Abstract:
An apparatus for assembling chip devices on a wire, each chip device comprising two substantially parallel lateral walls, and a groove in one of the lateral walls for receiving said wire. The apparatus includes a pinching device having two opposing surfaces, the distance between the opposing surfaces being substantially constant and substantially equal to the distance between the two lateral walls of a chip device. A wire feeder is adapted to continuously feed the wire in contact with one of the opposing surfaces of the pinching device. A chip device feeder is adapted to drive chip devices, one at a time, between the opposing surfaces, with their grooves turned towards the wire. The pinching device may comprise two cylindrical rollers having rotation axes substantially perpendicular to the wire, the opposing surfaces being formed by respective surfaces of the rollers.

Description:
FIELD OF THE INVENTION  
       [0001]    The invention relates to the assembly of small devices, having a size that can be smaller than one millimeter, especially devices embedding a microelectronic chip, on a wire in order to form a string of devices that is better adapted to further processing. 
       STATE OF THE ART  
       [0002]    Patent application EP2099060 discloses various methods of assembling such chip devices on a wire. Each chip device is provided with a groove adapted to the diameter of the wire. The disclosed methods involve temporarily fixing the chip devices on a tape and using conventional wire-bond equipment to individually run the wire through the groove of each chip device. The wire can be fixed in the grooves by gluing or soldering, or the grooves can be configured so that the wire clips into the grooves. 
         [0003]    Patent application GB2017038 discloses an apparatus for stringing resistances on a belt. The two wires of a resistance are each sandwiched between two adhesives tapes. 
         [0004]    The article “Packaging and wired interconnections for insertion of miniaturized chips in smart fabrics” from Jean Brun et al. disclosed in “MICROELECTRONICS AND PACKAGING CONFERENCE” of Jun. 15, 2009, discloses devices having grooves secured to a wire. 
       SUMMARY OF THE INVENTION 
       [0005]    There is a need for equipment better adapted to assembling chip devices on wires, enabling, in particular, a reduction of manufacturing times. 
         [0006]    This need is addressed by an apparatus for assembling chip devices on a wire, each chip device comprising two substantially parallel lateral walls, and a groove in one of the lateral walls for receiving the wire. The apparatus includes a pinching device comprising two opposing surfaces, the distance between the opposing surfaces being substantially constant and substantially equal to the distance between the two lateral walls of a chip device. A wire feeder is adapted to continuously feed the wire in contact with one of the opposing surfaces of the pinching device. A chip device feeder is adapted to drive chip devices, one at a time, between the opposing surfaces, with their grooves turned towards the wire. 
         [0007]    In a preferred embodiment, the pinching device comprises two cylindrical rollers having rotation axes substantially perpendicular to the wire, said opposing surfaces being formed by respective surfaces of the rollers. 
         [0008]    In a preferred embodiment, the chip device feeder comprises a storage groove adapted to lead a series of chip devices in contact with each other to the pinching device. A separator is arranged near the pinching device for creating a gap between the last and penultimate chip devices in the storage groove. A hook has an alternating movement between a first position in the gap, where it hooks the last chip device, and a second position near said opposing surfaces of the pinching device, where it releases the last chip device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  schematically shows a general view of an embodiment of an apparatus for assembling chip devices between two parallel wires. 
           [0010]      FIGS. 2A-2F  schematically show a side view of a detail of the apparatus, in several steps of processing chip devices. 
           [0011]      FIG. 3  shows a general perspective view of a detailed embodiment of the apparatus. 
           [0012]      FIG. 4  shows en enlarged detail of  FIG. 3 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0013]      FIG. 1  schematically shows a general view of an embodiment of an apparatus for assembling chip devices between two parallel wires  8   a,    8   b,  for forming a ladder-shaped string of chip devices. 
         [0014]    A series of chip devices  10  awaiting processing are stored in a pile at an input area  12  of the apparatus, for instance a groove adapted to the width of the chip devices. Each chip device  10 , generally in the shape of a parallelepiped, has two opposite, substantially parallel lateral walls, each provided with a longitudinal groove adapted to the diameter of the wires. The chip devices are piled up in area  12  such that their longitudinal grooves are aligned. 
         [0015]    A passive pinching device  14  placed at the bottom of area  12  comprises, in a preferred embodiment, two cylindrical rollers  14   a  and  14   b.  By “passive pinching device” it is understood that the rollers  14   a,    14   b  are at a substantially constant distance from each other during operation, i.e. no alternating pinching movement is implemented. The axes of the rollers  14   a,    14   b  are substantially perpendicular to the wires, and their spacing is such that two opposing surfaces  16   a,    16   b  of the rollers are at a distance substantially equal to the width of the chip devices (i.e. the distance between the lateral walls of the chip devices). 
         [0016]    The rollers  14   a,    14   b  are a preferred embodiment to define the opposing surfaces  16   a,    16   b  of the pinching device. Indeed, this will reduce friction and wear. They may be comprised of ball bearings. In a less favorable alternative, the opposing surfaces  16   a,    16   b  may be formed by fixed elements. 
         [0017]    Each wire  8   a,    8   b  is fed in continuous motion along a respective opposing surface  16   a,    16   b,  in alignment with the respective grooves of the chip devices in area  12 . Each wire  8   a,    8   b  is for instance fed from a reel, not shown, over an auxiliary roller  18   a,    18   b,  then along the respective opposing surface  16   a,    16   b,  and leaves the apparatus parallel to the other wire, at the distance defined by the opposing surfaces, thus the chip device size. Auxiliary rollers  18   a,    18   b  ensure that the wires  8   a,    8   b  enter the pinching device  14  at an angle avoiding interference with the chip devices  10  stored in area  12 . 
         [0018]    A chip device feeder  20  arranged between area  12  and pinching device  14 , described in more detail later, takes one chip device  10  at a time from storage area  12 , and moves it between rollers  14 . As the chip device approaches the rollers, its opposite grooves start engaging with the wires  8   a  and  8   b,  whereby the wires and chip device start aligning with each other. The feeder continues pushing the chip device through the gap between rollers  14 , whereby the opposing surfaces  16   a,    16   b  force the wires into the grooves of the chip device, throughout the length of the grooves, as the chip device travels with the wires through the gap. 
         [0019]    The assembled string thus leaving the rollers  14  is for instance stored on a reel, not shown, that may also provide the required traction to pull the wires through the assembly apparatus. 
         [0020]    The chip devices may be fixed to the wires in various manners. For example, the wires may be bare metal and the grooves of the chip devices include metal areas. The string may then go through a solder bath as it exits the apparatus, whereby the metal areas of the grooves are soldered to the wires. 
         [0021]    In a preferred embodiment, the grooves of the chip devices are configured to clip over the wires. No subsequent operation is then required in the assembly. 
         [0022]    In order to avoid breaking chip devices that may be wider than a nominal value, one of the rollers  14   a,    14   b  is preferably spring biased towards the other roller. The spring force is chosen sufficient to insert the wires in the grooves, but insufficient to break a chip device that has a width larger than the nominal value. This solution moreover allows the processing of chip devices having widths spanning over a range. 
         [0023]      FIG. 1  also partially shows a detail of the chip device feeder  20 . The feeder comprises three retractable pins  22   a - 22   c,  leaving room for a single chip device  10  between two consecutive pins. These pins form part of a device separator, described in more detail below, allowing to take one chip device at a time from the pile of chip devices stored in area  12 . 
         [0024]    The separation mechanism preferably operates with the aid of gravity, i.e. the apparatus is tilted so that the pinching device  14  lies below area  12 . The chip devices in area  12  then pile up naturally against the pins  22   a - 22   c,  and will tend to fall naturally as the pins are retracted. To aid the gravity effect, especially if the chip devices are very small (smaller than one millimeter), vibration may be applied to the apparatus. 
         [0025]    Instead of using vibration, the chips may also be transported by aid of an air cushion in combination with either gravity or a pushing mechanism. 
         [0026]    Furthermore, the chips may be transported by mechanical means, e.g. pushing rods. 
         [0027]    Instead of using a chip device feeder  20  in combination with a separation mechanism, the chips may be fed directly to the pinching device  14  by means of a conventional pick-and-place machine used to place surface-mount devices on printed circuit boards. 
         [0028]      FIGS. 2A-2F  schematically show a side view of the chip device feeder  20 , in several steps of processing chip devices. The apparatus is shown horizontally, although, as mentioned above, it is rather tilted so that the right portion, comprising the storage area  12 , is raised above the left portion. 
         [0029]    The elements of the apparatus are assembled around a base plate  24 . Roller  14   b  is shown only on FIG.  2 A—in  FIGS. 2B-2F  the rollers are represented by their axes. The chip devices  10  slide over plate  24 , preferably in a guiding groove. Only the bottom of the guiding groove is visible, the side walls of the groove not being shown for sake of clarity. The side walls of the guiding groove are interrupted in the area of rollers  14   a  and  14   b,  where the wires enter laterally (wire  8   b  is shown partially). The grooves of the shown chip devices are visible. The storage area  12  is partially covered by a plate  26  that prevents the stored chip devices  10  from exiting the groove due to vibrations generated by the apparatus. A hook  28  is arranged to alternately take a new chip device from the pile  12  and push it through the rollers  14   a,    14   b,  as explained below. 
         [0030]    In  FIG. 2A , pin  22   a  is retracted and pins  22   b  and  22   b  are up. A pile of chip devices  10  rests against pin  22   b  by gravity, covering retracted pin  22   a.  A single chip device  10 - 1  rests against pin  22   c.  As a chip device  10 - 2  leaves the rollers  14   a,    14   b  with wire  8   b  inserted in its groove, hook  28  arrives from between the rollers, first rising clear of chip device  10 - 1 , then descending behind it, in the gap left between chip device  10 - 1  and the remaining chip devices retained by pin  22   b.    
         [0031]    In  FIG. 2B , pin  22   b  is retracted and pin  22   a  is raised. The chip device  10  that happened to be over pin  22   a  is lifted against plate  26 . However, pin  22   a,  in its raised position, does not protrude more than the clearance between the chip devices and plate  26 , thus the chip device  10  over pin  22   a  can still slide. 
         [0032]    In  FIG. 2C , the two first chip devices that lied against pin  22   b  now slide over retracted pin  22   b  to come to rest against hook  28 . The remaining chip devices in area  12  are held back by pin  22   a.    
         [0033]    In  FIG. 2D , pin  22   c  is retracted and pin  22   b  is raised. The chip device  10 - 3  that happened to lie over pin  22   b  is lifted, but it can still slide. 
         [0034]    In  FIG. 2E , pin  22   a  is retracted and hook  28  starts moving towards the left, accompanying chip device  10 - 1  over retracted pin  22   c  towards the rollers. Chip  10 - 3  slides over pin  22   b  and follows the hook by gravity. The chip device  10 - 4  that was behind chip device  10 - 3  stops against pin  22   b.    
         [0035]    In fact, as soon as pin  22   c  is retracted in  FIG. 2D , chip device  10 - 1  is likely to start slipping leftwards by gravity. In the first portion of the travel of chip device  10 - 1  towards the rollers, hook  28  may have no active role. 
         [0036]    In  FIG. 2F , pin  22   c  is raised as hook  28  travels over it. Chip device  10 - 3  thus stops against pin  22   c.  Hook  28  is shown in its final position where it places chip device  10 - 1  between the rollers, where the wires are clipped into the chip device&#39;s grooves, and the chip device travels further with the wires. In the meantime, further chip devices contained in storage area  12  slide over pin  22   a  and come to rest against chip device  10 - 4 . 
         [0037]    In this final phase, hook  28  exerts on chip device  10 - 1  sufficient pressure to start inserting the wires into the chip device&#39;s grooves. Gravity alone may not be sufficient for this purpose. 
         [0038]    The cycle then starts over as in  FIG. 2A . The pitch of the chip devices in the final string is defined by the wire travel speed and the cycle time of hook  28 . 
         [0039]      FIG. 3  shows a general perspective view of a detailed embodiment of the apparatus. Same elements as in the previous figures are designated by same reference numerals. 
         [0040]    Wires  8   a  and  8   b  are fed from respective reels  30   a  and  30   b.  The wires are led to their respective auxiliary rollers through funnel shaped elements  32   a,    32   b,  which ensure that the wires arrive to rollers  18   a,    18   b  at a substantially constant position, regardless of the widely varying exit positions from reels  30   a,    30   b.    
         [0041]    Hook  28  has a first axis  28 - 1  by which a back and forth movement is transferred to the hook, and a second axis  28 - 2  arranged to follow a cam (not shown) that defines the up and down movements of the hook as it travels back and forth. 
         [0042]    In order to ensure a spring bias of roller  14   b  towards roller  14   a,  plate  24  comprises a split starting near roller  14   b  and extending along the chip device guiding groove towards the exit area of the apparatus. This split defines a splinter-like element  24 - 1 , having a far end, away from roller  14   b,  integral with plate  24 , and a free end, near roller  14   b,  cut away from the rest of plate  24 . Roller  14   b  is mounted on this free end. Thus the width and length of element  24 - 1  define the spring bias force. 
         [0043]      FIG. 3  further shows a hopper  34  containing chip device refills for the storage groove  12 . Hopper  34  comprises a series of parallel grooves, each containing a pile of chip devices having the desired orientation for assembly on wires  8   a  and  8   b.  The hopper  34  is initially attached to base plate  24  such that its first groove is in key with the storage groove  12 . As soon as the first groove of the hopper is empty, the hopper is shifted by one step, putting its next groove in key with groove  12 , and so on until the hopper is empty. 
         [0044]    Each hopper  34  may be pre-filled by a conventional pick-and-place machine used to place surface-mount devices on printed circuit boards. 
         [0045]      FIG. 4  shows an enlarged detail of  FIG. 3 , in the area of rollers  14   a,    14   b,  better revealing some shapes that were too small in  FIG. 3 . As is visible in this figure, the side walls of the groove in which the chip devices travel are interrupted only in close proximity to the rollers. This ensures that the chip devices are maintained laterally, and don&#39;t skew, all along the assembly process. 
         [0046]    The wires are guided in grooves just before they are fed to the rollers. These grooves ensure that the wires arrive on the rollers at the height corresponding to the lateral grooves in the chip devices. 
         [0047]    Although an assembly of chip devices between two wires has been described as a preferred embodiment, the teachings of the present disclosure apply similarly to the assembly of chip devices on a single wire. In such a case, the apparatus can simply be used with a single wire. One of rollers  18   a,    18   b  and one of rollers  14   a,    14   b  may be omitted.