Abstract:
A method and apparatus of separating integrated circuit (IC) devices according to magnetic properties of the devices is disclosed. A plurality of IC devices are subjected to a magnetic field. The IC devices containing only nonferrous material are not responsive to the magnetic field and are thus gathered to a first collection site. The IC devices containing ferrous material adhere to a moving surface proximate the magnetic field and are transported to a second collection site. The sorted devices are then transported to separate locations for further processing. The apparatus used for separating the IC devices may include a conveyor having a magnetic drum and an antistatic belt which travels about the magnetic drum. The conveyor allows nonferrous IC devices to fall off the edge of the magnetic drum into the first collection site while transporting the ferrous IC devices to another location for collection.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the sorting and classification of integrated circuit (IC) devices. More specifically, the present invention relates to the use of magnetism to separate and sort IC devices based upon the material content of the IC devices. 
     2. State of the Art 
     In the art of manufacturing IC devices (also known as semiconductor devices), inspection for quality is routine and often rigorous. Inspection of IC devices may include various techniques known in the art such as subjecting the devices to emission microscopy or X-ray analysis, connecting the IC devices to test circuits cycling the devices at temperature extremes and excessive power inputs and other methods well-known in the art. Such tests are employed to verify an IC device&#39;s functionality as well as its structural integrity. The process of inspecting IC devices is integral to any company&#39;s goal of efficiently producing devices that are stable, reliable and of sufficient longevity. Such tests are typically tailored to verify that a particular type of IC device will function properly in its intended capacity. In other words, testing standards are set for a specific IC device design, or lot of such devices, depending on an expectation of ultimate use. For example, memory chips designed for use in a typical home (personal) computer are inspected and tested to confirm operability and reliability for that particular purpose. IC devices of a different nature are tested to a different standard. 
     While the electronics industry has made great strides in producing high quality IC devices, defects are not uncommon. Because IC devices are produced in extremely high volumes, even the smallest defect occurrence rate will result in numerous IC devices being determined to be unsuitable for their intended use. As a result, IC devices are rejected and normally discarded. However, while an IC device may have been discarded based on a certain set of quality standards, the IC device may still have operational characteristics suitable for use in another application. 
     Discarded IC devices may be salvaged and retested using a second set of quality standards. The retesting is performed to determine suitability for a use independent of that for which the IC device was originally produced. Often, an IC device which fails a quality test for a specific use in terms of, for example, memory capacity or operation speed will satisfy the quality standards set forth for another defined use. For example, an IC device designed for use in a personal computer may fail to meet the quality standards set for such a use while still meeting the standards required for use in a household appliance. Thus, the IC device is not entirely unusable. Rather, it is simply redesignated as to the end use of the device. Redesignation of IC devices based on satisfaction of independent quality standards allows for greater efficiency of production. While the overall number or percentage of IC devices having defects as defined for a specified use is not reduced, the economic loss concerning those defects may be substantially ameliorated upon a proper redesignation or reclassification for a different use. 
     Prior to any retesting procedures, it may be necessary to properly sort rejected IC devices, as such rejected IC devices may be collected in massive quantities including a number of different types of IC devices with little or no effort made in classifying such devices at the time of testing and rejection. Therefore, a segregating and sorting operation is required. Such an operation is conventionally done by hand, sorting according to predefined criteria. For example, one sort operation may be directed to dividing out devices which are classifiable as “flip chips” from those which are not. Likewise, devices having certain types of lead frames may be separated from other in the lot. Regardless of the base criteria defined for preliminary sorting operations, the sorting is usually done by hand. Sorting by hand requires some training of the individuals performing the sort and tends to be rather inefficient, tedious and time consuming. 
     In a typical scenario, a fifty-five gallon drum or other large container of rejected IC devices is delivered for sorting and retesting. Perhaps fifty percent, or less, of the devices are of a desired preliminary classification suitable for potential testing and use. One or more individuals will laboriously sift through the entire lot, visually inspect each of the IC devices and determine whether they satisfy a preliminary sort criteria. Sorting by hand is, therefore, a rather time intensive task and is susceptible to human error. 
     In view of the shortcomings in the state of the art of sorting large quantities of such IC devices, providing an apparatus and method for an automated preliminary sorting of large quantities of IC devices would be advantageous based on a defined device characteristic. Such an apparatus or method should, among other things, be easy to implement, reduce the test time as well as the required amount of human effort, be accurate, and increase the overall efficiency of the retesting process. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a method is provided for sorting a plurality of IC devices, such as memory chips or other packaged semiconductor devices. Based on a preliminary sorting criteria of lead frame metallurgical characteristics, the method includes subjecting the plurality of IC devices to a magnetic field. Ferrous metal containing IC devices, such as those manufactured with a ferrous alloy lead frame, are attracted by the magnetic field, while nonferrous IC devices do not respond to the pressure of the magnetic field. The nonferrous IC devices may thus be isolated for removal and gathered or binned to a first collection category. The remaining IC devices responsive to the magnetic field are ferrous alloy containing IC devices which may then be gathered or binned to a second collection category. 
     The inventive method may include transporting the IC devices through the magnetic field by means of a conveyor. While various sources are contemplated for providing the magnetic field, the method preferably includes providing a conveyor with an end pulley, or roller, having permanent magnets installed on an interior surface of a stainless steel shell. The magnetic field may advantageously be assisted by gravity in sorting ferrous and nonferrous IC devices. For example, the conveyor may be configured and oriented to carry the IC devices through a magnetic field subjecting the IC devices to be sorted to both a magnetic field as well as a conflicting gravitational field contemporaneously. The nonferrous IC devices thus respond to the gravitational field but not the magnetic field to facilitate collecting them in a common location, while the ferrous IC devices are carried to another collection location. 
     In accordance with another aspect of the invention, an apparatus for sorting IC devices based on ferrous metal content is provided. The apparatus includes a roller having a stainless steel shell and housing a plurality of permanent magnets. A circuitous belt partially circumscribes the roller and is adapted to convey a plurality of IC devices to an area proximate the roller&#39;s surface. The belt is preferably formed or coated with an antistatic (ESD) material so as to not damage the IC devices or further impair their operation and performance. The apparatus may include a grounding mechanism to assist in preventing electrostatic discharge between the belt and the devices. 
     Various additional features may be incorporated into the apparatus such as a feeding mechanism for distributing the IC devices onto the conveyor at a predetermined rate. Other features might include, for example, individual collection bins, guides for maintaining the chips on the conveyor when not in a sorting zone, tensioning and tracking devices for proper operation and maintenance of the belt, secondary conveyors for transporting the sorted IC devices to other sites remote from the conveyor sites for additional processing, additional magnetic zones, or specific magnetic pole arrangements within the magnetic drum. 
    
    
     DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
     FIG. 1 is an elevational view of one exemplary apparatus according to an embodiment of the present invention; 
     FIG. 2 is a plan view of the apparatus depicted in FIG. 1; 
     FIG. 3A is a schematic of one embodiment of a magnetized drum according to the present invention; 
     FIG. 3B is a schematic of another embodiment of a magnetized drum according to the present invention; 
     FIG. 4 is an elevational view of an exemplary apparatus according to another embodiment of the present invention; 
     FIG. 5 is a plan view of the apparatus depicted in FIG. 4; and 
     FIG. 6 is an elevational view from one end of another embodiment of an apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, a magnetic separating conveyor  10  is shown. The conveyor includes a first roller or end pulley  12  and a second roller or end pulley  14 . Each roller  12  and  14  is mounted to a shaft  16  and  18  respectively, the shafts  16  and  18  each being supported by a bearing assembly  20  not in FIG.  1 . Each shaft  16  and  18 , and thus each roller  12  and  14  is respectively rotatable about an axis  22  and  24 . The shafts  16  and  18  may be formed as solid continuous shafts traversing through the width of the rollers, or they may be formed as stub shafts axially aligned at each end of the roller and secured to an external side surface thereof 
     A continuous transport belt  26  is positioned such that it partially circumscribes each roller or end pulley  12  and  14  and extends longitudinally between end pulley  12  and  14 . The transport belt  26  travels in a generally circuitous path as indicated by directional arrows  28 . Adjacent the first roller  12  is a feeding hopper  30  for distributing a plurality of IC devices  32  onto the transport belt  26  of the conveyor  10 . The feeding hopper  30  may include various devices or features, such as, for example, a vibratory mechanism (not shown) to assist in settling the IC devices  32  out of the feeding hopper  30  in a random spreading pattern. The feeding hopper  30  may utilize other mechanisms for motivating the IC devices  32  from feeding hopper  30  to the transport belt  26  of the conveyor  10 , such as a pneumatic feed, a paddle-type feed, or a screw feed. The feeding hopper  30  is preferably adjustable with regard to the rate at which the IC devices  32  are transferred thereby to the transport belt  26  of the conveyor  10  and photocell, proximity or other sensors adjacent the top surface of continuous transport belt  26  may be employed to detect the presence or absence of IC devices thereon to initiate or cease feeding. 
     It is noted that a frame or other foundation structure is required for mounting and fixing the location of the various components of apparatus  10  described herein. However, for sake of clarity and understanding no such frame is depicted in the drawings, and such a structure for providing adequate support is considered to be within the ability of one of ordinary skill in the art. Likewise, the bearing assembly  20  and an exemplary drive discussed further below are only shown in FIG. 2 for similar reasons. 
     A belt drive in the form of an electric motor  34  is engaged with the shaft  18  of the second roller  14  via a drive belt  36 , which may comprise, for example, a toothed or cogged belt to cooperatively engage the drive shaft of motor  34  and shaft  18  provided with mating teething. The electric motor  34  drives the shaft  18  of the roller  14  causing the roller to rotate in a counterclockwise direction as viewed in FIG.  1 . Proper tension in the transport belt  26  results in friction between the transport belt  26  and the second roller  14 . Rotation of the second roller  14  causes the continuous belt  26  to move in the direction as indicated by arrows  28  carrying with it the IC devices  32  placed on the transport belt  26  by the feeding hopper  30 . 
     The second roller  14  is fabricated with a cylindrical stainless steel shell  15  containing a plurality of permanent magnets  17  in the interior thereof. The magnets  17  are arranged within the shell  15  to create a predetermined magnetic field through which the IC devices  32  on transport belt  26  will pass. The second roller  14  may thus also be referred to as the magnetic roller  14 , or the magnetic drum  14 . FIG. 3A depicts one arrangement of the magnetic poles within the magnetic drum  14  according to one embodiment of the present invention. As shown in FIG. 3A, the magnetic poles are arranged across the face of the magnetic drum  14 , as well as around the circumference of the magnetic drum  14 , in an alternating pattern of north (N) poles and south (S) poles. This arrangement promotes the development of numerous magnetic flux lines above the exterior surface  19  (FIG. 1) of magnetic drum  14 . The resulting magnetic field is efficient in attracting all ferrous metal-containing objects which come within proximity of the surface of the magnetic drum  14  as transport belt  26  passes thereover. 
     FIG. 3B shows an alternative arrangement for the magnetic poles within the magnetic drum  14 . In the embodiment depicted in FIG. 3B, poles of like orientation are arranged in pairs. Thus, two North (N) poles are positioned adjacent to each other and likewise two South (S) poles are positioned adjacent each other. The pole pairs (N-N or S-S) are then arranged in an alternating pattern across the face of the drum while different single poles alternate (N-S-N-S) around the circumference of the magnetic drum  14 . Alternatively, the like oriented pole pairs could be positioned to alternate around the circumference of the drum. Additionally, it is contemplated that all N-poles (or all S-poles) could be outwardly facing. These arrangements may likewise be sufficient in magnetically attracting ferrous objects to the drum as is required by the process described below. 
     It is noted that the magnetic field produced by the magnetic drum  14  is comprised of multiple magnetic flux lines which penetrate the overlying drum shell  15  as well as the thickness of transport belt  26 . The properties of the transport belt  26  become an important consideration in the design of the conveyor  10 . The transport belt  26  should not substantially interfere with the magnetic flux lines produced by the magnetic drum  14 . At the same time, the transport belt  26  must satisfy certain tensile strength requirements and preferably be constructed from antistatic material, as it is important that the transport belt  26  be able to carry the IC devices  32  without significant concern of electrostatic discharge. As noted previously, electrostatic discharge may impair the subsequent operation and performance of the IC device  32 . The transport belt  26  may be constructed of stainless steel to perform as required. To assist with the prevention of electrostatic discharge, the belt may be thinly coated with an antistatic material such as, for example, polyester, PVC silicon, or polyethylene. Alternatively a grounding mechanism may be incorporated into the conveyor  10 . 
     Returning to FIGS. 1 and 2, after the IC devices  32  are dispensed, such as from the hopper  30  to the transport belt  26 , the transport belt  26  carries the IC devices  32  until they reach the magnetic drum  14 . As the transport belt  26  travels around the magnetic drum  14 , the IC devices  32  are subject to a sorting process. Among the plurality of IC devices  32  placed on the transport belt  26 , some are manufactured with lead frames which contain a ferrous material such as, for example, alloy  42  (ASTM F30). Other IC devices  32  include lead frames made from nonferrous material such as, for example, copper, aluminum or alloys thereof. The ferrous alloy containing IC devices  32   a  respond to the magnetic field created by the magnetic drum  14  by adhering to the surface of transport belt  26  as the transport belt  26  rotates from the upper side of the conveyor  10  to the underside of the conveyor  10 . The ferrous IC devices  32   a  are carried along the underside of the conveyor  10  away from the magnetic field of the drum  14  until the force of gravity is stronger than the magnetic field-induced force between the IC device  32   a  and magnetic drum  14 . When this occurs, each ferrous IC device  32   a  drops from the transport belt  26  and is collected in a first collection bin  40 . 
     The nonferrous IC devices  32   b  are not responsive to the magnetic field imposed by the magnetic drum  14 . Thus, as the nonferrous IC devices  32   b  rotate on transport belt  26  around the magnetic drum  14  from the upper side of the conveyor  10 , gravity causes them to fall off of the transport belt  26  into a second collection bin  44 . A barrier  46  or a divider is positioned between the first collection bin  40  and second collection bin  44  to help isolate the two collecting sites from one another and guide the IC devices  32   a  and  32   b  to their respective collection bins  40  and  44 . The apparatus embodiment depicted in FIGS. 1 and 2 further includes secondary conveying systems  48  and  50 , which is illustrated as belt-type conveyors oriented transverse to the drawing sheet. The secondary conveying systems  48  and  50  may be used to transport the sorted IC devices  42  and  38 , respectively, for further processing which may include additional sorting and testing. 
     Referring to FIGS. 4 and 5, an alternative embodiment of a magnetic separating conveyor  10 ′ is shown. The magnetic separating conveyor  10 ′ is similar to that previously described, including rollers  14 ′ and  16  and a transport belt  26 . It is noted that the second roller  14 ′ need not include a plurality of magnets therein, and may, therefore, need not be constructed of stainless steel. Rather, a magnetic field is provided by placing one or more permanent magnets  17 ′ beneath the transport belt  26  between the first and second rollers  14 ′ and  16 . A header  60  located to one side of the transport belt  26  may supply pressurized air to a plurality of jet nozzles  62  such that pressurized air sweeps across the upper surface of the transport belt  26  as IC devices  32  pass thereby. The magnet or magnets  17 ′ create a magnetic field to attract the ferrous IC devices  32   a  while the nonferrous IC devices  32   b  are blown off the side of the transport belt  26  by the force of the air created by the jet nozzles  62 . In this case the nonferrous IC devices are collected in the first collection bin  40 ′ while ferrous IC devices continue with the transport belt until the rotate around the second roller  14 ′ and drop into the second collection bin  44 . 
     FIG. 6 shows an end view of another embodiment of the magnetic separating conveyor  10 ″ wherein an least one of the rollers, in this case the second roller  14 ′, is set an angle β relative to the horizontal plane H. It is noted that the second roller  14 ′ is similar to that used in the embodiment of FIGS. 4 and 5 and thus does not require a plurality of magnets to be placed therein. 
     One or more magnets are located beneath the transport belt  26  along its upper path similar to the embodiment shown in FIG. 4. A vibrating mechanism  70  may likewise be utilized to cause the transport belt to vibrate along its upper path. In operation, the ferrous IC devices  32   a  will be attracted to the magnetic field and remain on the transport belt  26  while the vibrating mechanism  70  will urge any nonferrous IC devices  32   b  to slide down the inclined portion of the transport belt  26  and into a first collection bin  40 ′. The ferrous containing devices  32   a  will continue with the transport belt and rotate off the second roller  14 ′ and drop into a second collection bin  44 . 
     It is noted that the magnetic separating conveyor  10 ″ may configure both rollers  12  and  14 ′ at an angle β from the horizontal plane H, or alternatively keep one roller  12  or  14 ′ parallel with the horizontal plane H while the other is placed at an angle β. In the case where only one roller  12  or  14 ′ is placed at an angle β the transport belt  26  will have a slight twist in it as it travels from the first roller  12  to the second roller  14 ′. 
     The above-described apparatus thus presents a process for sorting IC devices according to their ferrous properties. While individual portions of the process have been discussed in conjunction with corresponding features of the apparatus and system, the process is summarized below for enhanced clarity and understanding. While the process is not to be limited to performance with the above described apparatus, it is summarized with reference to the above disclosed embodiment of the apparatus, and particularly with respect to the embodiment shown in FIGS. 1 and 2. 
     The process may begin by placing a plurality of IC devices  32  in the feeding hopper  30 . The IC devices  32  typically include packaged IC devices which have failed a particular regimen of testing but which still have value which may be realized through redesignation of use. The feeding hopper  30  distributes the IC devices  32  onto the transport belt  26  at a rate, which may be predefined or responsive to feedback from sensors placed adjacent the top surface of transport belt  26 , as previously noted. The transport belt  26  conveys the IC devices  32  into a magnetic field which, in the above described embodiment, is provided by a rotating magnetic drum  14  about which the transport belt  26  travels. The magnetic field serves to sort ferrous IC devices  32   a  from nonferrous IC devices  32   b . The nonferrous IC devices  32   b  do not respond to the magnetic field above the surface of the magnetic drum  14  and fall under the force of gravity after passing over magnetic drum  14  to a location wherein they are no longer held by friction against transport belt  26  to be gathered to a collection site such as collection bin  44 . Ferrous IC devices  32   a  adhere to the transport belt  26  by virtue of the magnetic field above the magnetic drum  14  and are thus transported by the transport belt  26  until they are beyond the range of the magnetic field as the transport belt  26  moves away from magnetic drum  14 . Once beyond the magnetic field, the ferrous IC devices  32   a  fall under gravity to be gathered to another collection site such as collection bin  40 . The ferrous IC devices  32   a  and the nonferrous devices  32   b  may then be transported for additional processing according to desired use of each class of device. The process is efficient in sorting IC devices based on the ferrous content or lack of same of each IC device while not damaging or impairing subsequent performance of the individual IC devices  32 . 
     While the invention is susceptible to various modifications and alternative implementations, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims. 
     For example, guide rails  72  (FIGS. 1 and 2) or a chute may be installed along the sides of transport belt  26  to maintain the IC devices  32  on the transport belt  26 . Such guide elements are preferably formed of stainless steel to minimize the effect of these components on the magnetic field. Additionally, the magnetic field may be extended to be present rotationally after the magnetic drum  14  to assist in the separating process and for further convenience in separating the collection bins  40  and  44 . Belt tensioning and tracking devices may be added for proper maintenance and operation of the belt  26 . Variable speed drives may be implemented for belt speed rate control. Such devices provide greater operational control and help to prevent undue wear to the belt and system. 
     It is also noted that numerous belt drives are compatible with the above described conveyor  10 . The conveyor  10  may be driven by chain, gear, or direct drive from electric motor  34 . Similarly, the belt drive may be powered by hydraulics rather than electric motor  34 . Also, the belt drive may be coupled to a roller other than a magnetic drum including, if desired, an independent drive roller. 
     It is further noted that the method of sorting IC devices according to magnetic properties may be conducted using other systems or apparatus and is not limited to sorting with a magnetic separating conveyor.