Abstract:
The invention relates to resettable chip-type over-current protection devices and methods of making the same, characterized by directly forming upper and lower electrode conductor and connection electrode conductor on a PPTC substrate so as to constitute a simplified three-layer structure of “electrode conductor-PPTC substrate-electrode conductor.”

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (A) Field of the Invention  
         [0002]     The present invention relates to a structure and manufacturing method of an over-current protection device. More specifically, the present invention relates to a resettable chip-like over-current protection device utilizing a polymeric positive temperature coefficient (PPTC) material as a substrate thereof.  
         [0003]     (B) Description of Related Art  
         [0004]     PPTC devices have been widely used in circuits of electronic devices today. The conductive composite material used in the PPTC devices is mostly composed of polyethylene and electrically conductive particles (mostly carbon black). Under normal operating temperatures, polyethylene confines the conductive particles tightly in a crystalline structure thereby to form a low resistance conductive network. When an abnormally high current is present, the heat generated on the device will reform the polyethylene from crystalline to amorphous. In such a situation, confined conductive particles will be separated due to quick expansion of the polyethylene, which breaks original conductive network. As a result, the resistance rises quickly so that the abnormal current passing through the device will be limited. After termination of the abnormal current, the temperature of the device will drop to room temperature and the conductive composite material will return to the original structure, which means that the polyethylene again confines the conductive particles in the crystalline structure, forming a low resistance conductive network, whereby the purpose of automatic resetting is obtained.  
         [0005]     Currently, PPTC devices are mostly used for the purpose of over-current protection. In additional to radial-leaded type devices similar to conventional fuses, the PPTC devices are applied to surface-mount type devices used in a printed circuit board (PCB), which is composed of an at least 5-layer structure of a PPTC substrate, two main electrode conductive metal foil on top and bottom surfaces of the substrate, and two surface connecting electrode layers. For instance, U.S. Pat. No. 6,292,088 (entitled “PTC Electrical Devices for Installation on Printed Circuit Boards”) shown in  FIG. 1A ˜ FIG. 1F  discloses that on a PPTC substrate  10 , two main electrode conductive metal foils  11   a  and  11   b  are applied on two surfaces of the PPTC substrate firstly, as shown in  FIG. 1A  and  FIG. 1B  so as to form a sandwich structure as shown in  FIG. 1C  and  FIG. 1D , then a via  12  necessary for connecting top and bottom electrode conductive layers is formed, as shown in  FIG. 1E  and  FIG. 1F . Subsequently, a connecting electrode layer  13  is formed on the via  12 , as shown in  FIG. 1G  and  FIG. 1H . Then electrode isolation areas  14  required in installation of terminal electrodes of the chip-like resettable over-current protection device are formed, as shown in  FIG. 1I  and  FIG. 1J . Finally, a finished substrate is separated into individual devices according to predetermined cutting lines  15  as shown in  FIG. 1K  and  FIG. 1L , and then the chip-like resettable over-current protection device with two terminal electrodes  16  and  17  is finished. The said terminal electrodes  16  and  17  are isolated from each other but connected to themselves located on top and bottom surfaces.  
         [0006]     After analyzing this prior art, it is understood that the prior art has the following drawbacks: 
        1. The structure of 5-layer “surface connecting electrode conductive layer-main electrode conductive metal foil-PPTC substrate-main electrode conductive metal foil-surface connecting electrode conductive layer” and the manufacturing method thereof are too complex.     2. In preparing the electrode isolation areas, parts of electrode conductive metal foils  11   a  and  11   b  on device need to be removed and this process consumes much power and produces pollution.        
 
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is a solution for eliminating the drawbacks mentioned in the prior art. According to the present invention, the purposes of reducing process steps, saving resources and mitigating pollution concern can be achieved.  
         [0010]     The present invention mainly relates to a method of manufacturing a chip-like resettable over-current protection device, comprising the step of:  
         [0011]     forming a plurality of vias on predetermined locations on a substrate of a PPTC material.  
         [0012]     Subsequently any one of the following two processes can be performed:  
         [0013]     Process 1 
        At least one metal interface layer is deposited on both surfaces of the substrate and walls of the vias by sputtering, electroless electroplating (such as chemical plating), or other chemical or physical processes (such as printing, projecting, and evaporation.) Then, a layer of conductive metal is formed on the metal interface layer for a thickness of at least 10 μm. Subsequently, at least one layer of conductive metal at predetermined locations on both surfaces of the substrate is removed so as to expose the substrate on locations of electrode isolation areas.        
 
         [0015]     Process 2 
        A plurality of electrically isolated protective layers are deposited on predetermined locations of both surfaces of the substrate. The protective layers are covered by a mask of the same size in area. At least one metal interface layer is applied on both faces of the substrate and walls of the vias by sputtering, electro-less plating (such as chemical plating), or other chemical or physical processes (such as printing, spraying, evaporation, etc.). Then, a layer of conductive metal is deposited on the metal interface layer for a thickness of at least 10 μm. Subsequently, all the masks are removed.        
 
         [0017]     Finally, the substrate is cut through a plurality of predetermined cutting lines so as to obtain a plurality of devices, wherein the cutting lines pass through the vias and make the inner walls of the vias become a part of side walls of each of the devices. The conductive inner walls are at locations of electrodes of the devices.  
         [0018]     The manufacturing process is completed so far. The completed chip-like over-current protection device comprises a three-layer structure of electrode conductive layer-PPTC substrate-electrode conductive layer, which is simpler than the conventional five-layer structure. Besides, the present invention comprises the following advantages: 
        1. The prior art metal foil is not required.     2. The prior art sandwich structure manufacturing process is not required, so that time and energy is saved.        
 
         [0021]     Because protective layers are applied on electrode isolation areas in advance, the process can be simplified by selectively processing areas in manufacturing the electrode conductive layer so as to simplify process, reduce resource consumption and mitigate pollution. Moreover, the protective layers are of the same thickness as electrode conductive layers, and the surface of the device will be flatter than conventional ones.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1A ,  FIG. 1C ,  FIG. 1E ,  FIG. 1G ,  FIG. 11  and  FIG. 1K  show structures obtained in manufacturing steps of a prior art device.  
         [0023]      FIG. 1B ,  FIG. 1D ,  FIG. 1F ,  FIG. 1H ,  FIG. 1J  and  FIG. 1L  are cross-section view of  FIG. 1A ,  FIG. 1C ,  FIG. 1E ,  FIG. 1G ,  FIG. 11  and  FIG. 1K  taken at line A-A′, respectively.  
         [0024]      FIG. 2A ,  FIG. 2C ,  FIG. 2E ,  FIG. 2G  and  FIG. 21  are top view of structures obtained in manufacturing steps of the first embodiment of the present invention.  
         [0025]      FIG. 2B ,  FIG. 2D ,  FIG. 2F ,  FIG. 2H  and  FIG. 2J  are cross-section view of  FIG. 2A ,  FIG. 2C ,  FIG. 2E ,  FIG. 2G  and  FIG. 2I  at line A-A′, respectively.  
         [0026]      FIG. 3A ,  FIG. 3C ,  FIG. 3E ,  FIG. 3G  and  FIG. 31  are top view of manufacturing steps of second embodiment of the present invention  FIG. 3B ,  FIG. 3D ,  FIG. 3F ,  FIG. 3H  and  FIG. 3J  are cross-section view of  FIG. 3A ,  FIG. 3C ,  FIG. 3E ,  FIG. 3G  and  FIG. 3I  at line A-A′, respectively.  
         [0027]      FIG. 4A ,  FIG. 4C ,  FIG. 4E ,  FIG. 4G ,  FIG. 4I  and  FIG. 4K  are top view of manufacturing steps of third embodiment of the present invention, wherein  FIG. 4E  and  FIG. 4G  are opposite faces of the same device at the same manufacturing step.  
         [0028]      FIG. 4L  is the opposite face of the same device of  FIG. 4K .  
         [0029]      FIG. 4B ,  FIG. 4D ,  FIG. 4F ,  FIG. 4H ,  FIG. 4J  and  FIG. 4M  are cross-section view of  FIG. 4A ,  FIG. 4C ,  FIG. 4E ,  FIG. 4G ,  FIG. 4I  and  FIG. 4K  at line A-A′, respectively. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]     Please refer to FIGS.  2 A˜ FIG. 2J ,  FIG. 3A .  FIG. 3J  and  FIG. 4A ˜ FIG. 4M  for procedure of implementation and structure of embodiments. The embodiments only illustrate possible methods for embodying the present invention so as to make the present invention easier to understand but not used to limit ways to embody the present invention. Persons skilled in the art can modify ways of embodying the present invention without departing from the scope and spirit of the present invention.  
         [0031]     Please refer to FIGS.  2 A˜ FIG. 2J  for the first embodiment of the present invention. Vias  12  are made at predetermined locations on a parallelepiped PPTC substrate  10  which has a top surface  1 , a bottom surface  2 , a left surface  3  and a right surface  4 , as shown in  FIG. 2A  and  FIG. 2B . Surface treatment of the whole PPTC substrate  10  and vias are done as preparation for subsequent plating process, as shown in  FIG. 2C  and  FIG. 2D . Subsequently, at least one metal interface layer is formed by sputtering, electroless plating (such as chemical plating). Then, an upper electrode conductive layer  21   a , a lower electrode conductive layer  21   b , and a connecting electrode conductive layer  13  for a thickness of at least 10 μm are formed by plating, as shown in  FIG. 2E  and  FIG. 2F . The upper and lower electrode conductive layers are not required to use conductive metal foil. Then, as what is done in the prior art, electrode isolation areas required for terminal electrodes  16  and  17  of the chip-like resettable over-current protection device are formed, as shown in  FIG. 2G  and  FIG. 2H . Finally, the completed conductive substrate is cut through cutting lines  15  into individual devices, as shown in  FIG. 21  and  FIG. 2J . Thus, the chip-like over-current protective device has separate terminal electrodes  16  and  17 , and each of the terminal electrodes  16  and  17  is of a single piece.  
         [0032]     Please refer to  FIG. 3A ˜ FIG. 3J  for the second embodiment of the present invention. Vias  12  are made at predetermined locations on a parallelepiped PPTC substrate  10  which has top surface  1 , a bottom surface  2 , a left surface  3  and a right surface  4 , as shown in  FIGS. 3A and 3B . Surface treatment of surfaces of the whole PPTC substrate  10  and vias are done as preparation for subsequent plating process, as shown in  FIG. 3C  and  FIG. 3D . Next, an electrically isolated, protective layer  31  is applied on predetermined locations of electrode isolation areas, as shown in  FIG. 3E  and  FIG. 3F . Subsequently, a mask on protective layer  31  is applied. At least one metal interface layer is deposited by sputtering, electroless plating (such as chemical plating). An upper electrode conductive layer  21   a , lower electrode conductive layer  21   b , and connecting electrode conductive layer  13  are deposited by electroplating technique for a thickness of at least 10 μm, as shown in  FIG. 2E  and  FIG. 2F . After the mask is removed, the result is shown in  FIG. 3G  and  FIG. 3H . The upper and lower electrode conductive layers  21   a  and  21   b  do not need the conventional conductive metal foil. Meanwhile, the upper and lower electrode conductive layers  21   a  and  21   b  cannot cover the protective layer  31 . More preferably, the upper and lower electrode conductive layers  21   a  and  21   b  are substantially at the same level with the protective layer  31 . Electrode isolation areas required by terminal electrodes  16  and  17  of the chip-like resettable over-current protective device are directly formed by the protective layer  31 . Finally, the completed substrate is cut through cutting lines  15  into individual devices, as shown in  FIG. 3I  and  FIG. 3J . Thus, the chip-like over-current protective device has separate terminal electrodes  16  and  17 . Each of the electrodes  16  and  17  is of a single piece.  
         [0033]     Please refer to  FIG. 4A ˜ FIG. 4M  for the second embodiment of the present invention. Vias  12  are formed at predetermined locations on a parallelepiped PPTC substrate  10  which has a top surface  1 , a bottom surface  2 , a left surface  3  and a right surface  4 , as shown in  FIG. 4A  and  FIG. 4B . Surface treatment of surfaces of the whole PPTC substrate  10  and vias are done as preparation for subsequent plating process, as shown in  FIG. 4C  and  FIG. 4D . Next, an electrically isolated protective layer  31  is applied on predetermined locations of electrode isolation areas, as shown in  FIG. 4E  and  FIG. 4G . Subsequently, a mask is applied on the protective layer  31 . Then at least one metal interface layer is deposited by sputtering electro-less electroplating (such as chemical plating). The upper electrode conductive layer  21   a , lower electrode conductive layer  21   b , and connecting electrode conductive layer  13  are deposited for a thickness of at least 10 μm, as shown in  FIG. 41  and  FIG. 4J . The mask covering the protective layer  31  is removed, the result is shown in  FIG. 4I  and  FIG. 4J . The upper and lower electrode conductive layer do not need the conventional conductive metal foil. The upper and lower electrode conductive layers cannot cover said protective layer  31 . More preferably, the upper and lower electrode conductive layers  21   a  and  21   b  are substantially at the same level with the protective layer  31 . Electrode isolation areas required by terminal electrodes  16  and  17  of the chip-like resettable over-current protective device are directly formed by the protective layer  31 . Finally, the completed conductive substrate is cut through cutting lines  15  into individual devices, as shown in  FIG. 4K ,  FIG. 4L  and  FIG. 4M . The chip-like over-current protective device has separate terminal electrodes  16  and  17 . Each of the terminal electrodes  16  and  17  is of a single piece.