Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/659,092, filed Aug. 30, 2012, entitled 3D TSV ASSEMBLY METHOD FOR MASS REFLOW. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    This disclosure relates generally to electronic assembly. More particularly, the present disclosure relates to the assembly method of a die on a substrate or a die on another die as part of a 3D assembly (also called 3D through-silicon vias (“TSV”)) for mass reflow or reflow soldering. 
         [0004]    2. Related Art 
         [0005]    The dies in a die on die or 3D TSV assembly can be so thin that during the heating or a mass reflow or bonding process the die has a tendency to curl up. This is referred to in the industry as the “potato chip” effect. The “potato chip” effect leaves many bad connections between the base die and the upper die. The current solution for this problem is to use a special nozzle that will enable in situ bonding of the die at the time of placement. The problem with this solution is that often the die needs to be thermally processed before the nozzle can be removed. To accelerate this, the nozzle must be heated and must also be able to be quickly cooled. The entire placement process, therefore, of the die by the nozzle, takes a significant amount of time for each die because the nozzle must remain at the placement location in order to heat and cool the die before moving to pick up another part. Even though progress has been made, the above process of heating and cooling results in a very low placement rate. Moreover, the equipment required to perform these processes is expensive because the accuracy of placement that is required. Therefore, the equipment cost and the time cost (with tact times in the 5 to 60 seconds per die) makes this an expensive process step in a TSV assembly. Additionally, the use of local heating and cooling at the nozzle tip makes it more difficult to reach the required accuracy in the placement and attachment steps. 
         [0006]    Thus, a die on die or 3D TSV assembly method and assembly machine compatible with a mass reflow method that alleviates or prevents many of the problems described hereinabove would be well received in the art. 
       BRIEF DESCRIPTION 
       [0007]    According to one embodiment, a method comprises: picking up a plate with a nozzle, the plate including at least one opening to allow air to flow therethrough; picking up a die with the nozzle such that the plate is located between the nozzle and the die; placing the die and the plate onto a device, substrate, or another die such that the plate is located on top of the die; and heating the device and the die in a heat chamber while the plate remains on top of the die to permanently attach the die to the device, substrate, or another die. 
         [0008]    According to another embodiment, a method comprises: a) picking up a combination of a plate and a die with a nozzle such that the plate is located between the die and the nozzle; b) placing the combination of the plate and the die on a device, substrate, or another die; c) repeating steps a) and b) to populate the device, substrate, or another die with a plurality of combinations of plates and die; d) heating the device, substrate, or another die and the plurality of combinations of plates and die simultaneously to attach each of the die to the device, substrate, or another die; and e) removing each of the plates from each of the die. 
         [0009]    According to another embodiment, an assembly system comprises: an assembly machine further comprising: a nozzle configured to pick up a combination of a plate and a die such that the plate is located between the nozzle and the die, wherein the plate includes at least one opening in it to allow air to flow therethrough, and wherein the plate is picked up at a first pickup location and wherein the die is picked up at a second pickup location; and a placement location for placing the combination of the plate and the die on a device, substrate, or another die by the nozzle, wherein the nozzle is configured to populate the device, substrate, or another die with a plurality of the combinations of the plate and the die; and a heat chamber configured to heat the entire device, substrate, or another die to attach the die to the device, substrate, or another die. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Some embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
           [0011]      FIG. 1   a  depicts a top view of a plate; 
           [0012]      FIG. 1   b  depicts a cut away view of the plate shown in  FIG. 1   a;    
           [0013]      FIG. 2   a  depicts a top view of a die with TSV; 
           [0014]      FIG. 2   b  depicts a side view of the die with TSV shown in  FIG. 2   a;    
           [0015]      FIG. 3   a  depicts a side view of a nozzle; 
           [0016]      FIG. 3   b  depicts a cut away view of the nozzle shown in  FIG. 3   a  taken at arrows  3   b - 3   b;    
           [0017]      FIG. 4   a - 4   c  depicts the process of picking the plate by the nozzle; 
           [0018]      FIG. 5   a - 5 C depicts the process of picking the 3D TSV by the nozzle with the plate; 
           [0019]      FIG. 6   a - 6   c  depicts the process of placing the 3D TSV and plate on a device by the nozzle; 
           [0020]      FIG. 7   a - 7   c  depicts the process of removing the plate from the 3D TSV mounted on the device via a cleaning process; 
           [0021]      FIG. 8   a - 8   c  depicts another process of removing the plate from the 3D TSV mounted on the device by a nozzle; and 
           [0022]      FIG. 9   a - 9   c  depicts another process of removing the plate from the 3D TSV mounted on the device via a different cleaning process. 
           [0023]      FIG. 10  depicts a top view of an assembly system capable of performing the processes shown in  FIG. 4-9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    A detailed description of the hereinafter described embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
         [0025]    Referring to  FIGS. 1-6  and  10 , a nozzle  16  is shown which may be a part of a pick and place head  110  mounted in an assembly machine  100  of an assembly system  1000 . As shown in  FIGS. 4   a - 4   c , the nozzle may first pick up from a feeder  112  a plate  10 , which is approximately the size of a 3D TSV or die  14  to be placed and attached. This plate  10  may be very flat, and may have a weight that is sufficient to maintain the flatness of the die  14  during a mass reflow process to prevent the “potato chip” effect when the plate  10  is resting on top of the die  14 . For example, the plate  10  may weigh as much or more than the die  14 . The plate  10  may have a greater thickness than the thickness of the die  14 . The plate  10  may be semi permeable to air. The permeability may be created by small orifice type holes  12  in the plate  10 . Alternately, the plate  10  may be made out of a sintered material that allows some, but not all air to pass from bottom to top. This may create a pressure difference between the bottom and the top of the plate  10  to allow the plate  10  to be picked up by the suction from the nozzle  16 . The plate  10  may be constructed out of a highly un-solderable material to prevent the plate from attaching to the die during the reflow process. In other words, the plate  10  may be made from a material that will not deform when exposed to the heat of a reflow process. The plate  10  may also be polished to such a surface finish that molecular attraction (van der Waal&#39;s force) may cause the die  14  to adhere to the plate  10  during the mass reflow/bonding process. 
         [0026]    The sequence of the assembly may be as follows. First, a nozzle  16  is lowered on top of the clean flat plate  10 , as shown in  FIGS. 4   a  and  4   b . The vacuum or suction in the nozzle  16  will build up sufficiently by the limited airflow through the plate  10  caused by the orifice sizing, or the structure of the sintered material of the plate, allowing the plate to be picked up by the nozzle  16 , as shown in  FIG. 4   c . An optional next step would be a vision centering of the plate  10  by a vision system  114  to optimize alignment of the plate  10  with respect to the nozzle  16  prior to picking up the die  14  so that the die  14  will be centered to on the die  14  at the time of the pickup of the die  14 . 
         [0027]    Once the nozzle  16  has picked up the plate, then the nozzle  16  and plate  10  are lowered to the top of the die  14 , as shown in  FIGS. 5   a  and  5   b , from another feeder  112 . The die  14  may include solder bumps  15  for the mass reflow process. Because the die  14  may not be air permeable like the plate  10 , putting the plate  10  in contact with the die as shown in  FIG. 5   b  may close the orifice openings and cause full vacuum to build. This may allow picking the die  14  up underneath the plate  10  by the nozzle  16 , as shown in  FIG. 5   c . Following this, the die  14  may go through the current process steps for flip chip placement, which may include dipping the solder bumps  15  in flux or adhesive, vision centering and placement on the board. 
         [0028]    As shown in  FIG. 6   a , after the picking up of the die  14  and the plate  10  combination, the nozzle  16  may move to a placement location over a substrate, base die, board, or other device  18 . When the vacuum is removed from the nozzle  16 , the die  14  plus the plate  10  may remain on the substrate, or base die, board or other device  18 , as shown in  FIG. 6   b . At this point, the nozzle  16  may immediately be removed to pick up another plate and die combination  10 ,  14  for placement on the device  18 . It should be understood, therefore, that the nozzle  16  need not include any heating or cooling mechanism. Moreover, no other device of the assembly machine needs to individually heat or cool the die  14  to attach it to the device  18 . 
         [0029]    Instead of individual heating of the individual die  14  to the device  18 , the device  18  may become fully populated by a plurality of the plate and die combinations  10 ,  14  prior to heating. From here, the populated device  18  may be transferred by the assembly machine  100  to a heat chamber  200  (shown in  FIG. 10 ). The heat chamber  200  may, for example, be an oven chamber or other heating chamber. The populated device  18  may move along the heat chamber  200  in an assembly line type fashion. Alternately, the populated device  18  may move to the center of the heat chamber  200  and may remain there until the mass reflow process is completed. Whatever, the embodiment, the heat chamber  200  may create an environment having a temperature sufficient to melt the solder bumps  15  and attach the die  14  to the device  18 . 
         [0030]    As shown in  FIGS. 7 and 9 , once the die  14  has been permanently attached to the device  18 , the plates  10  can be later removed in a later step by a plate removal machine  300 . Plate removal machine  300  could be another assembly machine, a cleaning station or other type of machine. For example, after mass reflow in the heat chamber  200 , the populated device  18  may be transferred to plate removal machine  300  and may be turned in a perpendicular position to aid in the removal of the plates  10  from dies  14  via gravity when a fluid  20  is used to facilitate removal of the plates  10 , as shown in  FIG. 7 . This may occur at a plate removal station or location of the plate removal machine  300 . The fluid  20  may or may not be necessary depending on the embodiment. For example, simply moving the device  18  and plates  10  in a vertical position as shown in  FIG. 7  may remove the plates  10  automatically due to gravity. Instead of being turned vertically, the device  18  and plates  10  may alternately be flipped upside down, as shown in  FIG. 9 . This embodiment also shows fluid  20  being used help assist in the removal of the plate  10  from the die  14 . 
         [0031]    In another embodiment shown in  FIGS. 8   a - 8   c , a nozzle, such as the nozzle  16 , may be configured to pick the plate  10  back up off the die  14  after the die  14  has been attached to the device  18 . Alternately, a different nozzle (not shown) than the original nozzle  16  may be utilized to pick the plate  10  back up off the die  14  after the heating. Referring now to  FIG. 10 , the plate removal machine  300  may include one or more removal nozzles, similar to the application nozzle  16 , for removing the plate  10  from the die  14 . These removal nozzles may be used instead of or in addition to the gravity or fluid methods described hereinabove in  FIGS. 7 and 9 . In one embodiment, the removal nozzles may be configured to sense any plates  10  that were not removed by other methods in order to pick the unremoved plates  10  off the die  14 . In other embodiments, the removal nozzles may be the exclusive removal mechanism, and may be configured to individually pick up each plate  10  from its respective die  14 . 
         [0032]    It should be understood that the process described hereinabove may be repeated as necessary to add additional layers on top of the first layer of 3D TSV die  14 . For example, a single die  14  may be applied as a bottom layer attached directly to the device  18 . Then the device  18  may be placed through the assembly machine  100  or another assembly machine (not shown) which runs the exact same process in order to attach a second die layer (not shown) directly on top of the first die  14 . This second die may be attached to the first die  14  with the same mass reflow process and using a plate to retain the shape of the die in the exact same manner as described hereinabove. 
         [0033]    Thus, the TSV die  14  with plates  10  can be mounted in significantly higher speeds than in prior art processes and the entire fully populated wafer/substrate or device  18 , with all the dies  14  and plates  10  can be attached in a mass reflow/bonding process without the risk of curling or potato chip effects on the individual dies  14 . This process prevents the need to individually heat and cool the dies  14  right at the time of placement or with a specific individual heating and cooling head. This may create a significant cost reduction for the assembly process of 3D TSV. The output of a one million dollar assembly machine may, for example, be increased by a factor of 50. The above described method and assembly machine may also enable production of the same quantity and speed in a smaller clean room space. 
         [0034]    In another embodiment, a layer of material may be attached or otherwise applied to the bottom side of the plate  10  prior to contact with the die  14 . This material may either be compliant, adhesive, or provide enhanced friction to allow the plate  10  to better stick to the die  14 . Materials such as high temperature silicon rubber could be used for this purpose. These materials may be even somewhat sticky to temporarily adhere to the top of the TSV die  14 . These materials may be resistant to heat and may not cause permanent adhesion of the plate  10  with the die  14  and rather may simply assist in creating friction and retaining the plate  10  in the proper position above the die  14  during the movement of the device  18  in the assembly machine  100  and heat chamber  200 . 
         [0035]    In another embodiment, it may be beneficial to keep the TSV die  14  flat to have a precision ground and a highly polished surface to interface with the plate  10 . This way molecular attraction can be the force to attach the plate  10  temporarily to the die  14 . In addition the plates  10  may have to have pockets or recesses to prevent contact to sensitive areas or non-flat areas on the top of the die  14 . For example, if a die  14  does not include a flat top surface to integrate with the plate  10 , the plate  10  may be specifically designed with a surface which corresponds to the surface of the die  14 . 
         [0036]    The above described apparatus and method for attaching a die to a device may also be used for attaching a die to substrate or another die. 
         [0037]    Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” and their derivatives are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The terms “first” and “second” are used to distinguish elements and are not used to denote a particular order. 
         [0038]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Technology Category: 5