US2749683A - Lapping plate - Google Patents

Description

June 12, 1956 w. SODERMAN 2,749,683

LAPPING PLATE Filed Oct. 5, 1954 INVENTO/Q 6 W 6ODRMHN H T roan/5y United States Patent LAPPING PLATE George W. Soderman, Teaneck, N. J., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York This invention relates to abrading devices and particularly to an improved surface lapping plate or disc.

One well known type of lapping plate used, for example, for grinding piezo-electrical crystal wafers, consists of a flat metal plate having grid, or straight-line intersecting, grooved lapping surface.

It is customary to make such plates quite thick to allow for wear but the intersecting grooves can be cut to only a limited initial depth without weakening the plate to the point where it tends to warp. As the plate wears, the grooves become too shallow for efficient operation but, due to the reduction in the mass of the plate, the grooves can be deepened without causing it to warp. This groove deepening operation may be repeated until the remaining metal becomes too thin to maintain a flat lapping surface. This procedure involves high maintenance expense, however, and when this type of lap is used thin quartz plates are sometimes chipped or broken by the sharp edges exposed at the ends of the grooves.

It is, therefore, the object of the present invention to overcome the disadvantages of such lapping plates and to provide a strengthened or stiffer plate which will not require such periodic maintenance.

According to the invention, the face of a lapping plate has a multiplicity of non-intersecting annular grooves uniformly distributed over the lapping surface. Such grooves have no exposed sharp edges which can damage the work pieces.

Moreover, since they do not weaken the plate as do the intersecting grid grooves, they may be cut initially to a depth giving a useful life equal to or greater than that obtainable by repeated regrooving of the old type plate.

These and other features of the invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

Fig. l is a plan view of the lapping surface of a plate according to the present invention;

Fig. 2 is a side elevational view partly in section of a pair of lapping plates of the type shown in Fig. 1.

In the drawing, an annular surface lapping plate 4 having an inner cylindrical surface 5 and a concentric outer surface 6 is provided with a flat lapping surface 7. A plurality of non-intersecting annular grooves 8 are cut into and are uniformly distributed over the surface 7. In a specific embodiment of the present invention designed for lapping quartz crystal Wafers, the plates 4 (and 11 as seen in Fig. 2) have outside diameters of inches, inner diameters of 3% inches and a thickness d1 of 1 /2 inches. A total of 112 annular grooves or holes 8 are provided in the lapping surface 7, the holes being substantially uniformly spaced in four concentric circles, 20 holes being in the smallest circle and 24, 32 and 36 being in the second, third and fourth larger circles. The annular grooves have an outer diameter of 7 of an inch, an inner diameter of of an inch and cut initially to a depth of inch as contrasted with an initial cut of inch which is the maximum groove depth feasible for a grid grooved plate of the prior art of similar dimensions.

The inner and outer peripheral edges 9 and 10 respectively of the lapping surface are rounded to eliminate sharp edges which could break wafers as the plates are moved in their circuitous lapping paths. In the prior art grid-grooved plates sharp edges cannot be entirely eliminated from the peripheral edges 14 and 15 since the grooves 19 extend through to these edges and some breakage of crystal wafers results when the plates are moved for the lapping operation.

As seen in Fig. 2 the top lapping plate 4 of a pair of lapping plates 4 and 11 is provided with a concentric well 16 of depth d3 of about A of an inch and a plurality of ports 17 for supplying abrasive paste to the lapping surfaces thereof. The crystal wafers being lapped are held between the two plates 4 and 11 in apertures in a positioning plate 12 located therebetween.

It is to be understood that the above described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

l. A lapping plate having a fiat lapping surface with a plurality of deep non-intersecting annular grooves distributed uniformly thereover, the diameters of the grooves being small compared to the radius of the plate and said grooves being spaced apart to provide structural rigidity.

2. A lapping plate comprising an annular metal disc having a flat lapping surface with a plurality of annular grooves distributed uniformly thereover, the diameters of the grooves being small compared to the radius of the plate, said grooves being spaced apart to provide structural rigidity and the peripheral edges of the lapping surface being rounded to prevent injury to articles being lapped thereby.

3. A lapping plate having a flat lapping surface with a plurality of non-intersecting annular grooves distributed uniformly thereover, all of the grooves being located entirely within the edges of the surface, the diameters of the grooves being small compared to the radius of the plate and said grooves being spaced apart to provide structural rigidity.

4. A lapping plate having a fiat lapping surface with a plurality of non-intersecting annular grooves distributed uniformly thereover, the grooves being narrow with respect to the diameter thereof, the diameters of the grooves being small compared to the radius of the plate and said grooves being spaced apart to provide structural rigidity.

5. A circular lapping plate having a flat lapping surface with a plurality of non-intersecting annular grooves, spaced apart and distributed uniformly thereover to provide structural rigidity, said grooves being spaced substantially uniformly about concentric circles in the plate and the grooves being narrow with respect to the diameter thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,405,424 Maynard Feb. 7, 1922 2,201,410 Simonds May 21, 1940 2,597,187 Roshong May 20, 1952

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