Patent Application
20110041308
The present invention generally relates to assemblies of rotary saw blades for the semiconductor industry.
In the making of electrical components from semiconductor materials and the like, multiple patterns are produced on a substrate that is subsequently sawed into smaller portions. The saws on which this is done are generally termed “dicing saws”. The circular blades used in such a saw are made of abrasive materials, for example, pieces of diamond held in a resin, CBN abrasive, or electrolytically deposited (electroformed) nickel bond matrix. The saw blades are thin so that they have a small width of cut, and thereby waste less material and generate less heat. But when a saw blade is thin it needs support near the outer edge where it is cutting. This support must be supplied without interfering with the planned cutting task. One way to provide support is to use a round disk of a smaller diameter than the blade. As an example, a saw blade of 2 inch diameter may be adjacent to and in contact with a support of 1.7 inch diameter, so that the blade can cut into a substrate to a depth of 0.1 inch, while still having a 0.05 inch clearance between the support and the substrate. In the example: (2−1.7)/2−0.1=0.05. In this example, 0.15 inches is known as the “blade exposure” or “cutting edge”.
As an example of prior art,
There are at least two kinds of dicing saws. The kind with a single supported blade, for example those disclosed in U.S. Pat. No. 5,261,385 to Kroll, that must do multiple passes across a substrate to achieve multiple cuts, and a ganged set of blades (as seen in
When a gang blade assembly is stacked for the first time, using freshly manufactured blades and spacers, the parts are usually free of warpage and stacking is not too difficult. However, after use, when re-stacking is needed with smaller spacers, the blades and previously used spacers are often found to be warped, making stacking more difficult. In an effort to get the least measured run-out, it is often necessary to angularly change (this process is commonly known as clocking) the blades and spacers relative to each other many times while measuring the run-out.
If the frequency of re-stacking procedures can be reduced then the gang blade assemblies will require less labor to use and will be more cost competitive.
One way to reduce the frequency of re-stacks is to machine or erode the spacers to a smaller diameter without unstacking them from the blades. If the spacers are of a hard material this could be difficult. But, it is known, to provide spacers of a softer material that can be eroded away relatively easily, by purposefully contacting it with a hard dressing material. Further, if the dressing material is substantially softer than the blades, then the blades can cut into the dressing material with no harm done. If desired, the dressing material can be specifically chosen to “dress” the blades, (i.e., selectively remove the blade bonding material to expose fresh particles). Such a process of eroding the spacers is described in U.S. Pat. No. 5,261,385 to Kroll, for single blade dicing saws. However, it is desirable to use erodible spacers in a ganged saw assembly to achieve even greater efficiencies.
In accordance with principles of the present invention, a marked improvement is accomplished in the allowable blade wear in a ganged saw blade assembly, such as a gang saw for dicing of wafers. This is accomplished by constructing the gang saw of saw blades separated by erodible pitch spacers. As the saw blades erode during use, the pitch spacers may be eroded in a controlled, matching fashion, e.g. by pausing the use of the tool and sawing into an abrasive material with the saw blade assembly at a controlled cut depth that abrades the pitch spacers so as to return the saw blades to the desired exposure.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.
As seen in
As explained in the background, as the blade 42 wears, D decreases while S remains constant, except for minor erosion from cutting fluid and debris. This causes E to decrease, and it is a limiting factor as to how long production can continue. In the present invention, the spacers 44,46 are made of an easily abraded material such as a plastic composite, or a molded/extruded/pressed graphite, or a pressed graphite, or a combination of these or any suitable material. They may be bisque-fired (i.e. partially-fused) ceramic. When E decreases to a limit, for example an E1 (
The exposure E is a critical parameter in thin-blade, precision slicing/dicing operations. Maximum exposure to thickness ratios have been empirically developed by the assignee of this application, based upon the bond composition (and stiffness) of the blade.
There are three fundamental bond types used in the dicing saw industry (in order of increasing stiffness—i.e. elastic modulus): resinoid, sintered metal and electroformed Ni. Experience has led to the use of the following maximum aspect ratios:
To assure that the above concept is understood, an example calculation is as follows: A blade that is 0.010 inches thick and 2 inch diameter is adjacent spacers that are 1.700 diameter, of any thickness. Then, E=(2−1.7)/2=0.150, and the ratio is 0.150/0.010=15:1, so this combination would be acceptable blade exposure for blades 42 made of metal or Ni, but not for blades 42 made of a resin.
An advantage of the erodible spacer concept is that maximization of initial exposure will not be required in order to maximize blade life. For example, it will only be necessary to erode the spacers enough to expose an additional 0.010″−0.015″ beyond the required cut depth. This means that cuts can be more precise and cutting speeds and production increased on a consistent basis. It also means that whereas the economics of cutter assembly life may have previously led to the use of a long blade exposure and therefore a metal or Ni blade, now it is possible to use the less expensive resin blades 42.
Referring again to
Although the embodiments described have pitch spacers 44 of all the same thickness, and flange spacers 46 that are flanged, any combination and quantity of spacers may be used. The flanged spacers provide another surface to grip while handling the gang cutter 40, which is especially beneficial for small sizes.
The embodiment described in
The table below lists some typical blade OD/ID/thickness dimensions. However, note that these are examples, and the possible OD/ID/thickness combinations are not limited to this list. The table also includes the associated pitch spacer thicknesses that might be included in a gang. Spacer OD would associate with required exposure and that exposure could range from zero to approximately the max ratio allowed by the blade bond type, which may change as materials and processes improve. The last column, containing a special symbol, is to identify some sizes that are expected to be a commonly used size.
The invention has been described herein with reference to specific embodiments, and those embodiments have been explained in substantial detail. However, the principles of the present invention are not limited to such details which have been provided for exemplary purposes.
