Lapping apparatus and process with raised edge on platen

• US 5,910,041 A
• Filed: 03/06/1997
• Issued: 06/08/1999
• Est. Priority Date: 03/06/1997
• Status: Expired due to Term

• Current Assignee: Keltech Engineering Incorporated
• Original Assignee: Keltech Engineering Incorporated
• Inventors: Duescher, Wayne O.
• Primary Examiner(s): Rose, Robert A.
• Application Number:
  US08/812,012
• Time in Patent Office: 824 Days
• Field of Search: 451/287, 451/285, 451/41, 451/28, 451/494, 451/259, 451/548, 451/538, 451/526
• US Class Current: 451/28
• CPC Class Codes: B24B 37/042 operating processes therefor
• CPC Class Codes: B24B 37/12 Lapping plates for working plane surfaces
• CPC Class Codes: B24B 37/245 Pads with fixed abrasives

Abstract

Lapping or polishing at high speeds with fine abrasive particles offers significant advantages in the speed of lapping, savings of time in lapping, and smoothness in the finished articles. An improved lapping system comprises a lapper platen system comprising a rotatable platen having I) a back surface and ii) a front surface, wherein the front surface of the rotating platen facing a work piece has a flat plateau or raised area which is continuous around a perimeter of the front side of said platen and the plateau is elevated with respect to a central area on the front surface. The front surface optionally has vents for air, the platen optionally has a back side to which a shaft is connected (directly or through intermediate connections) to rotate the platen and there is a front side on the platen to which is secured an abrasive sheet by reduced air pressure conveyed through said vents. The back side of the work piece holder is also optionally pivotally connected to a rotating joint which is in turn connected to a shaft which rotates said work piece. It is preferred that a frame for the system has a total weight of at least 200 kg supporting a work piece holder. It is also preferred that the work piece holder is movable on said frame. It is most preferred that the platen is rotated at a rotational velocity sufficient to generate a surface speed of at least 4,000 surface feet per minute (or even more than 20,000 surface feet per minute).

Claims

1. A process for lapping a surface comprising:

a) providing a work piece to be lapped, having at least one surface to be lapped which can be adjusted to a position parallel to said at least one surface of a rotating platen,

b) providing a rotating platen having i) a back surface and ii) a front surface with a periphery, said front surface of said rotating platen having a raised edge symmetrically disposed about said periphery,

c) providing a sheet of abrasive material having an abrasive face and a back side onto said raised edge to provide a symmetrical distribution of abrasive material on said rotating platen, said back side being on said front surface of said platen with the abrasive face of said sheet facing said at least one surface to be lapped,

d) securing said sheet of abrasive material to said front surface of said rotating platen, and

(1) rotating said rotating platen at a rotational speed of at least 500 revolutions per minute, and

(2) contacting said abrasive face and said at least one surface to be lapped on said work piece.

2. The process of claim 1 wherein said sheet of abrasive material comprises a surface having abrasive particles with an average diameter of from 1 to 100 micrometers.

3. The process of claim 1 wherein said abrasive surface comprises diamond particles having an average diameter of less than 50 micrometers.

4. The process of claim 3 wherein said platen is rotated at a speed of at least 2,000 rpm and an outer edge of abrasive sheet on said raised edge moves with a surface speed of at least 4,000 surface feet per minute relative to said surface to be lapped.

5. The process of claim 1 wherein said sheet of abrasive material is round.

6. The process of claim 5 wherein said round sheet has a) an outer edge and b) an inner edge defining a cut-out portion, and said sheet comprises an annular sheet, said inner edge having a diameter which is greater than one-third the diameter of said outer edge.

7. The process of claim 3 wherein said sheet is round and said round sheet has an outer edge and an inner edge defining an abrasive-free area and comprises an annular sheet, said inner edge having a diameter which is greater than one-third the diameter of said outer edge.

8. The process of claim 6 wherein during rotation of said platen a liquid is placed between said sheet and said work piece, said liquid forms a boundary layer as it moves from an inner portion of said sheet to an outer portion of said sheet, said sheet comprising abrasive particles which protrude by an average height on said surface of said sheet, and said boundary layer is less than 50% of the average height of abrasive particles protruding from said sheet.

11. A process for lapping a surface according to claim 1 wherein said front surface of said rotating platen facing said work piece has a flat plateau which is continuous around a perimeter of said front side of said platen and is elevated with respect to a central area on said front side,

providing a sheet of abrasive material on said flat plateau, said sheet of abrasive material having a front surface with an abrasive face and a back surface, with said abrasive face facing said at least one surface to be lapped,

securing said sheet of abrasive material to said flat surface of said plateau, and rotating said platen at at least 500 revolutions per minute and contacting said abrasive material and said work piece to remove material from said work piece.

12. The process of claim 11 wherein said plateau defines an annular shape on said front face.

13. The process of claim 12 wherein said platen is round.

14. The process of claim 12 wherein said sheet of abrasive material comprises an annular portion and a central open portion in which the central open portion is at least three times the radial dimension as the width of said annular portion.

15. The process of claim 14 wherein said sheet comprises an annular distribution of abrasive material on a backing material, with a center area of said sheet being a self-supporting structure which passes across said center area, contacting inner edges of said annular distribution of abrasive material.

16. The process of claim 15 wherein said abrasive sheet comprises a continuous substrate with a central area having no abrasive on said backing material, and an annular zone of said backing material surrounding said central area having abrasive material on a surface overlaying said plateau and facing away from said platen.

17. The process of claim 13 wherein said abrasive sheet comprises an annular zone and said central area, said central area being bonded to said annular zone, having less height than said annular zone when said sheet is lying flat, and there being a seam between said annular zone and said central area.

9. A process for lapping a surface comprising:

a) providing a work piece to be lapped, having at least one surface to be lapped which can be adjusted to a position parallel to said at least one surface of a rotating platen with abrasive thereon, said work piece being supported by a work piece holder on a pivot joint,

b) providing a rotating platen having i) a back surface, ii) a front surface, and iii) a raised edge forming an abrading plateau on said front surface of said rotating platen, said abrading plateau having a sheet of abrasive material having an abrasive face and a back side, and said back surface pivotally connected to a rotating joint which is in turn connected to a shaft which rotates said platen,

c) said abrasive face of said sheet facing said at least one surface to be lapped,

d) securing said sheet of abrasive material to said flat surface of said platen, and

e) rotating said platen at a rotational speed of at least 500 revolutions per minute by rotating said shaft, and

f) contacting said abrasive face and said at least one surface to be lapped on said work piece, and allowing said work piece to pivot around said pivot joint so that said abrading plateau and said at least one surface to be lapped become more parallel towards each other.

10. The process of claim 9 wherein pressure is applied between said work piece and said abrasive sheet by a gimbal pivot joint supporting said work piece.

25. The process of claim 9 wherein said abrasive sheet is secured to said rotating platen by a vacuum.

26. The process of claim 9 wherein said rotating platent is moving at at least 8000 surface feet per minute at the outer edge of said platen.

27. The process of claim 9 wherein said abrasive sheet comprises a continuous sheet of material with an annular ring of abrasive thereon.

28. The process of claim 9 wherein said abrasive on said abrasive sheet comprises metal plated diamond islands.

29. The process of claim 9 wherein said work piece is secured to said work piece holder by vacuum.

30. The process of claim 29 wherein adhesive tape is applied to a back side of said workpiece, and then the work piece with tape on its back side is secured to said work piece holder by said vacuum.

31. The process of claim 9 wherein the front surface of said platen has an inner edge and an outer edge, and at least one of the inner edge and outer edge are angled away from contact with work piece holder.

32. The process of claim 9 wherein a safety box surrounds said platen and work piece holder and is struck by debris from said work piece as said platen rotates.

33. The process of claim 9 wherein said abrasive sheet has an annular distribution of abrasive and said work piece holder is oscillated across a full width of said annular distribution of abrasive.

18. A lapper platen system comprising:

a) a rotatable platen having i) a back surface and ii) a front surface, wherein said front surface of said rotating platen facing a work piece and said front surface has a flat plateau which is continuous around a perimeter of said front side of said platen and is elevated with respect to a central area on said front surface and is defined by an area bounded by two concentric circles having different diameters,

b) said front surface also having vents for air,

c) said platen having a back side to which a shaft is connected and a front side on said platen to which is secured an abrasive sheet by reduced air pressure conveyed through said vents,

d) said back side also being connected to said shaft which rotates said platen;

e) a frame having a total weight of at least 200 kg supporting a work piece holder and said shaft connected to a rotatable platen,

f) a work piece holder which is movable on said frame;

g) said work piece holder is attached to a movable element on said frame which is capable of moving along said frame in a direction towards and away from said platen to perform lapping of a work piece held on said work piece holder,

h) said work piece holder having control element thereon which allow for independent;

movement and alignment of said work piece holder along three perpendicular axes so that a work piece on said work piece holder can be adjusted and oriented towards parallelity with said platen so that a work piece can be lapped; and

i) said control elements having at least 1,000 settings per rotation, each setting moving said shaft along one of said three axes by a dimension less than 0.001 mm.

19. A lapper system comprising:

a) a shaft which is connected to a rotatable platen having on a front surface of said platen vents for air, said rotatable platen having a back side to which said shaft is connected and a flat front side on said rotatable platen to which can be secured an abrasive sheet by reduced air pressure conveyed through said vents;

b) a frame having a total weight of at least 200 kg supporting a work piece holder and said shaft connected to a rotatable platen;

c) a work piece holder which is movable on said frame;

d) said work piece holder is attached to a movable element on said frame which is capable of moving along said frame in a direction towards and away from said platen to perform lapping of a work piece held on said work piece holder;

e) said work piece holder having control element thereon which allow for independent movement and alignment of said work piece holder along three perpendicular axes so that a work piece on said work piece holder can be adjusted and oriented towards parallelity with said rotatable platen so that a work piece can be lapped; and

f) said control elements having at least 1000 settings per rotation, each setting moving said shaft along one of said three axes by a dimension less than 0.005 mm;

wherein said lapper system includes a pivoting lapper platen system comprising;

g) a shaft which is connected to said rotatable platen, said rotatable platen having a back side to which said shaft is connected and a front side on said rotatable platen to which can be secured an abrasive sheet, said rotatable platen having i) a back surface, ii) a front surface, and iii) a raised edge forming an abrading plateau on said front surface of said rotatable platen, with an abrasive sheet secured to said raised edge.

20. The lapping system of claim 19 further having a pivoting joint comprising a shaped element selected from the group consisting of spherical and torroidal elements comprising a curved outside surface, and said pivoting joint being secured to said work piece holder, said pivoting joint having an arcuate surface area and a receding surface area of said outside surface of said pivoting joint, and said receding surface area is closest to said work piece holder;

said pivoting joint having a cross section with an effective center of its area, said receding surface area of said pivoting joint being defined by a surface which has average distances from said effective center which are smaller than the average distances from said effective center to said arcuate surface area;

a) arcuate surface area of the pivoting joint is supported by at least one pair of arcuate-faced bearings, said bearings comprising at least one upper bearing and at least one lower bearing, said bearings being attached to a portion of said work piece holder, and allowing said pivoting joint to pivot between said at least one pair of bearings;

b) said work piece holder being able to pivot about said pivot joint relative to said platen.

21. The lapper system of claim 20 wherein above said at least one upper bearing is a space between said shaft and a neck of said work piece holder, said shaft being restrained within said space by a cushioning means between said shaft and an interior surface of said neck, said cushioning means being selected from the group consisting of flexible compositions and springs.

22. The lapper system of claim 21 wherein said cushioning means comprises a flexible composition.

23. The lapper system of claim 21 wherein said cushioning means comprises an elastomeric composition.

24. The lapper system of claim 23 wherein between said flexible composition and said at least one upper bearing is a spring element, and above said spring element and below said flexible composition is a securing element, said securing element being capable of being adjusted in a direction parallel to said shaft to increase force upon said spring element, said force on said spring element in turn increasing force of said at least one upper bearing to press said bearing against an arcuate surface of said pivoting joint.