Abstract:
A circuit board and a smart card module and a smart card employing the circuit board are provided. The circuit board includes a substrate and a pad region provided on the substrate. The pad region is configured for mounting an electronic component. The pad region comprises a plurality of pads spaced from each other and traces connected to their respective pads. At least one of the traces comprises an extension which extends along a perimeter of the pad region. The present invention provides a reliable adhesion between the chip and pad region.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201610073310.5 filed in The People&#39;s Republic of China on Feb. 2, 2016. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to a circuit board, a smart card module and a smart card employing the circuit board. 
       BACKGROUND OF THE INVENTION 
       [0003]    With the development of human society, communication devices and identification devices have become more and more widely used. The use of smart cards and associated identification devices has brought greatly improved safety and convenience to people&#39;s travel. 
         [0004]    A smart card, also referred to as an IC card, is a portable plastic card with an IC chip adhered thereon or embedded therein. The card includes a microprocessor, an I/O interface and a memory, which provides functions of computing, access control and storage of data. The size and connecting terminals of the card are specified by relevant ISO standards such as ISO7810. Common smart cards include telephone IC cards, identification IC cards, and some transport tickets and memory cards. 
         [0005]    The smart card includes a card body and a smart card module mounted on the card body. The smart card module includes a circuit board and electronic components (such as a chip) mounted on the circuit board. Due to its light weight, small thickness, the circuit board has been widely used in various electronic devices, such as cell phones, notebook computers, tablet PCs and liquid crystal displays (LCDs). 
         [0006]    In currently available circuit board products, an adhesive layer between the chip and the circuit board has strong flowability and is inclined to flow randomly, which may result in some area in the pad region has no adhesive layer and some area outside of the pad region has the adhesive layer. This may cause poor adhesion between the chip and the circuit board and reduced reliability of the circuit board. 
       SUMMARY OF THE INVENTION 
       [0007]    Thus there is a desire for a new circuit board with improved reliability and a smart card module and a smart card using the circuit board, which can address the poor adhesion result. 
         [0008]    In one aspect, an circuit board is provided which includes a substrate and a pad region provided on the substrate. The pad region is configured for mounting an electronic component. The pad region comprises a plurality of pads spaced from each other and traces connected to their respective pads. At least one of the traces comprises an extension which extends along a perimeter of the pad region. 
         [0009]    In another aspect, a smart card module is provided. The smart card module includes a chip and the above-described circuit board. The chip is mounted to the pad region of the circuit board for mounting the chip. 
         [0010]    In still another aspect, a smart card is provided which includes a card body. The card body defines a groove. The smart card further includes the above-described smart card module, and the smart card module is disposed in the groove of the card body. 
         [0011]    In various embodiments of the present invention, the adhesive can flow along the pad region and can be uniformly applied in the pad region under the guiding and blocking of the plurality of extensions. The extensions can block the adhesive from flowing to an area outside the pad region, thus avoiding non-uniform applying and arbitrary flowing of the adhesive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a top plan view of an circuit board according to a first embodiment of the present invention. 
           [0013]      FIG. 2  is a top view of a conventional circuit board. 
           [0014]      FIG. 3  is a top plan view of an circuit board according to a second embodiment of the present invention. 
           [0015]      FIG. 4  is a top plan view of an circuit board according to a third embodiment of the present invention. 
           [0016]      FIG. 5  is a top plan view of an circuit board according to a fourth embodiment of the present invention. 
           [0017]      FIG. 6  is another top plan view of the circuit board according to the first embodiment of the present invention. 
           [0018]      FIG. 7  illustrates a smart card product according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    The technical solutions of the embodiments of the present invention will be clearly and completely described as follows with reference to the accompanying drawings. Apparently, the embodiments as described below are merely part of, rather than all, embodiments of the present invention. Based on the embodiments of the present disclosure, any other embodiment obtained by a person skilled in the art without paying any creative effort shall fall within the protection scope of the present invention. 
         [0020]    It is noted that, when a component is described to be “fixed” to another component, it can be directly fixed to the another component or there may be an intermediate component. When a component is described to be “connected” to another component, it can be directly connected to the another component or there may be an intermediate component. When a component is described to be “disposed” on another component, it can be directly disposed on the another component or there may be an intermediate component. 
         [0021]      FIG. 1  is a schematic plan view of a circuit board  1  according to one embodiment of the present invention. The circuit board  1  is preferred a flexible printed circuit (FPC) board, may be used in smart cards, or other electronic devices, such as cell phones, notebook computers, tablet PCs, LCDs, televisions, or electronic components in other electronic devices. In this embodiment, the circuit board  1  is preferably suitable for use in a smart card module. A chip (not shown) is assembled as a flip-chip. The circuit board  1  may also be provided with other necessary electronic components to form the smart card module. The smart card module is then disposed on a card body  10  ( FIG. 7 ) to form a complete smart card product. 
         [0022]    The smart card includes at least one plastic board body (card body  10 ) and a smart card module, i.e. the circuit board  1  and the electronic components on the circuit board  1 , mounted on the board body. It should be understood that, in order to reduce the thickness of the smart card, the card body may define a mounting groove that matches with the smart card module in thickness and shape. In some embodiment, the board body may include antennas that connect with the smart card module, thus achieving wireless communication function of the smart card. In some other embodiments, the antennas may be mounted in the smart card module at a side opposite from the chip mounting side, thus improving the manufacturing procedure. 
         [0023]    The circuit board  1  includes at least one pad region  2  (as indicated by the circular region enclosed by dotted line broken line in the  FIG. 1 ). A plurality of pads  3  (connecting pads) and a plurality of traces  5  are formed in the pad region  2 . Each pad  3  is connected with one trace  5 . The trace  5  is used to connect the electronic component (such as chip) mounted in the pad region  2  to another electronic component or an contact pad formed on the opposite side of the circuit board  1 . The pad  3  may be connected to the chip using a flip-chip process or wire-bonding process. 
         [0024]    It should be understood that, the number of the pads  2  and traces  5  may be determined based on the number of pins of the chip (not shown) soldered to the pad region  2 . The number of the chip pins is specified in relevant ISO standards. In this embodiment, there are five pads  3  and five traces  5 , with three pads  3  arranged in a row and uniformly spaced from each other, and the other two pads  3  arranged in another parallel row. 
         [0025]    The circuit board  1  includes at least one substrate  12 . In this embodiment, the substrate  12  is made of polyethylene terephthalate (PET). The pads  3  are disposed in the pad region  2  on the substrate  12  of the circuit board  1 . In this embodiment, a material of the pads  3  and traces  5  is copper foil with a nickel layer coated thereon. The circuit board  1  is a dual-layer circuit board (double-sided circuit board). At least one side of the substrate  12  of the circuit board  1  is mounted with the pads  3  and traces  5 . The other side may also be provided with the pads and traces. In this embodiment, by way of example, the pads  3  and traces  5  are illustrated as being mounted at the same side of the substrate  12 . 
         [0026]    It should be understood that, the pads  3  and traces  5  may be formed by printing conducting materials in the pad region  2 . Alternatively, the pads  3  and traces  5  may be formed at preset locations of the pad region  2  by plating and etching. 
         [0027]    In this embodiment, at least one of the plurality of pads  3  is round. In comparison with the ordinary square pad, the gap between two round pads  3  is reflected by a distance between two nearest points of two adjacent round pads  3 , the distance is easy to be controlled during fabrication. Under the condition of the same fabrication tolerance, the distance between adjacent pads  3  can be reduced, then the reduced distance between adjacent pads  3  facilitates better layout of the circuit board  1 . The chip pad pitch can decrease to allow for reduced chip size and hence reduced space to be occupied in the electronic device. In addition, the round pad  3  has the same size as an inscribed circle of the square of the square pad and, therefore, consumes less material. A minimum value of the distance A between two adjacent pads  3  can reach 40 um. In other words, the distance A is greater than or equal to 40 um, can be 75 um. A minimum value of the distance B between centers of two adjacent pads  3  can reach 142 um. In other words, the distance B is greater than or equal to 142 um, can be 177 um. 
         [0028]    Furthermore, as shown in  FIG. 2 , in the round pad region of the conventional circuit board with square pads, the area of the copper foils occupies 24.4% of the total pad region. Referring to  FIG. 1 , however, in the circuit board  1  having the round pads  3  according to this embodiment of the present invention, under the conditions that the pads  3  are arranged in the same layout and the pad region  2  has the same area, the area of the copper foils occupies 13% of the total pad region  2 . Obviously, the copper foils occupy less area in the pad region  2  of the circuit board of this embodiment of the present invention. Therefore, more adhesive may be applied on a greater area of the substrate  12  (PET film), which enhances the structure stability of the chip and the pad region  2 . 
         [0029]    It should be understood that the shape of the pads  3  is not limited to circle. The shape of the pads also can be ellipse. As long as the pads have an arc edge, the gap between two adjacent pads can be reflected by a distance between two nearest points of two adjacent pads, the distance is easy to be controlled during fabrication. As such, under the condition of the same fabrication tolerance, the distance between adjacent pads can be reduced, then the reduced distance between adjacent pads facilitates better layout of the circuit board. 
         [0030]      FIG. 3  to  FIG. 5  illustrate other embodiments according to another concept of the present invention. At least one trace  5  extends to form an extension  56 . The extension  56  extends from a portion of the associated trace  5  adjacent the pad  3  toward one adjacent trace  5  along a perimeter of the pad region  2 , until reaching a position closing to the adjacent trace  5 . It should be understood that the extension  56  of each trace  5  is insulated from any of the other traces. 
         [0031]    The extensions  56  extending along the perimeter of the pad region  2  cooperatively define the perimeter of the pad region  2 . Therefore, during the course of applying an adhesive layer for bonding the chip in the pad region  2 , the adhesive can flow along the pad region  2  and can be uniformly applied in the pad region  2  under the guiding and blocking of the plurality of extensions  56 . The extensions  56  can block the adhesive from flowing to an area outside the pad region  2 , thus avoiding non-uniform applying and arbitrary flowing of the adhesive. In this embodiment, a thickness of the extension  56  protruding beyond the surface of the substrate  12  is 10 um-15 um and, preferably, 10 um. The material of the extensions  56  is the same as the material of the traces  5 . In another embodiment of the present invention, the extensions  56  may also be made of PET, another metal material or plastic. 
         [0032]    It should be understood that the pad region  2  may be of any shape such as round, rectangle or polygon depending upon the shape of the chip. Accordingly, the region that is cooperatively defined by the plurality of extensions  56  is in the shape of round, rectangle or polygon. In this embodiment, the shape of the pad region  2  is round. 
         [0033]    Referring to  FIG. 3 , in a second embodiment of the present invention, the circuit board  1  includes a first pad  31 , a second pad  32 , a third pad  33 , a fourth pad  34 , a fifth pad  35 , and a first trace  51 , a second trace  52 , a third trace  53 , a fourth trace  54  and a fifth trace  55  that are connected to the pads, respectively. In this embodiment, two extensions  56  extend from each of the first trace  51  and third trace  53  at a position adjacent the associated pad toward opposite sides, respectively, and an extension  56  extends from the fourth trace  54  toward the fifth trace  55 . 
         [0034]    The two extensions  56  connected to the first trace  51  are in the form of a longer arc and a shorter arc, with the longer extension  56  extending toward the second trace  52  and the shorter extension  56  extending to the fifth trace  55 . The longer extension  56  partially overlaps with the first trace  51 . 
         [0035]    The two extensions  56  connected to the third trace  53  are in the form of a longer arc and a shorter arc, with the shorter extension  56  extending toward the second trace  52  and the longer extension  56  extending to the fourth trace  54 . 
         [0036]    The shorter extension  56  connected to the first trace  51 , the extension  56  connected to the fourth trace  54 , and the shorter extension  56  connected to the third trace  53  are the same in length and radians. 
         [0037]    The extensions  56  cooperatively define a non-closed circle along the pad region  2 . The second trace  52  is disposed in a gap between the longer extension  56  connected to the first trace  51  and the shorter extension  56  connected to the third trace  53 . The fifth trace  55  is disposed in a gap between the shorter extension  56  connected to the first trace  51  and the extension  56  connected to the fourth trace  54 . The portion of each trace within the pad region  2  has the same width. The portions of the traces connected to the corresponding pads adjacent the perimeter of the pad region  2  are substantially parallel to each other. 
         [0038]    Referring to  FIG. 4 , a third embodiment of the present invention differs from the second embodiment of the present invention in that, the portions of the first trace  51 , the third trace  53  and the fourth trace  54  adjacent the perimeter of the pad region  2  extend in radial directions of the circle within which the pad region  2  is located. 
         [0039]    Referring to  FIG. 5 , in a fourth embodiment of the present invention, the circuit board  1  includes a first pad  31 , a second pad  32 , a third pad  33 , a fourth pad  34 , a fifth pad  35 , and a first trace  51 , a second trace  52 , a third trace  53 , a fourth trace  54  and a fifth trace  55  that are connected to the pads, respectively. In this embodiment, an extension  56  extends from each of the first trace  51 , the second trace  52 , and a fourth trace  53  at a position adjacent the associated pad toward one side, and two extensions  56  extend from the fifth trace  55  at a position adjacent the fifth pad  35  toward opposite sides, respectively. 
         [0040]    The extension  56  formed on the first trace  51  extends toward the second trace  52 , the extension  56  formed on the second trace  52  extends toward the third trace  53 , and the extension  56  connected to the fourth trace  54  extends toward the third trace  53 . 
         [0041]    The two extensions  56  formed on the fifth trace  55  extend toward the adjacent first trace  51  and fourth trace  54 , respectively. 
         [0042]    The extensions  56  cooperatively define a non-closed circle along the pad region  2 . The third trace  53  is disposed in a gap between the extension  56  connected to the second trace  52  and the extension  56  connected to the fourth trace  54 . The portion of each trace within the pad region  2  has the same width. The portions of traces connected to the second, third and fifth pads  32 ,  33 , and  35  adjacent the perimeter of the pad region  2  are substantially parallel to each other. The portions of traces connected to the first and fourth pads  31  and  34  adjacent the perimeter of the pad region  2  are substantially parallel to each other and are perpendicular to the portions of traces connected to the second, third and fifth pads  32 ,  33 , and  35  adjacent the perimeter of the pad region  2 . The extensions connected to opposite sides of the fifth traces  55  are the same in length and radians, such that the distance between the first and fifth pads  31 ,  35  is the same as the distance between the fourth and fifth pads  34 ,  35 . 
         [0043]    It should be understood that the size of the pad  3  on the circuit board  1  depends on the fabrication tolerance and the size of the gold ball (not shown) on the pad  3  for soldering the chip. In the case of large fabrication tolerance and low assembly precision, the size of the pad  3  may increase; in the case of small fabrication tolerance and high assembly precision, the size of the pad  3  may decrease. The size of the pad  3  is directly proportional to the size of the gold ball. 
         [0044]    Referring to  FIG. 3 , the circuit board  1  further includes at least a group of positioning marks  57 . The group of positioning marks  57  includes at least two positioning marks. In this embodiment, the number of the positioning marks  57  is four. The positioning marks  57  and the traces  5  can be formed together. The positioning marks  57  facilitate a chip precisely identifying the mounting position of the chip on the circuit board  1 . When the chip is placed on the circuit board  1 , an operator observes the precision position of the chip through a display and can know whether the position of the chip deviates by means of the positioning marks. In this embodiment, the positioning marks  57  are made of the same material as the traces  5 , and are formed on the traces  5  at positions away from the pad region  2  to further reduce the copper foil area in the pad region  2 . 
         [0045]    Referring to  FIG. 6 , in this embodiment, the trace  5  defines a via hole  4  passing through the substrate  12 . The via hole  4  is defined at a position of the trace  5  away from the pad region  2 , and the size of the trace  5  at the position where the via hole  4  is defined is greater than the size of portions of the trace  5  where no via hole is defined. The via hole  4  is filled with a conducting medium. Preferably, the conducting medium and the pad  3  are made of the same material. The via hole  4  can connect the pad  3  to another pad  3  or trace  4  at a different layer of the circuit board  1 , such that signals transmitted through the pad  3  can be transmitted between different layers. 
         [0046]    It should be understood that the circuit board  1  may also be a single sided circuit board, and the pads  3  and traces  5  are disposed on the outer surface of the same side of the circuit board  1 . 
         [0047]    It should be understood that the circuit board  1  may also be a dual-layer circuit board. One layer provided with pads and traces for connecting the chip. Another layer provided with contact pads in communication with electronic devices. For example, the circuit board  1  includes at least two stacked substrates  12  with an adhesive layer filled therebetween. The pads  3  and traces  5  are formed on an outermost layer of the circuit board  1 . The trace  5  in the circuit of the outmost layer of the circuit board  1  defines a blind via or through hole  41  passing through the circuit board  1 . In this embodiment, the through hole  41  is defined at a position of the trace away from the pad region  2 , and the size of the trace  5  at the position where the through hole is defined is greater than the size of portions of the trace  5  where no through hole  41  is defined. The through hole  41  is filled with a conducting medium. Preferably, the conducting medium and the pad  3  are made of the same material, i.e. copper foil. The via hole  41  can connect the pad  3  to another pad or trace at a different layer of the circuit board  1 , such that signals transmitted through the pad  3  can be transmitted between different layers. 
         [0048]    The circuit board  1  of the present invention uses round pads  3 , such that the copper foils occupy less area in the pad region  2 , leaving more space for the PET film. Therefore, during the course of mounting the chip to the pad region  2 , the PET film with greater area allows for more adhesive to be applied thereon, which enhances the structural stability of the chip and pad region  2 . 
         [0049]      FIG. 7  illustrates the application of the smart card module mounted to a smart card according to one embodiment of the present invention. In this figure, the card body  10  is a plastic base plate with a hollow groove defined in a middle portion thereof. One side of the circuit board  1  is mounted with a chip (not shown), and the other side is provided with smart card contact terminals (as shown in the figure) according to the SIM card standard to form a smart card module. The smart card module is then mounted in the card body  10  to form a complete smart card. 
         [0050]    Although the invention is described with reference to one or more embodiments, the above description of the embodiments is used only to enable people skilled in the art to practice or use the invention. It should be appreciated by those skilled in the art that various modifications are possible without departing from the spirit or scope of the present invention. The embodiments illustrated herein should not be interpreted as limits to the present invention, and the scope of the invention is to be determined by reference to the claims that follow.