Abstract:
A dual interface smart card having a metal layer includes an IC module, with contacts and RF capability, mounted on a plug, formed of non RF impeding material, between the top and bottom surfaces of the metal layer. The plug provides support for the IC module and a degree of electrical insulation and isolation from the metal layer. The resultant card can have contact and contactless operating capability and an entirely smooth external metal surface except for the contacts of the IC module.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to “smart” cards and, more particularly, relates to smart cards which have at least one metal layer and are capable of radio frequency transmission (RF) and physical electrical interfacing. In particular, the invention relates to dual interface (i.e., capable of contactless and/or contact operation) smart cards having a metal layer and a rich and aesthetically pleasant appearance. 
     Smart cards are highly desirable and are in wide use, including: in payment and ticketing applications, such as mass transit and motorway tolls; in personal identification and entitlement schemes on regional, national, and international levels; in citizen cards; in drivers&#39; licenses; in patient card schemes; and in biometric passports to enhance security for international travel. 
     A smart card is a card that includes embedded electronic circuitry such as an integrated circuit (IC) chip that can be either: (a) a secure microcontroller, also referred to as a microprocessor, or equivalent intelligence device with internal memory; or (b) a memory chip alone. A smart card connects or couples to a card reader with direct physical contact and/or with a remote contactless radio frequency interface. 
     There are three general categories of smart cards of interest. They are referred to herein as (1) contact, (2) contactless and (3) dual interface. (1) A “contact” smart card includes an IC chip connected to a conductive contact plate on which are mounted a number of physical contact pads (typically gold plated) located generally on the top surface of the card. A contact smart card must be inserted into a contact type smart card reader and transmission of commands, data, and card status takes place over the physical contact pads. (2) A “contactless” smartcard contains an IC chip and a card antenna by means of which RF signals are coupled between the smart card&#39;s chip and the antenna of a card reader. This permits wireless (e.g., RF) communication between the card and a card reader with no direct electrical contact between the card and the card reader. A contactless smart card requires only close proximity to a reader. Both the reader and the smart card have antennae, and the two communicate using radio frequencies (RF) over a contactless link. Most contactless cards also derive power for the internal chip from electromagnetic signals emitted by the card reader. The range of operation may vary from less than an inch to several inches. (3) A “dual-interface” smart card has, typically, a single IC chip (but could have two) and includes both contact and contactless interfaces. With dual-interface cards, it is possible to access the IC chip(s) using a contact and/or a contactless interface. 
     It is desirable to make dual interface smart cards which can provide “contactless” and/or “contact” capability. It has also become very desirable and fashionable to make cards with one or more metal layers. A metal layer provides a desirable weight and a decorative pattern and/or reflective surface enhancing the card&#39;s appearance and aesthetic value. This is especially desirable for use by high-end customers. It is therefore desirable to make dual interface (contacts and contactless) smart cards having a metal layer. 
     However, several problems arise in the making of dual interface (“contactless” and “contact”) smart cards with a metal layer because of conflicting requirements. By way of example, to construct a dual interface smart card, the contact pads associated with the IC chip need to be located along an external surface (top or bottom, but normally top) of the card to make contact with a contact card reader and the IC chip will generally be located near the top surface. However, any metal layer in the card interferes with radio-frequency (RF) communication signals (e.g., attenuates) between the card and the reader, and this could render the contactless smart card useless. So, a dual interface smart card with a metal layer needs to solve the problem of RF interference with respect to the IC chip. Compounding the problem is the requirement that the dual interface metal smart card have a highly sophisticated appearance. Due to the prestige and aesthetic aspect of these cards it is desirable that there be no perceptible depression or bump along the surface of the card, except for the contact pads. 
     SUMMARY OF THE INVENTION 
     A dual interface smart card embodying the invention includes a top metal layer with a non-metallic plug formed within the metal layer to enable the placement of an IC module about the plug so the card can function as contact and/or contactless card. At the same time the card is made to have a relatively smooth and beautiful external surface. 
     In general, a hole (opening or cut-out) is formed in the plug for locating an IC chip module about the center area of the plug so the IC module is isolated and insulated from the metal layer. Thus, the plug functions to provide a physical separation and a degree of electrical insulation between the chip module and the metal layer in the horizontal and vertical directions. In addition, the hole in the plug provides a pathway for RF transmission. The chip module includes contacts which extend along the same horizontal surface as the metal layer to enable contact capability with a contact card reader and the chip module extends within the plug&#39;s hole to enable contactless (RF) operating capability. 
     In a particular embodiment the metal layer is a relatively thick layer having a top surface which defines the top surface of the card. A plug is formed in the metal layer below the top surface so the plug is not seen from the top and does not affect the appearance of the card. The lateral dimensions of the plug are greater than the lateral dimensions of the chip module to provide insulation and isolation. A hole is formed vertically down through the plug and an underlying ferrite layer to form a passageway for RF signals to pass between a card booster antenna and an IC module chip antenna. The lateral dimensions of the hole plug are smaller than the lateral dimensions of the IC chip module. 
     A dual interface smart metal card embodying the invention includes a metal layer in which is disposed an integrated circuit (IC) module to provide contactless (RF) and contact capability. The metal layer has a top surface and a bottom surface extending generally parallel to each other. At least two different sized cut outs are formed in the metal layer, one above the other, both cut outs extending in the horizontal plane, symmetrically about the same center line. One cut out is formed to position and nestle the IC module within the top surface of the metal layer and to enable the IC module, which has contacts to make to a card reader. The IC module and its corresponding one cut out have a depth of approximately D 1 , a length L 1  and a width W 1 . The other cut out (also called a “pocket”), underlying the one cut out, extends from the bottom surface of the metal layer until a distance D 1  from the top surface. The pocket is made to have a length L 2  greater than L 1  and a width W 2  greater than W 1  to enable RF transmission between the IC module and a card reader. A non-metallic plug designed to fit snugly within the pocket fills the pocket and is attached to the walls of the pocket. The plug has a centrally located opening having a length L 3  which is smaller than L 1  and a width W 3  which is less than W 1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be understood more completely from the following detailed description of presently preferred, but nonetheless illustrative, embodiments in accordance with the present invention, with reference being had to the accompanying drawings, which are not drawn to scale, but in which like reference characters denote like components; and 
         FIG. 1  is a simplified, isometric diagram of a smart card  10  with a metal layer  30 , embodying the invention; 
         FIG. 1A  is a highly simplified, idealized isometric diagram of an integrated circuit (IC) module capable of contactless and contact operation intended for use in making smart cards embodying the invention; 
         FIG. 1B  is a simplified idealized cross sectional diagram of the IC module of  FIG. 1A  used in the card shown in  FIG. 1 ; 
         FIG. 2  includes cross sectional diagrams of various processing steps ( 1  through  7 ) to form a card embodying the invention; 
         FIG. 3A  is a simplified cross sectional diagram of a card being made as shown in step  5  of  FIG. 2 ; 
         FIG. 3B  is a top view of a card being formed as shown in  FIG. 3A  with a plug ( 34 ) and the opening ( 36 ) formed in the plug; 
         FIG. 3C  is a top view of the top layer of a card embodying the invention formed in accordance with the process shown in  FIG. 2 ; 
         FIG. 4  includes cross sectional diagrams of various processing steps ( 1  through  5 ) to form a card according to another aspect of the invention; 
         FIG. 5A  is a cross sectional diagram corresponding to step  4  of  FIG. 4  showing a plug and openings formed in the plug prior to insertion of an IC module; 
         FIG. 5B  is a top view of a card having the cross section shown in  FIG. 5A  showing the plug and openings formed in the plug prior to insertion of an IC module formed in accordance with  FIG. 4 ; 
         FIG. 5C  is a top view of a card formed according to the process steps shown in  FIG. 4  and as shown in  FIGS. 5A and 5B  with an IC module inserted in the opening for the module; and 
         FIG. 6  is a cross-sectional diagram showing a masking layer formed on a card such as the one shown in  FIG. 5C . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An integrated circuit (IC) module  7  having multiple contacts as shown in  FIG. 1A  is to be mounted in, and on, a card  10  as shown in  FIG. 1  with the top surface of the IC module and its contacts generally flush with the top surface of the card. By way of example it is shown that the length, width and depth of the card may respectively be approximately 3.37 inches by 2.125 inches by 0.03 inches. For purpose of illustration and the discussion to follow assume, as shown in  FIG. 1A , that the IC module has a depth D 1 , a length L 1  and a width W 1 . Modules such as IC module  7  are commercially available, for example, from Infineon or NXP. The lateral dimensions of some of these modules were approximately 0.052 inches by 0.47 inches with a depth ranging from 0.005 inches to more than 0.025 inches. These dimensions are purely illustrative and IC modules used to practice the invention may be greater or smaller in size. 
     As shown in  FIG. 1B , IC module  7  contains an internal microprocessor chip  7   a , a chip antenna  7   b  and a contact pad  7   c . Pad  7   c  may be a conventional multi-contact pad used in contact-type smart cards and is positioned to engage contacts in a contact card reader (not shown) when the smart card is inserted therein. An epoxy blob  7   d  encapsulates the bottom side of the IC module. The epoxy blob allows the IC module to be easily attached (e.g., by gluing) to an underlying surface. 
     As noted above, the invention is directed to the manufacture of a smart metal card having dual interface capability and also having a top surface which is free of any bumps or depressions, except for: (a) the IC module and its contacts, and/or (b) any design or texture intentionally formed on the top surface. In accordance with the invention, a card can be made to have a highly aesthetic, smooth and visually pleasing appearance even though the card must include dual interface capability (i.e., contact and contactless capability). That is, smart cards having a metal layer as a top surface, for aesthetic reasons, must include an IC module and its associated contacts. For the card to be used in a contact mode, the contacts of the IC module have to be located along an exterior surface of the card. Typically, the contacts are located along the top surface of the card; although the contacts could conceivably be located along the bottom surface of the card. To enable effective wireless (RF) transmission there has to be a cut out (opening) in the metal layer underlying and surrounding the IC module. A challenge is to produce these cut outs (openings) in the metal layer without affecting the smooth, aesthetic, exterior (e.g., top) appearance of the card. 
     A method of forming a card in accordance with the invention includes the structure and processing steps illustrated in  FIG. 2 .
           1 —A metal layer  30  is selected which is intended to serve as the top layer of a card  10  (as shown in step  1  of  FIG. 2 ). The metal layer  30  has a top (front) surface  301  and a bottom (back) surface  302 ; the front and back surfaces are generally parallel to each other. The thickness (D) of the metal layer  30  may range from less than 0.01 inches to more than 0.02 inches. In one embodiment the metal layer  30  was made of stainless steel and its thickness was 0.0155 inches. Metal layer  30  may, by way of example and not by way of limitation, be selected to be iron, tantalum, aluminum, brass, copper or any alloy or compound thereof.     2 —A pocket  32  is formed along the underside of layer  30 . It may be referred to as a reverse pocket formed starting from the bottom surface of metal layer  30  (as shown in step  2  of  FIG. 2 ). The pocket  32  may be formed in any known manner including, but no limited to: milling, casting, 3D printing, laser cutting, water jet electro-discharge (EDM). The pocket  32  has a top  321  which ends a distance (or thickness) D 1  below top surface  301 , where D 1  is typically equal to (or nearly equal to) the depth of the IC module  7 . The depth (thickness) D 2  of pocket  32  is then equal to (D-D 1 ) inches. D 2  will generally always be set to equal the depth D of the metal layer  30  minus the thickness D 1  of the IC module used to form the card. The pocket  32  may be of regular or irregular shape, a rectangular solid or a cylinder whose planar projection in the horizontal plane may be a square, a rectangle or a circle. The lateral dimensions [length ( 12 ) and width (W 2 )] of the pocket  32  can be, respectively, equal to or greater than the lateral dimensions [length L 1  and width W 1 ] of the IC module as further discussed below. In the embodiments L 2  and W 2  are shown to be, respectively, greater than L 1  and W 1 , but that is not a necessary condition.     3 —A plug  34  of any material which does not substantially interfere with RF transmission (e.g., any non-metallic material, or even a material such as tungsten or a composite thereof) is formed or shaped to conform to the dimensions of the milled pocket  32  and is inserted in the pocket to fill the milled (cut out) region (as shown in step  3  of  FIG. 2 ). As discussed below the plug functions to electrically isolate and insulate the IC module from the metal layer and to also physically secure the IC module. The interior of the pocket  32  and/or the exterior of the plug  34  is/are coated with a suitable adhesive (e.g., such as acrylic or acrylic modified polyethylene, cyanoacrylate, silicone elastomer, epoxy) so the plug  34  adheres firmly to the walls of the pocket throughout the processing of the metal layer in the formation of the card. The plug  34  may be made of any thermoplastic material such as PET, PVC or other polymer or any material such as curable resin or epoxy or a ceramic or even of tungsten material which does not significantly impede radio frequency (RF) transmission.     4 —As shown in step  4  of  FIG. 2 , an adhesive layer  42  is used to attach a ferrite layer  44  to the back surface  302  of layer  30 . The ferrite layer  44  is placed below the metal layer  30  to act as a shield (reflector) to prevent/reduce metal layer  30  from interfering with radio frequency radiation to and from the smart card. Ferrite layer  44  decreases the “shorting” effect of metal layer  30  for enabling transmission or reception via antenna  47 . Those skilled in the art will appreciate that it would also be possible to form or lay out the ferrite material in a different manner.
           Also, an adhesive layer  46  is used to attach a plastic (e.g., PVC) layer  48  which contains and/or on which is mounted a booster antenna  47 . Layer  48  may be made of PVC or polyester and may be between 0.001 and 0.015 inches thick. The windings of booster antenna  47  may range from less than 80 microns to more than 120 microns in diameter and may be secured to layer  48  by ultrasonic welding or heating the wire prior to placing it in contact with the plastic layer or by any other suitable process. A layer  52  which includes a signature panel and a magnetic stripe may be attached to layer  48  before or after lamination. Layers  42 ,  44 ,  46 ,  48  (and possibly  52 ) may be formed as a sub-assembly  40  and attached to the bottom side  302  of metal layer  30 .   
             5 —The assembly comprising layers  30 ,  42 ,  44 ,  46  and  48  is laminated (as indicated in step  5  of  FIG. 2 ) to form a card assembly  50 .     6 —A hole (or opening)  36  is then formed (e.g., by milling) through the metal  30  to a depth D 1  from the top surface and, concurrently, a hole  362  is then formed in plug  34 , (e.g., by drilling about the center of the plug  34 ) and through the underlying layers  42 ,  44  and  46  until layer  48 , as shown in step  6  of  FIG. 2 . The lateral dimensions of hole  36  formed in the metal layer  30  are designed to correspond to the dimensions L 1  and W 1  of the IC module  7  so the IC module can be inserted in the hole (opening)  36 . The lateral dimensions of the hole  362  formed in the plug  34  will be L 3  and W 3 , where L 3  and W 3  are less than L 1  and W 1 . So made, plug ledges  341   a  will provide support for the IC module and keep it at its designed height of D 1  below the top card surface. The IC module can be snugly inserted and attached to the sides of opening  36  and to top  341   a  of the plug  34 . That is, the IC module can be inserted with tight clearance and glued in place. The smaller hole (opening)  362  formed below hole  36  accommodates the rear (bottom) end of module  7 . Hole  362  extends vertically down through ferrite layer  44  and is made sufficiently wide to enable RF signals to pass between antenna  47  and the chip antenna  7   b.          

     With respect to the operation of the card, booster antenna  47  is designed to capture radio frequency energy generated by an associated card reader (not shown) and to communicate with the card reader. By design, module antenna  7   b  is sufficiently close to couple inductively with antenna  47 , thereby providing signals from antenna  47  to chip  7   a , while keeping the chip electrically isolated from antenna  47 . In operation, ferrite layer  44  shields metal layer  30 , to make it possible for radio frequency radiation to enter and be emitted from card  10 . In operation, ferrite layer  44  shields metal layer  30 , to make it possible for radio frequency radiation to enter and be emitted from card  10 . Booster antenna  47  is designed to capture radio frequency energy generated by an associated card reader (not shown) and to communicate with the card reader. By design, module antenna  7   b  is sufficiently close to couple inductively with antenna  47 , thereby providing signals from antenna  47  to chip  7   a , while keeping the chip electrically isolated from antenna  47 .
           7 —As shown in Step  7  of  FIG. 2 , an IC module  7  which, as shown in  FIG. 1B , includes a chip  7   a , a chip antenna  7   b  and a set of contacts  7   c  is positioned within hole  36 . The IC module  7  is glued in place completing the formation of a card embodying the invention.
           To appreciate the appearance of the card as finally formed reference is first made to  FIG. 3A  (which is essentially a copy of step  6  of  FIG. 2 ) and to  FIG. 3B .  FIG. 3B  is a top view of the card being formed showing the openings ( 36  and  362 ) formed in the metal and the plug. Note the hole  36  in metal layer  30  will have edge(s)  361  and the hole  362  in the plug and the underlying layers  42 ,  44 ,  46  will have edge(s)  345 / 367 . The portion of the plug  34  below region  341   b  and the outer edge  343  of the plug will not be seen. Hence outer edge  343  is shown with dashed lines.   The resultant  FIG. 3C  is a top view of a card  10  showing the module  7  mounted and inserted in the top of the card. The plug  34  is not seen since it is underneath the metal layer. Thus, the top surface of a card  10  formed in accordance with the process steps shown in  FIG. 2  displays a completely smooth unbroken metal surface (except for the contact pad of the IC module). The underlying plug is covered (hidden) by an overlying metal region. Significantly, the card having the desired beautiful physical appearance can function as a wireless (contactless) card or as a contact card.   
               

     The dimensional tolerances of the various holes/openings and of the components need to be close enough so that on a platen lamination all parts fuse together with no airspace or sinks in the outward appearance of the card. 
     As shown in the Figures, metal layer  30  has a cut out  36  formed in its top surface. The thickness/depth D 1  of cut out  36  is made substantially equal to the depth of the IC module  7 . The hole/opening  36  is machined through metal layer  30  dimensioned to receive module  7 , which is secured therein, as by bonding. Module  7  contains a microprocessor chip  7   a  (internally), a chip antenna  7   b  and a contact pad  7   c . Pad  7   c  is a conventional contact pad used in contact-type smart cards and is positioned to engage contacts in a card reader when the smartcard is inserted therein. 
     By design, plug  34  is substantially wider than module  7 . Preferably, plug  34  extends at least 0.04 laterally beyond either side of module  7 . This prevents the metal in substrate  30  from interfering with communication between the card and chip. However, the plug does not have to be wider than module  7  (i.e., its lateral dimensions need not be greater than those of the module). 
     Module  7  is positioned vertically within metal layer  30  so as to provide a contact pad  7   c  along the top metal surface to realize the contact functions of the dual interface. Moreover, positioning module  7  on plug  34  which is made larger (though not necessarily so) in area than the module  7  makes it possible to decrease interference in the radio communication between module antenna  7   b  and the booster antenna  47 . 
     Although preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that many additions, modifications, and substitutions are possible without departing from the scope and spirit of the invention. 
     Alternatively, cards embodying the invention may be formed as shown in  FIGS. 4, 4A, 5A, 5B, 5C and 6 . These cards differ from those discussed above in that a plug is formed whose thickness is equal to the thickness of the metal layer. That is, there is no recessed pocket. 
     As shown in  FIG. 4 , a card formed in accordance with this aspect of the invention may include the following processing steps and structure: 
     
         
         
           
               1 —A metal layer  30  is selected (as shown in step  1  of  FIG. 4 ) which is intended to serve as the top layer of a card  10 . The metal layer  30  has a top (front) surface  301  and a bottom (back) surface  302  and a thickness (D) which may range from less than 0.01 inches to more than 0.02 inches. Metal layer  30  may have the same characteristics and properties as metal layer  30  shown and discussed above. 
               2 —A hole  420  of depth D is formed in the metal layer  30  (as shown in step  1  of  FIG. 4 ). The lateral dimensions of the hole are L 2  and W 2  (see  FIGS. 5A and 5B ). The hole  420  may be formed in any known manner (e.g., casting or milling). The hole  420  may be a regular or irregular solid cube, or a cylinder whose planar projection in the horizontal plane may be a square, a rectangle or a circle or an irregular shape. In the embodiment shown in  FIG. 4 , the lateral dimensions [length (L 2 ) and width (W 2 )] of the hole  420  are respectively greater than the lateral dimensions [length L 1  and width W 1 ] of the IC module as further discussed below. Generally, L 2  is greater than L 1  (by at least 0.04 inches and W 2  is greater than W 1  (by at least 0.04 inches). However, as noted above, L 2  may be made equal to L 1 , and W 2  may be made equal to W 1 . The advantage of making L 2  and W 2 , respectively, larger than L 1  and W 1  is to provide greater separation between the metal layer and the IC module and thus enhance RF transmission and reception. 
               3 —A plug  434  of any material like plug  34  which does not interfere with RF transmission is formed or shaped to conform to the dimensions of the hole  420  to fill the cut out region (as shown in step  2  of  FIG. 4 ). Plug  434  is processed and functions to secure the IC module. The interior walls of the hole  420  and/or the exterior walls of the plug  434  is/are coated with a suitable adhesive so the plug  434  adheres firmly to the walls of the hole throughout the processing of the metal layer in the formation of the card. The plug  434  may be made of any thermoplastic material such as PET, PVC or other polymer or any material such as epoxy resins and a ceramic. 
               4 —As shown in step  3  of  FIG. 4 , an adhesive layer  42  is used to attach a ferrite layer  44  to the back surface  302  of layer  30 . An adhesive layer  46  is used to attach a plastic (e.g., PVC) layer  48  which contains and/or on which is mounted a booster antenna  47  to the ferrite layer. Layers  42 ,  44 ,  46 , and  48  and the booster antenna  47  are formed in a similar manner as the corresponding number components shown in  FIG. 2  and serve the same or similar functions. 
               5 —The assembly comprising layers  30 ,  42 ,  44 ,  46  and  48  is laminated to form a card assembly  350  (as indicated in step  3  of  FIG. 4 ). 
               6 —A T-shaped hole/opening  436  is then formed through the plug  434 . The hole  436  is formed by milling, drilling and/or any other suitable means. The top portion  436   a  of T-shaped hole  436  is formed to have lateral and depth dimensions to accommodate the IC module. Where the dimensions of IC module  7  are L 1  by W 1  by D 1  the top portion of  436   a  will be formed to be just about L 1  by W 1  by D 1  to enable the IC module to be snugly inserted within the hole  436   a  and to be glued in place. The bottom portion  436   b  of the hole  436  formed in plug  434 , (by drilling vertically down about the center of the plug  434 ) extends through the underlying layers  42 ,  44  and  46  and until layer  48 , as shown in step  4  of  FIG. 4 . The lateral dimensions of hole  436   b  formed in plug  434  are made large enough to enable sufficient RF signals to pass between booster antenna  47  and the IC chip module  7  to enable RF communication to take place reliably. The lateral dimensions of the hole  436   b  formed in the plug  434  are denoted as L 3  and W 3 , where L 3  and W 3  are less than L 1  and W 1 . Note that making L 3  and W 3  less than L 1 , and W 1 , respectively, results in the formation of ledges  438  which will provide support for the IC module and keep it at its designed height of D 1  below the top card surface  301 . The IC module  7  can be snugly inserted and attached (glued) to the ledges  438  and the top interior walls of the plug  434 . 
               7 —As shown in Step  5  of  FIG. 4 , IC module  7  which includes a chip  7   a  and a chip antenna  7   b  and a set of contacts  7   c  is positioned within hole  436   a  is glued in place. 
           
         
       
    
       FIG. 5A  is an enlarged cross sectional diagram corresponding to step  4  of  FIG. 4 .  FIG. 5B  is a top view of a card showing the holes formed in the metal and the plug.  FIG. 5C  is a top view of a card showing the module  7  mounted and inserted in the top of the card. The smart metal card  10  can function as a wireless (contactless) card or as a contact card. Note that as shown in  FIGS. 5A, 5B and 5C  the hole portion  436   a  has an inner edge  440 . The plug has an outer edge  442 . As is evident from  FIGS. 5B and 5C , the IC module  7  will cover openings  436   a  and  436   b . As a result there is a space/area  450  between edges  440  and  442  extending around the outer periphery of the IC module between the module  7  and the metal layer  30 . The space/area  450  may be objected to on aesthetic grounds as it detracts from the continuous metal layer (except for the necessary module contact pad). However, it should be appreciated that the space area  450  may enhance RF transmission. The presence of space/area  450  and any depression or bump related to space  450  may be masked by the addition of a masking layer  470 , as shown in  FIG. 6 . This may be acceptable in many instances. However, in instances where such a solution is still not acceptable or feasible, the solution is to revert to making cards as per the process steps shown in  FIG. 2 . 
     Thus, a problem with the smart cards formed in accordance with the process shown in  FIG. 4  is that a portion of a plug may be seen. The portion of the plug may mar the continuous appearance of the card and/or as a bump on the surface or as a depression. This may be so, even if a masking (concealing) layer  470  is formed over layer  30 . 
     As taught and discussed with reference to  FIG. 2 , above, the spacing and any discontinuity in the metal surface (except for the IC module) are avoided by forming a recess pocket  32  in substrate  30  and filling the recess with a plug  34  which is not seen from the top of the card. Thus, In contrast to previous and other dual interface smart metal cards, the plug  34  does not appear as a bump on the surface or as a depression. It is not visible when the card is viewed from the outside. The process of  FIG. 2  thus differs from the process of  FIG. 4  where a through hole  420  is formed in the metal layer  30  and a plug  434  is formed which fills the hole  420 . 
     However, it should be noted that in all the embodiments shown herein a plug is used to separate an IC module from a surrounding metal layer to promote RF transmission capability and the plug is also used to position and secure the IC module within the card. Openings for the plug and its positioning within the card are designed to maintain the exterior of the card flat and visually pleasant.