Abrading – Abrading process – Roll – roller – shaft – ball – or piston abrading
Reexamination Certificate
1999-03-19
2001-04-24
Scherbel, David A. (Department: 3723)
Abrading
Abrading process
Roll, roller, shaft, ball, or piston abrading
C451S005000
Reexamination Certificate
active
06220938
ABSTRACT:
This invention relates to grinding machines and to grinding wheels for use in such machines for grinding notches in the edges of discs such as wafers of silicon for use in the construction of semi-conductor devices, and to methods of grinding edge regions of such discs so as to form notches therein. Since the notches are of relatively small dimensions relative to the size of the wafers, grinding wheels used to form such notches are commonly referred to as grinding pins.
BACKGROUND TO THE INVENTION
A grinding machine for grinding discs is disclosed in WO97/48522 and incorporated herein by reference. WO97/48522 discloses use of a metal-bonded CBN or diamond wheel on a grinding machine to rough grind the edge of a disc, such as a semiconductor wafer, before use of a softer resin-bonded CBN wheel for finish grinding the disc edge and further describes an in situ technique for forming and re-forming a groove in the resin bonded CBN grinding wheel to grind the correct shape around the disc edge.
The machine also includes a small diameter grinding pin for grinding a notch of predetermined proportions around the edge of the ground disc.
The use of a resin-bonded CBN wheel for notch grinding has the disadvantage that such wheels are relatively soft compared with metal-bonded CBN or diamond wheels, and as such wear rapidly and need to be replaced frequently. Therefore such wheels have tended not to be used in such applications although the reduced damage to the workpiece resulting from the use of such wheels means that it is desirable if they could be used for notch grinding.
The present invention aims to provide a formable grinding pin for notch grinding which can be used for longer before it has to be replaced, and to a method of forming such a notch grinding pin and to an improved method of notch grinding.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a grinding pin for notch grinding comprises a cylindrical region of formable grinding material, in which is formed a groove having a profile which corresponds to that desired for an edge of a notch to be forced, and wherein the axial extent of the cylindrical region is such that further grooves may be formed subsequently therein as the first and then each of the other grooves becomes too worn to be capable of being reformed, and reused.
The invention thus provides a notch grinding pin, or wheel, whose axial width is such as to enable a plurality of grooves successively to be machined therearound for notch grinding.
The advantage of the invention is obtained if the formable pin is mounted in a spindle of a grinding machine and is initially formed, and re-formed as required, in situ.
Desirably the formable material comprises a resin-bonded material, or a vitreous-bonded material, such as grinding grit bonded by a resin or vitreous material.
Preferably the grinding machine is a CNC grinding machine.
Using a wide (cylindrical) pin and forming and re-forming the grooves in situ, allows more grinding operations to be performed before the pin has to be replaced. Thus after each groove formed around the cylindrical surface of the pin is no longer capable of being reformed to accurately grind notches, a further groove can be formed at an axially spaced location across the width of the pin, so increasing the useful life of the pin and reducing the number of times the more complex operation of replacing the pin (involving considerable machine down-time) is required.
The length of the cylindrical region is typically of the order of 10 mm, preferably 6 mm, and its overall diameter is typically 4 mm.
In a method of notch grinding in accordance with the invention, a first groove is formed around a cylindrical region of a formable grinding material using a groove-forming grinding wheel also mounted on the same grinding machine, and after grinding to form one or more notches, or as required, the notch-forming groove is reformed using the same, or another, forming wheel, until it is not possible to accurately re-form the groove, after which a subsequent groove is formed in a similar manner in the cylindrical surface adjacent the first, to permit the notch grinding process to continue.
In a preferred embodiment of the invention, the cylindrical region of the grinding pin may comprise the formable grinding material region, and a metal-bonded grinding material region, wherein the metal-bonded region is provided with a groove for rough grinding a notch, and the formable grinding material region is formed with a groove to permit finish grinding of a notch previously formed by the groove in the metal-bonded region of the pin, and the axial extent of the formable grinding material region is sufficient to permit additional grooves to be formed therein as each groove becomes unusable.
According to a further aspect, the invention also relates to a machine having a work spindle, a grinding spindle having a small diameter notch-forming grinding pin as aforesaid mounted thereon and engageable with an edge region of a workpiece carried by the work spindle, and a forming wheel mounted on and rotatable by a spindle which when engaged with the notch grinding pin, will form a notch-forming groove therearound as required.
The notch grinding pin is preferably formed from formable grinding material but may also comprise a first region of metal bonded grinding material also formed with a notch grinding groove, to allow rough grinding of the metal to be performed first, and thereafter the formable region to be used to finish grind the notch.
The forming wheel may be mounted on the same spindle as the workpiece, and the notch forming pin is moved as required to engage the forming wheel or the workpiece edge.
It has been found that formable notch grinding pins, formed on the machine (in situ), produce a better finish in, and less sub-surface damage around, the notch.
Preferably the grinding material is resin-bonded diamond, or resin bonded CBN, or vitreous bonded material.
The invention also lies in disc-shaped workpieces with at least one notch around their edge having an internal edge profile formed at least in part using a formable grinding pin having a grinding groove formed therein by in situ forming on the machine by a forming wheel mounted for rotation on the workspindle of the machine.
REFERENCES:
patent: 3364630 (1968-01-01), Rusk et al.
patent: 3562702 (1971-02-01), Celovsky
patent: 4800686 (1989-01-01), Hirabayashi et al.
patent: 4841676 (1989-06-01), Barwasser
patent: 4841682 (1989-06-01), Waelti
patent: 5533931 (1996-07-01), Imai et al.
Ball Matthew James
Falkner Dermot Robert
Mawer Peter Vaughan
Morantz Paul Martin Howard
Stocker Mark Andrew
Lee Mann Smith McWilliams Sweeney & Ohlson
Ojini Anlhony
Scherbel David A.
Unova U.K. Limited
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