Abstract:
The invention concerns a method for extracting chips ( 20 ) from a silicon wafer ( 10 ) and for transferring each chip on an electronic device including the following steps: 
       Extracting the good chips from the silicon wafer ( 10 ) and transferring them on a roll-up adhesive film ( 28 ) so that the chips are spaced out by a certain distance,    Transferring the chips ( 20 ) from the roll-up film ( 28 ) directly and continuously on contacts ( 46, 48  or  58, 60 ) of the electronic device.

Description:
TECHNICAL FIELD  
       [0001]     The present invention concerns the installation of the electronic chip on RFID type radiofrequency labels and contactless smart cards and specifically concerns a method and device for extracting an electronic chip from a silicon wafer and transporting the chip to its installation location on an electronic device.  
       BACKGROUND ART  
       [0002]     Electronic chips or integrated circuits designed for the manufacture of electronic circuits for radiofrequency identification (RFID) devices such as contactless smart cards and radiofrequency labels must be connected to the antenna of the RFID device. The electronic chips are delivered by the chip suppliers on silicon slices known as wafers. These wafers that group several hundred integrated circuits are generally delivered glued to an adhesive sheet. The wafer is cut out beforehand so that the chips are detached from one another while remaining glued together on the adhesive sheet. Each chip is then extracted from the silicon wafer so that it can be directly positioned on the contacts of the circuit&#39;s antenna.  
         [0003]     The methods used to connect chips to the antennas of an electronic device including a chip and antenna are based on the “Flip Chip” assembly technique. This technique is characterized by a direct connection of the chip&#39;s active side onto the antenna and its substrate, in contrast to the older “Wire Bonding” wiring technique described earlier, which consisted in bonding the chip&#39;s passive side to the substrate and wiring it to the antenna.  
         [0004]     The “Flip Chip” assembly technique according to a patented method of the applicant includes the steps consisting in: 
    positioning the chip provided with contacts made of a non-deformable material on the antenna support so that the contacts are facing the contacts of the antenna, and     exerting a pressure on the chip so that the chip&#39;s contacts deform the antenna support and the antenna contacts as a result of the pressure, the support and the antenna contacts maintaining their deformation after the exerted pressure has been released, thus allowing a maximum contact surface to be obtained between the chip&#39;s contacts and the antenna contacts.    
 
         [0007]     The method also includes an additional step which consists in placing adhesive dielectric material directly on the active side of the chip between the contacts, prior to the chip positioning step, so as to maintain the chip in a fixed position relative to the support.  
         [0008]     For implementing this method, several types of machines exist depending on whether the chips are supplied with their active side against the adhesive or otherwise. When the chips present the passive side on top of the silicon wafer, the extraction and chip transfer machine presents an arm equipped with a flexible suction cup, which detaches the chip from the adhesive by suction and thanks to a tip located on the side of the adhesive that presses on the location of the chip to be extracted. The arm is equipped with cameras to view the exact location of the electronic device on which the chip must be positioned. According to the measurements made by the cameras, the position of the arm is adjusted. Once extracted, the chip is transported towards the electronic device and presented by the arm directly on the antenna contacts designed to come into contact with the chip&#39;s contacts. This method of extracting the chip and positioning it on the circuit requires a series of operations carried out by the machine arm, which performs a to-and-fro movement. Furthermore, the electronic devices assembled in a roll, such as a web, move as the transfer operation progresses. Because of the measurements that need to be made by the cameras and the adjustment time of the arm, the web moves by successive and discontinuous advances. Another type of machine is adapted to extract the chips from a silicon wafer in which the passive side of chips is glued on the adhesive. This type of machine features two arms so that the chip extracted from the silicon wafer by the first arm is turned over before being held by the second arm, which transports the chip to its final location on the electronic chip. Just as for the first type of machine, cameras are used to view the antenna contacts on which the chip must be connected so that the position of the second arm can be adjusted with respect to the position of the RFID device placed on the web. The rates obtained by these two types of machines do not exceed 40,000 units per hour due to the time required for to-and-fro movements of the machine arms and the time required for adjusting the position of the chip with respect to the electronic devices.  
       SUMMARY OF THE INVENTION  
       [0009]     This is why, the object of the invention is to mitigate these drawbacks by providing a method for extracting the chip from a silicon wafer and transferring said chip up to the contacts of an electronic device, and do this continuously so that rates greater than those of traditional chip transfer machines are obtained while ensuring the sturdiness and accuracy of the connection of the chip on the contacts.  
         [0010]     The purpose of the invention is thus a method for extracting chips from a silicon wafer and transferring each chip on an electronic device including the following steps: 
    Extracting the good chips from the silicon wafer and transferring them on a roll-up adhesive film so that the chips are spaced out by a certain distance,     Transferring the chips from the roll-up film directly and continuously on contacts of the electronic device.    
 
         [0013]     Another object of the invention is a device for extracting electronic chips from a silicon wafer including systems to transport the chip from the wafer on a roll-up adhesive film and means to directly and continuously transfer the chip from the roll-up film to contacts of an electronic device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The purposes, objects and characteristics of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which:  
         [0015]      FIG. 1  represents a silicon wafer equipped with precut chips,  FIG. 2  represents the extraction machine for chips according to the invention,  FIG. 3  represents a web for RFID type electronic device supports,  FIG. 4  represents a cross-section of the antenna support after the chip positioning step,  FIG. 5  represents an antenna for RFID type electronic device in UHF,  FIG. 6  represents an antenna for an RFID type electronic device in UHF after laser cutting,  FIG. 7  represents an antenna for an RFID type electronic device in UHF after the chip positioning step. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     According to  FIG. 1 , the silicon wafer  10  or “wafer” is shown in front view. It includes a support  12  which maintains a flexible adhesive  14 . The chips or integrated circuits are glued on the adhesive  14  in the form of a disk  16 . The chips have been precut so that they are independent of one another. The installation technique considered here is characterized by a direct connection of the active side of the chip on the antenna contacts. This assembly technique is known as the “Flip Chip” assembly technique and consists in placing a ball of conductive material commonly referred to as “bump”, usually made of gold, on each of the metal connections of the chip so as to form one or more contacts of preferably non-deformable material.  
         [0017]      FIG. 2  is a diagrammatic view of the extraction step of chips from the silicon wafer. The wafer  10  viewed from side presents chips glued  20  with their passive side on the adhesive  14 . The contacts  22  located on the active side of chips  20  are thus on the unconnected side of the chip opposite the side of the chip glued to the adhesive. Only the good chips  20  will be selected for being transferred to electronic devices. As a result, certain chips are declared bad and must not be used. To select only the good chips, a method consists in using an adhesive  14  sensitive to ultraviolet radiation. In this way, only the location of good chips is exposed to light in order to desensitize the adhesive at the location where the chip is glued. Another method consists in using the computer file provided with the silicon wafer, which helps locate the location of bad chips.  
         [0018]     The chips  20  are extracted from the wafer  10  by means of a suction wheel  24 . The wafer  10  is positioned in such a manner that the wheel  24  is aligned with one line of chips of the wafer  10 . The wheel  24  is installed on a fixed shaft driven in rotation by a motor and has a suction system over its entire periphery. The wafer  10  moves so that the wheel  24  aligned along a line of the chip takes off the chips  20  by suction, which creates a force that is sufficient to remove the good chips from the adhesive  14  and keeping them in contact on the periphery of the wheel  24 , their active side against the wheel. The contact of the wheel  24  with the chips of the wafer  10  is ensured by an auxiliary idler wheel  26  installed on a fixed shaft. The chips  20  held on the rotating wheel  24  are then transferred to an adhesive film  28  thanks to a transfer support system  30 , the film  28  being set in motion by means of a motor at an adjustable speed. The transfer support system includes a tip with a flattened point having the chip&#39;s size that is located near the film  28  and in line with the wheel  24 . The transfer support system rests against the film  28  on the non-adhesive side of the film  28  thanks to a translation motion so that the adhesive of the film  28  comes in contact with the chips  20  of the wheel  24 , one by one. The chips are thus transferred one by one from the wheel  24  to the adhesive  28  and are placed at a desired distance from one another according to the film  28  transfer speed. The film  28  is preferably parallel to the adhesive  14  of the silicon wafer  10  so that the chips perform half a rotation of the wheel  24  between the time when they are taken from the silicon wafer  10  and the time when they are transferred onto the film.  
         [0019]     The spacing between the chips placed on the film  28  is thus managed by adjusting the film speed. The control of this speed thus helps take up the free spaces left between the chips and the wheel  24  resulting from bad chips left on the wafer  10 . The adhesive film  28  carrying the chips can be stored in a roll before being integrated with the method for transferring chips on electronic devices.  
         [0020]     According to an alternate embodiment of the chips extraction step, the wheel  24  takes off several rows of chips  20  simultaneously over its periphery and transfers them to as many adhesive films.  
         [0021]     The next step that includes the transfer of chips on electronic devices is independent from the step consisting in extracting the chips from the silicon wafer as described earlier. Each radiofrequency (RFID) identification type electronic device features an antenna and a chip connected together, the shape of the antenna depending on the application, the range of frequencies used, etc. Prior to the step of connecting the chip, the antenna is made on a support of deformable material such as fibrous material, preferably made of paper, by printing with conductive ink such as ink loaded with silver or carbon particles. The antenna can be made, for example, by screen printing, flexography, rotogravure, offset printing or inkjet printing. The antenna support is in the form of a roll to enable the production of large quantities of electronic devices, which will then be cut out.  FIG. 3  shows a web  42  used to support the RFID type electronic devices  40  and featuring 13.56 MHz type antennas  44  such as those defined in the standards ISO 14443 and 15693 capable of being connected to a chip thanks to contacts  46  and  48 . At this manufacturing step, as mentioned below in the description of a second embodiment of the invention, the contacts  46  and  48  may not be formed, that is to say there are then connected together by the same material than the one they are made of. The film  28  including the chips is placed parallel to the web  42  so that the side of the film  28  featuring the chips  20  and the side of the web  42  featuring the antennas are facing each other. The web  42  advances in a continuous motion while the film  28  including the chips  20  unwinds as the chips are transferred. Adhesive material is applied on the chip between the contacts of the chip before it is placed on the antenna. The adhesive material used is preferably an epoxy resin or a cyanoacrylate glue.  
         [0022]     Once the adhesive material  50  has been applied, the chip is positioned on the antenna support in a manner that the contacts of the chip are in contact with the contacts  46  and  48  of the antenna  40 . The adjustment of contacts of the chip with those of the antenna is done by means of a camera located near the chip to be positioned.  FIG. 4  represents a cross sectional view of the chip-antenna assembly.  
         [0023]     Pressure is exerted on the chip  20  so that the contacts  22  of the chip  20  cause a deformation of the support and contacts  46  and  48  of the antenna  40  as shown in  FIG. 4 . The latter are then deformed so as to form an imprint whose inner surface exactly matches the outside surface of the contacts. Thanks to an intimate contact between the connection pads, the contact area between the chip&#39;s contacts  22  and the contacts  46  and  48  of the antenna  40  is maximum. The material which makes up the antenna support is preferably deformable and non-elastic such as conductive ink of the antenna&#39;s contacts  46  and  48 . As such, these two materials tend not to return to their original shape even when the pressure is released. This is particularly true when the material of the support is a fibrous material such as paper. As a result of the pressure, the adhesive dielectric material  50  spreads and covers the entire surface of the chip between the contacts. It thus enables the mechanical assembly between the chip  20  and the antenna support—and thereby the electric contact between the chip and the antenna—to be reinforced.  
         [0024]     According to a variant of the transfer step of the chip on the RFID type electronic chip, the antenna&#39;s contacts are created at the time of the transfer. This variant relates to RFID type electronic devices operating in all frequency ranges such as 13.56 MHz frequency defined in ISO 14443 and 15693 standards in the very high frequency range (frequency in the 860-960 MHz range and frequency of 2.45 GHz according to the ISO 18001 standard). An example of an antenna used for these frequency ranges is shown in  FIG. 5 . The antenna  54  has two wires connected together by a narrower portion  56  and, as in the first embodiment, the antennas are placed side by side to form a web similar to the one shown in  FIG. 3 . The web advances in a continuous motion whereas the film  28  including the chips  20  unwinds as the chips are transferred. Just before placing the chip on the antenna, a laser cutout is made to cut the portion  56  and create two contacts  58  and  60  disconnected from one another. The chip is then positioned in the same way as in the first embodiment. The chip-antenna assembly shown in  FIG. 4  is also applicable to the assembly of chip  62  on the contacts  58  and  60  of the antenna  54 . Adhesive material is applied on the chip between the contacts of the chip before being placed on the antenna. Once the adhesive material has been applied, the chip is positioned on the antenna support in such a manner that the contacts of the chip are opposite the contacts  58  and  60  of the antenna  54 . Pressure is exerted on the chip  62  so that the contacts of the chip  62  cause deformation of the antenna support and contacts  58  and  60  of the antenna  54 . The latter are then deformed so as to form an imprint whose inner surface exactly matches the outside surface of the contacts. Thanks to the intimate contact between the connection pads, the contact area between the chip&#39;s contacts and the contacts  58  and  60  of the antenna  54  is maximum. The material which makes up the antenna support is preferably deformable and non-elastic such as conductive ink of the contacts  58  and  60 . As such, these two materials do not tend to return to their original shape, even when the pressure is released. This is particularly true when the material of the support is a fibrous material such as paper. As a result of the pressure, the adhesive dielectric material spreads and covers the entire surface of the chip between the contacts. It thus enables the mechanical assembly between the chip  62  and the antenna support—and thereby the electrical contact between the chip and the antenna—to be reinforced. As a result of the pressure, the adhesive dielectric material spreads and covers the entire surface of the chip between the contacts. Unlike the first embodiment, laser cutting and formation of the antenna contacts immediately before positioning the chip, helps avoid an adjustment made using a camera.  
         [0025]     The transfer method of chips, owing to the continuous movement of the web and simplified adjustment, helps obtain high output rates in the order of 100,000 devices per hour.  
         [0026]     The transfer method of the chip, as described according to the invention, applies to all types of electronic devices such as an electric circuit featuring two contacts capable of receiving an integrated circuit or a chip.