Background: Polishing pad is used in several industries, such as in the manufacture of magnetic disk substrate and silicon wafer fabrication, where a smooth planar surface must be produced.

Stock removal rate during polishing is proportional to pressure, velocity, time and abrasive grain size. The circumferential speed is higher, so is the removal rate. This is aggravated by the ready supply of abrasive near the circumference of the work piece.

The work piece, invariably, becomes non-planar; this is normally overcome by polishing the workpiece in planetary motions.

A polishing pad must ideally be planar, rigid and durable and the surface must be porous and capable of holding the abrasive; as the workpiece is being rotated and moved in orbits, the polishing pad discharges the abrasive slurry. The problem with the current polyurethane foam is that the pocket-type pore's size and shape are not consistent and they are easily plugged up; once this occurs, the polishing efficiency is low and the foam surface has to be dressed periodically. The polyurethane material also changes its elasticity as it ages; the abrasive slurry is, therefore, not effectively discharged and the resultant non-uniform distribution of the abrasive over the polishing surface is not desirable. After manufacturing, the polyurethane foam surface is ground flat with a belt grinder; however, the ground surface is invariably wavy and, therefore, not desired.

Object of invention: It is the primary object of the invention to provide a new method for manufacturing a porous polishing pad, which has consistent pore sizes, shape, orientation and density, and a flat surface so as both to maintain constant polishing conditions and to give a super mirror-polished surface, which is both planar and scratch-free.

It is another object to improve on the yield of the polishing process and yet another to select both a durable and an elastic material.

Summary of the invention: The manufacture of a porous polishing pad comprising of implanting the metallic or polymeric filings onto the adhesive layer of a backing cloth in an electric field, roll coating of the pad polymer and after curing, etch away the metallic filings with acid or dissolve the polymeric filings with a solvent/acid to yield a porous polishing pad, which has consistent pore size, shape, orientation, density and pattern, and a flat surface that can maintain constant polishing conditions and, hence, able to produce a super mirror-polished surface, which is both planar and scratch-free.

This polishing pad with controllable pore size, shape, orientation, density and pattern allows uniform distribution of abrasives across the polishing surface and hence able to give a super mirror-polished surface to the workpiece.

Brief description of the figures: The accompanying drawings constitute a part of the description of the invention, illustrate and serve to explain the principles of the invention. It is understood, however, that the drawings are for purposes of illustration only, and not as a definition of the limits of the invention for which reference should be made to the claims at the end of this description: Figure 1 shows the set up for the manufacturing of the new polishing pad.

Figure 2 shows the porous polishing pad with different pore sizes, shapes, orientation, density and patterns.

Description of the invention: Figure 1 shows one embodiment of the present invention. A backing cloth 1 is coated with an adhesive 2. One means of preferred coating is known as roll coating 3.

Metallic filings 4 are dispersed on the backing cloth in an electrostatic field E. They are dispersed evenly by mutual repulsion, but aligned longitudinally to the electric field. At the other end, another set of roll coating 5 apply a layer of pad polymer 6 onto the implanted filings. The coating roller surface can be plain or patterned; a plain roller will coat a uniform layer of the pad polymer onto the implanted filings; a patterned roller will apply the polymer according to the pattern of the roller surface.

The thickness of the pad polymer is controlled by metering the roller gap; Many pad polymers can be used, such as polyurethane, polyamide, ultra high molecular weight polyethene and so on. After curing, the polymer pad is subjected to an acid, which etches away the metal filings and produces a uniform strip of porous pad; the pore size and shape can be controlled by the filing size and shape, while the pore orientation can be controlled by the inclination of the backing cloth with respect to the electric field direction. When the filings are plate-like, an electromagnetic field B perpendicular to the electric field can be applied and the orientation of the plate-like filings in the x-z plane can be controlled; a porous polymer with rectangular pores in different patterns can then be manufactured. The pore density can be controlled by both the electrostatic field strength E and the backing cloth feed speed, F. When a patterned roller is used to apply the pad polymer onto the backing cloth, the resultant porous pad with the polymer in any pattern can be produced.

Figure 2 shows some examples of the porous polishing pad with different pore sizes, shapes, orientation and patterns. The patterned porous pad is desirable because the polishing debris can be discharged during polishing, and prevents scratching the newly polished surface.

In another embodiment; instead of metallic filings, the filings 4 are made of another polymer, such as cellulose acetate for example. In the electric field, the polymeric filings are longitudinally aligned with the field and implanted on the adhesive. By roll coating the pad polymer, just as is described above and, thereafter, dissolving away the polymeric filings with a solvent, such as acetone for example or an acid, a porous polymer pad is also obtained.

In another embodiment, instead of a backing cloth, a plastic film, such as polyethene and so on, can be used. The tape is coated with an adhesive by roll coating, implanted with metallic or polymeric filings and the pad polymer is coated onto the implanted filings, the filings are then etched or dissolved to produce a porous polishing pad; the plastic film is then peeled off and a new backing cloth is adhered to the polishing pad to give it strength.

In another embodiment, the pad polymer 6 can be applied onto the implanted filings by other printing methods, such as screen printing for example, either uniformly or patterned, instead of roll coating as described earlier.

While only a few embodiments of the present invention have been described and illustrated, it will now be apparent to those skilled in the art that other modifications, improvements and variations can be made to the manufacturing process of the present invention without departing from the scope or spirit of this invention.