Abstract:
A method and apparatus for separating a chip from substrate where the chip is attached to the substrate by solder connections to form an assembly involve applying a loading force to drive a coil spring biased shearing element comprising a slide block with carrying a shearing blade into a loading position. Load the assembly of the substrate and the chip into a fixture with a window therethrough for the chip with the shearing blade in contact with the chip. Remove the loading force to arm the shearing blade to apply a shearing force from the shearing blade to the chip. Heat the solder connections of the assembly in the fixture to a predetermined temperature, preferably below the melting temperature of the solder at which shearing of the solder connections occurs. The shearing blade comprises a slidable plastic blade backed up by a metal blade. The shearing blades are affixed to a the slide block that is connected by a linkage to a coil spring which applies the biasing force thereto and which provides a nest for catching a chip which has been sheared away from a substrate.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention pertains to a method and an apparatus for removing soldered electronic components from a substrate. More particularly, it relates to non-destructive, low stress removal of chips temporarily soldered to a substrate during Known-Good-Die (KGD) testing an processing of flip chip devices.  
           [0003]    2. Description of Related Art  
           [0004]    As the state of the art advances, devices formed on semiconductor chips become smaller in dimensions and the devices become more densely crowded on the chip. As a result there is an increasingly important need to pretest devices as a quality control measure involving identification and elimination of defective chips before use thereof. To facilitate pretesting, a technology has developed which is commonly referred to as the KGD (Known Good Die) practice in which a chip is bonded to a temporary substrate in a temporary chip attachment (TCA) process wherein, during a testing interval, the chip is mounted temporarily to a chip carrier substrate which has electrical contacts which match contacts on the chip. During the testing interval, the chip is electrically tested through the substrate. After completion of testing, the chip is removed from the substrate for future use. During the testing interval, a burn-in process is used in which the chip to be tested is bonded temporarily to the substrate. It is desirable for the bonds between the substrate and the chip to be mechanically weak, but strong enough to hold the semiconductor chip in place and to good electrical connections during testing. The chip is normally positioned on the substrate so that the electrical contacts, e.g. C4 solder balls (hereinafter referred to as C4&#39;s) on the chip are aligned with the corresponding contacts on the substrate so that the C4&#39;s make electrical connections between the chip and the substrate.  
           [0005]    In one process for the testing of KGD flip chip devices, silicon chips are temporarily attached by solder balls (typically a SnPb alloy, such as 3% tin (Sn) and 97% lead (Pb), referred to as 3/97 solder) to a composite or ceramic substrate (chip carrier) and subjected to electronic component testing and burn-in. Following this testing, the chips are mounted in a first fixture and subjected at ambient temperature to shear forces across the solder balls to remove the chip from the substrate. These forces typically fracture the solder balls, leaving some solder attached to the substrate and the remainder of the solder attached to the chip. Thereafter, the chips are removed from the first fixture, and those which tested as good are then mounted in a second fixture for heat processing to liquefy the solder on the chip and reform the solder balls. The resulting chips are then packaged and eventually mounted in an array of chips on another substrate.  
           [0006]    A variety of processes and techniques have been devised and described in the art to form a temporary connection between semiconductor chips and substrates, so as to be able to readily separate the chip and the substrate after burn-in tests have been conducted. Several of these are described in U.S. Pat. No. 5,556,024 of Olson et al., commonly assigned for “Apparatus and Method for Removing Known Good Die Using Hot Shear Process” and the teachings thereof are incorporated herein by reference. In the process of the Olson et al. patent, the substrate which is referred to as device carrier and the device are placed in a fixture, heated to the solder liquidus temperature, and the device is then pulled away from the substrate. In one embodiment, after being heated to the solder liquidus temperature, shear forces are applied sufficient to overcome solder surface tension and to separate the die and carrier. Related patents of Olson et al. include U.S. Pat. Nos. 5,707,000; 5,636,781; 5,738,267.  
           [0007]    U.S. patent application (CA9-98-056) Ser. No. 09/460,279, filed Dec. 13, 1999, of Bergeron et al for “Apparatus and Method for Non-Destructive, Low Stress Removal of Soldered Electronic Components” describes an apparatus and a method for removing circuit chips from an assembly including a one or more circuit chips attached to at least one chip carrier, or substrate. The chips are subjected to static shear with respect to the substrate, and heated to a temperature facilitating shear within a temperature range at which solder connections are solid, such that the chip is sheared off with respect to the substrate at the plane of attachment of the solder to the substrate. In addition, the chips are further heated following disassembly to a temperature at which the solder is liquid to facilitate reforming the solder for subsequent attachment of the chip into an electronic device. In addition the substrate is held within a top plate and the circuit chips are positioned within successive chip cavities within a bottom plate. Each chip cavity includes a load surface separated by a cascade effect pitch with respect to adjacent chip cavities. A cascade effect shear force is sequentially applied to the circuit chips to remove them from the substrate seriatim. The substrate has reduced pad dimensions, which releases the C4&#39;s therefrom, thereby permitting the C4&#39;s to remain on the newly tested chips during the removal process so that the chips can be reattached to the final substrate in the product for which they were manufactured. In addition, the removal process is conducted at pre-reflow temperatures, i.e. below reflow temperatures. A linear shearing force is applied to the first substrate carrier by way of a single compression coil spring. This action pushes the substrate forward and forces the chip to press against a shear tab thus pre-loading the C4&#39;s on the first chip with a known shear force. The shear force being applied is set to shear the chip when it has been heated to an elevated temperature. Therefore, at room temperature the chip remains connected to the substrate. When the loaded fixture is placed into a furnace and heated to a critical temperature, the C4 joints and the chip are sheared away from the substrate. The heating raises the temperature until it softens the C4 solder balls on all the parts until they allow the shearing force to push the first carrier forward thus shearing the first chip away from the carrier. As this carrier is moved forward by the coil spring, the first substrate makes contact to the second substrate and the remaining coil spring force is applied to the chip on the second carrier. This action continues until all chips on all carriers are sheared seriatim. With the Bergeron et al. process, the is a variation in coil spring force as the coil spring moves the first substrate forward using the Bergeron et al. process, the coil spring force rate changes. Therefore, forces applied to each chip are different. In addition, the first chip in the row is the only chip that receives the maximum shear force at room temperature which results in an inconsistent application of force.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is concerned with a cost effective device and pre-load mechanism for removing known good dies from substrate carriers. The primary advantages over existing fixtures is tooling cost, flexibility and process improvement.  
           [0009]    An object of this invention is to provide apparatus for performing the chip removal from a substrate without a high tooling cost for machining during fabrication.  
           [0010]    Another object of this invention is to provide such a tool while at the same time avoiding any high costs associated with adapting the tool to operate with product variations.  
           [0011]    A very important object of this invention is to provide process consistency with uniform shear forces applied to each chip at room temperature.  
           [0012]    The invention includes a coil spring load mechanism-for each carrier/chip assembly thereby allowing each shear force for each chip to be set independently.  
           [0013]    The invention also includes a coil spring compression device which compresses the shear coil spring, positions the shearing blade to the load position and displays the force to the operator.  
           [0014]    With this design, shear forces on each chip are monitored during the fixture load operation and the shear process for each chip is the same.  
           [0015]    In accordance with this invention a method and apparatus are provided for separating a an assembly comprising a substrate and semiconductor device, e.g. a semiconductor chip. For example, the semiconductor device is attached to the substrate by solder connections. The assembly is to be placed into a fixture which includes a biased shearing element. First a loading force is applied which drives a biasing element such as a coil spring and the biased shearing element into a loading position for loading, i.e. placing, the assembly into the fixture. Then load/place the assembly of the substrate and the semiconductor device into a fixture. Preferably, the fixture has a window therethrough providing space for the semiconductor device. During loading the shearing element is held proximate to the semiconductor device but out of contact with therewith. Remove the loading force to permit the shearing element to contact the semiconductor device and to apply a shearing force from the shearing element to the semiconductor device. Then, upon heating the solder connections of the assembly in the fixture to a predetermined temperature, the force applied by the shearing element is sufficient to separate the semiconductor device from the substrate. Preferably the temperature is below the melting temperature of the solder at which shearing of the solder connections occurs; and the shearing element comprises a slidable blade. Alternatively, the shearing element is a blade affixed to a slidable element that is connected by a linkage to a coil spring which applies the biasing force thereto.  
           [0016]    In accordance with another aspect of this invention removal of a circuit chip from a substrate in a fixture having a shearing element, where the chip is secured to a substrate by bonding elements is provided by applying a loading force to move a shearing element from a mechanically biased home position into an armed, loading position, preferably under a top portion of the fixture, against a biasing force proximate to a position into which the chip is to be loaded. Then load the substrate with the chip onto the fixture. Then remove the loading force to permit the armed shearing element to move to a position in which it contacts the chip and thereby applies a mechanical shearing force to the chip in response to the biasing force applied to the shearing element by the mechanical bias. Then, heat the assembly located in the fixture to a predetermined temperature, e.g. a temperature below the melting temperature of the bonding elements, until shearing of the bonding elements occurs while continuously applying the mechanical shearing force with the shearing element.  
           [0017]    Preferably the shearing element is a blade affixed to a slidable element that is connected by a linkage to a coil spring that applies the biasing force thereto; and/or the shearing element is a blade affixed to a slidable block which is connected by a screw that is biased to a home position by a coil spring which applies the biasing force thereto.  
           [0018]    Preferably, the shearing element is a blade affixed to a slidable block which is connected by a screw that is biased to a home position by a coil spring which applies the biasing force thereto, and an adjustable element is provided for adjusting the bias applied by the coil spring. The bonding elements comprise solder balls or the like. The solder is heated to a temperature which facilitates the shearing of the C4 joints and removal of the chips from the substrate while the solder is in a solid state.  
           [0019]    Preferably, each substrate and the associated chip are loaded into a seat in an upper element with the chip extending through an open window through the seat. The shearing element is connected to a slide element which is connected by a screw that is biased to a home position by a coil spring which applies the biasing force thereto, and an adjustable element is provided for adjusting the biasing force applied by the coil spring. Preferably, the element includes a nest located below the window adapted and located for catching a chip sheared from a substrate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The foregoing and other aspects and advantages of this invention are explained and described below with reference to the accompanying drawings, in which:  
         [0021]    [0021]FIG. 1A is a perspective view of an assembly including an upper, framing boat and a lower support boat which performs the shearing operation in accordance with this invention.  
         [0022]    [0022]FIG. 1B is an exploded view of the assembly of FIG. 1A showing the two boats and additional elements.  
         [0023]    [0023]FIG. 1C is an enlarged perspective view of a portion of FIG. 1B showing the showing the seat on the top surface thereof with a window in the center of the seat for a substrate inserted into the seat and a chip extending below the window as seen in FIG. 2.  
         [0024]    [0024]FIG. 1D is an enlarged perspective view of a portion of FIG. 1B showing a perspective view of a pair of slide blocks (with both assembled and exploded views) on the lower boat.  
         [0025]    [0025]FIG. 2 which is an enlarged right side view of the assembly of FIG. 1A.  
         [0026]    FIGS.  3 A- 3 D show enlarged views of a portion of FIG. 2 showing the slide boat in various positions.  
         [0027]    [0027]FIG. 3A shows an enlarged portion of FIG. 2 showing the fixture with slide block in the home position.  
         [0028]    [0028]FIG. 3B shows the view of FIG. 3A with the slide block and the shearing blade moved to the left with the substrate and the chip loaded onto the fixture. FIG. 3C shows the view of FIG. 3B with the slide block and the attached shearing blade having moved to the right until the shearing blade is in contact with the chip; and with the shearing blade armed by a linear force from a coil spring which pulls the shearing blade to the right creating a shearing force which tends to shear the C4&#39;s and the chip away from the substrate.  
         [0029]    [0029]FIG. 3D shows the view of FIG. 3C with the chip and the C4&#39;s separated from the substrate resting in a nest on the top surface of the slide block and with the shearing blade and the slide block moved back to the home position.  
         [0030]    [0030]FIG. 4 is a perspective view of an tool employed during arming of the shearing blade and slide block by driving a screw which pushes the slide block to the left permitting insertion of the substrates with chips into the seats on an assembly and arming the shearing blade.  
         [0031]    [0031]FIG. 5 is a cross section of this device taken along line  5 - 5 ′ in FIG. 4 with the boat assembly in the armed and loaded position. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]    [0032]FIG. 1A shows a perspective view of the boat assembly  18  in accordance with this invention. FIG. 1B is an exploded view of the boat assembly  18  of FIG. 1A. FIG. 2 which is an enlarged right side view of the boat assembly  18  of FIG. 1A. As can be seen in FIG. 1B, the boat assembly  18  is formed by two boats  42 / 43  and other elements. The boat assembly  18  includes an upper, framing boat  42  and a lower support boat  43 . The boats  42 / 43  are formed from boats originally manufactured by Auer to be used for article handling in the semiconductor manufacturing environment. FIG. 1C is an enlarged perspective view of a of FIG. 1B showing the seat  54  on the top surface of the upper boat  42  with a window  53  in the center of the seat  54  for a substrate  41  to be inserted into the seat  54  with a chip  15  extending below the window  53  as seen in FIG. 2. FIG. 1D is an enlarged perspective view of a portion of the boat assembly  18  showing FIG. 1B slide blocks  47  (with both assembled view of slide block  47 L and an exploded view of slide block  47 R) which are slidably mounted on the lower boat  43 .  
         [0033]    After some modifications, boats  42 / 43  have been specially assembled to support a substrate  41  carrying a chip  15  as shown in FIG. 2, as well as FIGS. 3B and 3C where they are shown enlarged. FIG. 2 shows a view of the right end of the boat assembly  18 , which has been loaded with a substrate  41  carrying C4 solder joints which support a semiconductor chip  15  on its lower surface. FIGS. 3B and 3C are enlarged partial views of FIG. 2 with some modifications based upon the stage of the process involved with the method of this invention.  
         [0034]    [0034]FIG. 1C is an enlarged perspective view of a portion of FIG. 1B which shows an enlarged portion of upper, framing boat  42  showing the seat  54  on the top surface of upper boat  42  with a window  53  in the center of the seat  54 . The seat  54  is defined by four tabs  17  on the outer sides (with two tabs  17  on each side of the seat  54 ) of the upper boat  42  and four tabs  17 ′ (with two tabs  17  on each end of the seat  54 ) along the length of the upper boat  42 . The tabs  17 / 17 ′, which are an integral part of the upper, framing boat  42 , are located in positions which provide a snug fit for the substrate  41  when it is inserted onto the seat  54 . The window  53  is provided so that a chip  15  can extend below the top surface of the upper boat  42 . The bottom of surface surrounding the seat  54  of the upper boat  42  and the window  53  provide a frame around the lower surface of the substrate  41 . The attached chip  15  extends through the window  53  in the center of that frame.  
         [0035]    In FIG. 2, the substrate  41  is shown located in the seat  54  above the surface of the upper, framing boat  42 , and the substrate  41  carries the semiconductor chip  15  secured to the bottom thereof by C4 solder ball joints, as is well understood by those skilled in the art. The substrate  41  is located in the seat  54  between a pair of end tabs  17  as well as being between the side tabs  17 ′.  
         [0036]    At the stage of the manufacturing and testing process reached when the method and apparatus of the present invention are employed in a KGD process, the chips  15  have been tested in operation while temporarily bonded to the substrate  41  by C4 solder joints. The boat assembly  18  includes a coil spring load provided by a compressed coil spring  12  shown in FIGS. 1B and 2, which provides a return force that enables shearing the chip  15  away from the substrate  41  with a predetermined force. The amount of force to be applied upon blade  14  and chip  15  by compressed coil spring  12  is adjusted by turning a tension adjustment thumb nut  11  on compression screw  10  to tighten-increase compression or loosen-release compression of the coil spring  12 . The left end of the compression screw  10  is securely fastened to slide block  47  and compression screw  10  applies a force on slide block  47  which is transferred through the plastic (Vespel) shearing blade  14  backed up by a metal shearing blade  13 ; since the plastic shearing blade  14  and the metal shearing blade are secured to the slide block  47 . Thus, when the upper-right edge of shearing blade  14  is pulled to the right against the chip  15  while the substrate  41  is retained in position seated on upper boat  42  by the pair of tabs  17  on the right side of boat  42 , as explained in detail below, the blade  14  transmits a shearing force to the chip  15  and its C4&#39;s. When the C4&#39;s are soft enough blade  14  will shear the chip  15  and the C4&#39;s away from the substrate  41 , which is held in a fixed position in its seat  54 .  
         [0037]    Note that the configuration or scale of boats  42 / 43  is easily changed to accommodate various substrate carrier sizes and the coil spring load of the coil spring  12  is easily adjusted to accommodate various chip sizes by adjusting the compression adjusting thumb nut  11  on compression screw  10 , thus offering a great deal of flexibility in application of the apparatus of this invention to use with various product designs.  
         [0038]    [0038]FIG. 1A is a perspective view of the boat assembly  18  which includes five empty workpiece seats  54  along the length thereof, which are adapted to receive five substrates  41  carrying five chips  15 .  
         [0039]    It should be noted that while the embodiment shown in FIG. 1A includes five workpiece seats  54  and five substrates  41 , that is simply one example of how one may employ the present invention. However, one seat and one substrate or many more or less than five seats and many more or less than five substrates may be employed in accordance with this invention as a matter of choice and economy of scale.  
         [0040]    A side view of a single substrate  41 , loaded with a single chip  15 , is shown in FIG. 2, FIG. 3B and FIG. 3D. Before a substrate  41  and a chip  15  placed on a seat  54  on the boat assembly  18 , the chip  15  has been tested successfully and is ready to be removed from the substrate  41  so that it can be assembled into a commercial product or the like. Referring again to FIG. 1A, the five substrate seats  54  are formed in the upper, framing boat  42 . In addition, there are five empty slide blocks  47  supported by the lower support boat  42  (as shown in FIG. 2) visible through the empty windows  53  (shown in FIG. 1B) in upper framing boat  42 . The slide blocks  47  in FIG. 1A are located below the empty windows  53 , and they are shown centered below the seats  54 . Thus, the slide blocks  47  are framed by the windows  53 . The periphery of each of the windows  53  surrounds a slide blocks  47 . As can be seen in FIG. 2, the slide block  47  is located below the top surface of upper, framing boat  42  slidably secured to the lower, support boat  43  by a shoulder screw  48 . The shoulder screw  48  slides back and forth in a transverse travel-guide slot  49  in the top surface of the lower boat  43 . That is to say that each slot  49  extends partially across the top surface of the lower boat  43  permitting the corresponding slide block  47  to slide transversely (from right-to-left or from left-to-right as shown in FIG. 2. and FIGS.  3 A- 3 D).  
         [0041]    [0041]FIG. 2 is a right side view of the boat assembly  18  of FIG. 1A, which shows a substrate  41  carrying a semiconductor chip  15  loaded into the seat  54  at the right hand end of the assembly  18  as it is seen in FIG. 1A. The chip  15  is ready to be stripped from substrate  41  by the shearing action of the blade  14  in boat assembly  18  when the loaded fixture is located in an oven heated to a predetermined temperature at which the C4 solder joints which provided bonds between the substrate  41  and the chip  15  soften and release the chip  15  into a nest  47 N formed by a nest element  16  and the upper end of plastic shearing blade  14  on the top surface of the slide block  47 .  
         [0042]    Referring to FIG. 1D, a perspective view of a pair of slide blocks  47  located on the lower boat  43  is shown. The slide block  47 R to the right is shown in an exploded view and the slide block  47 L on the left is shown in an assembled view. Each set of the plastic shearing blades  14  and the metal shearing blades  13  is secured by screws in a slot  14 ′ on the left side of the slide blocks  47 L and  47 R, as best illustrated by the exploded view of right slide block  47 R in FIG.1D. Each of the nest elements  16  is secured by screws in a central slot  40  on the top surface of the slide blocks  47 L/ 47 R between the dual tops  47 T of slide blocks  47 L/ 47 R on either side of the central slot  40 . The assembled blade and nest parts  13 / 14 / 16  in the slide block  47 L show the nest  47 N on the top surface thereof between the top surfaces  47 T of the left slide block  47 L. The purpose of the nest  47 N can be seen by referring to FIG. 3D, where the chip  15 , which has been sheared away from the substrate  41  by blade  14 , is resting in the nest  47 N on top of the nest element  16 .  
         [0043]    Referring again to FIG. 1A, the largest elements of the boat assembly  18  comprise a pair of stainless steel sheet metal boats including upper, framing boat  42  and lower support boat  43  (known as Auer boats manufactured and sold by Auer Precision Co., Inc. which is located in Mesa, Ariz.) which are assembled together by stand-offs  44  and screws  45  connected by using common tooling holes  21  that are punched into the top surface of the upper boat  42 , and common tooling holes  46  that are punched into the top surface of the lower boat  43  during the cycle of manufacturing thereof. Boat  42  and boat  43 , if they are Auer boats, are employed as industry standard process carriers that are typically used in manufacturing of electronic substrate devices. Referring to FIGS. 1A, 3A and  3 B, there are shown five substrate seats  54  for five substrates  41  along the length of upper, framing boat  42 . There are five framing windows  53  through the surface of the upper, framing boat  42  centered inside of each substrate seat  54 . Each window  53  in FIG. 1A reveals one of the five slide blocks  47  below the corresponding substrate seat  54 . Each slide block  47  is slidably attached to the lower boat  43  by a shoulder screw  48  which extends through a corresponding long slot  49  provided along the length of the lower boat  43 . An example of how a slide block  47  is secured to lower boat  43  is shown in FIG. 2.  
       Operation of Slide Block  
       [0044]    Each of the slide blocks  47  is adapted for supporting a polyimide (Vespel brand), plastic shearing blade  14  which is adapted to shear a chip  15  away from its substrate  41 . Each of the slide blocks  47  also provides a nest  47 N formed by a nest element  16  and a shearing blade  14  into which a chip  15  falls when it is sheared away from the substrate  41  retained in its position in the seat  54  on the upper, framing boat  42  by the four pairs of tabs  17 ,  17 ′.  
         [0045]    Referring to FIGS.  2 , and  3 A- 3 D, as explained in part, above, a slide block  47  is shown secured to the lower boat  43  by means of one of a set of shoulder screws  48  and travel-guide slots  49  in boat  43 . Each shoulder screw  48  extends through a corresponding travel-guide slot  49 . The shoulder screw  48  is screwed all the way into a threaded hole in the bottom of a corresponding slide block  47  until it has seated to affix the screw  48  to the block  47 . As shown the shoulder screw  48  when seated leaves space permitting mechanical play between the slide block  47  and the surface of the boat  43 . That mechanical play permits the slide block  47  and the shoulder screw  48  to be free to slide from left-to-right and from right-to-left in FIGS. 2 and 3A- 3 D. The slot  49  guides the motion of the slide block  47  relative to the  43 . That is to say that the slide block  47  is free to slide within the lateral limits defined by the slot  49  with the guidance provided by both the body and the head of the shoulder screw  48 .  
       Operation of Compression Screw  
       [0046]    As shown in FIG. 2 the compression screw  10  is combined with a tension adjustment thumb nut  11  and a compression coil spring  12  and then inserted through a lateral surface construction hole  21  (see FIG. 1) located in the side of the upper boat  42  and attached to slide block  47 . The screw is threaded in part and has a smooth shank in part. The threads remain where the tension-adjustment-thumb nut  11  is located, near the head of the compression screw  10  and at the right end of compression coil spring  12 . The threads on screw  10  also remain at the left end of compression screw  10 , which is threadedly affixed and secured to the slide block  47 . However, between the nut  11  and the slide block  47 , the threads have been removed from the compression screw  10  to avoid any mechanical interference where the shank of screw  10  travels back and forth through the hole  21  in the side of the upper boat  42 . The thumb nut  11  can be turned in and out on compression screw  10 , to adjust the linear tension force to the right applied by compression coil spring  12  upon the compression screw  10 , and thus upon the shearing blades  13  and  14 .  
       Adjustable Stops  
       [0047]    Referring to FIG. 2, a threaded rod comprising an adjustable stop  36  is shown which passes through another one of the lateral surface construction holes  21  in the upper boat  42 . The adjustable stop  36  is provided to prevent the slide block  47  from traveling too far to the right when the chip  15  is released from the substrate  41 . The reason that adjustable stop  36  is required is that there are capacitors  38  extending down below the substrate  41  which could be damaged by excessive travel to the right of the upward extending foot on the right end of the nest element  16 . The adjustable stop  36  is held in position by a threaded nut  50  on the right side of the sidewall of the upper boat  42  and a self-clinching slide-type nut  52  (such as a nut manufactured by PEM Fastening Systems, a PennEngineering Company) on the left side of the same boat sidewall  42 .  
       Shearing Operation Steps  
       [0048]    [0048]FIG. 3A, shows an enlarged view of a portion of the boat assembly  18  seen in FIG. 2. Among other elements, the compression screw  10  is truncated, but the device is shown in the home position, before the time that the compression screw  10  is to be pushed to the left to put the shearing blades  13  and  14  far enough to the left to provide clearance for loading, i.e. placing, of a chip  15  and its substrate  41  onto the seat  54 . The nest  47 N is seen between the foot of nest element  16  and the plastic shearing blade  14 . The seat  54  is shown between the outboard tabs  17  near the sides of the boat  42 . It can be seen that the slide block  47  is in contact with the stop  36  which prevents the compression coil spring  12  from pulling the slide block  47  any farther to the right. As stated above, this view shows the substantial clearance between the surface of the lower boat  43  and the head of the shoulder screw  48  that allows the slide block  47  to slide freely to the left or to the right on the top surface of the lower boat  43 .  
         [0049]    [0049]FIG. 3B shows the boat assembly  18  of FIG. 3A after the compression screw  10  has been driven far enough to the left so that the shearing blade  14  is moved to provide enough clearance space for loading the chip  15  when the substrate  31  is loaded onto the seat  54  on the fixture  18 . Note that chip  15 , which it is attached to the substrate  41  by C4&#39;s, is located in a space below the substrate  41  to the right of the shearing blade  14  which would otherwise interfere with the chip  15  if blade  14  were farther to the right. In FIG. 3B, it can be seen that there is a slight clearance between the chip  15  and shearing blade  14  and that the chip  15  fits between the foot of nest element  16  and shearing blade  14 .  
         [0050]    [0050]FIG. 3C shows the boat assembly  18  of FIG. 3B after the compression screw  10  has been released from external pressure thereon to return the slide block  47  and blade  14  to a position farther to the right in response to the bias force applied by the coil spring  33 . The top edge of the shearing blade  14  is shown to be overlapping and in contact with the edge of chip  15 . Moreover, because of the small movement of the claim  19  and the blade  14 , the space between the foot of nest element  16  and the right edge of chip  15  is larger than it was in FIG. 3B. When all of five of the shearing blades  14  are in contact with the edges of all five of the chips  15  on the fixture  18 , then the fixture  18  and its load of substrates  41  is ready to be placed into an oven to raise the temperature to a high enough temperature to soften the C4 solder balls and at such temperatures, the shear force being exerted by shearing blade  14  is sufficient to release the C4 solder balls and the chip  15  from the substrate  41  causing the chip  15  it to fall down from the bottom of the substrate  41 .  
         [0051]    [0051]FIG. 3D shows the shearing blade  14  of FIG. 3C after the chip  15  has fallen into the nest  47 N provided by the nest element  16  and the shearing blade  14 , as result of the heating and shear force applied by shearing blade  14  described above. Note that the slide block  47  has returned to its home position in contact with the end of the adjustable stop  36 .  
         [0052]    As stated above, referring to FIG. 2, the nest element  16  which is also made from polyimide (Vespel brand) and which is attached to the top side of the slide block  47  has a foot which when combined with the blade  14  are located in positions on the left and the right of the chip which allow for slight gaps around the chip  15  prior to a shearing operation.  
         [0053]    The plastic shearing blade  14 , which is made from Vespel brand polyimide or the equivalent, is backed up with a metal backup shearing blade  13 . A metal backup shearing blade  13  and a plastic shearing blade  14  are attached to the distal end of each slide block  47  (farthest from compression coil spring  12 ) with screws into the left end of block  47  in FIG. 2, not shown. The plastic shearing blade  14  is positioned on each slide block  47  so that one edge is approximately 0.01 cm (0.005 inches) below the chip side surface of the substrate  41  during the shearing operation.  
         [0054]    The polyimide shearing blade  14  acts as a cushion to the chip  15  when forces are applied during chip shear and the polyimide nest  47 N cushions and catches the chip during the “flinging” action that takes place during the shear operation. Although other plastic materials may suit this application, Vespel brand polyimide is currently used for the high temperature characteristics thereof.  
         [0055]    The lateral surface construction hole  21  in upper, framing boat  42  is large enough to allow a slip fit for the compression screw  10  and small enough to act as a back stop to the compression coil spring  12 .  
         [0056]    This arrangement allows for each slide block  47  to be pushed forward with the compression screw  10  and retracted with its separate compression coil spring  12 .  
         [0057]    [0057]FIG. 4 is a perspective view of a tool  80  employed during arming of the shearing blade  15  by driving of the slide block  47  to the left and insertion of the substrates  41  with chips  15  into the seats  54  on an boat assembly  18 . The tool  80 , which is used to compress coil spring  12 , drives the slide block  47  into a position that allows the next substrate  41  with its chip  15  to be loaded into the seat  54  as indicated in FIG. 3B. After a substrate  41  and its chip  15  have been loaded, the boat assembly  18  is moved in a sequential process along to the next position on table  19  for each of the five positions where seats  54  are located, one at a time, along the length of the boat assembly  18 . At each seat position, a substrate  41  is loaded into the corresponding seat  54  and the chip  15  is placed under tension from the corresponding shearing blade  14  and compression coil spring  12 , as described above. The sequence of substrate  41  and chip  15  installation continues until all five of the substrates  41  with chips  15  at the five seat positions have been loaded onto their seats  54 .  
         [0058]    [0058]FIG. 5 is a cross section of this device taken along line  5 - 5 ′ in FIG. 4 with the boat assembly  18  in the armed and loaded position.  
         [0059]    The boat assembly  18  and other devices employed in accordance with this invention operate as follows.  
       Sequence of Operation  
       [0060]    The operator places an empty boat assembly  18  on a load table  19  and locates it such that a pin  20  engages the upper boat  42  by insertion into one of the tooling holes  21  in the upper boat  42 , that is determined by loading position of the boat assembly  18 . A hold down pin  22  is inserted into a tooling hole  46  located in the lower boat  43 . A load cell  31  with a centering tip  32  is attached to a pressure block  25  and is positioned so that the centering tip  32  is aligned with the compression screw  10 . Pressure block  25  is supported on a common plate  29  which is supported upon a slidable support  26 .  
       Applying Loading Stroke for Loading/Putting Substrate onto Upper Boat  
       [0061]    Referring to FIG. 4, then the operator pulls a handle  24  forward which drives pressure block  25  to the left as can be seen in FIG. 5. The pressure block  25  is guided by the slidable support  26 , towards the compression screw  10 . A hold-down block  27  is mounted to a second slidable support  28  which is attached to a common plate  29  shared by the pressure block  25  and slide  26 . The hold down block  27  is driven forward by a another compression coil spring  30  and it is designed to engage the lower boat  43  before centering tip  32  engages the compression screw  10 . As the operator continues to pull the handle  24  forward, hold down block  27  with pin  22  engages the lower boat  43  and a loading stroke comprising a substantial force is applied by the coil spring  30 . The centering tip  32  then makes contact to the compression screw  10  resulting in compression of the coil spring  12 . The end of the loading stroke is completed when a stop pin  34 , which is attached to common plate  29 , contacts the micrometer stop  35 . This locates the slide block  47  in a position that allows substrate  41  with its chip  15  to be located in the shear position as indicated in FIG. 3B and as described above. Once the substrate  41  and chip  15  are in the shear position as shown in FIG. 3B, the operator releases the handle  24  and the pressure block  25  and hold down block  27  are brought back to the home position by coil spring  33 . The plastic shearing blade  14  is now putting a shearing force onto the chip  15  and a controlled tension is being applied by the coil spring  12 , thus completing the load cycle for one of the five positions of device  18  as indicated in FIG. 3C.  
         [0062]    Adjustable stops  36  attached to the upper boat  42  are adjusted to allow a gap  37  of approximately 0.11 cm (0.03 inches) between the stops  36  and slide block  47 . This limits the shear stroke and prevents the capacitors  38  located around the perimeter of the chip  15  from being knocked off by the foot of the nest element  16  during the shear operation. The amount of force being applied to the chip  15  by coil spring  12  is a very important aspect of this invention. Too much force can cause damage to the bottom layer metallurgy of the chip  15  and too little force will not shear the C4&#39;s of chip  15  thereby failing to remove it from the substrate  41 . Therefore, a tight process window, in terms of grams of force per C4 solder connection, is required. To monitor this, the load cell  31  connected to a electronic force measuring system measures the force during each product load cycle. To adjust the ultimate shear force on the C4&#39;s bonded to the chip  15 , the tension adjustment, thumb nut  11  (seen in FIG. 2) is threaded to the compression screw  10 . Turning of the thumb nut  11  changes the tension provided by blade  14  by applying more or less compression to the coil spring  12 . This tension adjustment in conjunction with micrometer stop  35  allows for various chip sizes with varied numbers of C4 junctions to be sheared.  
       Advantages of the Invention  
       [0063]    The present device and method of the invention are effective for chip removal from a substrate; and they provide a pre-load mechanism for removing known good dies from substrate carriers.  
         [0064]    In addition costs are minimized by low tooling cost due to minimal machining during fabrication and by the flexibility of the apparatus and the process which permits adapting the tool to operate with product variations is achieved with minimal cost.  
         [0065]    In addition this invention provides process consistency with uniform shear forces applied to each chip at room temperature.  
         [0066]    While this invention has been described in terms of the above specific embodiment(s), those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims, i.e. that changes can be made in form and detail, without departing from the spirit and scope of the invention. Accordingly all such changes come within the purview of the present invention and the invention encompasses the subject matter of the claims which follow.