Abrasive tools for grinding electronic components

Details Abrasive tools for grinding electronic components Abrasive tools for grinding electronic components

1999-05-28

2002-05-28

Nguyen, George (Department: 3723)

Abrading

Rigid tool

Rotary disk

C451S541000, C451S551000, C051S309000

Reexamination Certificate

active

06394888

ABSTRACT:

This invention relates to porous, resin bonded abrasive tools suitable for surface grinding and polishing of hard materials, such as ceramics, metals and composites comprising ceramics or metals. The abrasive tools are useful in backgrinding of silicon and alumina titanium carbide (AlTiC) wafers used in the manufacture of electronic components. These abrasive tools grind ceramics and semi-conductors at commercially acceptable material removal rates and wheel wear rates with less workpiece damage than conventional superabrasive tools.
An abrasive tool designed to yield faster and cooler cutting action during grinding is disclosed in U.S. Pat. No. 2,806,772. The tool contains about 25 to 54 volume percent abrasive grain in about 15 to 45 volume percent resin bond. The tool also contains about 1-30 volume percent of pore support granules, such as vitrified clay thin walled hollow spheres (e.g., Kanamite balloons) or heat expanded (intumescent) perlite (volcanic silica glass) to separate the abrasive grain particles for better cutting and less loading of the grinding face with debris from the workpiece. The pore support granules are selected to be about 0.25 to 4 times the size of the abrasive grain.
An abrasive tool containing only fused alumina bubbles and no abrasive grain is disclosed in U.S. Pat. No. 2,986,455. The tool has an open, porous structure and free-cutting characteristics. Resin bonded wheels made according to the patent are used to grind rubber, paper fiber board and plastics.
Erodable agglomerates useful in making abrasive tools are disclosed in U.S. Pat. No. 4,799,939. These materials contain abrasive grain in resin bond materials and up to 8 weight percent hollow bubble material. The agglomerates are described as being particularly useful in coated abrasives.
An abrasive tool suitable for grinding surfaces of sapphire and other ceramic materials is disclosed in U.S. Pat. No. 5,607,489 to Li. The tool is contains metal clad diamond bonded in a vitrified matrix comprising 2 to 20 volume % of solid lubricant and at least 10 volume % porosity.
The abrasive tools known in the art have not proven entirely satisfactory in fine precision surface grinding or polishing of ceramic components. These tools fail to meet rigorous specifications for part shape, size and surface quality in commercial grinding and polishing processes. Most commercial abrasive tools recommended for use in such operations are resin bonded superabrasive wheels designed to operate at relatively low grinding efficiencies so as to avoid surface and subsurface damage to the ceramic components. These commercial tools typically contain over 15 volume percent diamond abrasive grain having a maximum grain size of about 8 microns. Grinding efficiencies are further reduced due to the tendency of ceramic workpieces to clog the wheel face, requiring frequent wheel dressing and truing to maintain precision forms.
As market demand has grown for precision ceramic and semi-conductor components in products such as electronic devices (e.g., wafers, magnetic heads and display windows), the need has grown for improved abrasive tools for fine precision grinding and polishing of ceramics and other hard, brittle materials.
SUMMARY OF THE INVENTION
The invention is an abrasive tool comprising a backing and an abrasive rim containing a maximum of about 2 to 15 volume percent abrasive grain, the abrasive grain having a maximum grit size of 60 microns, wherein the abrasive rim comprises resin bond and at least 40 volume percent hollow filler materials, and the abrasive grain and resin bond are present in the abrasive rim in a grain to bond ratio of 1.5:1.0 to 0.3:1.0.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The abrasive tools of the invention are grinding wheels comprising a backing having a central bore for mounting the wheel on a grinding machine, the backing being designed to support a resin bonded abrasive rim along a peripheral grinding face of the wheel. The backing may be a core disc or ring formed into a planar shape or into a cup shape, or an elongated spindle or some other rigid, preformed shape of the type used to make abrasive tools. The backing is preferably constructed of a metal, such as aluminum or steel, but may be constructed of polymeric, ceramic or other materials, and may be a composite or laminate or combination of these materials. The backing may contain particles or fibers to reinforce the matrix, or hollow filler materials such as glass, silica, mullite, alumina and Zeolite® spheres to reduce the density of the backing and reduce the weight of the tool.
Preferred tools are surface grinding wheels, such as type 2A2T superabrasive wheels. These tools have a continuous or a segmented abrasive rim mounted along the narrow lip of a ring- or cup-shaped backing. Other abrasive tools useful herein include type 1A superabrasive wheels having a planar core backing with an abrasive rim around the outer circumference of the core, inner diameter (I.D.) grinding abrasive tools with an abrasive rim mounted on a shank backing, outer diameter (O.D.) cylindrical grind finishing wheels, surface grinding tools with abrasive “buttons” mounted on a face of a backing plate, and other tool configurations used to carry out fine grinding and polishing operations on hard materials.
The backing is attached to the abrasive rim in a variety of ways. Any cement known in the art for attaching abrasive components to metal cores, or to other types of backings, may be used. A suitable adhesive cement, Araldite™ 2014 Epoxy adhesive is available from Ciba Specialty Chemicals Corporation, East Lansing, Mich. Other means of attachment include mechanical attachment (e.g., abrasive rim may be mechanically screwed to the backing plate through holes placed around the rim and in the backing plate, or by dovetail construction). Slots may be grooved into the backing element and the abrasive rim, or abrasive rim segments, if the rim is not continuous, may be inserted into the slots and fastened in place by an adhesive. If the abrasive rim is used in the form of discrete buttons for surface grinding, the buttons also may be mounted onto the backing with an adhesive or by mechanical means.
The abrasive grain used in the abrasive rim is preferably a superabrasive selected from diamond, natural and synthetic, CBN, and combinations of these abrasives. Also useful herein are conventional abrasive grains, including, but not limited to alumina oxide, sintered sol gel alpha alumina, silicon carbide, mullite, silicon dioxide, alumina zirconia, cerium oxide, combinations thereof, and mixtures thereof with superabrasive grains. Finer grit abrasive grains, i.e., a maximum grain size of about 120 microns, are useful. A maximum size of about 60 microns is preferred.
Diamond abrasives are used to grind ceramic wafers. Resin bond diamond types are preferred (e.g., Amplex diamond available from Saint-Gobain Industrial Ceramics, Bloomfield, Conn.; CDAM or CDA diamond abrasive available from DeBeers Industrial Diamond Division, Berkshire, England; and IRV diamond abrasive available from Tomei Diamond Co., Ltd., Tokyo, Japan).
Metal coated (e.g., nickel, copper or titanium) diamond can be used (e.g., IRM-NP or IRM-CPS diamond abrasive available from Tomei Diamond Co., Ltd., Tokyo, Japan; and CDA55N diamond abrasive available from DeBeers Industrial Diamond Division, Berkshire, England).
Grain size and type selection will vary depending upon the nature of the workpiece, the type of grinding process and the final application for the workpiece (i. e., the relative importance of material removal rate, surface finish, surface flatness and subsurface damage specifications dictate grinding process parameters). For example, in the backgrinding and polishing of silicon or AlTiC wafers, a superabrasive grain size ranging from 0/1 to 60 micrometers (i.e., smaller than 400 grit on Norton Company diamond grit scale) is suitable, 0/1 to 20/40 microns is preferred, and 3/6 microns is most preferred. Metal bond, or “blocky”, diamond abrasive types may be used (e.g., MDA diamond abr

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