Abstract:
The invention discloses a multi-layer structure of the battery protection device, which uses a plurality of over-current protection modules connected in parallel to reduce the normal resistance value. The polypropylene, glass fiber or other harder materials are appended among the plurality of over-current protection modules. Therefore, even if the over-current protection is burned out due to improper use, the short circuit of the metal conductive sheet connecting to the positive and negative poles of the battery can be avoided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a battery protection device, particularly to a multi-layer structure of a battery protection device.  
           [0003]    2. Background of the Invention  
           [0004]    Following the current popular applications of portable electronic products such as mobile phone, notebook PC, hand-held camera and personal digital assistant, etc., the importance of the battery protection device preventing the circuit from over-current or over-temperature phenomenon gets more and more significant.  
           [0005]    The conventional battery protection device  10 , as shown in FIG. 1, includes a current sensing unit  11 , an upper metal conductive sheet  16  and a lower metal conductive sheet  15 . The current sensing unit  11  includes an upper electrode foil  13 , a lower electrode foil  12  and a conductive material  14  with positive temperature coefficient (PTC). The upper metal conductive sheet  16  and the lower metal conductive sheet  15  are connected with the surfaces of the upper electrode foil  13  and the lower electrode foil  12  to act as conductive wires between the positive and negative poles of the secondary battery. The PTC conductive material  14  includes a polymer and a conductive filler.  
           [0006]    Because the resistance value of the PTC conductive material  14  is sensitive to temperature variation that, during a normal operation, the resistance value thereof may be kept in extremely low value, enabling the circuit to operate normally. However, while the over current or over temperature phenomenon is happening, the resistance value thereof will increase instantly to a high resistance value state (e.g. above 10 4  ohm) to reversely eliminate the excess current to achieve the object of protecting circuit device.  
           [0007]    Generally, the normal resistance value of the current sensing unit  11  can be obtained with the conventional formula:  
         R   =       ρ   ×   l     A       ,                         
 
           [0008]    wherein ρ represents the conductive coefficient, l represents the length and A represents the area. Because the volume of portable electronic instrument gets smaller and smaller, the space occupied by the battery protection device  10  needs to be reduced. Thus, according to the above formula, the normal resistance value of the battery protection device  10  will get higher and higher.  
           [0009]    Furthermore, while the conventional battery protection device  10  burns down due to improper use, the metal conductive sheets  15 ,  16  connecting to the positive and negative poles of the battery will short circuit (referred to as “unsafe failure”) so that not only is the objective of battery protection not achieved, but the safety use of the battery will also be influenced.  
           [0010]    As the volume of the secondary battery gets smaller and smaller, the requirements for the power efficiency and safety use increases. If the conventional battery protection device  10  is being assembled, not only will the normal resistance value become too high, but the safety usage will also be influenced. Thus, it is necessary to provide an effective solution for the problem.  
         SUMMARY OF THE INVENTION  
         [0011]    The major object of the invention is to provide a battery protection device with low normal resistance value, which can effectively reduce the power consumption of the battery protection device.  
           [0012]    The second object of the invention is to provide a battery protection device which can avoid the short circuit phenomenon which occurs during burning out of the device, causing danger for the battery use.  
           [0013]    In order to achieve the above objects and to avoid the disadvantage of the prior art, the invention discloses a multi-layer structure of the battery protection device, which uses a plurality of over-current protection modules connected in parallel to reduce the normal resistance value. The polypropylene, glass fiber or other harder materials are appended among the plurality of current protection modules. Therefore, even if the battery protection device is burned out due to improper use, the short circuit of the metal conductive sheet connecting to the positive and negative poles of the battery can be avoided.  
           [0014]    The multi-layer structure of the battery protection device according to the invention includes a plurality of metal conductive sheets connecting to the positive and negative poles of the battery and a current sensing unit. The invention is characterized that the current sensing unit includes at least two over-current protection modules electrically connected in parallel vertically, and the at least two over-current protection modules are separated from each other by a hard insulation layer. Furthermore, the over-current protection module includes an upper electrode layer, a PTC conductive material layer and a lower electrode layer in sequence. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The invention will be described following the accompanied drawings, wherein:  
         [0016]    [0016]FIG. 1 shows a conventional battery protection device;  
         [0017]    [0017]FIG. 2 shows a multi-layer structure of the battery protection device according to the first embodiment of the invention;  
         [0018]    [0018]FIG. 3 shows an exploded diagram of each metal layer of the multi-layer structure of the battery protection device according to the first embodiment of the invention;  
         [0019]    [0019]FIG. 4 shows a cross-sectional view along A-A′ line of the multi-layer structure of the battery protection device according to the first embodiment of the invention;  
         [0020]    [0020]FIG. 5 shows a multi-layer structure of the battery protection device according to the second embodiment of the invention;  
         [0021]    [0021]FIG. 6 shows an exploded diagram of each metal layer of the multi-layer structure of the battery protection device according to the second embodiment of the invention;  
         [0022]    [0022]FIG. 7 shows a cross-sectional view along B-B′ line of the multi-layer structure of the battery protection device according to the second embodiment of the invention;  
         [0023]    [0023]FIG. 8 shows another exploded diagram of further each metal layer of the multi-layer structure of the battery protection device according to the second embodiment of the invention;  
         [0024]    [0024]FIG. 9 shows a multi-layer structure of the battery protection device according to the third embodiment of the invention;  
         [0025]    [0025]FIG. 10 shows an exploded diagram of each metal layer of the multi-layer structure of the battery protection device according to the third embodiment of the invention; and  
         [0026]    [0026]FIG. 11 shows a cross-sectional view along C-C′ line of the multi-layer structure of the battery protection device according to the third embodiment of the invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0027]    [0027]FIG. 2 is the multi-layer structure of battery protection device  20  according to the first embodiment of the invention. The major difference between the battery protection device  20  and the prior art is that there are at least two over-current protection modules  23 ,  24  connected with each other in parallel being included between the upper metal conductive sheet  21  and the lower metal conductive sheet  22  of the invention, thereby the resistance value and the power consumption of the device can be reduced. Referring to FIG. 2, the multi-layer structure of the battery protection device  20  of the invention includes an upper metal conductive sheet  21 , a lower metal conductive sheet  22 , a first over-current protection module  23 , a second over-current protection module  24  and a third insulation layer  25 . The first over-current protection module  23  includes a first welding layer  231 , a first insulation layer  232 , a first upper electrode layer  233 , a first PTC conductive material layer  234  and a first lower electrode layer  235 . The second over-current protection module  24  includes a second welding layer  241 , a second insulation layer  242 , a second lower electrode layer  243 , a second PTC conductive material layer  244  and a second upper electrode layer  245 . The third insulation layer  25  can be the material of polypropylene (PP) or glass fiber, etc., which not only can provide insulation effect, but can also maintain specific hardness. The first insulation layer  232  and the second insulation layer  242  can be coated with solder mask in a simpler manner, to protect the first welding layer  231  with the upper metal conductive sheet  21 , and the second welding layer  241  with the lower metal conductive sheet  22  from short circuit effect due to improper connection. From the top view, the edge of the battery protection device  20  is provided with through holes  26 ,  27 , and the inner edge thereof can be coated with conductive material by electroplating, electroless plating or filled with conductive glue.  
         [0028]    [0028]FIG. 3 is the exploded diagram of each metal layer of the multi-layer structure of the battery protection device  20  according to the first embodiment of the invention, wherein each metal layer can adopt the copper foil, nickel foil, nickel-plating copper foil, gold foil or the alloy thereof. One side of the first upper electrode layer  233 , the first lower electrode layer  235 , the second upper electrode layer  245  and the second lower electrode layer  241  are provided with an etching ring  33  respectively for isolating electrical connection to the through holes  26 ,  27 . Thus, the electrical connection of the multi-layer battery protection device  20  should include two paths, wherein a first path is from the upper metal conductive sheet  21  electrically connecting to the first welding layer  23   1 , the first upper electrode layer  233  and the second upper electrode layer  245  by the through hole  26 , and a second path is from the lower metal conductive sheet  22  electrically connecting to the second welding layer  241 , the second lower electrode layer  243  and the first lower electrode layer  235  by the through hole  27 . Through the electrical connection described above, the first over-current protection module  23  and the second over-current protection module  24  are connected with each other in parallel between the upper metal conductive sheet  21  and lower metal conductive sheet  22 , thereby the power consumption and the resistance value of the device can be reduced.  
         [0029]    [0029]FIG. 4 is the cross-sectional view along the A-A′ line of the multi-layer structure battery protection device of the first embodiment of the invention. Obviously, the two electrically connecting paths can be verified by the cross-sectional view of FIG. 4.  
         [0030]    [0030]FIG. 5 is the multi-layer structure of the battery protection device  50  according to the second embodiment of the invention. The major difference between the battery protection device  50  and the multi-layer structure of the battery protection device  20  according to the first embodiment is that the through holes  51 ,  52  are of full circle, and not positioned at the side of the multi-layer structure of the battery protection device (i.e. semicircular conductive hole). The through holes  51 ,  52  pass through the whole battery protection device  50  in full circle manner, and the inner edge can be coated with conductive material through electroplating, electroless plating or filled with conductive glue. Therefore, compared with the multi-layer structure of the battery protection device  20  according to the first embodiment, the disadvantage thereof is the more consumed PTC conductive material. However, the conductive area of the full-circled through holes  51 ,  52  is larger than the area of the semi-circular through holes  26 ,  27 , thus the conductive characteristic of the multi-layer structure of the battery protection device  50  according to the second embodiment will be better than the multi-layer structure of the battery protection device  20  according to the first embodiment.  
         [0031]    [0031]FIG. 6 is the exploded diagram of each metal layer of the multi-layer structure of the battery protection device  50  according to the second embodiment of the invention, wherein each metal layer can adopt the copper foil, nickel foil, nickel-plating copper foil or of other form. Similar to the battery protection device  20  of the first embodiment, the first welding layer  531  and the second welding layer  541  provide with an insulation region  55  and a welding region  56  respectively. The insulation region  55  can be coated with solder mask or made with the etching line (not shown) to prevent the first welding layer  531  with the upper metal conductive sheet  21  and the second welding layer  541  with the lower metal conductive sheet  22  from short circuit caused by improper use. The peripheries of the through holes  51 ,  52  of the first upper electrode layer  533 , the first lower electrode layer  535 , the second upper electrode layer  545  and the second lower electrode layer  543  provide with an etching ring  33  for isolating the electrical connection to the through holes  51 ,  52 . Thus, the electrical connection of the multi-layer structure of the battery protection device  50  should include two paths, wherein a first path is from the upper metal conductive sheet  21  electrically connected to the first welding layer  531 , the first upper electrode layer  533 , the second upper electrode layer  545  by the through hole  52 , and a second path is from the lower metal conductive sheet  22  electrically connected to the second welding layer  541 , second lower electrode layer  543  and first lower electrode layer  535  by the through hole  51 . Through the above described electrical connection, the first over-current protection module  53  and the second over-current protection module  54  are connected with each other in parallel between the upper metal conductive sheet  21  and the lower metal conductive sheet  22 , thereby the power consumption and the resistance value of the device can be reduced.  
         [0032]    [0032]FIG. 7 is the cross-sectional view along the B-B′ line of the multi-layer structure of the battery protection device  50  according to the second embodiment of the invention. Obviously, the above two electrically connecting paths can be verified through the cross-sectional view of FIG. 7.  
         [0033]    [0033]FIG. 8 is another exploded diagram of each metal layer of the multi-layer structure of the battery protection device  50  according to the second embodiment of the invention. The difference from FIG. 6 is that, as shown in FIG. 8, there is an etching line  81  provided between the side and the through holes  51 ,  52  of the first upper electrode layer  533 , the first lower electrode layer  535 , the second upper electrode layer  545  and the second lower electrode layer  541 , which is used to solve the short-circuit problem resulted from improper welding.  
         [0034]    [0034]FIG. 9 is the multi-layer structure of the battery protection device  90  according to the third embodiment of the invention. The major difference between the multi-layer structure of the battery protection device  90  and the multi-layer structure of the battery protection device  50  of the second embodiment is that the first metal conductive sheet  91  and the second metal conductive sheet  92  are on the same side, but not on the opposite sides.  
         [0035]    [0035]FIG. 10 is the exploded diagram of each metal layer of the multi-layer structure of the battery protection device  90  according to the third embodiment of the invention, wherein each metal layer can adopt the copper foil, nickel foil, nickel-plating copper foil or of other forms. Similar to the battery protection device  50  of the second embodiment, the first welding layer  531  provides with an insulation region  55 , a first welding region  57  and a second welding region  58 , and the insulation region  55  can be coated with solder mask and made with the etching line (not shown) to protect the first welding layer  531  and the first and second metal conductive sheets  91 ,  92  from short circuit due to improper use. The peripheries of the through holes  51 ,  52  of the first upper electrode layer  533 , the first lower electrode layer  535 , the second upper electrode layer  545  and the second lower electrode layer  543  are provided with an etching ring  33  for isolating the connection to the through holes  51 ,  52 . Thus, the electrical connection of the multi-layer battery protection device  90  should include two paths, wherein a first path is from the first metal conductive sheet  91  electrically connecting to the first welding layer  531 , the first upper electrode layer  533 , and the second upper electrode layer  545  by the through hole  52 , and a second path is from the second metal conductive sheet  92  electrically connecting to the first welding layer  531 , the first lower electrode layer  535  and the second lower electrode layer  543  by the through hole  51 . Through above described electrical connection, the first over-current protection module  53  and second over-current protection module  54  are connected with each other in parallel between the first metal conductive sheet  91  and second metal conductive sheet  92 , thereby the power consumption and the resistance value of the device can be reduced. Furthermore, because the first metal conductive sheet  91  and the second metal conductive sheet  92  are welded in the first welding layer  531 , the second welding layer  541  in FIG. 5 can be omitted in the battery protection device  90 .  
         [0036]    [0036]FIG. 11 is the cross-sectional view along the C-C′ line of the multi-layer structure of the battery protection device  90  according to the third embodiment of the invention. Obviously, the aforementioned two electrically connecting paths can be verified by the cross-sectional view in FIG. 11.  
         [0037]    The technical contents and technical characteristics of the invention have been disclosed as the above, however, one skilled in the art can make various modifications and alternations, without departing from the spirit of the invention based on the teaching and disclosure of the invention. Thus, the protected scope of the invention is not restricted in the disclosure of the embodiment, and should include various modifications and alternations, without departing from the invention and should be indicated by the appended claims.