots  44  in the receptacle housing  16  and extend from the opposite wall surface portions in the slot. These projections  48   a ,  48   b  are arranged in an alternately staggered array in an axial direction of the slot  44 , that is, along a direction perpendicular to the attaching surface  16   a  and mating surface  16   b  of the receptacle housing  16 . On the other hand, a projection  29  extends from the retaining section  28  of the female terminal  24  and, together with the projection  48   a , supports a force with which the projection  48   b  compresses the female terminal  24 . As a result, the projection  29  retains the retaining section  28  in the slot  44  substantially along the axial direction. Although, in the present embodiment, the projection  29  is formed on the side opposite to the projection  48   a , the present embodiment-is not restricted thereto. Such a projection may be of any type so long as it can support a rotation moment (moment acting in a counterclockwise direction in FIG. 2) acting upon the female terminal  24  by the projections  48   a ,  48   b  arranged in the alternately staggered array. Contrary to the case of FIG. 2, the projection  29  is formed on a side opposite to the projection  48   b  in the case where the projection  48   b  is arranged nearer the attaching surface  16   a  than the projection  48   a . In either case it is preferred that a distance from the forward end of the retaining section  28  to the projection  29  be so formed as to be set longer than a distance between the mating surface  16   b  and the projection  48   b  on a side apart from the mating surface  16   b.    
     FIG. 5 shows the order with which the female terminal  24  is sequentially mounted in the receptacle housing  16 . Although an explanation will be given below about the receptacle connector  12  in FIG. 5, the something can also be said about the case of the plug connector  14  with any further explanation omitted. 
     As shown in FIG.  5 (A), female terminals  24  are arranged in the insertion inlets of the slots  44  in an aligned relation. And as shown in FIGS. 5B to  5 D the female terminal is inserted into the slot  44  from the connection section  30  on the forward end side and sequentially brought into engagement with the projections  48   b ,  48   a . After engaging the connection section  30  with the projection  48   a  which is situated near the attaching surface  16   a , the projection  29  extending from the retaining section  28  engages the wall surface of the slot. The retaining section  28  of the female terminal is moved in slide motion between the projections  48   a  and  48   b , while slidably moving the projection  29  along the wall surface of the slot  44 , and the connection section  30  is externally exposed from the opening on the attaching surface  16   a  side of the slot  44 . Finally, as shown in FIG.  5 (E), the solder ball  34  is attached to the connection section  30  on the attaching surface  16   a  side of the receptacle housing  16  and, by doing so, the mounting of the female terminal  24  is completed. The solder ball  34 , together with the shoulder, not shown, in the slot  44 , is retained in place in the slot  44  and is prevented from dropping from the slot  44 . 
     In the receptacle housing  16 , the projections  48   a ,  48   b  are arranged in a staggered fashion along the axial direction of the slot  44 . After the forward end of the female terminal  24  has engaged the projection  48   a  near the attaching surface  16   a , the projection  29  engages the wall surface of the slot  44  and, when the female terminal  24  is inserted into the slot  44 , the projection  29  from the retaining section  30  provides no bar and the female terminal is smoothly inserted into the slot without any undue force to the projections  48   a ,  48   b . Further, the projection  20  together with the projection  48   a  provided on the same side of the projection  48   a  supports a force by which the projection  48   b  pushes the female terminal  24 . Therefore, the female terminal  24  is positively supported in the slot  44  and the receptacle housing  16  receives almost no stress from the female terminals  24  in the slots  44 . Even if high temperature acts upon the receptacle housing  16  in a reflow soldering process, there is no thermal deformation and the solder balls  34  on the connection sections  30  of the respective female terminals  24  can be maintained in a common plane. 
     FIGS.  6 (A) to (C) show an embodiment in which both male and female terminals are formed as plate-like ones with the same reference numerals employed in this embodiment to designate parts or elements corresponding to those shown in the previous embodiment and any further explanation omitted. 
     In this embodiment, a female terminal  54  has its retaining section  58  retained between projections  48   a ,  48   b  of a receptacle housing  16  and a solder ball  34  is mounted on a connection section  60  near an attaching surface  16   a  and a plate-like contact section  62  with a projection  59  therefrom is arranged in an insertion inlet of a slot  44 . The projection  59  together with a projection  48   a  supports a force by which a projection  48   b  pushes the female terminal. In the same way as in the above-mentioned embodiment, the female terminal  54  is supported in the slot  44  at three points. A shoulder  45  formed in the slot  44  latches a step formed between the retaining section  58  and the connection section  60 . 
     On the other hand, a male terminal  56  has its retaining section  66 , that is, a retaining section with a projection  67 , retained between projections  50   a  and  50   b  and is supported at three points, that is, at projections  67 ,  50   a ,  50   b . A blade-like or flat plate-like contact section  70  is outwardly projected from a mating surface  20   b . A step is formed between the contact section  70  and the retaining section  66  and is latched at the mating surface  20   b  of a plug housing  20 . 
     In an electric connector  10  of this embodiment, the female terminal  54  has its projection  59  on the contact section  62  abutted against the wall surface of the slot  44  in a state in which the receptacle connector  12  and plug connector  14  are separated from each other. When the plug connector  14  is mated to the receptacle connector  12 , the contact section  70  of the male terminal  56  is inserted into the slot  44  in the receptacle housing  16  and engages the projection  59  on the contact section  62  of the female terminal  54 . By doing so, the male terminal  56  can receive a greater urging force from the female terminal  54 . In order to facilitate the easiness with which the contact section  70  of the male terminal  56  is inserted, the contact section  62  of the female terminal  54  is preferably bent, as shown in FIGS.  6 (A) and  6 (B), toward a side opposite to a side on which the projection  59  is provided. 
     In the electric connector  10  of this embodiment, the female terminal  54  is supported in the slot  44  of the receptacle housing  16  at three points, that is, at the projection  59  and projections  48   a ,  48   b  arranged in a staggered fashion and the male terminal  56  is supported in the slot  46  of the plug housing  20  at three points, that is, at the projection  67  and projections  50   a ,  50   b  arranged in a staggered fashion, so that no greater stress is produced in the housings  16  and  20 . Further, when these housings are mated together, the projection  59  on the female terminal  54  is contacted with the contact section  70  of the male terminal  56  and a rotation moment resulting from the two projections  48   a ,  48   b  arranged in the staggered fashion acts upon the contact section  70  of the male terminal  56  through the projection  59  of the female terminal, so that the female terminal  54  and male terminal  56  can be positively electrically connected to each other. 
     In FIG. 6, P shows a semiconductor pad formed on a mother board M and daughter board D. Solder balls  34  and  42  mounted on the female and male terminals are soldered to solder pad P by a reflow soldering method. It is preferred that, as in the aforementioned embodiment, the female terminal  54  and male terminal  56  be formed of a proper material, such as phosphor bronze or beryllium bronze, and their contacting portions be gold-plated. 
     As evident from the above, according to the present invention, the respective terminal is retained in the slot at three points, that is, at the projections formed in the staggered fashion on the opposed wall surface portions of the slot and at the projection from the terminal. This very simple structure can positively retain the terminals in place without producing any greater stress in the housing. 
     The projection of the terminal is so formed as to be projected from the retaining section. And, if the distance from the forward end portion of the retaining section to the projection is made longer than a distance between the mating surface and the projection spaced apart from the mating surface, the terminal can be smoothly inserted into the slot without the projection being damaged by the forward end portion of the retaining section. 
     Further, in the case where the projection of the terminal constitutes a contact against the plate-like terminal of a mating connector, the female terminal, being simpler in structure, can be positively set in engagement with the male terminal.