Patent Application
20080092714
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
In
The core 120 comprises the first grit 125, which in one embodiment may be diamond grit, bonded in the matrix 150. The matrix 150 should be comprised of a material sufficient to bond or hold the first grit 125 in place during cutting. In one embodiment, the matrix 150 may comprise a metal, such as nickel. The first grit 125 has a grit size of less than about 10 microns. For example, the first grit 125 size may range from about 4 microns to about 6 microns. However, the second different grit 135 is smaller than the first grit 125. In one embodiment, the second different grit 135 may have a grit size less than about 5 microns. For example, the second different grit size 135 may range from about 2 microns to about 4 microns. The third grit 145 may be either the same size or a different size than the second different grit 135. In one embodiment, however, the third grit 145 is the same size as the second different grit 135. It should be noted that the smaller the grit size, the finer the cut and the better the end product with fewer risks of testing failures or damage to adjacent electrical structures. While the thickness may vary, in one embodiment, a thickness 160 of the cutting portion 115 is less than about 30 microns. For example, the thickness 160 may be about 20 microns. It is important that this overall thickness be a thin as possible without sacrificing blade strength because the blade thickness 160 determines the majority of the kerf width. Furthermore, a thinner blade with standard blade exposure 115 will increase the likelihood of blade instability that can result in blade breakage. Reducing the blade exposure 115 introduces the need for more frequent blade changes resulting in more blades used and more operator time to install the blades, thereby raising cost of both materials and labor. With a blade thickness of about 20 microns designed as provided by the invention, it is now possible to achieve kerf widths compatible with scribe street widths of 52 microns or less. This may be compared to previous scribe street widths of 62 microns from blades with a 30 micron thickness. Thus, die yield per wafer is significantly enhanced.
The dicing blade 100 has a core overall diameter 127 that is a diameter of the core 120 comprising the first grit 125. The first surface region 130 has a first surface region diameter 137 that is slightly less than the core overall diameter 127. The second surface region 140 has a second surface region diameter 147 that is also slightly less than the core diameter 127. The first surface region diameter 137 and the second surface region diameter 147 are substantially equal. The relative sizes of the core diameter 127 to the first surface region diameter 137 and the second surface region diameter 147 enable a leading edge 128 of the core 120 with first grit 125 to cut the semiconductor wafer before the grit of the first and second surface regions 130, 140, respectively. Of course, one who is of skill in the art will recognize that this condition of a larger relative core diameter 127 is the ideal of a new blade. As the blade wears, many factors will affect the actual condition of the core diameter 127 versus the first and second surface region diameters 137, 147.
In one embodiment, the cutting portion 115 has a new blade exposure less than about 900 microns. Specifically, the new blade exposure 115 may range from about 760 microns to about 890 microns. The term “new blade exposure” 115 is used here because the blade exposure will change, i.e., be reduced by blade wear, as wafer cutting is performed; ultimately reaching a minimum useable point where the blade exposure 115 equals the cut depth plus the safety exposure.
Note also that an increased grit concentration, i.e., number of grit pieces per volume, will also assist in reducing chipping. Additionally, the bonding material that holds the grit may be of varying hardness, i.e., soft, medium, or hard, and that the harder bond will result in more chipping, but less blade wear. Therefore, the exact natures of the first and second surface regions 130, 140, as well as the core 120, need to be optimized for these factors: grit size, grit concentration, region thickness, and bond hardness. The outer layer can have a smaller grit size as explained above, a higher grit concentration, and a soft to medium bond material to produce less chipping or peel off. By comparison, the core 120 should have a larger grit size, high concentration, and hard bond to resist wear.
Thus, a dicing blade has been described for precision cutting of semiconductor wafers using a core material comprising a first grit in the core and a second different, finer grit in the surface regions of the dicing blade. In use, the coarser first grit does the majority of the cutting of the scribe street while avoiding the ground ring. The finer, second different grit performs the necessary cutting in the vicinity of the ground ring and therefore reduces the probability of peel off and chipping of the ground ring.
Those skilled in the art to which the invention relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments without departing from the scope of the invention.
