Abstract:
An electronic circuit including a planar base having first and second base surfaces, an antenna attached on the first surface of the base, and a chip connected to the antenna, characterized in that a double faced adhesive is glued on one of the base surfaces, the double faced adhesive having an opening and the chip being arranged at least partially in the opening.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the attaching of electronic circuits. 
   DISCUSSION OF RELATED ART 
   Labels bearing indications readable by a computer peripheral, like a bar code readable by an optical analyzer, have recently appeared. Such a system enables fast identification of a labeled product. For a label to be read, it has to be in front of the analyzer, which implies a handling of the product, the label of which is desired to be read. Finally, the information contained in the bar code cannot be modified. 
   An electronic label including an antenna connected to a chip enables, by means of an electromagnetic antenna coupled to a computer system, reading and writing information in the chip. It is not necessary to have the electronic label face the antenna for the information exchange to be possible. This type of label has many advantages, since a large amount of immediately rewritable information can be stored therein, without having to handle the object, the label of which is being read. However, conventional electronic devices including a chip generally are too stiff, too thick and too expensive to enable making a robust, inexpensive electronic label of small bulk. Further, attaching the label to the object always is a problem. 
   SUMMARY OF THE INVENTION 
   The present invention enables producing in a simple way and with a low cost thin flexible self-adhesive electronic labels which are easy to lay, by machine or by hand. 
   To achieve this object, the present invention provides an electronic circuit including a planar base, an antenna attached on a first surface of the base, a chip connected to the antenna and a double faced adhesive glued on one of the base surfaces, a slot being made in the double faced adhesive and the chip being arranged at least partially in this slot. 
   According to an embodiment of the present invention, the chip is glued on the first surface of the base and is connected to the antenna by connection wires, the wires and the chip being covered with a drop of resin. 
   According to an embodiment of the present invention, the etched surface of the chip faces the first surface of the base, and the chip is connected to the antenna by welding beads. 
   According to an embodiment of the present invention, the etched surface of the chip faces the back of the first surface of the base, the chip is placed in a slot made through the base, and the chip is connected to the antenna by welding beads, the chip being attached to the base by a drop of resin. 
   According to an embodiment of the present invention, the etched surface of the chip faces the back of the first surface of the base and the chip is connected to the antenna by welding beads located in connection slots going through the base, the chip being attached to the base by a drop of resin. 
   According to an embodiment of the present invention, the base is formed of a flexible sheet. 
   According to an embodiment of the present invention, the surface of the base which does not receive the double-faced adhesive is provided to receive the printing of a pattern, of a text or of a code. 
   The present invention also provides a method of manufacturing an electronic circuit such as mentioned hereabove, which includes the steps of: forming a rectangle of double faced adhesive including a slot, gluing the adhesive rectangle on a packaging protective film, ungluing the adhesive rectangle from the protective film, and assembling it on the base. 
   The foregoing objects, features and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings wherein 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a top view of a label according to a first embodiment of the present invention; 
       FIG. 2  shows a cross-sectional view of the label of  FIG. 1 ; 
       FIG. 3  shows a top view of a label made according to a second embodiment of the present invention; 
       FIG. 4  shows a cross-sectional view of the label of  FIG. 3 ; 
       FIG. 5  shows a top view of a label made according to a third embodiment of the present invention; 
       FIG. 6  shows a cross-sectional view of the label of  FIG. 5 ; 
       FIG. 7  shows a top view of a label made according to a fourth embodiment of the present invention; 
       FIG. 8  shows a cross-sectional view of the label of  FIG. 7 ; 
       FIG. 9  shows a cross-sectional view of a label made according to a fifth embodiment of the present invention; 
       FIG. 10  shows a method of manufacturing self-adhesive electronic labels according to an embodiment of the present invention; and 
       FIG. 11  schematically shows a final packaging of labels according to the present invention. 
   

   DETAILED DESCRIPTION 
   The same references designate same elements in the various drawings.  FIGS. 1 and 2  show in top view and in cross-section a label  10  according to a first embodiment of the present invention. This label includes a chip  12  attached by a glue layer  13  on a first surface of a base  14 . An antenna  16  is also attached to the first surface of base  14 . Chip  12  is electronically connected to antenna  16  by connection wires  18 . The chip and the wires are caught in a drop of protection resin  19 . In the following description, a “double faced adhesive” will designate a segment of a plastic tape conventionally processed to be adhesive on its two surfaces, on a strip of solid glue. A first surface of a double faced adhesive  20  pierced by a slot  21  is glued on the first surface of base  14  to cover the first surface except for the vicinity of resin drop  19 , located in slot  21 . A strippable sheet  24  covers the second surface of double-faced adhesive  20 . 
   Chip  12  may be glued to the base by means of a glue, epoxy, or other, and connection wires  18  may be attached by a conventional wiring machine. Antenna  16  may be formed on the base in a known manner by metal deposition followed by an etching. The resin drop can be formed by coating, by casting, or by cloisonné. Base  14  is made of a flexible material of low thickness, for example, a piece of a polyester sheet. 
   The double faced adhesive is thicker than the resin drop and it forms both the adhesive portion of the self-adhesive label and the protective housing of chip  12 . The double-faced adhesive is made in a slightly resilient flexible material so that the self-adhesive label is adapted to being glued on a non-planar surface, and is resistant to vibrations and shocks. The glue coating the double-faced adhesive is a joiner&#39;s glue enabling a lasting and reliable bond. Double faced adhesives currently available for sale that may be used, for example, are sold by 3M Company under trade name VHB. 
   As an example, the thickness of base  14  may be 75 μm, the thickness of antenna  16  may be 17 μm, the thickness of glue  13  may be 20 μm, the thickness of chip  12  may be 180 μm, the thickness of drop  19  may be 300 μm, and the thickness of double faced adhesive  20  may be 400 μm. Thus, according to this embodiment, label  10  has a thickness of approximately 500 μm. The thickness of double faced adhesive  20  here is much greater than the height of drop  19  so that a variation of the height of the drop upon its forming may be tolerated. 
     FIGS. 3 and 4  show in top view and in cross-section a label  10  according to a second embodiment of the present invention. In this embodiment, connection wires  18  and chip  12  are protected by a resin drop  22  formed by filling slot  21  with resin. The forming of drop  22  here is faster than according to the previous embodiment. Indeed, the methods of forming drop  19  discussed in relation with  FIGS. 1 and 2  are slow, whereas it is here sufficient to fill slot  21  with resin. In this embodiment, in addition to the previously mentioned functions, slot  21  through the double-faced adhesive is used to limit the spreading of the resin, which can be chosen to be very fluid. 
     FIGS. 5 and 6  show in top view and in cross-section a label  10  according to a third embodiment of the present invention. The front surface or etched surface of chip  12 , that is, the surface having received the various processings intended for the forming of an integrated circuit in planar technology, is placed against the first surface of support  14  according to a so-called flip-chip assembly mode, to be electrically connected to antenna  16  via welding beads  26 . A resin collar  23  is formed on the circumference of the chip to seal chip  12  on base  14 . This embodiment requires an assembly by welding beads, which is delicate to implement, but it enables decreasing the thickness of label  10 . 
   As an example, it is assumed that the welding beads have a substantially constant thickness of 20 μm, and that an allowed variation of 10 μm only can be provided for the depth of slot  21 . With a thickness of chip  12  of 180 μm, a double-faced adhesive of a 210-μm thickness can be used. If the total thickness of base  14  and of antenna  16  is close to 95 μm, a label  10  with a thickness close to 300 μm only is obtained. 
     FIGS. 7 and 8  show in top view and in cross-section a label  10  according to a fourth embodiment of the present invention. Antenna  16  here is located on the surface of base  14  which is not covered by double faced adhesive  20 . Further, base  14  is crossed by a slot  21  which substantially prolongs slot  21  of double-faced adhesive  20 . Chip  12  is located in slot  21 , with its etched surface facing the back of antenna  16  and being connected to the back of the antenna by welding beads  26 . Slot  21 , in base  14  and double faced adhesive  20 , is filled with a drop of resin  22 . This embodiment requires a slot  21  of the base and a connection by welding beads, but it enables decreasing the thickness of label  10 . 
   As an example, if the thickness of the base is 75 μm, the thickness of the antenna is close to 20 μm, the thickness of chip  12  is 180 μm and the thickness of welding beads  26  is approximately 20 μm, then an adhesive of approximately 135 μm can be used, to obtain a label  10  of a thickness close to 230 μm. This thickness is substantially that of a conventional non-electronic self-adhesive label. 
     FIG. 9  shows in cross-section a label  10  according to a fifth embodiment of the present invention. Antenna  16  is located on the same surface of base  14  as in  FIGS. 7 and 8 . Chip  12  is located in slot  21  of double faced adhesive  20 , its etched surface facing the back of antenna  16 , and being connected to the back of the antenna by welding beads  26  through connection slots  25  made in base  14 . 
     FIG. 10  illustrates a method of manufacturing self-adhesive labels according to the embodiment described in relation with  FIGS. 3 and 4 . A series of antennas (not shown) has been formed on a mechanically indexed strip  28  intended for being cut into a series of bases. A chip  12  has been glued at the level of each antenna on the indexed strip, which is provided to a laminating machine  30 . The machine also receives a double faced adhesive  20  covered with a protective film  24  on both its surfaces. A sensor  32  spots the position of each chip  12  and controls a punch  34  to form, in the double faced adhesive, a slot  21  corresponding to this position. Protective film  24  is removed from a first surface of cut-up double-faced adhesive  20 , which is laminated and glued on the indexed strip. Each chip  12  is then connected to the corresponding antenna by connection wires (not shown), after which slot  21  is filled with drops of resin (not shown). After assembly of the labels, the indexed strip is cut to form the labels, each label is magnetically tested and the functional labels are separated from their protective film to be placed on a packaging strip. 
   An alternative manufacturing method includes using rectangles of double faced adhesive  20  which are precut (separated from one another and comprising slot  21 ), for example, by the adhesive manufacturer. Double faced adhesive rectangles  20  are then delivered maintained together by a strip of protective film  24 , and they are unglued one by one from the protective film, by a machine or by an operator, to be glued to the bases. The labels can then be manufactured according to the embodiment of  FIGS. 1 and 2 . In this case, connections  18  and resin drop  19  of protection of the chip and connections will be formed before gluing the double faced adhesive on base  14 . The electromagnetic testing of each connected chip  12  may also be performed before gluing the double faced adhesive, which implies that a rejected defective component represents a smaller loss. The labels of  FIGS. 3 to 9  may also be formed according to this alternative. 
     FIG. 11  shows a packaging strip  36  comprising labels  10 , the second surface of which has been covered with a logo or a code  38 , ready to be sold. 
   Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. In the embodiment of  FIGS. 1 and 2 , a cavity may for example be formed in the upper half of the thickness of base  14  to receive chip  12 , and thus decrease the label thickness and facilitate the forming of drop  19 . Further, the surface of the base which is not glued to the double-faced adhesive may be painted or printed or covered with an easily paintable or printable material. Moreover, the preceding descriptions relate to self-adhesive labels, but the present invention may also apply to any self-adhesive electronic circuit, for example, a sensor. In this regard, protection resin  22 , which is conventionally opaque, may be replaced in the embodiment of  FIGS. 7 and 8  with a transparent protection resin if the chip includes light-sensitive circuits such as photo-voltaic or charge coupling circuits. Resin drop  22  may then be lens-shaped for a better reception of the light by the chip. 
   Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.