Abstract:
Apparatus and methods are provided for handling packaged integrated circuits (IC&#39;s), particularly for inserting packaged IC&#39;s in and removing packaged IC&#39;s from low-insertion-force (LIF) sockets. The apparatus includes a precisor having a chip precisor feature for receiving an IC package and a socket precisor feature for receiving a socket in a predetermined alignment relative to the chip precisor feature. One or more releasable chip retainers are provided, such as a vacuum nozzle for pulling the packaged IC into a seated position within the chip precisor feature and a pair of gripper fingers for holding the packaged IC within the chip precisor feature during extraction from a LIF socket. A method of inserting a packaged IC into a socket comprises centering a precisor relative to an expected location of a packaged integrated circuit, moving the precisor to a predetermined height relative to the expected location, applying vacuum to a nozzle so that a packaged IC is pulled into a chip precising feature of the precisor, centering the precisor relative to a socket, and moving the precisor into a seated position on the socket in which the packaged IC is aligned with and inserted into the socket. A method of removing a packaged IC from a socket comprises positioning a precisor relative to a socket containing a packaged IC, moving the precisor into a seated position on the socket in which the packaged IC is seated in a chip precising feature of the precisor, closing a gripper to retain the packaged IC within the chip precising feature, and moving the precisor away from the seated position while retaining the packaged IC within the chip precising feature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to methods and apparatus for handling of packaged integrated circuits. 
     2. The Prior Art 
     Production of integrated circuit (IC) chips involves considerable handling, particularly of packaged IC&#39;s during the burn-in and test phases. Efficient production requires fully automatic transfer of IC&#39;s, for example, from carrying-tray bins to burn-in-board sockets and, after burn-in, back to carrying-tray bins. Transfer must be fast, avoid damage to the IC&#39;s and the sockets, assure correct placement of the IC&#39;s in the sockets so that device functionality can be checked, and permit sorting of the IC&#39;s based on results of the burn-in operation. 
     An example of a system for loading and unloading IC&#39;s on burn-in boards is the BLU300 Burn-In Board Loader/Unloader, commercially available from Schlumberger ATE Automated Systems, Westerville, Ohio, USA. Such a system can be adapted for use with bum-in boards of various sizes, can be fitted with component tooling to handle IC&#39;s having various package types, and can be programmed for automated operation in various modes. 
     Burn-in boards (BIB&#39;s) used in such a system typically have an array of sockets, each of which receives a single packaged IC. FIGS. 1A,  1 B and  1 C show one type of commercially-available “Zero Insertion Force” (ZIF) socket  100  used on BIB&#39;s, in respective top, side elevation and end views. FIGS. 2A,  2 B and  2 C show a type of IC package  200  intended to be inserted in such a socket, in respective top, side elevation and end views. ZIF socket  100  has a body  105  opposed rows of spring contacts  110  and  115 , a cover  120 , and rows of connector pins  125  and  130 . Cover  120  is resiliently biased upwardly as shown. When cover  120  is pressed downwardly, spring contacts  110  and  115  are retracted so that an IC package  200  can be dropped into the well area of socket  100  without resistance. When IC package  200  is in place and cover  120  is allowed to return to its upward position, spring contacts  110  and  115  extend toward the center of socket  100  to make electrical contact with respective rows  205  and  210  of pins of IC package  200 . 
     While generally effective, the use of such ZIF sockets has drawbacks. The cost of the sockets is higher than for “Low Insertion Force” (LIF) sockets of the type described below with reference to FIGS. 3A-3C. The BIB area required for ZIF sockets is greater than that for LIF sockets, primarily because of the area required for the cover surrounding the well area of the ZIF socket, such as cover  120 . Thus, fewer IC&#39;s can be loaded on each BIB with ZIF sockets than might be possible with LIF sockets. The tooling required to load IC&#39;s into ZIF sockets is complicated by the need for an actuator to depress the cover before an IC can be inserted or removed and to release the cover after an IC is dropped into or picked out of the socket. The need to move the cover down and then up again adds to the time needed each time an IC is inserted in or removed from the ZIF socket. When the IC is dropped into the ZIF socket, gravity and chamfered walls in the upper portion of the chip well are all that can guide the IC into correct position. If the IC is not sufficiently aligned with the well before being dropped in, it may not seat properly and may have to be removed for another try. Because there is little or no sliding contact between the ZIF socket&#39;s spring contacts and the IC&#39;s pins, surface corrosion and impurities which may interfere with electrical conductivity are not displaced during the insertion process. 
     FIGS. 3A,  3 B and  3 C are sectional views showing one type of commercially-available “Low Insertion Force” (LIF) socket  300 . FIGS. 3A and 3B are a sectional views taken along centerline  3 A/ 3 B— 3 A/ 3 B of FIG.  3 C. FIG. 3C is a sectional view taken along centerline  3 C— 3 C in FIGS. 3A and 3B. Socket  300  has a socket body  305  with a well  310  for receiving an IC, horizontally-opposed rows of contact springs  315  and  320 , and horizontally-opposed rows of connector pins  325  and  330 . Precise alignment of an IC package in the horizontal (x- and y-directions) is required before the package can be inserted vertically (in the z-direction) into well  310  and into contact with contact springs  315  and  320 . 
     The left side of each of FIGS. 3A and 3C shows in phantom lines at  335  a packaged IC in a first position just prior to insertion in socket  300 . The IC package is mis-aligned to the left by an amount  340  which would cause the end pin of the package to hit the end wall  345  of socket body  305  and thus to prevent further insertion into well  310 . The right side of each of FIGS. 3A and 3C shows in phantom lines at  350  a packaged IC in a second position just as contact is being made between contact springs  320  of the socket and pins  355  of the IC package. In the second position, the IC package is mis-aligned to the right by an amount  360  which would cause the end  365  of the IC package to hit the end wall of socket body  305  and thus to prevent further insertion into well  310 . 
     The left side of FIG. 3B shows in phantom lines at  370  a packaged IC in a third position just prior to insertion in socket  300 . The IC package is mis-aligned to the left by a maximum amount  375  which would still permit insertion into well  310  of a socket without locator pins. The right side of FIG. 3B shows in phantom lines at  380  a packaged IC in a fourth position just prior to insertion in socket  300 . The IC package is mis-aligned to the left by a maximum amount  385  which would still permit insertion into well  310  of a socket having locator pins. 
     Precise alignment of the IC package with the socket is difficult to achieve in a high-speed, automated, production environment. BIB&#39;s can be slightly misaligned in the burn-in board loader/unloader due to manufacturing tolerances and wear. Positioning of sockets on the BIB&#39;s can vary within some tolerance. The automated handler which positions the IC package over the socket can have some small positioning error from operation to operation due to manufacturing tolerances and wear. LIF sockets are in general less forgiving of mis-alignments than are ZIF sockets. 
     Beside the requirement to precisely align the IC package with the LIF socket, insertion of the IC package into well  310  requires a force which will cause pins of the IC package to deflect contact springs  315  and  320  outwardly. Removal of the IC package from the LIF socket also requires a force. The amount of force depends upon the particular design of the IC package and the socket, but is significant enough that it does not allow use of the package-handler tooling designed for dropping packaged IC&#39;s into and vacuuming packaged IC&#39;s out of ZIF sockets. To use LIF sockets in an automated setting such as on burn-in boards, tooling is required which will apply the needed insertion and removal forces, but without damage to the IC or the socket even when the two are mis-aligned. Bent IC pins, broken sockets and the like are not acceptable. 
     A new type of handler is needed to allow use of LIF sockets in such applications. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the invention offer apparatus and methods for handling packaged integrated circuits (IC&#39;s), particularly for inserting packaged IC&#39;s in and removing packaged IC&#39;s from low-insertion-force (LIF) sockets. The apparatus preferably includes a precisor having a chip precisor feature for receiving an IC package and a socket precisor feature for receiving a socket in a predetermined alignment relative to the chip precisor feature. One or more releasable chip retainers is provided, such as a vacuum nozzle for pulling the packaged IC into a seated position within the chip precisor feature and a pair of gripper fingers for holding the packaged IC within the chip precisor feature during extraction from a LIF socket. A method of inserting a packaged IC into a socket comprises centering a precisor relative to an expected location of a packaged integrated circuit, moving the precisor to a predetermined height relative to the expected location, applying vacuum to a nozzle so that a packaged IC to be pulled into a chip precising feature of the precisor, centering the precisor relative to a socket, and moving the precisor into a seated position on the socket in which the packaged IC is aligned with and inserted into the socket. A method of removing a packaged IC from a socket comprises positioning a precisor relative to a socket containing a packaged IC, moving the precisor into a seated position on the socket in which the packaged IC is seated in a chip precising feature of the precisor, closing a gripper to retain the packaged IC within the chip precising feature, and moving the precisor away from the seated position while retaining the packaged IC within the chip precising feature. 
    
    
     These and other features of the invention will become apparent to those of skill in the art from the following description and the accompanying drawing figures. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIGS. 1A,  1 B and  1 C show respective top, side elevation, and end views of a prior-art “Zero Insertion Force” (ZIF) socket; 
     FIGS. 2A,  2 B and  2 C show respective top, side elevation, and end views of a prior-art IC package intended to be inserted in a socket of the type shown in FIGS. 1A-1C; 
     FIG. 3A is a sectional view taken along line  3 A/ 3 B— 3 A/ 3 B of FIG. 3C showing a prior-art “Low Insertion Force” (LIF) socket with an IC package in two possible misaligned states; 
     FIG. 3B is a sectional view taken along line  3 A/ 3 B— 3 A/ 13 B of FIG. 3C showing a prior-art “Low Insertion Force” (LIF) socket with an IC package in two further states of possible mis-alignment; 
     FIG. 3C is a sectional view taken along lines  3 C— 3 C of FIGS. 3A and 3B showing a the LIF socket with an IC package in two further states of possible mis-alignment; 
     FIG. 4A shows in partially cut-away front elevation view an example of a packaged-IC handing apparatus in accordance with the invention; 
     FIG. 4B is a bottom view of the packaged-IC handler head of FIG. 4A; 
     FIG. 4C is a partially cut-away left side view of portions of the apparatus of FIG. 4A; 
     FIG. 4D is a top view of the portions of the apparatus shown in FIG. 4C; 
     FIG. 4E is a partial left side view of portions of the apparatus of FIG. 4A, with the head raised relative to a socket; 
     FIG. 4F is a partially cut-away front elevation view showing internal structure of a resilient mount in accordance with the invention; 
     FIG. 5A is a partially cut-away elevation view of a packaged-IC handling apparatus in accordance with the invention; 
     FIG. 5B is a partially cut-away right-side view of the apparatus of FIG. 5A; 
     FIG. 6A shows an enlarged elevation view of the portions of the handler head which engage a socket and an IC package; 
     FIG. 6B is an enlarged right side view of the arrangement of FIG. 6A; 
     FIG. 7 shows an enlarged right side view with gripper fingers open and with the handler head raised; 
     FIG. 8A is an enlarged, top view of a precisor block in accordance with the invention; 
     FIG. 8B is a sectional view taken along line  8 B— 8 B of FIG. 8A; 
     FIG. 8C is a sectional view taken along line  8 C— 8 C of FIG. 8A; 
     FIG. 9A is a detail view of a portion  9 A of FIG. 8B; 
     FIG. 9B is a detail view of a portion  9 B of FIG. 8B; 
     FIG. 10A shows a further elevation view of a handler head in accordance with the invention; 
     FIG. 10B is a left side view of the handler head of FIG. 10A; 
     FIG. 10C is a sectional view taken along lines  10 C— 10 C of FIG. 10B; 
     FIG. 10D is a top view of the arrangement of FIG. 10A; 
     FIG. 11A is an elevation view of a gripper finger in accordance with the invention; 
     FIGS. 11B,  11 C and  11 D are respectively top, bottom and side views of the gripper finger of FIG. 11A; 
     FIG. 12 is a schematic illustration of a possible use of handling apparatus in accordance with the invention; 
     FIG. 13A is a bottom view of a socket precisor portion of a two-piece precisor block in accordance with the invention; 
     FIG. 13B is a sectional view taken along line  13 B— 13 B of FIG. 13A; 
     FIG. 13C is a sectional view taken along line  13 C— 13 C of FIG. 13A; 
     FIGS. 14A,  14 B and  14 C are respective bottom, end and right-side views of a chip precisor insert of a two-piece precisor block in accordance with the invention; 
     FIG. 15A is a bottom view of an assembled two-piece precisor block in accordance with the invention; 
     FIG. 15B is a sectional view taken along line  15 B— 15 B of FIG. 15A; 
     FIG. 15C is a sectional view taken along line  15 C— 15 C of FIG. 15A; and 
     FIG. 15D is a top view of the two-piece precisor block of FIG.  15 A. 
    
    
     DETAILED DESCRIPTION 
     FIG. 4A shows in partially cut-away elevation view an example of a packaged-IC handing apparatus  400  in accordance with the invention. As is conventional in a BIB loader/unloader such as the Schlumberger model BLU300 (and as shown schematically in FIGS.  4 A and  4 C), an X-servo  402  and a Y-servo  404  are directed by a programmable controller  415  to position a head  420  in the X- and Y- directions relative to sockets of a BIB  425 , and a Z-servo  406  is directed by programmable controller  415  to move head  420  vertically (in the Z-direction). Fitted with a head  420  in accordance with the present invention, such a system can be used to insert a packaged IC  435  in or remove of packaged IC  435  from a socket  440 . In the embodiment shown, servos  402 ,  404  and  406  position a bracket  408  to which head  420  is attached by a theta-axis assembly  412  and a resilient mount  455 . The structure and operation of resilient mount  455  are described below. Theta-axis assembly  412  comprises a housing  430  supported by bracket  408  and in which a spindle assembly  462  is mounted for rotation in the theta direction (about the Z-axis). Spindle assembly  462  is rotated by a theta-axis servo  405  under control of programmable controller  415 . A drive belt  414  (visible in section in FIG. 4A) connects the shaft of servo  405  to a spindle  460  of spindle assembly  462 . A theta-axis encoder  410  reports the rotational position of spindle  460  to controller  415 . Programmable controller  415  is shown as a single box, but typically includes a variety of elements including as a programmable general-purpose processor with memory and input/output devices, pneumatic source and control elements, solenoids, switches, sensors and other well-known elements required to control the system in the manner described. 
     Head  420  includes a parallel gripper assembly  465  having gripper fingers  470 , a nozzle body  475 , and a precisor block  480 , the structure and operation of which are described below. Gripper fingers  470  are operated by control signals from controller  415  to gripper assembly  465 . A nozzle (not shown in FIG. 4A) passing through nozzle body  475  is connected by a line to a source of “puff” air pressure or to a vacuum source via fitting  485  as directed by controller  415 . A sensor communicating with controller  415  detects vacuum/pressure in the line. A gripper-detector assembly shown schematically at  490  indicates to controller  415  whether the gripper fingers are closed or not-closed. A “hit-detect” sensor shown schematically at  495  provides an indication to controller  415  when head  420  has bottomed out during downward movement so that a “stop” command can be sent to Z-servo  430 . FIG. 4B is a bottom view of head  420  in which nozzle body  475 , precisor block  480 , and portions of gripper assembly  465  can be seen. 
     FIG. 4C is a partially cut-away left side view of portions of the apparatus of FIG.  4 A. FIG. 4D is a top view of the portions shown in FIG.  4 C. “Hit detect” sensor  495 , visible in FIG. 4C, comprises a light source and detector for sensing the presence or absence of reflection from a reflector  498 . In the embodiment shown, resilient mount  455  comprises an upper housing  487 , a plate  496  having a threaded shank  494  which engages a threaded opening at the lower end of spindle  460 , a block  488  of rubber or other suitable material affixed to plate  496 , and an adapter plate  489  to which head  420  is affixed. Resilient mount  455  permits slight pivoting motion of head  420  away from the vertical when lateral force is applied to precisor  480 , but is stiff enough to quickly damp any pivoting motion of head  420  which may result from acceleration and deceleration of head  420  as it is moved in the X- and Y- directions by servos  402  and  404 . Other configurations of resilient mount  455  are possible, though the arrangement illustrated in FIG. 4C has been found effective to permit lateral movement at the lower end of the precisor of up to 0.025″ with hysteresis within 0.001″ when using stiff rubber composite bonded to plate  496 . FIG. 4F is a partially cut-away front elevation view showing in more detail internal structure of a resilient mount  455 . 
     As shown in FIGS. 4A and 4C, head  420  is in a bottomed-out position with precisor  480  positioned over an IC package. A nozzle (not shown in FIGS. 4A and 4C) within nozzle body  475  carries a rubber cup at its lower end which is in contact with the upper surface of the IC package. Referring to FIG. 4E, the nozzle  484  is resiliently biased downwardly by a spring or other suitable means (not shown) so that, when head  420  is raised from the IC package  486 , the nozzle  484  and cup  482  extend downwardly below the bottom portion of precisor  480 . Suction applied to nozzle  484  via fitting  485  causes nozzle  484  to retract upwardly against the spring force when cup  482  is in contact with the upper surface of an IC package. While this lifting force is in general not sufficient to pull an IC from a LIF socket, it is in general enough to pick an IC from a tray and to retain the IC on the cup during transport of the IC from a tray to a position above a socket on a BIB. 
     FIG. 5A is a partially cut-away elevation view of a packaged-IC handling apparatus in accordance with the invention, similar to FIG.  4 A. FIG. 5B is a partially cut-away right-side view of the apparatus of FIG.  5 A. Gripper fingers  470  are shown in the open position in FIG.  4 A and in the closed position in FIGS. 5A and 5B. With precisor  480  bottomed against an IC package as in FIGS. 5A-5B and with gripper fingers closed, the end portions of gripper fingers  470  engage the IC package so that upward movement of head  420  provides the force needed to extract the IC package from a LIF socket. Also visible in FIGS. 5A-5B are nozzle  484 , cup  482 , and a spring  478  which biases nozzle  484  and cup  482  downwardly. 
     FIG. 6A shows an enlarged elevation view of the portions of head  420  which engage socket  440  and an IC package  600 . FIG. 6B is an enlarged right side view of the arrangement of FIG.  6 A. Precisor  480  fits snugly over the outer walls of socket  440  and the upper portion of package  600 , while cup  482  passes through an opening in precisor  480  to engage the upper surface of package  600 . 
     FIG. 7 shows an enlarged right side view similar to the view of FIG. 6B except that gripper fingers  470  are open and head  420  is raised relative to socket  440 . Precisor  480  is disengaged from socket  440 . Nozzle  484  is extended and cup  482  is in contact with the upper surface of IC package  600 . 
     FIG. 8A is an enlarged, top view of precisor block  480 . FIG. 8B is a sectional view taken along line  8 B— 8 B of FIG.  8 A. FIG. 8C is a sectional view taken along line  8 C— 8 C of FIG. 8A. A central bore  805  is provided through which nozzle  484  extends. Bores  810  and  815  each receive a screw for affixing precisor block  480  to the lower  10  surface of nozzle body  475 . At each corner of precisor block  480  is a leg having chamfered inner surfaces: leg  820  has chamfered inner surfaces  840  and  845 , leg  825  has chamfered inner surfaces  850  and  855 , leg  830  has chamfered inner surfaces one of which is visible at  856 , and leg  835  similarly has chamfered inner surfaces. FIG. 9A shows a detail of the chamfered surface  855  of leg  825 . 
     Together, legs  820 ,  825 ,  830  and  835  serve as a socket precising feature to precise head  420  relative to a socket. When lowered over a socket, as shown for example in FIGS. 6A and 6B, the chamfered inner surfaces of precisor block  480  serve to apply a lateral force to deflect the lower end of head  420  so that precisor block  480  can seat itself on the socket as head  420  is lowered. Resilient mount  455  allows modest deflection of the lower end of head  420  as described above to produce reliable and precise positioning of precisor block  480  on the socket. The angle of chamfer  858  is a matter of design choice, dependent on dimensions of the particular IC package type to be handled, socket type to be used, socket positioning tolerances in the BIB and other such factors. In one design a chamfer angle of 20° proved effective. 
     Precisor block  480  also has a flat interior surface  860 , visible in FIGS. 8B,  8 C and  9 B, with mutually-parallel, opposed ridges  865  and  870  extending downwardly at its sides. 
     Ridges  865  and  870  have chamfered surfaces such as chamfered surface  875  of ridge  870  shown in FIG.  9 B. Surface  860  and ridges  865  and  870  serve as a chip precising feature to position an IC package accurately relative to precisor block  480 . That is, the dimensions of surface  860 , the spacing between ridges  865  and  870 , and the angle of the chamfered edges of ridges  865  and  870  are designed to engage the upper portion of the IC package to assure precise and repeatable positioning of the IC package relative to precisor block  480 . While the chamfer angle is a matter of design choice for each IC package, an angle of 25° was found effective for one type of memory package. The height of ridges  865  and  870  is determined so as not to interfere with or short out the connector pins of an IC package contained in the chip precising feature. To minimize the chance of shorting connector pins, all or critical portions of precisor block  480  may be coated with or fabricated in whole or in part of a suitable insulative material; an example is described below with reference to FIGS. 13A-13C,  14 A- 14 C and  15 A- 15 D. 
     Thus, precisor block  480  serves a dual precising function: (1) alignment of the IC package with the precisor block, and (2) alignment of the IC package with the socket. As head  420  is positioned over and lowered toward a packaged IC sitting upright in a tray, vacuum is applied to nozzle  484  via fitting  485 . As cup  482  contacts the upper central surface region of the IC package, the vacuum causes cup  482  to adhere to the IC package. As vacuum continues, the force of spring  478  is overcome, nozzle  484  retracts upwardly into nozzle body  475 , and the IC package is drawn into the well defined by surface  860  and ridges  865  and  870 . If lengthwise positioning of the IC package between ridges  865  and  870  is adequate, no further precising of the package relative to precisor block  480  is needed. If not adequate, gripper fingers  470  can be temporarily closed to assure lengthwise positioning. Gripper fingers  470  can also be closed during transport from tray to BIB, or vice versa, if needed to prevent the IC from separating from cup  482  due to bumps or jolts which may occur during transport. 
     Once the IC package is accurately aligned with precisor block  480 , head  420  is moved into position over a socket and lowered until precisor block  480  is seated on the socket. As head  420  is lowered, the IC package is firmly pressed into the socket by surface  860  and is maintained in lateral position relative to the socket by ridges  865  and  870  during insertion. 
     FIG. 10A shows a further elevation view of head  420 . FIG. 10B is a left side view and FIG. 10D is a top view of the arrangement of FIG.  10 A. FIG. 10C is a sectional view taken along lines  10 C— 10 C of FIG.  10 B and showing internal elements of nozzle body  475 . Located between nozzle body  475  and gripper actuator body  465  is a spacer block which has a passage providing pneumatic communication between fitting  485  and nozzle  484 . Gripper fingers  470  are attached to gripper bars  1010  and  1015  which are in turn attached to actuator arms  1020  and  1025  extending from gripper actuator body  465 . Gripper fingers  470  are closed by the gripper actuator on command from controller  415 . 
     FIG. 11A is an elevation view of a gripper finger  470 . FIGS. 11B,  11 C and  11 D are respectively top, bottom and side views of the gripper finger of FIG. 11A. A mounting portion  1105  has bores  1110  and  1115  for affixing the gripper finger to one of gripper bars  1010  or  1015 . An arm portion  1120  extends from mounting portion  1105 , culminating in a finger portion which is narrowed so as not to touch the contact pins of an IC package when the gripper fingers are closed. Arm portion  1120  is angled and radiused as indicated at  1130  and  1135 . to prevent interference of gripper fingers  470  with adjacent sockets when precisor  480  is seated on a socket of a BIB. The precise dimensions are a matter of design choice dependent on the type of socket, type of IC package and socket-to-socket spacing on the BIB. 
     FIG. 12 is a schematic illustration of one possible use of handling apparatus in accordance with the invention. Apparatus  400  is operated under the direction of controller  415  to pick a packaged IC  1205  from a bin of a source tray  1210  and insert the packaged IC into a socket of a BIB  1215 . This sequence is repeated to insert packaged IC&#39;s from bins of tray  1210  into any number of sockets on BIB  1215 . When loaded with IC&#39;s, BIB  1215  is subjected to testing, burn-in and/or other conventional processes. If desired, a map of the BIB sockets indicating which of the IC&#39;s have “passed” and which have “failed” is supplied to controller  1215 . After completion of these processes, apparatus  400  is operated under the direction of controller  415  to pick each of the  10  packaged IC from BIB  1215  and to place it in a bin of an output tray. For example, the “passing” IC&#39;s are placed in respective bins of a “pass” tray  1220  and the “failing” IC&#39;s are placed in respective bins of a “fail” tray  1225 . Other binning criteria may of course be used. 
     Following are sequences of steps which can be programmed into controller  415  to perform the specified activities with handler apparatus in accordance with the invention. 
     Picking an IC from a Tray: 
     a. Operate X-servo  402  and Y-servo  404  to approximately center the precisor block  480  over a selected tray location, with grippers  470  open. 
     b. Operate Z-servo  406  to move handler head  420  downwardly to a predetermined height above the tray. 
     c. Turn on vacuum to nozzle  484 , causing the packaged IC in the selected tray location to be pulled up into the chip precisor portion of precisor block  480 . (Because of the inherent delay in achieving vacuum at cup  482  after turning on vacuum to nozzle  484 , vacuum may be turned on earlier such as when beginning to move handler head  420  downwardly. Proper timing of the commands can produce vacuum sufficient for cup  482  to engage the upper surface of the IC package just as it reached the upper surface of the IC package. Turning on vacuum too early may cause the chip to be pulled too rapidly into the chip precising feature, which could cause loss of vacuum seal between cup  482  and the upper surface of the IC. ) 
     d. If a chip was picked up from the tray, the grippers may be closed (optional). While generally not required, closing the grippers can serve to precise the packaged IC in the chip precisor portion of precisor block  480  and can prevent inadvertent dropping of the IC while in transit to a selected drop-off location. 
     Inserting an IC into a Socket: 
     a. Operate X-servo  402  and Y-servo  404  to approximately center the precisor block  480  over a selected socket 
     b. Open grippers  470  (if not already open). The IC package will be held in its seated position in the chip precising portion of precisor block  480  by vacuum in nozzle  484 . 
     b. Operate Z-servo  406  to move handler head  420  downwardly so that precisor block  480  seats itself on the selected socket. (Resilient mount  455  allows lateral movement of precisor block  480  to compensate for small mis-alignments of head  420  with the socket.) The packaged IC will be aligned with and forced into the socket as precisor block  480  seats itself on the socket. 
     c. Monitor hit detector  495  for indication that precisor block  480  is seated on the socket. (The function of hit detector  495  is two-fold: positive indication that precisor block  480  has bottomed out against something, and to signal that the Z-servo is to stop downward motion.) 
     d. Stop operation of Z-servo. 
     e. Turn off vacuum to nozzle  484 , allowing the packaged IC to be released from cup  482 . (Optionally, “puff” air pressure is applied to nozzle  484  to assure separation of cup  482  from the packaged IC.) 
     f. Operate Z-servo (piston  450 ) to move handler head  420  upwardly so that precisor block  480  separates from the selected socket and is raised to a height suitable for travel to another location. 
     Extracting an IC from a Socket: 
     a. Operate X-servo  402  and Y-servo  404  to approximately center the precisor block  480  over a selected socket, with grippers  470  open. 
     b. Operate Z-servo  406  to move handler head  420  downwardly so that precisor block  480  seats itself on the selected socket. (Resilient mount  455  allows lateral movement of precisor block  480  to compensate for small mis-alignments of head  420  with the socket.) 
     c. Monitor hit detector  495  for indication that precisor block  480  is seated on the socket. (The function of hit detector  495  is two-fold: positive indication that precisor block  480  has bottomed out against something, and to signal that the Z-servo is to stop downward motion.) 
     d. Stop operation of Z-servo. 
     e. Close grippers  470 . (This step can be optionally performed as soon as hit detector  495  indicates seating of precisor  484  on the socket.) 
     f. Turn on vacuum to nozzle  484 . Vacuum build-up indicates that an IC package is present in precisor block  480 . Failure to build up vacuum indicates that the socket is empty. (Because of the inherent delay in achieving vacuum at cup  482  after turning on vacuum to nozzle  484 , vacuum may be turned on earlier such as when beginning to move handler head  420  downwardly. Correct timing of the commands will produce vacuum sufficient to indicate presence of the IC package when cup  482  engages the upper surface of the IC package. ) 
     g. Operate Z-servo (piston  450 ) to move handler head  420  upwardly and thus extract the IC package from the socket. Continued vacuum in nozzle  484  assures that the IC package is seated in the chip precising portion of precisor block  480 . 
     h. When the component handler has reached the travel position height the grippers can (optionally) be opened. The IC package will then be fully seated in the chip precising portion of precisor block  480 . 
     Dropping an IC into a Tray: 
     a. Operate X-servo  402  and Y-servo  404  to approximately center the precisor block  480  over a selected tray location. 
     b. Open grippers  470  (optional, not required if already open). 
     c. Operate Z-servo  406  to move handler head  420  downwardly to a predetermined height above the tray. (Optional, depending on whether needed to assure that the packaged IC will be safely deposited in an acceptable position in the selected tray location.) 
     d. Turn off vacuum to nozzle  484 , allowing the packaged IC to be dropped from precisor block  480  into the selected tray location. (Optionally, “puff” air pressure can be applied to nozzle  484  to speed release of packaged IC from cup  482  and to impart a slight downward force to the packaged IC.) 
     FIG. 13A is a bottom view of a socket preciser portion  1300  of a two-piece preciser block in accordance with the invention. FIG. 13B is a sectional view taken along line  13 B— 13 B of FIG. 13A, and FIG. 13C is a sectional view taken along line  13 C— 13 C of FIG.  13 A. In this example, socket preciser  1300  has chamfered preciser legs  1305 ,  1310 ,  1315  and  1320 . Corners  1325  and  1330  are without preciser legs in order to avoid interference with components mounted adjacent the sockets on a particular BIB. Legs  1305 - 1320  are arranged to assure precising relative to the socket without touching the adjacent BIB components. A lengthwise groove  1335  receives a separately-fabricated chip preciser insert  1400  as described below. 
     FIG. 14A,  14 B and  14 C are respective bottom, end and right-side views of a chip preciser insert  1400 . While socket preciser  1300  may be fabricated of metal or other suitable material, chip preciser insert  1400  is in this embodiment of a non-conductive, synthetic material, such as polyurethane, so as to avoid shorting pins of an IC package being handled. As illustrated in FIGS. 14A-14C, chip preciser insert  1400  has a raised, longitudinal boss  1405  which is dimensioned to fit within groove  1335  of socket preciser portion  1300 . As initially fabricated, chip preciser portion  1400  does not have chip-precising ridges. Instead, a surface  1410  is provided into which the chip precising feature is milled after assembly of portions  1300  and  1400 . That is, boss  1405  is coated with a suitable adhesive and glued into position within groove  1335 . After curing, surface  1410  is milled to define the chip-precising feature of an assembled preciser block  1500 . 
     FIG. 15A is a bottom view of a completed two-piece preciser block  1500 . FIG. 15B is a sectional view taken along line  15 B— 15 B of FIG. 15A, FIG. 15C is a sectional view taken along line  15 C— 15 C of FIG. 15A, and FIG. 15D is a top view of the two-piece preciser block of FIG.  15 A. As completed, preciser block  1500  has a pair of mutually-parallel ridges  1505  and  1510  and a milled surface  1515  which together define the chip precising feature. Ridges  1505  and  1510  and surface  1515  are advantageously milled after assembly of the two-piece preciser block to assure accurate positioning of the chip precising feature relative to the socket precising feature, though other fabrication techniques could be used if desired. 
     The foregoing description is intended as illustrative of the present invention and are not intended to limit the scope of the invention. It will be recognized that the drawing figures are not drawn to scale but are structured to illustrate the principles of the invention. Details not required for an understanding of the inventive aspects of the disclosure are omitted from the drawings for clarity of explanation. 
     The apparatus described is designed to make it easy to make a tooling change. For example, various sizes and types of IC packages can be accommodated merely by installing a precisor block  480  having dimensions suitable to the IC package to be handled, and suitably reprogramming the controller  415  with information about BIB layout, travel distances, and the like. There is no need to replace the handler head  420  or the gripper fingers  470  when changing the equipment to handle IC packages of a different size. 
     Those of skill in the art will recognize that many modifications can be made within the spirit and scope of the invention as defined in the claims which follow.