Abstract:
A resistive device includes a resistive layer, a flexible substrate arranged on the resistive layer, and an electrode layer. The electrode layer includes two electrode sections arranged below the resistive layer and separate to each other. Moreover, a method for manufacturing the resistive device with flexible substrate is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to a resistive device, and in particular to a resistive device with flexible substrate. 
     2. Description of Prior Art 
     As technology of electric circuit has a continuous development, the requirement for stability of resistance of a resistive device is increased. Some features such as temperature coefficient of resistance (TCR) of traditional chip type resistive device have been not satisfied for the requirement of high stability so that the application is limited. 
     As shown in  FIG. 1 , in order to enhance the heat stability of resistance of a resistive device, there has a conventional resistive device  10  provided. The resistive device  10  has a substrate  11  made of ceramic material, a resistive layer  12  located on a lower surface of the substrate  11 , a copper foil layer  13  located on an upper surface of the substrate  11 , side electrodes  14  respectively located at two sides of the substrate  11  and a protective layer  15  located on the copper foil layer  13 . The operative power of the resistive device  10  can be enhanced by the copper foil layer  13  which has excellent heat dissipation to dissipate the heat generated when the resistive device  10  is operated. 
     However, as the electric device pursues a trend of miniaturization, the resistive device should follow the trend of miniaturization. The substrate of the above resistive device is made of ceramic which is easy to crack during the manufacturing process due to hardness and brittleness. Therefore, there is a limitation for further miniaturizing the resistive device. Moreover, a conventional adhesive for adhering the substrate  11  and the resistive layer  12  or the copper foil layer  13  may contain glass fiber material to provide a preferable support after curing. However, the glass fiber material has poor flexibility after curing, so that there is another limitation for the application of the resistive device. Also, because glass fiber material has poor heat dissipation and may block the heat transfer from the substrate  11  toward the resistive layer  12  or the copper foil layer  13 , the operative power of the resistive device  10  cannot be enhanced. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to provide a resistive device having a substrate made without using ceramic material in order to reduce the size. 
     To achieve the above object, the present invention provides the resistive device having flexible substrate. The resistive device comprises a flexible substrate, a resistive layer and an electrode layer. The flexible substrate may be located on the resistive layer. The electrode layer has a first electrode part and a second electrode part located on the resistive layer opposed to the flexible substrate and separated with each other. 
     The invention provides a method for manufacturing a resistive device having flexible substrate comprising steps of providing a flexible substrate; forming a resistive layer on the flexible substrate; and forming an electrode layer located on the resistive layer opposed to the flexible substrate. The electrode layer has a first electrode part and a second electrode part separated with each other. 
     In addition, the invention provides another method for manufacturing a resistive device having flexible substrate comprising steps of providing a flexible substrate and a resistive layer directly attached with each other; and forming an electrode layer located on the resistive layer opposed to the flexible substrate. The electrode layer has a first electrode part and a second electrode part separated with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a sectional view of a convention resistive device. 
         FIG. 2  shows a sectional view of a first embodiment of resistive device according to the invention. 
         FIG. 3  shows a sectional view of a second embodiment of resistive device according to the invention. 
         FIG. 4  shows a sectional view of a third embodiment of resistive device according to the invention. 
         FIG. 5  shows a sectional view of a fourth embodiment of resistive device according to the invention. 
         FIG. 6(A)  to  FIG. 6(G)  show schematic view of steps of a method for manufacturing a resistive device of the invention. 
         FIG. 7(A)  to  FIG. 7(E)  show schematic view of steps of another method for manufacturing a resistive device of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The detailed description and technical content of the present invention with reference to the drawings, which merely provides reference and illustration without having an intention to limit the present invention, illustrates as following. 
     Please refer to  FIG. 2 .  FIG. 2  shows a first embodiment of a resistive device according to the present invention. The resistive device  20  mainly includes a flexible substrate  100 , a resistive layer  110  located on the flexible substrate  100 , an electrode layer  120  located on the resistive layer  110  opposed to the flexible substrate  100 , and an adhesive layer  130  between the resistive layer  110  and the flexible substrate  100 . 
     The resistive layer  110  is made of Ni—Cu alloy, Ni—Cr alloy, F—Cr alloy, Cu—Mn alloy, Cu—Mn—Sn alloy, Ni—Cr—Al alloy, Ni—Cr—Fe alloy, and so on. In the embodiment, the resistive layer  110  is a sheet of Ni—Cu alloy with a thickness of 50˜300 μm. The resistive layer  110  is a whole rectangular sheet or may form special shape of opening or groove thereon to have a predetermined resistance value. 
     The flexible substrate  100  is plastic material, such as polyimide (PI), polyethylene terephthalate (PET), bismaleimide-triazine resin (BT resin), having preferable chemical stability with a thickness of 12˜45 μm. 
     The adhesive layer  130  may be material of epoxy and acrylic resin etc. with a thickness of 13˜102 μm. Also, the adhesive layer  130  may be a heat dissipation adhesive with a property of heat dissipation. 
     The electrode layer  120  includes a first electrode part  121  and a second electrode part  122  located at two opposite sides of a lower surface of the resistive layer  110 . The first electrode part  121  and a second electrode part  122  have material of copper or copper alloy. In addition, the resistive device  20  of the embodiment may further include a first outer welding layer  126  covering the first electrode part  121  and a second outer welding layer  127  covering the second electrode part  122 . The first outer welding layer  126  and the second outer welding layer  127  may be used to connect other external components. The first outer welding layer  126  and the second outer welding layer  127  may include a single welding layer or welding multi-layer such as Ni layer and Sn layer formed by electroplating or sputtering process. 
     In order to prevent the resistive layer  110  from contamination or oxidation, a first protective layer  140  may cover on the lower surface of the resistive layer  110  between the first electrode part  121  and the second electrode part  122 . Furthermore, the resistive device  20  of the embodiment may further cover a second protective layer  150  on an upper surface of the flexible substrate  100 . The first protective layer  140  and the second protective layer  150  may have material of epoxy and acrylic resin. 
     In the embodiment, there is not provided a ceramic substrate that is hard to work in the resistive deviceso that the resistive device can be easily further reduced the size. In addition, because both the flexible substrate  100  and the adhesive layer  130  are flexible, the resistive device  20  may have preferable flexibility, and thus the use of the resistive device is wide-spreading. 
     Also, the flexible substrate  100  may be easily made thinner because of good workability in such a manner that the resistive device  20  of the present invention has lower thermal impedance. The adhesive layer  130  of the present invention may have preferable heat conductivity due to without using glass fiber. 
     Please refer to  FIG. 3 .  FIG. 3  shows a second embodiment of a resistive device according to the present invention. The difference between the second embodiment and the first embodiment is that the resistive device  30  of the second embodiment may further include a metal layer  160  sandwiched between the flexible substrate  100  and the second protective layer  150 . The effect of heat dissipation of the resistive device  30  can be enhanced by preferable heat conductivity of the metal layer  160 . In this embodiment, the metal layer  160  may preferably have a thickness of 8˜105 μm, further preferably have a thickness of 8˜70 μm, and particularly preferably have a thickness of 8˜35 μm of copper, copper alloy or other metal material with preferable heat dissipation. 
     Please refer to  FIG. 4 .  FIG. 4  shows a third embodiment of a resistive device  40  according to the present invention. The difference between the third embodiment and the second embodiment is that the resistive device  40  of the third embodiment may further include a metal layer  160  having a first metal sheet  162  and a second metal sheet  164  separated with each other, and sandwiched between the flexible substrate  100  and the second protective layer  150 . There is no limitation for the shape of the first metal sheet  162  and the second metal sheet  164 , and the shape may be directed according to the required heat dissipation. In this embodiment, the second protective layer  150  covers the first metal sheet  162  and the second metal sheet  164 , and fills into an area between the first metal sheet  162  and the second metal sheet  164 . In another embodiment, the second protective layer  150  may only fill into the area between the first metal sheet  162  and the second metal sheet  164  without covering the first metal sheet  162  and the second metal sheet  164 . In the embodiment, the first metal sheet  162  and the second metal sheet  164  may have material of copper or copper alloy with a preferable thickness of 8˜105 μm, a further preferable thickness of 8˜70 μm and a particular preferable thickness of 8˜35 μm. 
     Please refer to  FIG. 5 .  FIG. 5  shows the fourth embodiment of a resistive device according to the present invention. The difference between the fourth embodiment and the first embodiment is that the resistive device  50  of the fourth embodiment has no adhesive layer for adhering the resistive layer  110  on the lower surface of the flexible substrate  100 . The resistive layer  110  is directly attached to the flexible substrate  100 . 
     A method for manufacturing a resistive device of the invention is described as following. Please refer to  FIG. 6(A)˜FIG .  6 (G). At first, as shown in  FIG. 6(A) , a flexible substrate  100  and an adhesive layer  130  are provided, wherein the flexible substrate  100  has a metal layer  160  attached on an upper surface thereof, and the adhesive layer  130  may attach on a release film  170 ; the release film  170  can be removed after the adhesive layer  130  is attached on the flexible substrate  100 . Next, as shown in  FIG. 6(B) , the flexible substrate  100  is attached on the resistive layer  110  with the adhesive layer  130 , and the flexible substrate  100  and the resistive layer  110  adhere close with the adhesive layer  130  by thermal press to form a plate assembly, as shown in  FIG. 6(C) . 
     Next, as shown in  FIG. 6(D) , the resistive layer  110  is etched to form a recess  111  for adjusting the resistance value of the resistive layer  110 . Also, the metal layer  160  is etched to form a groove  161 , and thus a first metal sheet  162  and a second metal sheet  164  separated with each other are formed. 
     Next, as shown in  FIG. 6(E) , a first electrode part  121  and a second electrode part  122  having electrical conductive function located at two opposite sides of a lower surface of the resistive layer  110  are formed by electroplating, press fitting or welding process. 
     Next, as shown in  FIG. 6(F) , a first protective layer  140  is formed on the lower surface of the resistive layer  110  between the first electrode part  121  and the second electrode part  122  to prevent the resistive layer  110  from contamination or oxidation. Also, a second protective layer  150  is formed on an upper surface of the flexible substrate  100  to provide enough strength for supporting the resistive device. 
     At last, as shown in  FIG. 6(G) , a first outer welding layer  126  covering the first electrode part  121  and a second outer welding layer  127  covering the second electrode part  122  are formed to increase the adhesion of the first electrode part  121  and the second electrode part  122 , and to increase the bonding strength between the resistive device and PCB. 
     It should be noted, with the above manufacturing method, the flexible substrate  100  having a metal layer  160  on an upper surface thereof is provided in the beginning. In the another embodiment, the above manufacturing method may proceed by only the remaining flexible substrate  100 . For example, the embodiment of the method may manufacture the resistive device of  FIG. 3  or  FIG. 4  with the metal layer  160 . The embodiment of the method may manufacture the resistive device of  FIG. 2  without the metal layer  160 . 
     As shown in  FIG. 7(A)˜FIG .  7 (E), which illustrate another method for manufacturing a resistive device of the present invention. As shown in  FIG. 7(A) , a flexible substrate  100  and a resistive layer  110  directly attached with each other are provided, wherein there is no adhesive layer between the flexible substrate  100  and a resistive layer  110  for adhering them. In one embodiment, the flexible substrate  100  is directly formed on the resistive layer  110 , for example, a liquid soft material is coated or printed on the resistive layer  110 , and then the flexible substrate  100  is formed and attached on the resistive layer  110  by curing the liquid soft material. In another embodiment, the resistive layer  110  may be formed on the flexible substrate  100  by film-forming method, for example, the resistive layer  110  is formed on the flexible substrate  100  by thick film or thin film process. 
     Next, as shown in  FIG. 7(B) , a first electrode part  121  and a second electrode part  122  having electrical conductive function located at two opposite sides of a lower surface of the resistive layer  110  are formed by electroplating, press fitting or welding process. Also, in this embodiment, a metal layer  160  is further formed on the flexible substrate  100 . It should be noted, the metal layer  160  is used for increasing the heat dissipation of the resistive device, and it can be removed if need. 
     As shown in  FIG. 7(C) , the resistive layer  110  is etched to form a recess  111  for adjusting the resistance value of the resistive layer  110 . Also, the metal layer  160  is etched to form a groove  161 , and thus a first metal sheet  162  and a second metal sheet  164  separated with each other are formed. 
     As shown in  FIG. 7(D) , a first protective layer  140  is formed on the lower surface of the resistive layer  110  between the first electrode part  121  and the second electrode part  122  to prevent the resistive layer  110  from contamination or oxidation. Also, a second protective layer  150  is formed on an upper surface of the flexible substrate  100  to provide enough strength for supporting the resistive device. 
     As shown in  FIG. 7(E) , a first outer welding layer  126  covering the first electrode part  121  and a second outer welding layer  127  covering the second electrode part  122  are formed to increase the adhesion of the first electrode part  121  and the second electrode part  122 , and to increase the bonding strength between the resistive device and PCB. 
     The described embodiments are preferred embodiments of the present invention. However, this is not intended to limit the scope of the invention. The equivalent changes and modifications may be made in accordance with the claims of the invention without departing from the scope of the invention.