US2998680A

US2998680A - Lapping machines

Info

Publication number: US2998680A
Application number: US749923A
Authority: US
Inventors: Morton S Lipkins
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-07-21
Filing date: 1958-07-21
Publication date: 1961-09-05
Anticipated expiration: 1978-09-05

Description

M. S. LlPKlNS APPING Sept. 5, 1961 MACHINES Filed July 21, 1958 INVENTOR Mama/v 5 L/P/mvs BY l I ATTORNEY United States Patent 2,998,680 LAPPING MACHINES Morton S. Lipkins, Malverne, N.Y. Filed July 21, 1958, Ser. No. 749,923 11 Claims. (Cl. 51-131) The present invention relates to lapping machines and the like.

A known form of lapping machine has an apertured nest for keeping the articles distributed about the lapping plate. The articles are moved across the lapping surface while pressure is maintained against them, commonly by a pressure plate. The nest usually is in the form of a thin member having a distributed pattern of holes whose edges encircle the articles being lapped. The nest is thin enough so that the articles resting on the lapping surface can project above the nest an ample amount for engagement by the pressure plate. An object of the present invention is to provide an improved lapping machine adapted to handle articles that are thinner than the minimum practical thickness of a nest.

Articles to be lapped are commonly carried relatively along the surface of the lapping disc in an orbital path that is off-center relative to the axis of the disc, The lapping plate tends to wear unevenly, and commonly has to be resurfaced after only a limited number of lapping operations. I have found that it is important to provide for considerable overhang of the nest and the article beyond the edge of the lapping ring or disc during part of the orbital path for, with an empirically determined extent of overhang, such unequal wear can be practically eliminated. In the case of relatively small articles, the best overhang may well amount to one or more piece diameters.

Accordingly, a further object of this invention resides in the improvement of lapping machines having overhang in the lapping path. A feature of the invention in this connection is in the provision of a vacuum holder to retain the articles during the overhang portions of their lapping paths. In the illustrative embodiment of the invention described in detail below, a nest and the articles to be lapped bear against the flat lapping surface of a rotary lapping ring or disc, and pressure against the articles is applied by projecting elements into the holes in the nest. In practice the wafers are normally of unequal thicknesses at the start. The projecting elements are formed on a single rigid member, and the faces of the projecting elements that apply pressure are coplanar. This feature promotes reduction of all the wafers to the same finished thickness.

The nest in the embodiment below includes a circular pattern of article-retaining apertures; or apertures arranged in multiple concentric circles may be used where a large number of articles are to be handled. In order to help keep the nest in close face contact with the lapping surface (to guard against thin wafers slipping under the nest) the nest is made rigid, and preferably heavy, and is much thicker than the wafers. The pressure member is loosely complementary to the nest, in that the projections of the pressure member fit loosely in the article-confining holes in the nest, and the pressure member has a recessed pattern corresponding to the nest which it accommodates. In such an organization, the wafers are prevented from slipping out of the confining holes in the nest and under the nest, and despite the relative thickness of the nest compared to the thin Wafers, the necessary pressure is applied for the lapping operation.

The nest and the pressure member move as a unit relative to the lapping member, moving each wafer in an orbital path which at times carries the wafers into overhanging positions. This is highly advantageous in pre- -ratus where appropriate.

Patented Sept. 5, 1961 serving the flatness of the lapping surface, as noted above (or in preserving the sphericity of a lapping surface if such were used). Vacuum ports are provided in the pressure member of the illustrative apparatus. The pressure member therefore both presses the wafers against the lapping surface and firmly holds the Wafers in the pressure plane even during the overhang portions of their travel.

The nature of the invention and its further objects and features of novelty will be more apparent from the following detailed description of the illustrative embodiment shown in the accompanying drawings which form part of this disclosure. In the drawings:

FIG. 1 is a vertical cross-section of illustrative embodiment of the invention, shown largely in cross-section along the line 11 in FIG. 2; and

FIG. 2 is a cross-section of the apparatus in FIG. 1 viewed from the line 2-2 in FIG. 1.

In the drawings, a lapping member 10 is shown as a disc having a supporting shaft 12 on which it is rotatably supported, and it is operated by any suitable rotary drive means 14 that is diagrammatically illustrated.

Articles 16 to be lapped are shown round, although they may be of any shape, and they are constrained by nest 18 to move in a circular orbit eccentric to lapping member 10. A circular array of apertures 20 are provided in nest 18, although any expedient pattern of apertures may be used. conventionally, the apertures are arranged with one in the center of the nest as illustrated, a circle of six apertures for as many articles, a larger circle of 12 apertures and successive concentric circles of 19, 26 apertures, each larger circle containing seven more apertures than the preceding smaller. one. Only a center aperture and a circle of six more are shown for simplicity, but a larger number of apertures is of course contemplated for inclusion in the illustrative appa- The walls of these apertures engage the edges of wafers 16 to react against the fricttional drag of the lapping surface againstthe wafers, to force the wafers to travel relatively across the. lapping surface during rotation of plate 10. j V j A pressure member 24 is provided having integral pr ojections 26 extending with a, loose fit into openings 20 in the nest. The bottom faces of projections 26 that engage wafers 16 are all in a common plane. These faces contain ports 30 which extend to a vacuum manifold 34 and hollow shaft 38, which communicates. via hole 40 in the shaft to a non-rotatably supported gland 42, and to vacuum line 45. This is connected to a suitable source of weak vacuum, of sufiicient capacity to hold Wafers 16 against projections 24 without being so hard a vacuum as to deform wafers 16. A pattern of passages 30 may be used in each projections 26 for-relatively large or especially thin wafers.

A stationary shaft 44 locates shaft 38 and thereby fixes the axis of pressure member 24. as Well as that of nest 18. Shaft 44 is intended to avoid imposing other constraint on

members

18 and 34, such as might force them out of their natural resting position or rotational motion. Other equivalent means may be used to arrest the axis of nest 18 and thereby arrest the axis of the pressure plate 24 without interfering with their natural pressure attitudes, and without restraining their rotation. It will be understood that the pressure plate and the nest arecaused to rot-ate by rotation of lapping plate 10, although any suitable drive of member 24 or of'member 18 may be used, with the remaining members appropriately supported free of the restraints considered above.

A radiating pattern of grooves 46 are formed in the bottom face of nest 18, to distribute slurry or lapping compound to all parts of the lapping surface. Slurry may be dropped onto the projecting part of the lapping plate 10, at the right in the drawings.

Pressure member 26 can freely shift up and down relative to the nest 18, to accommodate different thicknesses of wafers, and to maintain pressure against the wafers as lapping reduces their thickness. Pressure is greatest on the thickest of the wafers, which are thereby quickly reduced to the thickness of the thinnest wafers; and then they are then all lapped to a smooth, true finish. Both top and bottom surfaces of the wafers can be lapped if desired. The apparatus is effective with wafers whose finished thickness may be only 0.002 inch or less, much thinner than is practical for the conven tional thin nest and flat pressure plate.

Rotation of lapping plate produces a rotation of the assembly 161824 as a unit. Wafers 16 move in a circular path, which carries each of them periodically into the overhang position shown at the left in FIG. 1. This is important in preserving the flatness of the lapping surface against the natural tendency of the system to produce uneven Wear. The vacuum system provided in pressure member 24 is important in the overhang regions, for holding the wafers in the lapping plane as they leave and as they enter the area of the lapping surface, and to support them against gravity where they completely leave the lapping surface in the overhang region.

Both the lapping plate and the nest are of cast iron, and the latter is thick enough to be rigid and to remain flat. The nest wears (as does the lapping surface) during the lapping surface, but the nest remains flat and true with the proper extent of overhang.

The foregoing represents what is presently regarded the preferred embodiment of the invention; but it is naturally susceptible to a wide variety of modification in details and of rearrangement, and it is undoubtedly useful in various applications. Consequently, the invention should be broadly construed, in accordance with its full spirit and scope.

What I claim is:

l. Lapping apparatus including a rota'tahly mounted flat-topped lapping member, a flat-bottomed relatively thick nest embodying a pattern of wafer-surrounding apertures, said nest being in face contact with said member peripherally of said apertures, and a rigid pressure member having a series of projections extending into said apertures, the bottom surfaces of said projections lying in a common plane and said pressure member being ver- 'tically movable relative to said nest for allowing the projections of the pressure member to descend progressively deeper into the nest apertures and bear against wafers in said apertures as the wafers are reduced in thickess, said pressure member also being rotatably mounted and the axes of said lapping member and said pressure member being offset in relation to each other, and rotary drive means connected to one of said members.

2. Lapping apparatus including a lapping member, a relatively thick nest having a pattern of wafer-retaining apertures, said nest being in face contact with said member peripherally of said apertures, and a unitary pressure member whose surface is relieved in a pattern that is loosely complementary to said nest so as to receive the nest where it rises from the lapping member and to project into said nest where the latter is apertured, said pressure member being adapted to bear against wafers 'retained in the nest, and drive means for causing travel of said wafers along the lapping surface of said lapping member.

3. Lapping apparatus including a fiat-topped rotary lapping disc, an apertured wafer-retaining nest having Wafer-confining portions in face contact with the flat top of said disc, and a unitary pressure plate having a relief pattern therein loosely complementary to said apertured nest so as to embody projecting Wafer-engaging means, said nest and pressure member being mounted for rotation about an axis olfset from that of said disc, and rotary drive means producing rotation of said disc and of said nest and pressure plate about their respective axes.

4. Lapping apparatus including a lapping plate, an apertured wafer-retaining nest having wafer-confining portions in face contact with said plate, and a pressure member having rigid projecting patterned means loosely complementary to said nest shaped so as to be received in said nest where the latter is apertured, said rigid projecting means disposed above said lapping plate and being adapted to bear against at least one wafer retained in the nest, and means for driving said lapping plate relative to said nest and said pressure member to effect orbital travel of the wafer over the surface of said lapping plate and into an overhang region, and vacuum means including at least one passage in said rigid projecting means for holding said water against said projecting means during travel of the wafer outside full face contact with the lapping plate in said overhang region.

5. Lapping apparatus including a lapping plate having a first rotational axis, an apertured wafer-retaining nest overlying said lapping plate and having wafer-confining portions in face contact therewith, and a pressure member overlying said nest and having a pattern of projecting portions unitary therewith and loosely complementary to said nest so as to project into said nest where the latter is apertured, said projecting portions having surfaces spaced uniformly from the lapping plate and adapted to bear against wafers retained in the nest, said nest and said pressure member being mounted for rotation about a second axis offset from that of the lapping plate, and means for driving said lapping plate relative to said nest and said pressure member to effect orbital travel of wafers over the surface of said lapping plate.

6. Lapping apparatus including a flat-faced lapping plate, a flat-faced nest having a pattern of wafer-retaining apertures, said nest having portions peripherally of said apertures in face contact with said plate, and a pressure member having a pattern of projections unitary therewith loosely complementary to and received in the apertures of said host, the faces of said projections of said pressure member that are engageable with wafers retained in the nest being coplanar, said nest and said pressure member being mounted for rotation about a first axis and said lapping plate being mounted for rotation about an axis off-set from said first axis sufliciently to carry peripheral wafers in the nest into an overhang region, and means for rotating said lapping plate relative to said nest and said pressure member to effect orbital travel of wafers over the surface of 'said lapping plate.

7. Lapping apparatus including a lapping plate, an apertured wafer-retaining nest having Wafer-confining portions in face contact with said plate, and a pressure member having projecting means loosely complementary to said nest so as to project into said nest where the latter is apertured, said pressure member being adapted to bear against at least one wafer retained in the nest, means for supporting and driving said lapping plate in relation to said nest and said pressure member to effect orbital travel of the wafer over the surface of said lapping plate and into an overhang region, and vacuum means including at least one vacuum passage in said projecting means for holding the wafer flush against the pressure member during travel of the water outside full face contact with the lapping plate.

8. Lapping apparatus including a lapping plate, an apertured wafer-retaining nest overlying said plate and having wafer-confining portions in face contact therewith, and a pressure member overlying said nest, said pressure member having a surface engaging and bearing against wafers retained in the nest, means for supporting and driving said lapping plate relative to said nest and said pressure member to effect orbital travel of wafers over the surface of said lapping plate and into an overhang region, and vacuum means including a pattern of vacuum passages in said pressure member terminating in the wafer-engaging surfaces thereof for holding the wafers flush against said pressure member during travel of the Wafer outside full face contact with the lapping plate in Said overhang region.

9. Lapping apparatus including a rigid rotatably mounted fiat-topped lapping member, a flat-bottomed relatively thick nest embodying a pattern of wafer-surrounding apertures, said nest being in face contact with the top of said member peripherally of said apertures, and a rigid rotatably mounted pressure member having a corresponding pattern of projections extending into said apertures, said pressure member and said nest being constrained for rotation about a common axis, the bottom surfaces of said projections lying in a common plane and said pressure member being vertically movable relative to said nest for allowing the projections of the pressure member to descend progressively deeper into the nest apertures and bear against waters in said apertures as the Wafers retained in the nestare reduced in thickness, the axis of said lapping member being offset from the common axis of the pressure member and the nest sufiiciently to carry an overhang travel region, vacuum means including passages opening at said bottom surfaces for holding the wafers flush against said projections throughout said overhang travel region, and rotary drive means connected to one of said members.

10. Lapping apparatus including a flat-topped rotary lapping'disc, an apertured Wafer-retaining nest having Wafer-confining portions in face contact with the flat top of said disc, and a unitary pressure plate having a pattern of Wafer-engaging projections loosely complementary to said apertured nest, said nest and pressure member overf lying said lapping disc and being mounted for rotation about an axis offset from that of said disc, and said projections embodying vacuum passages for holding wafers,

flush thereto.

11. Lapping apparatus including a lapping plate, an apertured Wafer-retaining nest overlying said plate and having wafer-containing portions in surface contact therewith, and a pressure member overlying said nest and bearing against Wafers contained in the nest, means for supporting and driving said lapping plate relative to said References Cited in the file of this patent UNITED STATES PATENTS 2,405,417 Fruth Aug. 6, 1946 2,539,561 Wolfskill Jan. 30, 1951 2,634,558 Wolfskill Apr. 14, 1953 2,687,603 White Aug. 31, 1954 2,842,906 Carter et al July 15,1958 i