Abstract:
A method for connecting conductive members includes a step of providing a first conductive member, a step of providing a second conductive member, and a step of jetting droplets of molten metal so as to form a connecting portion which electrically connects the first conductive member to the second conductive member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a method for connecting conductive members, such as connecting FPCs (flexible printed circuit) each other, or connecting the FPC to a terminal.  
           [0002]    In FIG. 11 of the attached drawings, the FPC  1  is formed by arranging a circuit pattern (conducting portion  3 ) being a conductor such as copper on an insulating film  2  as polyimide through an adhesive material, and further pasting thereon the same insulating film  4  as the above mentioned film through the adhesive material. Since such an FPC  1  has flexibility and a conducting portion  3  is patterned between the insulating films  2  and  4 , wiring is very easy, and in particular, the FPC is much adopted to connections between complicated circuits or units.  
           [0003]    Incidentally, for connecting the FPCs  1  each other, as shown in FIGS.  12  or  13 , it is generally practiced to employ a connecting method using a supersonic welding technique or a spot welding technique.  
           [0004]    In FIG. 12, the connecting method using the supersonic welding technique comprises arranging the mutual FPCs  1  by piling them in vertical directions, holding their vertical both sides between a supersonic welding horn  5  and an anvil  6 , and applying supersonic vibration thereto so as to weld conducting portions  3  each other (as to a connected condition, refer to FIG. 14).  
           [0005]    In FIG. 13, the connecting method using the spot welding technique comprises arranging the mutual FPCs  1  having parts removing insulating films  2  and  4  by meeting parts  7  without the insulating films  2  and  4  to pile them in the vertical directions, holding both vertical ends between electrodes  8 , concentrating electric current and pressure for locally heating them so as to weld the conducting portions each other (resistance welding) (as to a connected condition, refer to FIG. 14).  
           [0006]    The above mentioned related methods have the following problems.  
           [0007]    Firstly, the connecting method using the supersonic welding technique is involved with a problem that a connection accomplished state cannot be confirmed from the outside. Unless confirming from the outside, occurrence of non-welded parts as shown with an arrow P in FIG. 15 cannot be found (only the insulating films  2  and  4  are welded, and the mutual FPCs  1  are thereby fixed each other). Further, another problem is that in the connecting method using the supersonic welding technique, if frictional heat by the supersonic vibration is large, a conducting portion  3  is ruptured.  
           [0008]    Secondly, the connecting method using the spot welding technique has a problem that because current is applied between electrodes  8 , the insulating films  2  and  4  must be in advance removed from both upper and rear faces for forming the parts  7  removing the insulating films  2  and  4 , taking very much trouble.  
           [0009]    As to other problems, being in common to the respective connecting techniques, the insulating films  2  and  4  are deformed owing to connecting heat, spoiling insulation. In addition, when connecting, pressure must be effected from vertical direction by connecting units, inviting rupture of the conducting portion  3  or large sizing scales of units. After connecting (after welding), since exposed parts occur in the conducting portion  3  in vertical direction, both sides must be sealed with insulators  9 , also herein taking very much trouble.  
         SUMMARY OF THE INVENTION  
         [0010]    It is therefore an object of the present invention to provide a method for connecting FPCs capable of heightening workability, avoiding ruptures in the conducting portions and reduction of insulation, and enabling to confirm the connection accomplished state from the outside, thereby to increase reliability.  
           [0011]    In order to achieve the above object, according to the present invention, there is provided a method for connecting conductive members comprising the steps of:  
           [0012]    providing a first conductive member;  
           [0013]    providing a second conductive member; and  
           [0014]    jetting droplets of molten metal so as to form a connecting portion which electrically connects the first conductive member with the second conductive member.  
           [0015]    Preferably, the method further comprising the steps of:  
           [0016]    solidifying the connecting portion provided between the first conductive member and the second conductive member: and  
           [0017]    sealing the connecting portion and an exposed portion of the first and second conductive members with an insulator.  
           [0018]    Preferably, the first conductive member and the second conductive member are contacted with each other.  
           [0019]    Preferably, the first conductive member and the second conductive member are separated from each other.  
           [0020]    Preferably, the first conductive member and the second conductive member are piled each other in a vertical direction.  
           [0021]    Here, it is preferable that an insulating film is interposed between the first conductive member and the second conductive member.  
           [0022]    In the method, the conductive members are easily electrically connected by the connecting portion comprised of the molten metal drops, and after connection, whether the connection is accomplished or immature is seen through visual confirmation of an adhered condition of jetted or dripped the molten metal drops. Further, heat toward the conductive members at connecting is low in parts under connection because of using molten metal drops, and molten metal drops never make heat causing rupture of the conductive member or reduction of insularity of insulating film when the conductive member is a conductive portion of a flexible printed circuit. Besides, a part exposed in the conductive member is limited as small as possible, and sealing of an insulator after connection is enough only at the exposed portion of the conductive member, thereby to increase workability.  
           [0023]    Preferably, at least one of the first conductive member and the second conductive member has -a through-hole in which the connecting portion electrically connects the first conductive member with the second conductive member via the through-hole.  
           [0024]    In the method, the conductive members are easily electrically connected by the connecting portion comprised of the molten metal drops, and after connection, whether the connection is accomplished or immature is seen through visual confirmation of an adhered condition of jetted or dripped the molten metal drops. Further, heat toward the conductive members at connecting is low in parts under connection because of using molten metal drops, and molten metal drops never make heat causing rupture of the conductive member or reduction of insularity of insulating film when the conductive member is a conductive portion of a flexible printed circuit. Besides, a part exposed in the conductive member is limited as small as possible, and sealing of an insulator after connection is enough only at the exposed portion of the conductive member, thereby to increase workability.  
           [0025]    Preferably, a flexible printed circuit is constituted of a conductive portion covered with an insulating film. The first conductive member and the second conductive member are exposed conductive portions, each of the exposed conductive portions which formed by removing the insulating film from the flexible printed circuit so as to expose the conductive portion.  
           [0026]    Preferably, a flexible printed circuit is constituted of a conductive portion covered with an insulating film. One of the first conductive member and the second conductive member is an exposed conductive portion which formed by removing the insulating film from the flexible printed circuit so as to expose the conductive portion, and another is a terminal.  
           [0027]    In the methods, since the conductive member is the flexible printing circuit or the terminal, the connection is available in the flexible printing circuit to the flexible printing circuit or the flexible printing circuit to the terminal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0029]    [0029]FIG. 1 shows a perspective view (including a cross section) when connecting an FPC to another FPC according to a first embodiment of the FPC connecting method of the invention;  
         [0030]    [0030]FIG. 2 shows a perspective view (including a cross section) of the state immediately before connecting the FPC to the FPC;  
         [0031]    [0031]FIG. 3 shows a cross sectional view of the state while connecting the FPC to the FPC;  
         [0032]    [0032]FIG. 4 shows a cross sectional view of a molten metal drop jetting apparatus;  
         [0033]    [0033]FIG. 5 shows a perspective view (including the cross section) immediately before the FPC connection according to a second embodiment of the FPC connecting method of the invention;  
         [0034]    [0034]FIG. 6 shows a cross sectional view of a condition when connecting the FPC to the FPC of FIG. 5;  
         [0035]    [0035]FIG. 7 shows a perspective view (including a cross section) when connecting an FPC to another FPC according to a third embodiment of the inventive FPC connecting method;  
         [0036]    [0036]FIG. 8 shows a cross sectional view (including a cross section) of a condition before connecting the FPC to the FPC of FIG. 7;  
         [0037]    [0037]FIG. 9 shows a cross sectional view (including a cross section) of a condition immediately before connecting the FPC to the FPC of FIG. 7;  
         [0038]    [0038]FIG. 10 shows a cross sectional view of a condition when connecting the FPC to the FPC of FIG. 6;  
         [0039]    [0039]FIG. 11 shows a cross sectional view of an FPC of a related example;  
         [0040]    [0040]FIG. 12 shows a cross sectional view of piled FPCs for explaining the related example using a supersonic welding technique;  
         [0041]    [0041]FIG. 13 shows a cross sectional view of piled FPCs for explaining the related example using a spot welding technique;  
         [0042]    [0042]FIG. 14 shows a cross sectional view of the FPCs connected by the related method using the supersonic welding technique or the spot welding technique;  
         [0043]    [0043]FIG. 15 shows a cross sectional view of the FPCs for explaining problems caused in the related method using the supersonic welding technique or the spot welding technique; and  
         [0044]    [0044]FIG. 16 shows a cross sectional view of the FPCs sealed on the insulating part after connection explained in FIG. 14. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]    A first embodiment of a method for connecting FPCs according to the invention will be described in detail by reference to the drawings.  
         [0046]    [0046]FIG. 1 is a perspective view (including a cross section) when connecting the FPC, showing the first embodiment of the FPC connecting method of the invention. FIG. 2 is a perspective view (including a cross section) showing a state immediately before connecting the FPC. FIG. 3 is a cross sectional view showing the state while connecting the FPC. Note that, in the present specification, the structures are shown by overdrawing thickness for easily understanding.  
         [0047]    Composing members will be firstly explained in detail. In FIGS.  1  and  2 , the FPC (flexible printed circuit)  11  includes an insulating film  12  made of, for example, polyimide, a plurality of conducting portions  13  (only one shown) made of, e.g., copper having conductivity on the insulating film  12  via an adhesive material, and an insulating film  14  made of, e.g., polyimide pasted thereon through the adhesive material. The FPC  11  has a part of removing the upper sided-insulating film  14  being a terminal part thereof, and the surface of the conducting portion  13  is formed under an exposed condition in an appropriate range.  
         [0048]    In contrast, the FPC  15  includes an insulating film  16  being the same as the FPC  11 , a plurality of conducting portions  17  (only one shown) and an insulating film  18 . The FPC  15  has parts of removing the insulating films  16  and  18  being terminal parts thereof, and the surface of the conducting portion  17  is formed under the exposed condition in an appropriate range.  
         [0049]    On the other hand, a molten metal drop  19  is formed by melting a metal having conductivity. The molten metal drop  19  is formed by jetting from a nozzle by using, e.g., a piezoelectric element or gas, sending liquid droplet of a wire molten by discharge, or jetting metal powders from a nozzle and melting by a laser. In the first embodiment, the molten metal drop  19  is formed by a molten metal drop jetting apparatus  21  (later mentioned) having a nozzle  20 .  
         [0050]    The FPC connecting method of the invention will be detailed described below on the basis of the above mentioned respective structures. The inventive FPC connecting method passes through the following procedures.  
         [0051]    In a first process, as shown in FIG. 2, the FPC  11  and the FPC  15  are arranged by piling in the vertical direction such that the conducting portion  13  of the FPC  11  is connected at the upper surface thereof to the rear surface of the conducting portion  17  of the FPC  15 . Preferably, the arrangement is made such that the conducting portion  13  of the FPC  11  contacts at its end portion to an end portion of the lower sided-insulating film  16 .  
         [0052]    In a second process after the first process, a step  22  is formed between the surface of the conducting portion  13  of the FPC  11  and the surface of the conducting portion  17  of the FPC  15 , and the molten metal drops  19  are jetted or dripped thereon. The molten metal drops  19  are adhered to the surface of the conducting portion  13  of the FPC  11  and the surface of the conducting portion  17  of the FPC  15 , holding the step  22  therebetween. By an agglomerate  23  of the adhered molten metal drops  19 , states as shown in FIGS. 1 and 3 are produced, and as a result, the FPC  11  and the FPC  15  are electrically connected.  
         [0053]    After accomplishing the second process, a third process is performed as follows. In the third process, for protecting from the outside the surface of the conducting portion  13  of the FPC  11  under the exposed condition, the surface of the conducting portion  17  of the FPC  15 , and the agglomerate  23  of the molten metal drops  19 , an insulator  24  is sealed over the upper insulating films  14  and  18  (see FIG. 3).  
         [0054]    The FPC connecting method is characterized by mutually connecting the FPC  11  and the FPC  15  by use of the molten metal drops  19 . Therefore, as seen from the above explanation and the drawings, the FPC  11  and the FPC  15  can be easily connected. Further, since the FPC  11  and the FPC  15  are connected by use of the molten metal drops  19 , the adhering condition (the condition of the agglomerate  23 ) of the molten metal drops  19 , that is, the connection accomplishing condition can be visually confirmed, so that reliability depending on the connection can be more heightened than the connecting method using the related supersonic welding technique.  
         [0055]    Further, since the FPC  11  and the FPC  15  are connected by use of the molten metal drops  19 , heat toward the conducting portion  13  of the FPC  11  and the conducting portion  17  of the FPC  15  at connecting is low enough at these connected parts than in the connecting method using the related supersonic welding technique or the spot welding technique, consequently enabling to avoid rupture in the conducting portions  13  and  17  or reduction of insulation of the insulating films  12 ,  14 ,  16  and  18 .  
         [0056]    Besides, parts exposed in the conducting portions  13  and  17  are limited as small as possible, and the sealing on the insulator  24  after connection is enough only at surface sides of the conducting portions  13  and  17  of the FPCs  11  and  15 , thereby to increase workability.  
         [0057]    Next, the structure of the molten metal jetting apparatus  21  will be described below, referring to FIG. 4 which is a cross sectional view of the molten metal drop jetting apparatus.  
         [0058]    The molten metal drop jetting apparatus  21  includes a molten metal drop forming portion  25 , a molten metal supply source (not shown) for melting a metal having conductivity and supplying it to a molten metal drop forming portion  25 , and a moving unit (not shown) for moving the molten metal drop forming portion  25 .  
         [0059]    The molten metal drop forming portion  25  has a casing  26 , a nozzle  20  having a hole  27  and projecting at the lower end of the casing  26 , a diaphragm  28  disposed, e.g., in opposition to the hole  27 , a piezoelectric element  29  for vibrating the diaphragm  28 , and a heater  31  for heating or keeping hot the molten metal  30  filled in the nozzle  20 , and when the molten metal  30  passes through the hole  27 , it becomes a molten metal drop  19  and gets out intermittently (each time when the diaphragm  28  vibrates, the molten metal drop  19  is formed).  
         [0060]    Vibration of the diaphragm  28  may depend on a manner of applying pressure by such as gas other than the piezoelectric element  29 . The amount of the molten metal drops  19  jetted intermittently by vibration of the diaphragm  28 , time-interval thereof and diameter of the same are appropriately determined. Other than the structure using the diaphragm  28 , a structure using a cylinder may be listed.  
         [0061]    Subsequently, a second embodiment of the FPC connecting method according to the invention, referring to FIGS. 5 and 6. FIG. 5 is a perspective view (including the cross section) immediately before the FPC connection showing the second embodiment. FIG. 6 is a cross sectional view showing a condition when connecting the FPCs of FIG. 5. The composing members being basically the same as those of the first embodiment will be given the same numerals for omitting detailed explanation.  
         [0062]    In FIG. 5, the FPC  11  has a part of removing the upper insulating film  14  being a terminal part thereof, and the surface of the conducting portion  13  is formed under the exposed condition in an appropriate range. On the other hand, the FPC  15  also has a part of removing the upper insulating film  18  being a terminal part thereof, and the surface of the conducting portion  17  is formed under the exposed condition in an appropriate range (in the first embodiment, the rear face of the conducting portion  17  is exposed, but in the second embodiment, the rear face of the conducting portion  17  is covered with the insulating film  16 ).  
         [0063]    A FPC connecting method according to the second embodiment of the invention will be described below on the basis of the above mentioned respective structures. The inventive FPC connecting method in the second embodiment passes through the following procedures.  
         [0064]    In the first process, the FPCs  11  and  15  are arranged by piling them in the vertical direction. Namely, the FPCs  11  and  15  are arranged by piling them in the vertical direction such that the conducting portion  13  of the FPC  11  is contacted on the surface thereof to the lower sides insulating film  16  of the FPC  15  (as the rear face of the conducting portion  17  is not exposed, is does not contact to the conducting portion  13  of the FPC  11  as the first embodiment).  
         [0065]    In the second process after the first process, a step  32  is formed between the surface of the conducting portion  13  of the FPC  11  and the surface of the conducting portion  17  of the FPC  15 , and the molten metal drops  19  are jetted or dripped thereon. The molten metal drops  19  are adhered to the surface of the conducting portion  13  of the FPC  11  and the surface of the conducting portion  17  of the FPC  15 , holding the step  32  therebetween. By an agglomerate  33  of the adhered molten metal drops  19 , a state as shown in FIG. 6 is produced, and as a result, the FPC  11  and the  15  are electrically connected.  
         [0066]    After accomplishing the second process, the third process is performed as follows. In the third process, for protecting the surface under the exposed condition of the conducting portion  13  of the FPC  11 , the surface of the conducting portion  17  of the FPC  15 , and the agglomerate  33  of the molten metal drops  19 , an insulator  34  is sealed over the upper insulating films  14  and  18 .  
         [0067]    The inventive FPC connecting method of the second embodiment is characterized by mutually connecting the FPCs  11  and  15  by use of the molten metal drops  19  similarly to the FPC connecting method explained in the first embodiment. Accordingly, similar effects can be brought about as in the FPC connecting method referred to in the first embodiment.  
         [0068]    Subsequently, a third embodiment of the FPC connecting method according to the invention will be explained, referring to FIGS.  7  to  10 . FIG. 7 is a perspective view (including the cross section) at the FPC connection showing the third embodiment. FIG. 8 is a cross sectional view showing a condition before connecting the FPCs of FIG. 7 (including the cross section). FIG. 9 is a perspective view (including the cross section) showing a state immediately before the FPC connection of FIG. 7 (including the cross section). FIG. 10 is a cross sectional view showing a state when connecting the FPCs.  
         [0069]    Composing members will be firstly explained in detail. In FIGS. 7 and 8, the FPC (flexible printed circuit)  41  includes an insulating film  42  made of, for example, polyimide, conducting portion  43  made of, e.g., a plurality of coppers (only one shown) having conductivity arranged on the insulating film  42  via the adhesive material, and an insulating film  44  made of, e.g., polyimide pasted thereon through the adhesive material. The FPC  41  has a part of removing the upper sided-insulating film  44  being an intermediate part thereof (the terminal part may be sufficient), and the surface of the conducting portion  43  is formed under the exposed condition in an appropriate range. The exposed conducting portion  43  is provided with a through-hole  45  of an appropriate size (the through-hole corresponding to a lower sided-insulating film  42  may be arbitrarily determined).  
         [0070]    In contrast, the FPC  46  includes an insulating film  47  being the same as the FPC  41 , a plurality of conducting portions  48  (only one shown) and an insulating film  49 . The FPC  46  has a part of removing the upper sided-insulating film  49  being an intermediate part thereof (a terminal part is sufficient), and the surface of the conducting portion  48  is formed under the exposed condition in an appropriate range (the FPC  46  does not have the through-hole, but this is not applied to a case where the FPC  46  is disposed on the FPC  41  when connecting as later mentioned).  
         [0071]    A FPC connecting method according to the third embodiment of the invention will be described below on the basis of the above mentioned respective structures, passing through the following procedures.  
         [0072]    In the first process, as shown in FIG. 8, an FPC  41  and an FPC  46  are opposed vertically, and as shown in FIG. 9, the mutual FPCs  41  and  46  are piled in the vertical direction.  
         [0073]    In a second process, the molten metal drops  19  are jetted or dripped on the through-hole  45 , and when the lower sided-insulating film  42  of the FPC  41  is melted by the molten metal drop  19  and penetrates, the molten metal drops  19  are adhered to the surface of the conducting portion  43  of the FPC  41  and the surface of the conducting portion  48  of the FPC  46 . By the agglomerate  50  of the adhered molten metal drops, the states are produced as shown in FIGS.  7  or  10 , and consequently the FPCs  41  and  46  are electrically connected.  
         [0074]    After accomplishing the second process, a third process is performed as follows. In the third process, for protecting at the outside the surface under the exposed condition of the conducting portion  43  of the FPC  41 , and the agglomerate  50  of the molten metal drops  19 , an insulator  51  is sealed over both sides of the parts of removing the upper sided-insulating film  44  (see FIG. 10).  
         [0075]    The inventive FPC connecting method according to the third embodiment is characterized by mutually connecting the FPCs  41  and  46  by use of the molten metal drops  19  similarly to the first and second embodiments. Accordingly, similar effects can be brought about as in the FPC connecting method referred to the first and second embodiments.  
         [0076]    Of course, so far as not altering the subject matter of the invention, various modifications are available. That is, the FPC  15  is substituted with a tab-like terminal for connecting it to the FPC  11 . Further, similarly, the FPC  46  is substituted with the tab-like terminal for connecting it to the FPC  41 . A bas-bur, PCB or FPC may be enumerated other than the tab-like terminal.