U.S. patent number 3,748,790 [Application Number 05/172,103] was granted by the patent office on 1973-07-31 for lapping machine and vibratory drive system therefor.
Invention is credited to Daniel Medellin, Frank A. Pizzarello.
United States Patent |
3,748,790 |
Pizzarello , et al. |
July 31, 1973 |
LAPPING MACHINE AND VIBRATORY DRIVE SYSTEM THEREFOR
Abstract
Disclosed is a unitary spring assembly for a lapping machine
whereby a lapping plate may be reciprocally vibrated at mechanical
resonance at varying loads. Drive or vibration is provided by
peripherally mounted electromagnetic solenoids whose force is
applied tangential to the direction of rotation (or in the
direction of displacement of the lapping plate). This invention
relates to the art of lapping and polishing articles by abrasion so
as to provide such articles with one or more surfaces having a high
finish, free of blemishes such as scratches or the like as might
result from cutting or sawing. More particularly, the invention
relates to a mechanically resonant vibratory drive system capable
of producing a continuous lapping and polishing action or motion
between a surface of an article and an abrasive or polishing
member.
Inventors: |
Pizzarello; Frank A. (Santa
Ana, CA), Medellin; Daniel (Buena Park, CA) |
Family
ID: |
22626375 |
Appl.
No.: |
05/172,103 |
Filed: |
August 16, 1971 |
Current U.S.
Class: |
451/163;
451/165 |
Current CPC
Class: |
B24B
37/042 (20130101); B24B 31/00 (20130101); B23Q
1/36 (20130101); B24B 37/102 (20130101) |
Current International
Class: |
B23Q
1/36 (20060101); B23Q 1/26 (20060101); B24B
31/00 (20060101); B24B 37/04 (20060101); B24b
007/00 (); B24b 009/00 () |
Field of
Search: |
;51/7,58,59,59SS,57,161,163 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Simpson; Othell M.
Claims
What is claimed is:
1. In a lapping machine having a base member and a lapping member
adapted to be moved reciprocally with angularly different
components of displacement, at least one of which is radial, the
improvement comprising:
means for applying a displacement force to said lapping member
tangential to the direction of said radial component of
displacement.
2. The invention according to claim 1 wherein said means includes
motor means mounted on peripheral portions of said base member and
a unitary spring assembly disposed between and coupling said
lapping member and said base member.
3. A lapping machine comprising:
a. a base member,
b. a lapping member,
c. motor means mounted on peripheral portions of said base member
for applying a rotational displacement force to said lapping
member,
d. and a unitary spring assembly disposed between and coupling said
lapping member and said base member.
4. The invention according to claim 3 wherein said unitary spring
assembly comprises a plurality of spring rods affixed between first
and second support members coupled, respectively, to said base
member and said lapping member.
5. The invention according to claim 4 wherein said spring rods are
inclined in the same direction and to the same extent between said
first and second support members.
6. The invention according to claim 3 wherein said motor means
includes a pair of electromagnetic solenoids mounted on
diametrically opposite peripheral portions of said base member.
Description
BACKGROUND OF THE INVENTION
There are a wide variety of articles which must be lapped and
polished to provide them with one or more surfaces having a high,
flaw-free finish. It is also quite often necessary to uniformly
reduce the thickness of an article from opposite, parallel sides or
surfaces. Of particular interest in connection with the art of
lapping and polishing is the semi-conductor industry which requires
highly polished wafers of silicon or germanium free of mechanical
damage. Such wafers are usually obtained by sawing or slicing
ingots of single crystalline silicon or germanium, for example,
which leaves these wafers with "damaged" surfaces exhibiting saw
marks and scratches or the like. Since this industry also requires
such wafers to be extremely thin (i.e., of the order of thousandths
of an inch) and since materials such as silicon and germanium are
very brittle, it will be appreciated that it is either impossible
or economically unattractive to saw or slice wafers thereof to the
desired thickness. It is therefore necessary to lap and polish
these wafers on opposite surfaces to not only remove the blemishes
or "damage" therefrom but to also uniformly reduce the wafers to
some predetermined thickness.
Heretofore the motion for creating the abrading-lapping action has
been provided by the reciprocatory motor-driven vibratory movement
of a lapping plate in an inclined arcuate path which effectively
conveys the articles to be lapped over and in contact with the
abrasive surface of the lapping plate. The movement of the abrasive
surface is provided by a motor, usually electromagnetic and of the
type shown and described in U.S. Pat. No. 3,088,247 to W. G.
Mushrush. As shown in this patent the lapping plate is connected to
an electromagnetic reciprocatory motor via a base member and four
sets of discrete cantilever leaf springs symmetrically disposed
with one set on each side of the base member. The electromagnetic
motor, through its armature, is coupled to the base member so that
when the coil is energized, the energy impulses of the coil draws
the armature downwardly forcing the springs to both rotate and flex
so as to move the lapping member in a helical or inclined arcuate
path. When the energy impulses pass or cease, the springs recoil so
as to reverse the movement of the lapping member equal in magnitude
and opposite in direction from that of the motion imparted during
the energy impulse cycle. In this prior art arrangement the motor
armature is centrally mounted relative to a vertical central axis
as well as with respect to the cantilever springs which support the
lapping member thereabove. It will thus be appreciated that
rotational motion on the part of the lapping member is imparted
thereto by a force applied in a direction perpendicular (or nearly
so) to the surface or plane of rotation of the lapping member.
Because the vibratory drive systems of the prior art provide the
force to achieve rotation of the lapping member in a direction of
perpendicular to the plane of rotation, the efficiency of these
systems to accommodate a variety of loads has been greatly
impaired. In addition, the multiple cantilever spring units each
comprising a plurality of discrete leaf springs, utilized in these
prior art systems required the springs in each unit to be firmly
secured together by bolts, for example, as shown in the
aforementioned patent to Mushrush. These same bolts are also
employed to secure the cantilever springs to an upper frame or
member (which supports the lapping plate) and to a base member.
This construction therefore makes it extremely tedious and
difficult to change the cantilever spring units in order to
accommodate varying loads.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an
improved vibratory drive system.
Another object of the invention is to provide an improved vibratory
drive system for lapping and polishing apparatus.
Yet another object of the invention is to provide an improved
vibratory drive system for lapping and polishing apparatus which is
capable of accommodating a wide load range.
Sti l another object of the invention is to provide an improved
vibratory drive system for lapping and polishing apparatus which
drive system can be easily and quickly adapted or changed to meet
different load demands.
Another object of the invention is to provide an improved vibratory
drive system for lapping and polishing apparatus which can be
easily and quickly adapted or changed to permit either material
removal and/or polishing.
Yet another object of the invention is to provide an improved
spring assembly for a vibratory drive system in lapping and
polishing apparatus.
SUMMARY OF THE INVENTION
These and other objects of the invention are realized by providing
a peripherally driven interchangeable unitary spring unit. More
particularly, the unitary spring unit of the invention comprises a
pair of superimposed plate members separated by and secured
together by a plurality of symmetrically disposed unitary spring
members. A base plate member and a lapping plate member are
provided which are adapted to receive therebetween the spring unit
as a whole (or more particularly, to receive the upper and lower
plate members of the spring unit respectively). In addition, the
armatures of a pair of electromagnetic solenoid drive members are
disposed on diametrically opposite points of the base plate so as
to impart a torque thereto and to the lapping member, the direction
of the torque being tangential to the direction of rotation of the
lapping member. Since the drive unit acts on peripheral portions of
the driven members, maximum torque is exerted, thus permitting a
wide range of loads to be accommodated. The spring unit, since its
individual springs are unitary therewith, avoids the necessity of
assembling and disassembling individual springs. Hence spring units
may be quickly and easily replaced to accommodate various load
conditions or operational needs (i.e., lapping and polishing).
DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail by reference to
the drawings in which:
FIG. 1 is an exploded view in perspective of lapping and polishing
apparatus according to the invention;
FIG. 2 is an elevational view in section of an assembled lapping
and polishing apparatus according to the invention; and
FIG. 3 is a set of curves useful in explaining the operation and
advantages of the invention.
DETAILED DESCRIPTION
Referring now to the drawings the lapping and polishing apparatus
of the invention comprises an electromagnetic vibratory drive unit
for driving a lapping and polishing plate and bowl assembly. More
particularly, the vibratory drive unit includes a base plate member
2, a spring unit 4, a top plate member 6, and a pair of
electromagnetic solenoid drive units 8, 9. The lapping and
polishing plate and bowl assembly includes a bowl base plate member
10, a lap surface support 12, a lap surface retaining ring 15, and
a pair of toggle clamps 18. It will be understood that the lapping
and polishing plate and bowl assembly is mounted onto the vibratory
drive unit as will be described more fully hereinafter.
The base plate member 2 of the vibratory drive unit may be of
stainless steel, for example, and is provided with a "blind" hole
or recess 2' symmetrically located at the center of the plate 2
with the opening or recess portion being disposed in the top
surface thereof. By means of brackets 11, 13, the coil and armature
portions of a pair of solenoid drive units 8, 9 are affixed to
diametrically opposite points on the surface of the base plate 2
and adjacent the periphery thereof. The solenoid drive units each
include an E-shaped armature 8' having an electromagnetic field
coil 8" mounted on the middle "leg" of the E. It will be understood
that the field coils 8" are force-fitted onto the armature members
8' and are adapted to be connected to a source of alternating
current for operation. The "legs" of each armature member extend in
opposite linear directions (or in the same angular direction, i.e.,
counter-clockwise).
The novel spring unit assembly 4 of the invention comprises a pair
of plates 14 and 24, one being disposed above the other and the two
being secured together by a cage-like assembly of spring rods 34 of
which there may be four in number. The bottom plate 14 is
configured and adapted to fit into the recessed portion 2' of the
base plate 2 so as to be flush with the top surface thereof and
secured thereto by means of machine screws, for example. The spring
rods 34, which may be of tempered, unhardened steel about
three-fourths inch in diameter, are more or less permanently
affixed to the top and bottom plates 14 and 24 as by welding or the
like. Each spring element or rod is preferably positioned so as to
lie on the surface of an imaginary cylinder disposed between the
plates 14 and 24 with the axis of each spring element being
uniformly or equally inclined in the same direction and to the same
extent with respect to the axis of the cylinder. Typically the
angle of inclination may be 17.degree., for example, and the extent
thereof determines the extent of vertical displacement of the top
plate 24 upon rotation.
The vibratory drive unit assembly is completed by a top plate
member 6 which contains a "blind" hole or recessed portion 6' which
is configured and adapted to receive the upper plate 24 of the
spring unit assembly 4 and to be secured thereto by means of screws
or the like. Pendent from beneath the top plate member 6 are a pair
of magnetically attractable bar members 16 which may be I-shaped
bars of laminated soft iron, for example. The I-bars 16 are
disposed on diametrically opposite peripheral portions of the top
plate member 6 and are adapted to be adjacent but slightly spaced
from the ends of the E-shaped armatures 8' mounted on the base
plate 2. The I-bars 16 are secured to the top plate 6 by means of
bracket members 16'.
The lapping and polishing bowl assembly is mounted onto the drive
unit assembly as follows. The bowl base member 10 is bolted to the
top plate 6 of the drive unit by means of the threaded bolts 10'
depending from the bowl base member. The lap surface support member
or plate 12 is then affixed to the bowl base member 10 by means of
screws or the like inserted up through the bowl base plate 10 and
threaded into the screw holes 12' provided in the under-surface of
the lap surface support plate 12. The diameter of the support plate
12 is somewhat less than the diameter of the bowl base plate 10. A
suitable lapping surface may then be provided in the form of an
abrasive cloth 19 or the like which is placed over the lap surface
support plate 12. It will be understood that the abrasive cloth
will be larger in extent than the support plate 12. The retaining
ring member 15 is then placed onto the periphery bowl base plate 10
with the overhanging peripheral portions of the abrasive cloth 19
being contained between the retaining ring 15 and the bowl base
plate 10. The inside diameter of the retaining ring 15 is just
slightly greater than the diameter of the support plate 12 so that
the ring may fit snugly therearound and, when pressed down in
position, will draw the abrasive cloth 19 taut across the surface
of the lap surface support plate 12. The retaining ring is held
firmly in place by means of toggle clamps 18 which also permit
quick and easy disassembly of the bowl assembly for the changing of
abrasive cloths or the like.
OPERATION
Upon energizing the solenoid coil members 8" with alternating
current the I-bars 16 affixed to the top plate 6 will be attracted
toward the armatures affixed to the bottom plate 2 so as to cause
the top plate 6 and hence the bowl assembly to start to rotate (in
a clockwise direction, for example). Rotation against the spring
unit 4 however also results in a downward vertical displacement of
the top plate member 6 and the bowl assembly. The bowl assembly
thus moves in a reciprocatory manner with angularly different
(i.e., vertical and horizontal) components of displacement
resulting in movement of the lapping surface in an inclined arcuate
path. It will also be appreciated that one component (i.e., the
horizontal) of displacement is greater than the other (i.e., the
vertical). The resultant direction may also be described as a
displacement normal to the inclination of the spring members.
Articles placed in the lapping bowl will experience short, repeated
rotational thrusts which imparts a circular motion thereto as
explained below. Due to centrifugal force the articles will also
move outwardly into contact with the retaining ring which
thereafter restricts the path of the articles to circumferential
portions of the lapping surface. Articles having a diameter less
than the radius of the lapping surface will rotate about the axis
of the lapping surface since the magnitude of the horizontal
component of displacement increases as the distance from the center
of the lapping surface increases. Rotation of the articles is
produced since elements thereof closest to the outer edge of the
lapping surface are given the greatest horizontal displacement
whereas elements of the articles closer to the center of the
lapping surface will be given smaller horizontal displacement
forces.
The frequency and amplitude of the vibratory movement of the bowl
is governed by the frequency of the alternating current and power
energizing the solenoid. It will be understood, however, that the
effective reciprocationg movement may be varied by the use of
controls known to the vibratory motor art. Thus the reciprocating
movement may be the same as, one-half, or double that of the
alternating current frequency.
Thus, the movement of the lapping surface produces a rotary motion
of the article being lapped about its own axis as well as
simultaneously moving this article around the axis of the plate.
Thus the lapping or polishing action is applied to the face of the
articles in constantly changing directions. This produces a
smoothly lapped surface, free of scratches or unequal reduction in
thickness.
It is also possible to lap opposite surfaces of an article
simultaneously, simply by placing a weighted abrasive member on the
top of the article or articles. The bowl assembly of the invention
also permits usage of lapping materials whether they be liquid,
powder suspended in liquid, or merely powder. It will be understood
that the lapping slurry will be retained along with articles being
lapped by the retaining ring member 15. It is also possible to
provide a polishing surface by utilizing a cloth or covering of
cork, felt, or flannel.
Upon the application of alternating current to the solenoid coils
of a frequency equal to the mechanical frequency of the system,
resonance vibration will occur. The natural mechancial frequency
may be adjusted by appropriate selection of the diameter of the
spring rods in the spring unit. For example, 3/4 inch diameter rods
are used at a vibratory frequency of 120 cps with a lapping fixture
weighing 18 lb. to achieve resonance vibration. To attain a
resonance vibration at this same frequency with a lapping fixture
weighing 22 lb., rods of 7/8 inch in diameter are employed.
Conversely, a spring unit change to achieve a different spring rate
will cause a lapping fixture of a given weight to vibrate at a
different resonant frequency. Thus, a spring unit having a greater
soring rate (i.e., one having stiffer springs) will have a
mechanical resonance at a higher frequency for lapping fixtures of
the same weight. The unique aspects of the invention and its
advantages are clearly illustrated by reference to FIG. 3. In this
figure the amplitude of angular displacement of the load on the top
plate of the spring unit is plotted against the load on the top
plate for Curves I, II, and III. The imput power per angular
displacement is plotted against the load on the top plate for Curve
IV.
Curves I and II illustrate the mechanical loading distribution for
two different spring units at a fixed power imput and frequency.
These curves show that different loads can be made to vibrate at
the same frequency by utilizing different spring units. Thus, by
maintaining mechanical resonance maximum or any desired
displacement can be achieved with a minimum of power imput.
Curve III illustrates the mechanical loading distribution of prior
art vibratory drive systems wherein drive is conventionally applied
in the direction of the vertical component of displacement. This
curve indicates that the fixed spring systems of the prior art
could accommodate narrower load ranges in comparison with the
apparatus of the present invention. Thus, in the prior art systems
small load changes can result in a large reduction in the
displacement. In contrast, the present invention achieves a much
broader load range by providing peripheral drive in the direction
of the horizontal component of displacement.
Curve IV illustrates the imput power per angular displacement
required to maintain a constant displacement over a range of loads.
At the maximum of the loading distribution (mechancial resonance),
the power demand is minimum. Conversely, if the power imput is
constant, a maximum of displacement will occur at the minimum point
of Curve IV.
It will be appreciated that the disposition of the electromagnetic
driving or motor means on the periphery of the vibratory drive unit
permits the attainment of maximum torque to sustain large radial
displacements under maximum loading conditions. In addition,
peripheral drive also permits the one to maintain large
displacements when lapping fixtures of widely different weights are
utilized.
By the present invention a vibratory lapping apparatus is provided
which utilizes the principle of resonance vibration at different
frequencies. In addition, the present invention makes it possible
to obtain maximum torque over wide loading ranges. Furthermore,
mechanical resonance according to the invention is easily tuneable
by means of readily replaceable unitary spring units. Thus, both
lapping and polishing can be readily and quickly accomplished since
the length of the working stroke is readily adjustable so as to
permit material removal or polishing. It is to be understood that
as used herein the term "lapping" is intended to be generic for
both material removal as well as polishing.
* * * * *