Abstract:
The present disclosure relates to a transponder for object identification comprising at least one semiconductor component ( 36 ) for storing information and at least one antenna ( 11 ) for communicating the information with an external unit, the antenna ( 11 ) being formed by a conductor on a circuit board ( 7 ) and the semiconductor component ( 36 ) being mounted on the circuit board ( 7 ), the circuit board ( 7 ) being included in a housing ( 2 ), and it relates to a fabrication method of a generic kind. In order to improve the resistance of the transponder against harmful external influences, such as high temperatures, and to prolong its life cycle, the invention suggests that the semiconductor component ( 36 ) is included in an enclosure ( 18 ) that is hermetically sealed and fixed on a surface ( 12, 13 ) of the circuit board.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to a transponder for object identification comprising at least one semiconductor component for storing information and at least one antenna for communicating the information with an external unit, the antenna being formed by a conductor on a circuit board and the semiconductor component being mounted on the circuit board, wherein the circuit board is included in a housing. The invention also relates to a fabrication method of such a transponder. 
       BACKGROUND OF THE INVENTION 
       [0002]    Such a transponder typically operates in a radio frequency range and is often called by the acronym RFID tag. The widespread usage of RFID tags in many industries, e.g. for object tracking in production lines, warehouses, etc., makes it desirable to improve its performance and reliability with respect to its temperature resistance, contamination protection and mechanical robustness. Particularly in the field of automotive industry, RFID tags are required which can resist elevated temperatures between 200° C. and 220° C. 
         [0003]    The latter problem has been addressed in European patent application No. EP 2 348 461 A1. To this end, a RFID tag with a housing consisting of a high temperature plastic and an overmolded top portion is disclosed. The circuit board with a semiconductor component in the form of an integrated circuit placed thereon is arranged inside the housing with a thin layer of a compressible high temperature textile on both sides. In this way, an improvement with respect to the thermal insulation and the compressibility of the circuit board inside the RFID tag shall be achieved. 
         [0004]    The most sensitive component in such an RFID tag, however, is the integrated circuit. More specific provisions are needed to protect this weak point from detrimental external impacts such as high temperature and contamination. Moreover, the thin textile layer may only provide a comparatively weak protection of the internal electronic components against mechanical forces. 
         [0005]    It is therefore an object of the present invention to remedy at least one of the above mentioned deficiencies and to provide a transponder of the kind mentioned in the introduction and a corresponding fabrication method so as to improve its resistance against harmful external influences, such as high temperature, and/or its long life cycle. 
       SUMMARY OF THE INVENTION 
       [0006]    This object is achieved by the transponder according to claim  1  and the fabrication method according to claim  16 . The dependent claims define preferred embodiments. 
         [0007]    Accordingly, the invention proposes that the semiconductor component is included in a hermetically sealed enclosure that is fixed on a surface of the circuit board. The enclosure can provide a protection for the semiconductor component against external impacts on the transponder and can contribute to extend its life cycle. In particular, thermal degradation and/or corrosion effects at the semiconductor crystal of the semiconductor component and on the semiconductor component wiring can be advantageously reduced by the provision of such an enclosure. In a corresponding fabrication method, the semiconductor component is inserted in a hermetically sealed enclosure and the enclosure is fixed on a surface of the circuit board. In the following, the hermetically sealed enclosure containing the at least one semiconductor component is referred to as enclosure. 
         [0008]    In the present context, the term semiconductor component in particular refers to a semiconductor device, such as a transistor or a diode, and more generally to any other component that exploits the electronic properties of a semiconductor material contained therein. In a preferred configuration, the term semiconductor component refers to an integrated circuit comprising one or more semiconductor devices. 
         [0009]    Subsequently, various features for a further improvement of the capability of resistance and/or durability of the transponder are described which can be correspondingly applied to the transponder and to its fabrication method. 
         [0010]    Preferably, the enclosure is under vacuum or filled with an inert gas and the enclosure is hermetically sealed to maintain an inert or vacuum atmosphere. In this way, a good protection against corrosion and external contamination can be achieved and the operational life and reliability of the transponder under exposure to high temperature and thermal cycles can be improved. Preferably, the enclosure is filled with nitrogen in order to provide the inert atmosphere. Alternatively, a vacuum atmosphere inside the enclosure can be applied. 
         [0011]    Preferably, the enclosure comprises a lid. The lid can be used to delimit a hermetically sealed volume inside the enclosure and/or to provide an additional outer mechanical protection of the semiconductor component. More preferred, the lid is metallic or ceramic. A metallic or ceramic lid offers the advantage of an easy installation combined with a good protection and/or hermetic sealing. 
         [0012]    Preferably, the enclosure comprises a support section with a side on which the semiconductor component is fixed and with an opposed side fixed to the circuit board. The support section preferably consists of a material that matches the thermal expansion of the circuit board, in particular the mechanical temperature coefficient of the circuit board, by a deviation of at most 50 ppm/° C., more preferred at most 10 ppm/° C. The matching of the temperature coefficient can be exploited to prevent damage to the transponder induced by thermal cycling at increased operation temperatures. 
         [0013]    The term mechanical temperature coefficient, which may also be referred to as thermal expansion coefficient or thermal expansion linear coefficient, is to be understood as the relative change of the respective mechanical dimension when the temperature is changed by 1 K. 
         [0014]    The match of the temperature coefficient between the support section of the enclosure and the circuit board is preferably provided at least over a range of an intended operation temperature of the transponder. The temperature range may comprise, for instance, an upper temperature value of at least 180° C., more preferred at least 250° C., and/or a lower temperature value of at most 0° C., more preferred at most −25° C. Preferably, the respective temperature coefficient is substantially constant over the intended temperature range. 
         [0015]    Preferably, the material of the enclosure comprises exclusively inorganic materials, e.g. ceramics, metal and/or glass. A particularly preferred material to achieve the advantageous match of the thermal expansion between the support section of the enclosure and the circuit board comprises a ceramics provided on the support section of the enclosure. More preferred, at least the support section of the enclosure entirely consists of the ceramics. 
         [0016]    Suitable materials for the circuit board comprise thermo resistant plastics, ceramics, glass and enameled metal. A preferred material of the circuit board to match the thermal expansion with the support section of the enclosure comprises a thermoresistant polyimide. More preferred, a poly-(diphenyl oxide)-pyromellitimide (or poly(4,4′-oxydiphenylene-pyromellitimide)) is used. This material is also known as “Kapton”® and offers the advantages of an applicability over a large temperature range, e.g. from below −200° C. up to 400° C., no inflammability and no melting point. Preferably, the circuit board also comprises a reinforcement material, preferably a glass material, to provide a more suitable thermal expansion and a higher mechanical stability. 
         [0017]    Preferably, substantially only inorganic components are provided on the circuit board and/or inside the enclosure. More preferred, no synthetic or plastic components are provided on the circuit board and/or inside the enclosure. Most preferred, exclusively ceramic and/or semiconductor and/or metallic components are arranged on the circuit board and/or in the enclosure. Preferably, the circuit board itself only consists of thermoresistant material components. Preferably, the electric conductors connecting the components on the circuit board are at least partially attached to a surface of the circuit board and plated with a noble metal, preferably gold. 
         [0018]    Preferably, the antenna is formed by a conductor printed on the circuit board. The use of a printed circuit board as compared to a coiled wire has the advantage that short circuits induced by a degradation of an isolator at high temperatures can be avoided. Preferably, the circuit board is impregnated before printing of the antenna to achieve a high stability and reliability at high temperatures. 
         [0019]    Preferably, the enclosure is mounted on the opposed side of the circuit board with respect to the side of the circuit board on which the antenna is provided. Preferably, the antenna extends around an outer portion of the circuit board to maximize its effective length. Preferably, the enclosure is mounted under the antenna on the opposed side of the circuit board to reduce the connection length between the antenna and the semiconductor component included in the enclosure. 
         [0020]    Preferably, a contact circuit for contacting the semiconductor component to the antenna is provided on the circuit board. Preferably, the enclosure is arranged on top of the contact circuit. Preferably, the contact circuit is substantially formed by a conductor printed on the circuit board. 
         [0021]    To electrically connect the semiconductor component included in the enclosure to the circuit board, the enclosure preferably comprises at least two connection pads that are electrically connected to a conductor on the circuit board. In particular, corresponding contacts on the enclosure bottom which are in electrical contact with connection pads inside the enclosure are preferably attached to respective contacts on the circuit board. 
         [0022]    Preferably, the electrical connection between at least one contact of the semiconductor component and a corresponding connection pad of the enclosure is established via a thermocompression bonding. A gold wire is preferably used as a connection. Preferably, at least one connection pad comprises a gold metallization layer. These measures with respect to the electrical connection of the semiconductor component to the circuit board can further contribute to an improved high temperature resistance of the transponder and the enclosure with the semiconductor component contained therein. Further, the use of a single type of metal can reduce the effects of ion migration at the junction of the metal parts. 
         [0023]    To further improve the mechanical stability and to facilitate the further fabrication steps, the circuit board is preferably fixed on a carrier plate. The carrier plate preferably comprises a recess for receiving the enclosure, thus providing an additional protection for the semiconductor component. Preferably, the carrier plate comprises surface structures for engaging with the circuit board to provide a first mechanical fixation. Preferably, the carrier plate comprises a liquid crystal polymer (LCP). Preferably, the carrier plate is reinforced with fibers. For instance, a composition with a content of 10% to 20%, more preferred approximately 15%, of glass fibers can lead to a good mechanical stability. 
         [0024]    Preferably, the circuit board is overmolded by a molding compound. The molding compound can provide an encapsulation of the circuit board for a protection against temperature, contamination and mechanical impacts. Moreover, the molding compound can prevent or delay an oxidation of metallic parts, in particular metallic connections, due to the presence of gases at high temperatures. Preferably, a flexible molding compound is applied. The molding is preferably a thermoplastic compound. Preferably, the molding compound substantially consists of the same material as the carrier plate. 
         [0025]    Preferably, the circuit board is overmolded with the molding compound after it is mechanically fixed on the carrier plate. Preferably, the molding compound extends over at least a portion of the surface of the circuit board and over at least a portion of the surface of the carrier plate. Thus, the molding compound can provide an additional fixation of the circuit board to the carrier plate. More preferred, the molding compound extends over substantially the total surface of the circuit board on one side of the circuit board. 
         [0026]    Preferably, the molding compound extends over the side of the circuit board on which the antenna is provided. In this way, the molding compound can provide an additional fixation of the antenna to the circuit board. Such an additional fixation is particularly beneficial at high temperatures at which other fixations, such as an antenna formed by a conductor printed on the circuit board, can tend to disconnect. 
         [0027]    Preferably, the circuit board is fully enclosed on one side by the molding compound and on the opposed side by the carrier plate. The molding compound and/or the carrier plate preferably also surrounds the lateral edges of the circuit board. More preferred, the molding compound substantially entirely surrounds the circuit board and the carrier plate. In this way, the housing in which the circuit board is included can be formed by substantially only the molding compound or the molding compound and the carrier plate. 
         [0028]    During the overmolding process, however, strong forces are applied on the circuit board which could break off the enclosure from the circuit board. In order to avoid breakage of the enclosure, before the overmolding takes place, a protecting cap is preferably disposed on the surface of the circuit board around the enclosure. Then the protecting cap is preferably inserted into the corresponding recess of the carrier plate together with the enclosure. 
         [0029]    Preferably, the protecting cap is placed on the circuit board in such a way that the contact circuit for contacting the semiconductor component to the antenna and the enclosure disposed on the contact circuit are fully enclosed by the protecting cap. This can provide an additional protection of the semiconductor component inside the enclosure and of the contact circuit. Thereby, the contact circuit on the circuit board may laterally protrude over the adjoining surface of the enclosure. 
         [0030]    Preferably, the protecting cap is metallic. To provide a first mechanical fixation, the protecting cap preferably comprises fixation lobes that engage in corresponding engagement slots on the surface of the circuit board. Preferably, the inner volume of the protecting cap exceeds the volume of the enclosure contained therein. This can contribute to the prevention of thermal expansion stress of the components contained inside the protecting cap. 
         [0031]    Preferably, a volume filler is arranged in the inner volume of the protecting cap that is not occupied by the enclosure. The volume filler is preferably constituted by a spatially extended object. Preferably, the volume filler comprises a synthetic fluoropolymer, more preferred a polytetrafluoroethylene (PTFE), also known as “Teflon”®. In this way, the strong forces acting on the protecting cap in particular during the overmolding process can be counterbalanced by the presence of the volume filler inside and thus can prevent the protecting cap to bend. 
         [0032]    Preferably, the housing is composed of two pieces. More preferred, the housing substantially consists of the carrier plate and the overmolding of the circuit board. Preferably, the housing is ring shaped in order to correspond to industrial demands on the shape and size of the transponder, thus allowing an easy attachment of the transponder to an associated object. Correspondingly, the circuit board and/or the carrier plate are preferably ring shaped. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The invention is explained in more detail hereinafter by means of preferred embodiments with reference to the drawings which illustrate further properties and advantages of the invention. The figures, the description, and the claims comprise numerous features in combination that one skilled in the art may also contemplate separately and use in further appropriate combinations. In the drawings: 
           [0034]      FIG. 1  is a perspective view of a transponder according to the invention; 
           [0035]      FIG. 2  is an exploded view of the transponder shown in  FIG. 1  without an overmolding from an upper viewing angle; 
           [0036]      FIG. 3  is an exploded view of the transponder shown in  FIG. 1  without an overmolding from a lower viewing angle; 
           [0037]      FIG. 4  is a bottom view of a circuit board of the transponder shown in  FIG. 1 ; 
           [0038]      FIG. 5  is a top view of the circuit board shown in  FIG. 4 ; 
           [0039]      FIG. 6  is a sectional view of the circuit board shown in  FIG. 5  along VI; 
           [0040]      FIG. 7  is a sectional view of a carrier plate of the transponder shown in  FIG. 1 ; 
           [0041]      FIG. 8  is a sectional view of an assembly of the circuit board shown in  FIG. 6  and the carrier plate shown in  FIG. 7 ; 
           [0042]      FIG. 9  is a sectional view of the transponder shown in  FIG. 1 ; 
           [0043]      FIG. 10  is a top view of an enclosure for a semiconductor component without a lid; 
           [0044]      FIG. 11  is a top view of the enclosure shown in  FIG. 10  comprising a lid; and 
           [0045]      FIG. 12  is a sectional view of the enclosure shown in  FIGS. 10 and 11  along XII. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0046]      FIG. 1  shows a transponder  1  comprising a ring shaped housing  2  with a through hole  4  in its center region. Through hole  4  comprises an upper tapering portion  5  and a lower portion  6  having a constant diameter. Through hole  4  can be used to facilitate an attachment of transponder  1  to an associated object by means of a screw or a similar fixing means. The surface material of housing  2  at an outer radial section is constituted by an overmolding of a molding compound  3 . Overmolding  3  is a thermoplastic compound. The surface material of housing  2  at an inner radial section adjoining through hole  4  is constituted by a liquid crystal polymer (LCP) that is reinforced with glass fibers with a volume content of approximately 15%. 
         [0047]      FIG. 2  and  FIG. 3  depict constituent parts of transponder  1  in an exploded view, apart from overmolding  3 . Transponder  1  comprises a circuit board  7  and a carrier plate  8 . Circuit board  7  is a circular plate with a central circular cut-out  9  and four smaller circular cut-outs  10  equidistantly spaced from one another and equidistantly spaced from central cut-out  8 . The material of circuit board  7  is constituted by a poly-(diphenyl oxide)-pyromellitimide, also known as “Kapton”®, that is reinforced with glass fibers. 
         [0048]    An antenna  11  is printed on the upper surface  12  of circuit board  7 . Antenna  11  is a conductor stripe of homogenous width substantially extending in a spiral shaped course. Thus, antenna  11  comprises a plurality of substantially circular interconnected conductor loops, for instance five to ten conductor loops, that are neigboring each other. Antenna  11  extends over the outer radial third of upper surface  12  of circuit board  7 . The conductor material is gold. 
         [0049]    A contact circuit  14  is printed on the lower surface  13  of circuit board  7 . Contact circuit  14  comprises a conductor of the same material than antenna  11 . Contact circuit  14  is arranged at an outer radial portion of lower surface  13  of circuit board  7 , opposite to a portion of upper surface  12  over which antenna  11  extends. Via a connection extending through circuit board  7 , contact circuit  14  is electrically interconnected with antenna  11 . 
         [0050]    At its center portion, contact circuit  14  comprises a contact field  15  on which a semiconductor component can be mounted such that an electrical connection can be established between antenna  11  and the semiconductor component. Contact circuit  14  further comprises circuit elements  16  laterally protruding over contact field  15 . Contact circuit  14  is surrounded by an indentation  17  on lower surface  13  of circuit board  7 . 
         [0051]    An enclosure  18  containing a semiconductor component is mounted on contact field  15 . Enclosure  18  comprises contacts at its bottom which are electrically connected to a respective conductor on contact field  15 . In this way, an electrical connection is established between antenna  11  and the semiconductor component inside enclosure  18  via contact circuit  14 . Thereby, lateral circuit elements  16  are laterally protruding over the bottom surface of enclosure  18 . 
         [0052]    A cylindrical protecting cap  19  with a closed lid at its bottom is placed inside indentation  17 . Thus, contact circuit  14  and enclosure  18  disposed on contact circuit  14  are fully enclosed inside protecting cap  19 . An additional anchoring of protecting cap  19  inside indentation  17  is provided by fixation lobes  20  at the upper end of protecting cap  19  that fit snugly in corresponding engagement slots  21  inside indentation  17 . An additional fixation of protecting cap  19  can be provided by soldering on top of contact circuit  14 . The material of protecting cap  19  is metallic providing a robust covering of contact circuit  14  and enclosure  18 . 
         [0053]    A volume filler  22  is arranged inside protecting cap  19  substantially filling out the inner volume of protecting cap  19  that is not occupied by enclosure  18 . Volume filler  22  is a ring-shaped spacer with an inner hole substantially matching the size of enclosure  18 . The material of volume filler  22  is a polytetrafluoroethylene (PTFE), also known as “Teflon”®, allowing to counterbalance the forces applied on the cylindrical protecting cap during the overmolding process. 
         [0054]    Carrier plate  8  is a circular plate with an upper surface  23  substantially corresponding to the size and shape of circuit board  7 , wherein the radius of carrier plate  8  is slightly larger than the radius of circuit board  7 . The thickness of carrier plate  8  exceeds the thickness of circuit board  7  by at least a factor of two. At the center region of its upper surface  23 , carrier plate  8  has a ring shaped projection  24  around upper tapering portion  5  of through hole  4 . The outer circumference of central projection  24  substantially matches the inner circumference of central cut-out  9  of circuit board  8 . 
         [0055]    Several snapping projections  25  are arranged around the outer circumference of central projection  24 . Snapping projections  25  engage with the inner circumference of central cut-out  9  of circuit board  8  when it is placed around central projection  24 . Moreover, four side projections  26  are provided on upper surface  23  of carrier plate  8 . Side projections  26  are equidistantly spaced from central projection  24  and have an outer circumference substantially matching the inner circumference of circular cut-outs  10  of circuit board  7 . In this way, an additional fixation of circuit board  7  on carrier plate  8  is provided. 
         [0056]    Upper surface  23  of carrier plate  8  further comprises a circular recess  27  for receiving protecting cap  19  when circuit board  7  is mounted on carrier plate  8 . Lower surface  28  of carrier plate  8  is substantially flat, except several through holes  6 ,  29 ,  30  at the respective positions of central projection  24 , snapping projections  25 , and side projections  26  on upper surface  23 . The material of carrier plate  8  is constituted by a liquid crystal polymer (LCP) that is reinforced with glass fibers with a volume content of approximately 15%. 
         [0057]      FIG. 4  shows lower surface  13  of circuit board  7  with enclosure  18  mounted on contact field  15  of contact circuit  14  and protecting cap  19  enclosing enclosure  18 , volume filler  22  and contact circuit  14 .  FIG. 5  shows upper surface  12  of circuit board  7  with antenna  11  printed thereon.  FIG. 6  shows a sectional view of circuit board  7  according to VI in  FIG. 5 . A corresponding sectional view of carrier plate  8  is shown in  FIG. 7 . 
         [0058]    Subsequently, a method of fabricating the above described transponder  1  is specified: At first, antenna  11  and contact circuit  14  are printed on respective upper surface  12  and lower surface  13  of circuit board  13 . Then, the bottom contacts of enclosure  18  are soldered to respective connection pads on contact field  15  of contact circuit  14  such that the interior semiconductor component of enclosure  18  is in electrical contact with antenna  11 . By means of the soldering, enclosure  18  is fixed on lower surface  13  of circuit board  13 . 
         [0059]    In a next step, volume filler  22  is disposed around enclosure  18  on top of contact circuit  14  and protecting cap  19  is placed inside indentation  17  around contact circuit  14 . An additional fixation of protecting cap  19  in this position is provided by an insertion of fixation lobes  20  inside engagement slots  21  and a soldering of protecting cap  19  to lower surface  13  of circuit board  13 . In this way, circuit board  7  as shown in  FIGS. 4 to 6  is obtained. 
         [0060]    In a following step, lower surface  13  of circuit board  7  is placed on upper surface  23  of carrier plate  8 , as shown in  FIG. 8  in a sectional view. Central projection  24  and snapping projections  25  of carrier plate  8  are inserted into central cut-out  9  of circuit board  7  such that central projection  24  and snapping projections  25  protrude over upper surface  12  of circuit board  7 . Snapping projections  25  engage at the inner circumference of circuit board  7  providing a fixation of circuit board  7  preventing a translational displacement with respect to upper surface  23  of carrier plate  8 . Side projections  26  of carrier plate  8  are inserted into smaller cut-outs  10  of circuit board  7  providing a fixation of circuit board  7  preventing a rotational displacement with respect to upper surface  23  of carrier plate  8 . Protecting cap  19  on lower surface  13  of circuit board  7  substantially fills out the volume of circular recess  27  at the upper surface  23  of carrier plate  8 . 
         [0061]    In a subsequent step, the arrangement shown in  FIG. 8  is overmolded with molding compound  3 , as shown in  FIG. 9  in a sectional view. Overmolding  3  extends from protruding central projection  24  and snapping projections  25  over upper surface  12  of circuit board  7  over the lateral edges of circuit board  7  and carrier plate  8  to an outer radial section of lower surface  28  of carrier plate  8 . In this way, carrier plate  8  is fully enclosed by means of carrier plate  8  and overmolding  3 , which are constituting housing  2  of circuit board  7 . Overmolding  3  can also be applied to entirely surround carrier plate  8  and circuit board  7 . 
         [0062]    Overmolding  3  provides a protection of upper surface  12  of circuit board  7 . Thus, antenna  11  printed on upper surface  12  is securely fixed in its position due to the direct application of overmolding  3  on the top, in particular in the case of a detachment of the conductor printing due to high temperature influences. The more sensitive components comprising the semiconductor component inside enclosure  18  are even more protected against external influences of temperature, contamination and mechanical impacts due to their arrangement inside protecting cap  19 . This protection is further enhanced since protecting cap  19  is positioned in between carrier plate  8  and circuit board  7  with overmolding  3  on top and contains volume filler  22  for an additional protection. Already during the overmolding procedure, protecting cap  19  serves as a protection for the components contained therein when the high pressure impacts typically occurring during the overmolding represent a risk of tearing out enclosure  18  from its soldering. 
         [0063]      FIG. 10  depicts enclosure  18 , wherein a lid  32  on top of enclosure  18  (as shown in  FIG. 11 ) is removed, in order to illustrate the internal configuration of enclosure  18 . Enclosure  18  comprises a ceramic body  31 . A base of ceramic body  31  is formed by a flat support section  33 . Outer side walls  34  vertically delimit an inner volume  35  inside enclosure  18 . Ceramic body  31  has a substantially quadratic cross-section. 
         [0064]    Support section  33  is used as a support of a semiconductor device  36 , more particularly an integrated circuit (IC). Integrated circuit  36  is fixed on the upper surface of support section  33 . A first connection pad  43  and a second connection pad  44  are arranged on support section  33  in close proximity to integrated circuit  36 . Connection pads  43 ,  44  comprise a gold metallization layer. Via respective gold wires  52 ,  54 , integrated circuit  36  is connected to connection pads  43 ,  44 . 
         [0065]      FIG. 11  depicts enclosure  18 , wherein lid  32  is attached on top of enclosure  18 . Lid  32  is metallic and is applied on enclosure  18  after the internal wiring of integrated circuit  36  has been carried out. The metallic composition of lid  32  is suitable for an easy installation and can offer a good mechanical protection and a tight sealing of the inner volume  35  of enclosure  18 . 
         [0066]      FIG. 12  shows a cross-sectional view of enclosure  18  shown in  FIG. 11  at the position of the attachment of gold wires  52 ,  54  on connection pads  43 ,  44  shown in  FIG. 11 . Gold wires  53 ,  54  are attached to the gold metallization layer of connection pads  43 ,  44  via a thermocompression bonding  55 ,  56 . In this way, the resistance against heating induced degradation and corrosion is further improved. 
         [0067]    Connection pads  43 ,  44  are electrically connected to respective bottom contacts  57 ,  59  on the lower surface of support section  31 . Enclosure  18  is fixed on contact field  15  of contact circuit  14  printed on circuit board  7 . Thereby, bottom contacts  57 ,  59  are attached to respective contacts on contact field  15  by a high temperature solder. In this way, a good corrosion and heating resistant fixation of enclosure  18  on circuit board  7  is provided. The protection of integrated circuit  36  on circuit board  7 , in particular during high temperature operation of transponder  1 , is further improved after the application of volume filler  22  and protecting cap  19  around contact circuit  14 . 
         [0068]    After fixation of enclosure  18  on circuit board  7 , substantially only support section  34  of enclosure  18  is in direct contact with lower surface  13  of circuit board  7 . Thus, the thermal expansion between enclosure  18  and circuit board  7  can be advantageously matched due to the advantageous material selection of circuit board  7  and enclosure  18 . 
         [0069]    Inner space  35  of enclosure  18  is filled with nitrogen. Due to the tight sealing provided in between ceramic body  31  and metallic lid  32 , the inert atmosphere inside inner space  35  can be maintained over a comparatively long time period. The inert atmosphere  35  leads to a further improvement of the avoidance of corrosion, contamination and thermoinduced degradation effects and contributes to a long lifetime of transponder  1 . 
         [0070]    From the foregoing description, numerous modifications of the transponder according to the invention are apparent to one skilled in the art without leaving the scope of protection of the invention that is solely defined by the claims.