Abstract:
By forming a terminal at a tip of a lead part of a lead frame, and by fixing this terminal and a connecting pad which was formed on an upper surface of a first printed circuit board, the lead frame is attached to the first printed circuit board. By cutting off a frame part and a tie bar part from the lead frame which was attached to the first printed circuit board, the lead part is separated, and forming is applied to the lead part so as for its tip to be extended over the first printed board. After the lead part which is expanded upward is inserted into a through-hole which was opened in a second printed circuit board, by soldering the lead part and the through-hole, the first printed circuit board and the second printed circuit board are electrically connected.

Description:
[0001]    The present disclosure relates to the subject matter contained in Japanese Patent Application No.2002-295896 filed Oct. 9, 2002, which is incorporated herein by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a connecting structure and a connecting method of printed circuit boards, and in particular, relates to a method for connecting printed circuit boards, which are disposed in a stacked manner.  
           [0004]    2. Description of the Related Art  
           [0005]    In order to control electric power to be supplied from a power supply to a load, a control module is inserted into a power supply line.  
           [0006]    In this control module, it is common that, besides a power control device for controlling electric power, a control device for controlling this power control device is mounted thereon.  
           [0007]    Therefore, it is normal that the control module includes two kinds of substrates, i.e., a control substrate on which the control device is mounted and a power substrate on which the power control device is mounted, and a copper system lead is used for an electric connection between these substrates.  
           [0008]    It is usual that the lead is fixed to a predetermined position by a resinous frame (JP-A-10-229261; page 3 and FIG. 1).  
         SUMMARY OF THE INVENTION  
         [0009]    The invention has an object to provide a method for connecting printed circuit boards in which printed circuit boards can be stacked and connected simply and precisely.  
           [0010]    According to a first aspect of the invention, a method for connecting printed circuit boards includes forming a terminal at one end of a lead portion of a lead frame, fixing the terminal to a connecting pad formed on a surface of a first printed circuit board to attach the lead frame to the first printed circuit board, cutting off a frame portion and a tie bar portion from the lead frame, making the other end of the lead portion extend in an upward direction of the first printed circuit board, inserting the lead portion into a through hole defined in a second printed circuit board, and fixing the lead portion to the through hole to connect the first printed circuit board and the second printed circuit board electrically.  
           [0011]    After the lead frame is attached to the first printed circuit board, the lead frame and the tie bar are removed, and the lead is made to extend in the upward direction of the first printed circuit board. Then, by inserting the lead portion into the through-hole defined in the second printed circuit board, the first printed circuit board and the second printed circuit board are connected. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is an exploded perspective view of a connecting structure of printed circuit boards according to the embodiment of the invention.  
         [0013]    [0013]FIG. 2 is a perspective view ( 1 ) of a lead frame.  
         [0014]    [0014]FIG. 3 is a perspective view ( 2 ) of the lead frame.  
         [0015]    [0015]FIG. 4 is an explanation view ( 1 ) showing an assembling method of the connecting structure of printed circuit boards according to the embodiment of the invention.  
         [0016]    [0016]FIG. 5 is an explanation view ( 2 ) showing an assembling method of the connecting structure of printed circuit boards according to the embodiment of the invention.  
         [0017]    [0017]FIG. 6 is an explanation view ( 3 ) showing an assembling method ( 3 ) of the connecting structure of printed circuit boards according to the embodiment of the invention.  
         [0018]    [0018]FIG. 7 is an explanation view ( 4 ) showing an assembling method of the connecting structure of printed circuit boards according to the embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    [0019]FIG. 1 is an exploded perspective view of a connecting structure of printed circuit boards according to an embodiment of the invention. The connecting structure includes a base  20 , a power substrate  21 , a control substrate  22  and a lid  23 .  
         [0020]    The base  20  is an aluminum casting product, and radiates heat generated by the power substrate, which is attached in closely contact thereto. The power substrate  21 , the control substrate  22  and the lid  23  are fixed the base  20 .  
         [0021]    A power control device, which is for example IGBT (Insulated Gate Bipolar Transistor), is mounted on the power substrate  21 . Also, crank type control leads  211  and power leads  212  are fixed to the power substrate  21  by soldering. However, there is no resinous frame as in the connecting structure described in the background of the invention. The control lead 2   211  and the power leads  212  stand alone on the power substrate  21 .  
         [0022]    A method for attaching the control leads  211  and the power leads  212  to the power substrate  21  will be described later.  
         [0023]    This power substrate  21  is closely contacted to and fixed by screw cramp to a bed  201 , which is formed on the base  20  through an electrically insulating member.  
         [0024]    The control substrate  22  on which a control device, which is for example a microcomputer, is mounted, is stacked above the power substrate  21  with a predetermined gap being formed between the control substrate  22  and the power substrate  21 . In the control substrate  22 , control through-holes  221  and power through-holes  222  are opened. When the control substrate  22  is stacked, the control leads  211  and the power leads  212  are inserted into the control through-holes  221  and the power through-holes  222 , respectively.  
         [0025]    After that, the control leads  211  and the power leads  212 , and, the control through-holes  221  and the power through-holes  222  are electrically connected to each other by soldering.  
         [0026]    In addition, the control substrate  22  is fixed by a screw to support pillars  202  formed at four corners of the base  20 .  
         [0027]    Finally, the lid  23  is fixed to the base  20  so that a component is finished.  
         [0028]    [0028]FIG. 2 is a perspective view ( 1 ) of the lead frame  210 . the control leads  211  and the power leads  212  are extended toward inside from the frame  213 . The frame  213  and the control leads  211  and the power leads  212 , and, both of the control leads  211  and the power leads  212  are connected to each other by tie bars  214 .  
         [0029]    The lead frame having the above-described structure can be easily formed by punching out an aluminum plate.  
         [0030]    [0030]FIG. 3 is a perspective view ( 2 ) of the lead frame  210 . Tip ends of the control leads  211  and the power leads  212  undergo press working to have a crank shape. Thereby, a terminal is formed.  
         [0031]    FIGS.  4  to  6  are explanation views showing an assembling method of the connecting structure of printed circuit boards according to the embodiment of the invention. The lead frame  210 , which has undergone the press working, is fixed to the power substrate  21  by soldering. In addition, in the figures subsequent to FIG. 4, in order to easily understand the figures, one control lead  211  and one power lead  212  are shown. However, as shown in FIGS. 2 and 3, even in case that a plurality of control leads  211  and power leads  212  are disposed, this assembling method is also applicable thereto.  
         [0032]    At this stage, since the control lead  211  and the power lead  212  are fixed to the frame  213 , if the frame  213  is positioned with respect to the power substrate  21 , there is no necessity to position each of the control lead  211  and the power lead  212  with respect to the power substrate  21 .  
         [0033]    On the power substrate  21 , formed are connecting pads  215  to which terminals of the control lead  211  and the power lead  212  are attached. The terminals and the connecting pads  215  are connected by, for example, flow-soldering (A).  
         [0034]    After that, the frame  213  and the tie bars  214  are cut off so that each of control lead  211  and power lead  212  are separated (B).  
         [0035]    Next, folding positions of the control lead  211  and the power lead  212  are pinched by a damper  51 , and by use of an appropriate method, carried out is a forming process in which tip ends of the control lead  211  and the power lead  212  are folded back upwardly. In addition, a folding angle is set to 85 degrees, which is smaller than 90 degrees by approximately 5 degrees, and the tip ends of the control lead  211  and the power lead  212  are formed in an expanded state toward outside (C).  
         [0036]    That is, according to the embodiment of the invention, after the control lead  211  and the power lead  212  are attached to the power substrate  21 , the control lead  211  and the power lead  212  undergo the forming process. Therefore, it is possible to correct, on the occasion of the forming process, misalignment between the control lead  211  and the control through-hole  222  and between the power lead  212  and the power through-hole  222  of the control substrate  22 , which is caused due to attaching the frame  213  to the power substrate  21 . Thus, it becomes possible to assure the relative positional precision therebetween.  
         [0037]    As a result, completed is the power substrate  21  to which the control lead  211  and the power lead  212  are fixed by soldering (D).  
         [0038]    This power substrate  21  is disposed on the bed  201  of the base  20 , and fixed to a top of the base  20  by an appropriate method such as screw cramp (E).  
         [0039]    Next, the tip ends of the control lead  211  and the power lead  212  are held down by jigs  61  from outside so as to be substantially perpendicular, and the control substrate  22  is disposed from thereabove.  
         [0040]    In the control substrate  22 , the control through-hole  221  and the power through-hole  222  are opened. The control lead  211  and the power lead  212  are inserted into the control through-hole  221  and the power through-hole  222 , respectively (F).  
         [0041]    That is, according to the embodiment of the invention, assured are the relative positional precision between the control lead  211  and the power lead  212 , and the relative positional precision between the control through-hole  221  and the power through-hole  222 . This facilitates assemble of the power substrate  21  and the control substrate  22 .  
         [0042]    When the jigs  61  are removed, the control lead  211  and the power lead  212  are expanded toward outside due to elasticity thereof, and the control lead  211  and the power lead  212  fall in such a situation that they contact to the control through-hole  221  and the power through-hole  222 , respectively.  
         [0043]    That is, according to the embodiment of the invention, since the leads and the through-holes are in contact with each other prior to soldering, it is possible to make sure a connection therebetween.  
         [0044]    After that, the control lead  211  and the power lead  212 , and, the control through-hole  221  and the power through-hole  222  are electrically connected by, for example, local flow-soldering, respectively. If necessary, the tip ends of the control lead  211  and the power lead  212 , which are extended over the control substrate  22 , may be cut off. Finally, by covering the base  20  with the lid  23  (G), a product is finished.  
         [0045]    The above-described one is on the assumption that it is possible to hold down both of the control lead  211  and the power lead  212  by the jigs  61 . However, there may be such a case that it is possible to hold down only one of the leads by the jig  61 , because of existence of a large component, which is mounted on the substrate.  
         [0046]    [0046]FIG. 7 is an explanation view of an assembling method in this case. Since a large component  223  is mounted on an under surface of the control substrate  22 , it is impossible to hold down the power lead  212  by a jig.  
         [0047]    In this case, the power lead  212  (a lead which can not be held down by a jig) is formed to be longer than the control lead  211  (a lead which can be held down by the jig  61 ) by approximately 1 mm.  
         [0048]    Further, in the forming process (C) of folding down the tip ends, a folding angle of the control lead  211  remains to be approximately 85 degrees, but a folding angle of the power lead  212  is made to be 90 degrees. Then, the tip ends is made to be perpendicular.  
         [0049]    In this situation, the control lead  211  is held down from outside by the jig  61 , and the control substrate  22  is disposed from above (F′).  
         [0050]    Then, the power lead  212  is inserted into the control through-hole  221  on ahead, and after that, the control lead  211  is inserted into the control through-hole  221 .  
         [0051]    That is, even when it is impossible to hold down one of the leads by the jig, this method makes it possible to surely insert the other of the leads into the through-hole.  
         [0052]    When the jig  61  is removed, the control lead  211  and the power lead  212  are fixed by soldering to the control through-hole  221  and the power through-hole  222 .  
         [0053]    In a method of connecting printed circuit boards according to the embodiment of the invention, the forming process is applied to a lead after the lead has been attached to one of substrates. Thus, it becomes possible to stack and connect the printed circuit boards simply and precisely.