Patent Publication Number: US-2009218667-A1

Title: Smart cards and methods for producing a smart card

Description:
FOREIGN PRIORITY 
     This application claims priority to German Patent Application. No. 102008011611, filed Feb. 28, 2008, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Smart cards are finding more and more applications worldwide. Thus, smart cards have for example already long been known as storage cards for telephone applications. 
     With increasing computing power and storage capacity of the semiconductor chips, however, smart cards are finding diverse further uses, such as, for example, as a card for those with health insurance, or as an identity card. 
     Contactless smart cards, in particular, in which power and data are transmitted without direct electrical coupling between card and terminal, are increasingly being used. 
     The materials, the construction and the production of the card body are essentially determined by functional elements of the cards and by the loading of the card in the course of handling during the application. 
     For applications in which high strength and longevity are required, polycarbonate (PC) is often used at the present time. It is a typical material for identity cards, but has a high stress corrosion cracking sensitivity. 
     SUMMARY 
     Embodiments are related to smart cards comprising a card body which is at least partly composed of polycarbonate, and to a method for producing such a smart card. 
     One embodiment relates to a smart card comprising a card body, wherein the card body has at least a first, a second and a third layer. The first and the second layer are at least partly composed of polycarbonate. The third layer is arranged between the first and the second layer and is composed of a material having a melting point T s &lt;150° C. 
     In one embodiment, a method for producing a card body for a smart card comprises constructing the card body from at least a first, a second and a third layer. The first and the second layer are at least partly produced from polycarbonate. The third layer is arranged between the first and the second layer and produced from a material having a melting point of T s &lt;150° C. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood from the following detailed description of various embodiments in connection with the accompanying drawings, in which: 
         FIG. 1  shows a schematic cross-sectional view of an embodiment of a partial excerpt from a smart card body. 
         FIG. 2  shows a schematic cross-sectional view of an embodiment of a smart card with a smart card body and a semiconductor chip. 
         FIG. 3  shows a schematic cross-sectional view of an embodiment of a smart card with a smart card body and a semiconductor module. 
         FIG. 4  shows a schematic cross-sectional view of an edge region of a chip module for a smart card. 
         FIG. 5  shows a schematic cross-sectional view of an exemplary embodiment of a prefabricated film for a smart card body. 
     
    
    
     Identical elements in the figures are provided with the same or similar reference symbols, and that a repeated description of these elements is omitted. 
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a partial excerpt from a smart card body in cross section. The smart card body comprises at least a first layer  11  and a second layer  12 , which are at least partly composed of polycarbonate. Arranged between the two polycarbonate layers  11  and  12  is a third layer  13 , which is composed of a material having a melting point of T s &lt;150° C. In one embodiment a smart card comprising a card body which contains polycarbonate may have a lower stress corrosion cracking sensitivity than a conventional card body comprising polycarbonate. 
     By virtue of the arrangement of such a third layer  13  having a low melting point in comparison with polycarbonate, polycarbonate layers can be combined with the aid of this interlayer  13  with lower temperature loadings than if the polycarbonate layers have to be directly connected to one another. By virtue of the lower melting point of the third layer  13 , the polycarbonate layers  11  and  12  can be combined with the third layer  13  for example at lower temperatures by means of laminating technology. The third layer  13  thus constitutes an adhesion layer between two polycarbonate layers. By virtue of the lower temperature loading during the production of the card body, inherent stresses possibly occurring in the polycarbonate layer around a foreign body in the polycarbonate layer will correspondingly also turn out to be lower. Moreover, inherent stress cracks that normally propagate in polycarbonate on account of stress corrosion cracking are stopped at said third layer  13 . The card body therefore has a lower notch sensitivity. 
     The arrangement of the third layer between the two polycarbonate layers significantly reduces the notch sensitivity of the card body. The use of the interlayer having a low melting point enables a card body production process with low temperatures. Inherent stresses brought about by temperature loadings can thus be reduced. The interlayer can additionally serve as a stop layer for microcracks in the polycarbonate layers. 
     Appropriate material for the third layer  13  includes for example a material at least from one of the groups of polyethylene terephthalate (PET), such as e.g. amorphous PET (APET), PET with glycol (PET-G), PET with fluorine (PET-F), and polyvinyl chloride (PVC). 
     The third layer  13  can have a thickness within the range of 3 μm to 10 μm. In possible embodiments, at least one of the polycarbonate layers  11  or  12  can be optically transparent. In exemplary embodiments, the third layer  13  can have one or a combination of the states amorphous, uncolored and transparent. However, it can also have one or a combination of the states partly crystalline, uncolored and translucent. Furthermore, the third layer can also be colored, e.g. in order to increase the contrast on the overlying layer. 
     The third layer  13  can additionally serve as a carrier for optical security features such as, for example, a hologram, a kinegram, a microtext, a micro-coding (barcode), one or a plurality of reflection layers (e.g. in displays) and/or a carrier for electronic security features (e.g. a structured metal film in the form of a security thread or in the form of a closed antenna). 
       FIG. 2  illustrates an exemplary embodiment of a smart card  20 . The smart card  20  has a card body composed of two layer stacks  14  and an intermediate film  22  between the two layer stacks  14 . In this case, as already explained with regard to  FIG. 1 , the layer stack  14  is composed of two polycarbonate layers  11  and  12  and a third layer  13  lying in between. 
     The intermediate film  22  arranged between the two layer stacks  14  can likewise be at least partly composed of polycarbonate. In the exemplary embodiment shown, the intermediate film  22  has an interruption in which a semiconductor chip  21 , for example a microcontroller, is likewise arranged between the two layer stacks  14 . The semiconductor chip  21  is thus arranged in the card body and is completely enveloped by the card body in the example shown. 
       FIG. 2  additionally illustrates an antenna  23 , which is arranged in the semiconductor body. The antenna can be introduced for example in a polycarbonate layer of the layer stack  14 . The embodiment shown in  FIG. 2  provides a coil antenna, above the coil eye of which the semiconductor chip  21  is arranged. The semiconductor chip  21  will generally be connected to the antenna  23  in order to enable power and/or data transmission with external terminals. 
       FIG. 3  shows a further exemplary embodiment of a smart card  30  comprising a smart card body and a semiconductor module. The smart card body of this exemplary embodiment is likewise composed of two layer stacks  14  and an intermediate film  22  arranged between the two layer stacks  14 . In  FIG. 3 , a layer stack  14  has three polycarbonate layers  301 ,  303 ,  305  and  308 ,  310 ,  312  with in each case third layers  302 ,  304  and  309  and  311 , respectively, arranged between two polycarbonate layers. By virtue of this arrangement, as already explained with regard to  FIG. 1 , the card body can be made less notch-sensitive on account of lower temperature loading during the laminating process during the production of the layer stack  14  and by means of the stop function of the third layers for microcracks. 
     As illustrated in  FIG. 3 , the intermediate film  22  can be composed of a plurality of individual layers  306 ,  307 . This enables for example the dimensionally accurate adaptation of the intermediate film  22  to a semiconductor chip or, as illustrated in  FIG. 3 , to a semiconductor chip module  317 . 
     The semiconductor chip module  317  comprises for example a chip carrier  314 , a semiconductor chip  315  and a housing  316  for the semiconductor chip  315 . The semiconductor chip module  317  is arranged in an interruption of the intermediate film  22  between the two layer stacks  14 . Consequently, the semiconductor chip module  317  is likewise arranged in the semiconductor body and is completely enveloped by the semiconductor body. 
     In the exemplary embodiment illustrated in  FIG. 3 , an antenna  313  is arranged in the semiconductor body. As already explained in  FIG. 2 , the antenna can be a coil antenna, for example, which is incorporated in a polycarbonate layer. The semiconductor chip module  317  is situated above the coil eye between the coil strands of the antenna and is generally connected to the two ends of the coil antenna in order to enable the power and data exchange between the semiconductor chip  315  and an external terminal. 
       FIG. 4  shows a possible embodiment of a semiconductor chip module. The illustrated edge region of a semiconductor chip module  50  comprises a semiconductor chip carrier  52 , e.g. a leadframe, a semiconductor chip  51  on the chip carrier  52  and a housing  53  for the semiconductor chip  51 . The edges K of this exemplary semiconductor chip module  50  are rounded in this case. This embodiment alleviates critical locations for stress cracking in the polycarbonate layers surrounding the semiconductor chip module  50  because the notch effect in the polycarbonate layers is reduced by the rounded edges. In this case, the edge rounding has an edge radius r where
     r≦0.1 mm.   
       FIG. 5  shows a composite film  40  that can be used for a production variant of the card body of a smart card according to the invention. The composite film  40  is composed of a first layer  41 , which is at least partly composed of polycarbonate, and a third layer  42 , which is composed of a material having a melting point of T s &lt;150° C. The composite film can be used as a prefabricated product for the production of the card body of the smart cards described above. 
     The composite film  40  can be produced in such a way that the third layer  42  is laminated onto the first layer  41 . A further possibility for producing the composite film  40  consists in the first layer  41  and the third layer  42  being coextruded, that is to say that the materials of the first layer  41  and of the third layer  42  are brought together before leaving a profile die and a composite film as illustrated in  FIG. 5  thus emerges from the profile die.