Abstract:
A method of singulating a wafer starts with fracturing the wafer. The method may also include attaching the dicing tape sheet to a ring frame; relatively raising a portion of the dicing tape sheet supporting the wafer with respect to the ring frame; and attaching support tape to the ring frame and the dicing tape sheet.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of and claims priority to U.S. patent application Ser. No. 13/894,177 filed on May 14, 2013. Said application herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Integrated circuit “dies” or “dice” are small cubes of semiconductor material such as silicon that have various interconnected electrical circuits formed therein. Each die typically has a metalized surface layer with electrical contact regions thereon that allows the die to be connected to other electronic components. Integrated circuit dice are produced by “singulating” (“dicing”) a unitary semiconductor wafer having identical circuits formed in adjacent regions thereof that are arranged in a rectangular generally waffle-shaped grid. Saw cuts or laser fractures are made along “saw streets” to cut the wafer into dice. A diced wafer is often supported on a deformable sheet known as dicing tape. The dicing tape may be stretched by force applied to its outer perimeter. Stretching the dicing tape causes the diced wafer supported on it to expand laterally, thereby separating the dice. The separated dice may then be picked up, one at a time, by pick and place machines or the like. With very small dice, i.e., less than about 1.0 mm, current methods of expanding the dicing tape tend to provide insufficient space between dice, or the space provided shrinks sufficiently after initial expansion, such that handling of the dice is difficult and often ends with damage to adjacent dice. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic top isometric view of a wafer, illustrating singulation thereof with a stealth laser. 
         FIG. 2  is a schematic bottom isometric view of a wafer, illustrating mounting of a dicing tape sheet and ring frame. 
         FIG. 3  is a schematic top isometric view of a wafer, dicing tape sheet and ring frame. 
         FIG. 4  is a schematic cross sectional elevation view of a wafer support table, dicing tape sheet, wafer and ring frame with the wafer in an unseparated state. 
         FIG. 5  is a schematic cross sectional elevation view of a wafer support table, dicing tape sheet, wafer and ring frame with the wafer support table raised relative to the ring frame and with the dicing tape sheet stretched and with the wafer in an expanded state. 
         FIG. 6  is a schematic cross sectional elevation view of the wafer support table, dicing tape sheet, wafer and ring frame in the state illustrated in  FIG. 5  and further showing a support tape ring just prior to application thereof. 
         FIG. 7  is a schematic cross sectional elevation view of the wafer support table, dicing tape sheet, wafer and ring frame of  FIG. 6 , with the support tape ring applied to the ring frame and dicing tape sheet and with the wafer support table lowered relative to the ring frame. 
         FIG. 8  is a top plan view of the dicing tape sheet, wafer, ring frame and support tape in the state illustrated in  FIG. 7 . 
         FIG. 9  is a detail view of the assembly of  FIG. 7 . 
         FIG. 10  is a top plan view of an another embodiment of dicing tape sheet, wafer, ring frame and support tape in which circumferentially extending strips of support tape are used. 
         FIG. 11  is a top plan view of still another embodiment of dicing tape sheet, wafer, ring frame and support tape in which radially extending strips of support tape are used. 
         FIG. 12  is a top plan view of still another embodiment of dicing tape sheet, wafer, ring frame and support tape in which chord wise extending strips of support tape are used. 
         FIG. 13  is a flow chart of a method of separating dice of a singulated wafer that is supported on a dicing tape sheet. 
         FIG. 14  is a flow chart of a method of separating dice of a singulated wafer that is supported on a relatively elastically deformable dicing tape sheet. 
     
    
    
     DETAILED DESCRIPTION 
     In general, this specification discloses, as illustrated by  FIGS. 4-8 and 13 , a method of separating dice  32 ,  34  of a singulated wafer  30  that is supported on a dicing tape sheet  10 . The method includes attaching the dicing tape sheet  10  to a ring frame  40 , as shown at block  201  of  FIG. 13 . The method also includes, as shown at block  202  of  FIG. 13 , relatively raising a portion  13  of the dicing tape sheet  10  supporting the wafer with respect to the ring frame  40 . The method further includes attaching support tape  60  to the ring frame  40  and the dicing tape sheet  10 , as shown at block  203  of  FIG. 13 . 
       FIG. 1  is a schematic top isometric view of a wafer  30 , illustrating singulation thereof with a stealth laser  20 . The stealth laser  20 , produces fractures in the wafer that form a plurality of singulation lines  21 ,  22 ,  23 ,  24 , etc. that form a rectangular grid and divide the wafer  30  into a plurality of dies or dice  32 ,  34 , etc. The wafer  30  may instead be singulated by saw cutting. Both stealth laser and saw cutting singulation are now in the art and are thus not further discussed herein. 
       FIG. 2  is a schematic bottom isometric view of a wafer, illustrating mounting of a generally circular dicing tape sheet  10  on a back surface  36  of the wafer  30 . The dicing tape sheet  10  has a tacky top surface  11  that is attached to the back surface  36  of the wafer  30 . The dicing tape sheet  10  has a non-tacky bottom surface  12 . A ring frame  40  is attached at a bottom surface  41  thereof to the tacky top surface  11  of the dicing tape sheet  10  at its periphery. Thus an assembly is formed as illustrated in  FIG. 3  in which a generally circular wafer  30  is supported on a generally circular dicing tape sheet  10 . Both the wafer  30  and most of the circular dicing tape sheet  10  are circumscribed by the ring frame  40 . Such an assembly is known in the art. 
     As illustrated by  FIG. 4 , the assembly of  FIG. 3  may be positioned on a generally flat top surface  51  of a support table  50 , such that the table top surface  51  is below a portion  13  of the dicing tape sheet  10  that supports the wafer  30  and associated dice  32 ,  34 . An outer annular portion  15  of the dicing tape sheet  10  that extends out in coplanar relationship with portion  13  and the ring frame  40  are not supported by the table top surface  51 . An alternate support such as a support ring/stand (not shown) or a human hand (not shown) may support the ring frame  40  and dicing tape sheet portion  15 . 
     Next, as illustrated by  FIG. 5 , the table  50  is raised relative to the ring frame  40 . As a result the entire dicing tape sheet  10  is stretched radially and, as a result, the dice  32 ,  34  mounted on inner dicing tape sheet portion  13  are radially spread apart. In other words, the singulation lines  21 ,  22 ,  23 ,  24 , etc. become wider. In one embodiment the width of each singulation lines  21 ,  22 ,  23 ,  24 , etc. is about 0.020 mm or more after the expansion shown in  FIG. 5 . 
     As shown by  FIG. 6 , a ring of support tape  60  is then positioned over the ring frame  40  and an annular part of the outer annular portion  15  of the dicing tape sheet  10 . The support tape has a smooth, non-tacky surface  61  and a tacky surface  63 . The tacky surface  63  of the support tape  60  is then pressed onto the ring frame  40  and the dicing tape sheet  10  when they are positioned as shown in  FIG. 6 . The table  50  is then raised relative to the ring frame  40  so that the dicing tape sheet  10  is returned to a generally planar configuration as shown in  FIGS. 7 and 8 . Dimensional parameters of the ring frame  40 , support tape  60 , dicing tape sheet  10  and the wafer are illustrated in  FIG. 9 . In one nonlimiting embodiment these parameters may have the following values: a=15.0 mm, b=5.0 mm, c=10.0 mm, d=1.6 mm, e=5.0 mm, f=10.0 mm, g=23.0 mm, h=10.0 mm, i=13.0 mm, j=0.050 mm to 0.900 mm, and k=0.180 mm. The thickness of the dicing tape may be 0.09 mm. It will be understood that these dimensions are only provided to give the reader a relative sense of scale for one typical embodiment. These dimensions will of course vary with wafers of different diameters and thicknesses and with different types of singulation and with different sizes and materials used for the dicing tape sheet and the support tape. In some embodiments the dicing tape sheet is made from relatively stretchable (elastic) material, such as polyvinyl chloride (PVC) or polyolefin (PO) and the support tape is made from relatively nonstretchable (inelastic) material such as polyethylene terephthalate (PET). 
       FIG. 10  is a top plan view of an another embodiment of dicing tape sheet  10 , wafer  30 , ring frame  40  and support tape  60 A in which a plurality of circumferentially (arcuately) extending support tape strips  60 A 1 ,  60 A 2 ,  60 A 3 , etc. are attached to the dicing tape sheet  10  and the ring frame  40  to prevent inward retraction of the dicing tape  10  and an associated reduction in width of the spaces  21 ,  22 ,  23 ,  24 , etc., between dice  32 ,  34 , etc. 
       FIG. 11  is a top plan view of an another embodiment of dicing tape sheet  10 , wafer  30 , ring frame  40  and support tape  60 B in which a plurality of radially extending support tape strips  60 B 1 ,  60 B 2 ,  60 B 3 , etc., are attached to the dicing tape sheet  10  and the ring frame  40  to prevent inward retraction of the dicing tape  10  with an associated reduction in width of the spaces  21 ,  22 ,  23 ,  24 , etc., between dice  32 ,  34 , etc. 
       FIG. 12  is a top plan view of an another embodiment of dicing tape sheet  10 , wafer  30 , ring frame  40  and support tape  60 C in which a plurality of chord wise extending support tape strips  60 C 1 ,  60 C 2 ,  60 C 3 , etc., are attached to the dicing tape sheet  10  and the ring frame  40  to prevent inward retraction of the dicing tape  10  with an associated reduction in width of the spaces  21 ,  22 ,  23 ,  24 , etc., between dice  32 ,  34 , etc. 
     In each of the above discussed embodiments the support tape  60  will reduce the amount of radial inward creep or inward retraction that the dicing tape sheet  10  would undergo without the support tape  60 . As a result, individual dies  32 ,  34 , etc. may be picked up with a conventional pick and place machine (not shown) without damaging adjacent dice. 
       FIG. 14  discloses a method of separating dice of a singulated wafer that is supported on a relatively elastically deformable dicing tape sheet. The method includes, as shown at block  221 , stretching the dicing tape sheet. The method further includes, as shown at block  222 , resisting a tendency of the dicing tape sheet to retract from said stretching by applying relatively nonelastically deformable support tape to the dicing tape. 
     Certain methods of separating dice of a singulated wafer and associated apparatus are expressly disclosed in detail herein. Various alternative embodiments of such methods and apparatus will occur to those skilled in the art after reading this disclosure. The appended claims are intended to be broadly construed so as to cover such alternative embodiments, except as limited by the prior art.