Patent Publication Number: US-2006005672-A1

Title: Blades, saws, and methods for cutting microfeature workpieces

Description:
TECHNICAL FIELD  
      The present invention is related to blades, saws, and methods for cutting microfeature workpieces.  
     BACKGROUND  
      Conventional microelectronic devices are manufactured for specific performance characteristics required for use in a wide range of electronic equipment. A die-level packaged microelectronic device can include a die, an interposer substrate or lead frame attached to the die, and a molded casing around the die. The die generally has an integrated circuit and a plurality of bond-pads coupled to the integrated circuit. The bond-pads are coupled to terminals on the interposer substrate or lead frame. The interposer substrate can also include ball-pads coupled to the terminals by conductive traces in a dielectric material. A plurality of solder balls can be attached to corresponding ball-pads to construct a “ball-grid” array. Packaged microelectronic devices with ball-grid arrays are generally higher grade packages that have lower profiles and higher pin counts than conventional chip packages that use a lead frame.  
      Die-level packaged microelectronic devices are typically made by (a) forming a plurality of dies on a semiconductor wafer, (b) cutting the wafer to singulate the dies, (c) attaching individual dies to corresponding interposer substrates, (d) wire-bonding the bond-pads to the terminals of the interposer substrate, and (e) encapsulating the dies with a molding compound. Mounting individual dies to individual interposer substrates is time consuming and expensive. Therefore, packaging processes have become a significant factor in producing semiconductor and other microelectronic devices.  
      Another process for packaging microelectronic devices is wafer-level packaging. In wafer-level packaging, a plurality of microelectronic dies are formed on a wafer and a redistribution layer is formed over the dies. The redistribution layer includes a dielectric layer, a plurality of ball-pad arrays on the dielectric layer, and a plurality of traces coupled to individual ball-pads of the ball-pad arrays. Each ball-pad array is arranged over a corresponding microelectronic die, and the traces couple the ball-pads in each array to corresponding bond-pads on the die. After forming the redistribution layer on the wafer, a stenciling machine deposits discrete blocks of solder paste onto the ball-pads of the redistribution layer. The solder paste is then reflowed to form solder balls or solder bumps on the ball-pads. After forming the solder balls on the ball-pads, the wafer is cut to singulate the dies. Microelectronic devices packaged at the wafer level can have high pin counts in a small area, but they are not as robust as devices packaged at the die level.  
      One drawback of conventional die-level and wafer-level packaging processes is that during singulation the cutting blades may break or wobble and, consequently, cut the wafer or workpiece out of specification. For example,  FIG. 1  is a schematic side cross-sectional view of an annular blade  30  in accordance with the prior art cutting a workpiece  70  to singulate a plurality of dies  82 . The annular blade  30  includes an inner portion  32  sandwiched between two support members  50  and an outer portion  34  projecting a distance W 1  from the inner portion  32 . The outer portion  34  of the blade  30  is sized to project down between the dies  82  and through the workpiece  70 . Because the exposed outer portion  34  of the blade  30  is relatively thin and unsupported, it may break or wobble during singulation. This can cause the workpiece  70  to be cut out of specification. Accordingly, there is a need for an improved blade for cutting workpieces to singulate dies.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic side cross-sectional view of a blade in accordance with the prior art cutting a workpiece.  
       FIG. 2  is a schematic side cross-sectional view of a saw in accordance with one embodiment of the invention.  
       FIG. 3  is an isometric view of one of the annular blades of  FIG. 2 .  
       FIG. 4  is a schematic side cross-sectional view of the saw of  FIG. 2  cutting a microfeature workpiece.  
       FIG. 5  is a schematic side cross-sectional view of the saw of  FIG. 2  cutting a microfeature workpiece and forming features in the workpiece.  
       FIG. 6A  is a schematic side cross-sectional view of a portion of an annular blade in accordance with another embodiment of the invention.  
       FIG. 6B  is a schematic side cross-sectional view of a portion of an annular blade in accordance with another embodiment of the invention.  
       FIG. 6C  is a schematic side cross-sectional view of a portion of an annular blade in accordance with another embodiment of the invention.  
       FIG. 6D  is a schematic side cross-sectional view of a portion of an annular blade in accordance with another embodiment of the invention.  
       FIG. 6E  is a schematic side cross-sectional view of a portion of an annular blade in accordance with another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
      A. Overview  
      The following disclosure is directed to blades; saws, and methods for cutting microfeature workpieces. The term “microfeature workpiece” is used throughout to include substrates in and/or on which microelectronic devices, micromechanical devices, data storage elements, and other features are fabricated. For example, microfeature workpieces can be semiconductor wafers, glass substrates, insulated substrates, or many other types of substrates. The term “microfeature device” is used throughout to include microelectronic devices, micromechanical devices, data storage elements, read/write components, and other articles of manufacture. For example, microfeature devices include imagers, SIMM, DRAM, flash-memory, ASICS, processors, flip chips, ball-grid array chips, and other types of electronic devices or components. Several specific details of the invention are set forth in the following description and in  FIGS. 2-6E  to provide a thorough understanding of certain embodiments of the invention. One skilled in the art, however, will understand that the present invention may have additional embodiments and that the embodiments of the invention may be practiced without several of the specific features described below.  
      Several aspects of the invention are directed to saws for cutting microfeature workpieces. In one embodiment, a saw includes a shaft for attachment to a spindle, an annular blade coupled to the shaft, and a support member coupled to the shaft and juxtaposed to the annular blade. The blade has a first thickness at a first diameter and a second thickness at a second diameter. The second thickness is different than the first thickness and sized to cut a microfeature workpiece. For example, the first thickness can be greater than the second thickness, and the second diameter can be greater than the first diameter. The saw can further include a second annular blade coupled to the shaft. The second annular blade has a first thickness at a first diameter and a second thickness at a second diameter. The second thickness is different than the first thickness.  
      Another aspect of the invention is directed to blades for cutting a microfeature workpiece having a first microfeature device and a second microfeature device adjacent to the first microfeature device. In one embodiment, a blade includes an inner portion, an outer portion radially outward of the inner portion, and an intermediate portion between the inner and outer portions. The inner portion has a generally uniform first thickness and the outer portion has a second thickness less than the first thickness. The second thickness is sized to cut the microfeature workpiece between the first and second microfeature devices. The intermediate portion can include a beveled, convex, concave, and/or step-down portion.  
      Another aspect of the invention is directed to methods for cutting a microfeature workpiece. In one embodiment, a method includes providing a blade having a first surface and a second surface opposite the first surface. The first surface has an interior region and a perimeter region noncoplanar with the interior region, and the second surface has an interior region and a perimeter region noncoplanar with the interior region. The method further includes moving the blade relative to the microfeature workpiece to cut the workpiece. As the blade cuts the workpiece, the intermediate portion can form a feature in the workpiece.  
      B. Embodiments of Saws with Blades for Cutting Microfeature Workpieces  
       FIG. 2  is a schematic side cross-sectional view of a saw  100  for cutting microfeature workpieces in accordance with one embodiment of the invention. The illustrated saw  100  includes a blade assembly  110 , a spindle  160  on which the blade assembly  110  is mounted, and a motor  162  operably coupled to the spindle  160 . The motor  162  drives the spindle  160 , which in turn rotates the blade assembly  110  about an axis A 1  to singulate or otherwise cut microfeature workpieces, as described in detail below.  
      The illustrated blade assembly  110  includes a hollow shaft  120 , a plurality of annular blades  130  attached to the shaft  120 , and a plurality of annular support members  150  attached to the shaft  120  between the blades  130 . The hollow shaft  120  is sized to receive and be detachably coupled to the spindle  160  so that the spindle  160  can drive the shaft  120 . The annular support members  150  are arranged in pairs, which sandwich corresponding annular blades  130  to provide lateral support to the blades  130 . The support members  150  have a thickness S 1  and include a surface  152  juxtaposed to a side surface  140  of the corresponding blade  130 . The blade assembly  110  can further include a plurality of spacers  158  carried by the shaft  120  between adjacent pairs of support members  150 . The spacers  158  can have a length S 2  sized so that the spacer  158  and the support members  150  separate adjacent blades  130  by a desired distance, which may correspond to the spacing between microfeature devices on a microfeature workpiece. In other embodiments, the blade assembly  110  may not include a pair of support members  150  for each blade  130  and/or spacers  158  between blades  130 . In additional embodiments, the blade assembly  110  may include washers between the support members  150  and the blades  130 .  
       FIG. 3  is an isometric view of one of the annular blades  130  of  FIG. 2 . Referring to  FIGS. 2 and 3  together, the individual annular blades  130  include an inner portion  132 , an outer portion  134  radially outward of the inner portion  132 , and an intermediate portion  136  between the inner and outer portions  132  and  134 . The inner portion  132  can include a hole  138  sized to receive the shaft  120  ( FIG. 2 ). Referring only to  FIG. 2 , the illustrated inner portion  132  has a first thickness T 1 , and the illustrated outer portion  134  has a second thickness T 2  less than the first thickness T 1 . The ratio of the first thickness T 1  to the second thickness T 2  can be 2:1, 5:1, 10:1, 20:1, or another suitable ratio.  
      The second thickness T 2  of the outer portion  134  can be sized to cut a microfeature workpiece between adjacent microfeature devices to singulate the devices while limiting the kerf in the workpiece. For example, the second thickness T 2  can be from approximately 260 microns to approximately 300 microns. In other embodiments, however, the second thickness T 2  can be less than 260 microns or greater than 300 microns. Although in the illustrated embodiment the inner and outer portions  132  and  134  each have generally uniform thicknesses, in additional embodiments, the inner and/or outer portion may have a nonuniform thickness. For example, in the embodiment described below with reference to  FIG. 6E , the outer portion is tapered.  
      The illustrated intermediate portion  136  is a beveled portion having the first thickness T 1  at a first diameter D 1  and the second thickness T 2  at a second diameter D 2 . As such, the side surfaces  140  of the blades  130  include an interior region  142  and a perimeter region  144  noncoplanar with the interior region  142 . The intermediate portion  136  can be shaped and sized to form a desired corresponding feature in a microfeature workpiece, as described below with reference to  FIG. 5 . In other embodiments, such as those described below with reference to  FIGS. 6A-6E , the intermediate portion  136  may not be beveled but can have other configurations.  
      The outer portion  134  and the intermediate portion  136  can be sized and configured based on the dimensions of a microfeature workpiece. For example, the difference between an outer diameter D 3  of the individual blades  130  and the second diameter D 2  can correspond to a thickness of the microfeature workpiece. More specifically, a width W 2  of the outer portion  134  can be approximately equal to the thickness of the microfeature workpiece such that only the outer portion  134  cuts the workpiece, as described with reference to  FIG. 4 . Alternatively, the width W 2  of the outer portion  134  can be less than the thickness of the microfeature workpiece such that the outer and intermediate portions  134  and  136  cut the workpiece, as described with reference to  FIG. 5 . In other embodiments, however, the width W 2  of the outer portion  134  can be greater than the thickness of the microfeature workpiece.  
       FIG. 4  is a schematic side cross-sectional view of the saw  100  cutting a microfeature workpiece  170 . In this embodiment, the microfeature workpiece  170  includes a plurality of imagers  172  formed in and/or on a substrate  180 . The individual imagers  172  include a die  182  having an integrated circuit  183  (shown schematically), an image sensor  184  operably coupled to the integrated circuit  183 , and an array of bond-pads  185  electrically coupled to the integrated circuit  183 . The image sensor  184  can be a CMOS device or CCD for capturing pictures or other images in the visible spectrum. The individual imagers  172  can further include a spacer  190 , a cover  192  mounted to the spacer  190  to form an enclosure for protecting the image sensor  184 , and an optics unit  193  to transmit the desired spectrum of radiation to the image sensor  184 . In other embodiments, the microfeature workpiece  170  can have other configurations.  
      As shown in  FIG. 4 , the illustrated saw  100  can cut the microfeature workpiece  170  to singulate the individual imagers  172  by rotating the individual blades  130  about the axis A 1  ( FIG. 2 ) while moving the blade assembly  110  across the workpiece  170 . The support members  150  and spacers  158  ( FIG. 2 ) are sized such that the outer portions  134  of adjacent blades  130  are spaced apart by a distance S 3  that corresponds to the spacing of the imagers  172  on the workpiece  170  so that the blade assembly  110  can singulate the imagers  172 . Moreover, in this embodiment, the width W 2  of the outer portion  134  of the blades  130  is sized such that only the outer portion  134  cuts the microfeature workpiece  170 , and the first thickness T 1  of the inner portion  132  is sized to fit between adjacent imagers  172 . Accordingly, as the outer portion  134  of the blades  130  cuts the microfeature workpiece  170 , the inner and intermediate portions  132  and  136  move between adjacent imagers  172 . In additional embodiments, such as the embodiment described below with reference to  FIG. 5 , the intermediate portion  136  and/or the inner portion  132  can also cut or otherwise form features in the workpiece.  
      One feature of the blades  130  illustrated in  FIGS. 2-4  is that the first thickness T 1  of the inner portion  132  is greater than the second thickness T 2  of the outer portion  134 . Another feature of the blades  130  is that the inner portion  132  is sized to fit between adjacent imagers  172  in order to reduce the width W 2  of the outer portion  134 . An advantage of these features is that the larger first thickness T 1  of the inner portion  132  and reduced width W 2  of the outer portion  134  increase the strength and rigidity of the blade  130  without increasing the kerf in the microfeature workpiece  170 . Because the illustrated blades  130  are stronger and more rigid, the blades  130  are less likely to break and/or wobble while singulating imagers or other devices.  
       FIG. 5  is a schematic side cross-sectional view of the saw  100  cutting a microfeature workpiece  270  to singulate a plurality of microfeature devices  272  and form features in the devices  272 . The illustrated microfeature workpiece  270  includes a support member  280  and a plurality of dies  282  arranged in an array on the support member  280 . The illustrated dies  282  include an integrated circuit  283  (shown schematically), an image sensor  284  operably coupled to the integrated circuit  283 , and a plurality of bond-pads  285  electrically coupled to the integrated circuit  283 . A plurality of wire-bonds  289  electrically couple the bond-pads  285  to corresponding contacts  286  on the support member  280 . The illustrated individual microfeature devices  272  further include a barrier  290  circumscribing the die  282  and a radiation transmissive window  292  attached to the barrier  290 .  
      As shown in  FIG. 5 , the illustrated saw  100  can cut the microfeature workpiece  270  to singulate the microfeature devices  272  by rotating the individual blades  130  about the axis A 1  ( FIG. 2 ) and moving the blade assembly  110  across the workpiece  270 . In this embodiment, the width W 2  of the outer portion  134  is less than a thickness X of the workpiece  270  such that the outer and intermediate portions  134  and  136  of the blades  130  cut the workpiece  270 . As such, the beveled intermediate portion  136  forms a chamfer  291  in the barrier  290  as it cuts the workpiece  270 . In other embodiments, such as those described below with reference to  FIGS. 6A-6E , the intermediate portion  136  can have different configurations and form other features in the microfeature devices  272 . An advantage of this aspect of the illustrated blades  130  is that the features can be formed on the microfeature devices  272  for aesthetic purposes or to create space for other components when the devices  272  are used in electronic devices.  
      C. Additional Embodiments of Blades for Cutting Microfeature Workpieces  
       FIGS. 6A-6E  illustrate various configurations of annular blades in accordance with additional embodiments of the invention. For example,  FIG. 6A  is a schematic side cross-sectional view of a section of an annular blade  330  having an inner portion  332 , an outer portion  334 , and an intermediate portion  336  between the inner and outer portions  332  and  334 . The inner portion  332  has a first thickness T 3  and the outer portion  334  has a second thickness T 4  less than the first thickness T 3 . The illustrated intermediate portion  336  has a concave configuration shaped to form a corresponding feature on a microfeature workpiece.  
       FIG. 6B  is a schematic side cross-sectional view of a section of an annular blade  430  in accordance with another embodiment of the invention. The illustrated blade  430  includes an inner portion  432 , an outer portion  434 , and an intermediate portion  436  between the inner and outer portions  432  and  434 . The intermediate portion  436  has a convex configuration shaped to form a corresponding feature on a microfeature workpiece.  
       FIG. 6C  is a schematic side cross-sectional view of a section of an annular blade  530  in accordance with another embodiment of the invention. The illustrated blade  530  includes an inner portion  532 , an outer portion  534 , a beveled intermediate portion  536  between the inner and outer portions  532  and  534 , a first side surface  540   a,  and a second side surface  540   b  opposite the first side surface  540   a.  The inner portion  532  has a first thickness T 5  and the outer portion  534  has a second thickness T 6  less than the first thickness T 5 . The first side surface  540   a  includes an interior region  541   a  and a perimeter region  542   a  radially outward and noncoplanar with the interior region  541   a.  The second side surface  540   b  includes an interior region  541   b  and a perimeter region  542   b  radially outward and generally coplanar with the interior region  541   b.    
       FIG. 6D  is a schematic side cross-sectional view of a section of an annular blade  630  in accordance with another embodiment of the invention. The illustrated blade  630  includes an inner portion  632 , an outer portion  634 , and an intermediate portion  636  between the inner and outer portions  632  and  634 . The illustrated intermediate portion  636  includes a step-down portion.  
       FIG. 6E  is a schematic side cross-sectional view of a section of an annular blade  730  in accordance with another embodiment of the invention. The illustrated blade  730  includes an inner portion  732 , an outer portion  734 , and an intermediate portion  736  between the inner and outer portions  732  and  734 . The illustrated intermediate portion  736  includes a beveled portion, and the illustrated outer portion  734  includes a tapered portion. In additional embodiments, the blade  730  may not include an intermediate portion and the tapered outer portion  734  can project from the inner portion  732 .  
      From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, many of the features of one embodiment can be combined with other embodiments in addition to or in lieu of the features of the other embodiments. Accordingly, the invention is not limited except as by the appended claims.