US3685110A

US3685110A - Manufacture of piezoresistive bars

Info

Publication number: US3685110A
Application number: US68165A
Authority: US
Inventors: George J J Randolph Jr
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-08-31
Filing date: 1970-08-31
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22

Abstract

A method of preparing multiple bars from an elongated cylinder of piezoresistive material, which results in each bar, in its finally prepared state, being releasably joined to another bar which has come from an adjacent region in the cylinder.

Description

KP? 3,685,110 [151 3,685,1 10 Randolph, 7/ ms c {451 Aug. 22, 1972 MAN] 935 Klingsporn ..3l0/9.5 X BARS .956 Crooks et al. ..29/25.35 Inventor George Randolph, R R. 1, ii ifiii $33 $3227.31:11111113111113234233 Box 391, Corvallis, Oreg. 97330 [22] Filed: Aug. 31, 1970 Primary Examiner-John F. Campbell Assistant Examiner-Carl E. Hall [21] Appl' 68l65 Attorney-Kolisch & Hartwell 52 US. Cl. ..29/25.35, 29/423, 29/424, ABSTRACT 4 310/9, 310/95 A method of preparing multiple bars from an elon- Int. Clgated cylinder of piezoresisflve material results 0f each bar prepared state 57 156/264 releasably joined to another bar which has come from an adjacent region in the cylinder.

[56] References Cited 5 Claim, 5 Drawing Figures I UNITED STATES PATENTS 2,332,447 10/ 1943 Higgins 156/264 X 36851? 1 UR IN 2 i25a35 PATENTEUws 22 m2 INVENTOR MM 4. M.

HHg S.

MANUFACTURE or PIEZO isTivE BACKGROUND OF THE INVENTION This invention pertains to the preparation of piezoresistive bars suitable for use in various kinds of electromechanical applications. More particularly, it pertains to a method of obtaining from a unitary mass of such material, groups (two or more) of bars having closely matching electrical and mechanical charactenstics.

There are many applications today where piezoresistive bars are used. For example, various types of deflection-sensing devices and the like may employ such has as mechanical-to-electrical transducers. Frequently, it is desirable that matched pairs (or a larger group) of bars be used in order to maximize accuracy in the operation of a device. The term matched herein is used in the sense that the bars in a particular pair or group have substantially the same electrical and mechanical characteristics. In the past, however, the obtaining of matched bars has been quite costly, since it has usually required time-consuming comparative testing (after manufacturing) of different bars to find ones that are similar. Manufacturing practices heretofore have not incorporated satisfactory techniques for producing pairs (or larger groups) of matched bars which avoid such comparative testing procedures.

SUMMARY OF THE INVENTION A general object of the present invention, therefore, is to provide a novel method of producing piezoresistive bars which takes care of the problem of obtaining matched bars in a practical and satisfactory manner.

More specifically, an object of the invention is to provide a novel method of dividing a mass of piezoresistive material into multiple bars, or units, of smaller dimensions, with bars which come from adjacent re gions in the mass maintained in close proximity to one another throughout the production process. Experience has shown that two or more bars coming from adjacent regions in such a parent mass of material exhibit substantially the same electrical and mechanical properties. By maintaining each bar (during the manufacturing process) closely adjacent another bar which has come from substantially the same region in the original mass, the guesswork encountered heretofore in obtaining matched bars is avoided. In other words, the bars which are held in close proximity, as contemplated herein, during the preparation process from the mass are assured of having similar, and in most cases, substantially the same electrical and mechanical characteristics.

According to a preferred manner of practicing the invention, the proposed method comprises the steps of dividing a mass into one set of substantially planar and generally parallel slabs, releasably adhering such slabs with a dissolvable adhering agency to form an assembly wherein the slabs have substantially the same positions relative to each other that they had in the original mass, and then dividing the assembly along planes disposed at angles to the planes of the first-mentioned slabs to form another set of substantially planar slabs. It will be apparent that each slab in the second-mentioned set will contain adjacent bars, releasably joined through the adhering agency. Further, it will be apparent that adjacent bars in such a slab are ones which have come from adjacent regions in the original mass. Thus, merely by selecting two or more adjacent bars in such a slab, a user is assured of obtaining bars having closely matching characteristics.

DESCRIPTION OF THE DRAWINGS These and other objects and advantages attained by the invention will become more fully apparent as the description which follows is read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a fragmentary perspective view of an elongated cylinder of piezoresistive material suitable as a parent for the preparation of bars as contemplated herein;

FIG. 2 is a perspective view of the cylinder of FIG. 1 divided into one set of substantially planar and generally parallel slabs;

FIG. 3 is a perspective view illustrating an assembly ascontemplated herein formed by releasably adhering the separate slabs shown in FIG. 2.

FIG. 4 is a perspective view illustrating the assembly of FIG. 3 divided into another set of slabs along planes which are substantially at right angles to the planes of the first-prepared slabs; and

FIG. 5 is a perspective view illustrating the bars which result in one of the slabs of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION Indicated generally at 10 in FIG. 1 is an elongated solid cylinder, or mass, of a piezoresistive material, such as a suitable P-type silicon. The particular cylinder shown has a diameter of about 1 inch, and an axial length of about 0.4 inches. Cylinder 10 may, for example, comprise a cut-off section of a considerably longer cylindrical rod, in which form silicon of the type generally described above is often manufactured.

Cylinder 10, it should be understood, is merely illustrative of one type of mass with which the present invention may be practiced. Put another way, neither the configuration nor the dimensions of the mass are critical, so long as the selected mass is large enough to permit its economical division (as will be more fully described) into bars of the size desired, and so long as it has one dimension at least equaling the longest dimension desired in the final bars. In the specific practice of the invention illustrated and described herein, bars are to be prepared which have a length of about 0.4 inches, and a substantially square transverse cross-sectional configuration with each side about 0.004 inches. It should be noted that while particular dimensions are mentionedherein by way of illustration, the relative sizes of pieces shown in the drawings are intentionally distorted in order to obtain better clarity therein.

According to the invention, cylinder 10 is first divided, preferably by slicing it, axially as shown in FIG. 2 along spaced substantially parallel planes to produce a first set of slabs 12. Each slab l2 herein has a substantially uniform thickness of about 0.004 inches. The dividing operation, by slicing or otherwise, may of course be performed in any one of a number of conventional ways.

After preparation of slabs 12, the same are joined as indicated in FIG. 3 to form a unitary assembly 14. As

contemplated herein, such joining is accomplished through adhering adjacent ones with a suitable dissolvable adhering medium, or agency, such as a dissolvable cement. There are numerous types of such cement which will perform satisfactorily for this purpose, and the particular one employed is a matter of choice. It should be noted that the slabs in assembly 14 are separated by and joined through layers 13 of such a cement, and have substantially the same positions relative to each other that they had in cylinder 10.

Referring to FIG. 4 in the drawings, after formation of assembly 14, the same is divided, preferably by slicing, as indicated in the figure. More specifically, the assembly is divided along multiple spaced substantially parallel planes which, in the particular case being described, are substantially at right angles to the planes of slabs 12. This dividing operation may be performed in the same manner as the one previously described. What results from this operation is another set of slabs 16.

Referring to FIG. 5, one of slabs 16 is shown therein. It will be noted that a slab 16 contains a plurality of elongated bars, or units, such as bars 18, with adjacent bars joined through a portion of a layer of the cement previously mentioned. And, it will be apparent that adjacent bars in a slab 16 are ones which have come from adjacent regions in cylinder 10.

What results, therefore, from the various steps described herein are slabs containing multiple adjacent bars which have come from adjacent regions in the original mass from which they have been prepared, and which, therefore, have, to a high degree of probability, substantially the same electrical and mechanical characteristics. When it is desired to separate two or more matched bars for use, a slab 16 may be placed in a suitable solvent for the particular cement used, with the various bars in the slab then being freed. In any suitable manner, after freeing of the bars from he slab, groups of two or more adjacent bars may be separated and stored for use. Bars which do not have the desired cross-sectional configurations, by virtue of their having come from adjacent the outside regions of the original mass, may be discarded.

The method described herein, therefore, proposes a simple and reliable way of introducing into the steps of manufacturing piezoresistive bars techniques for greatly simplifying the selection of groups of matched bars. More specifically, the method of the invention contemplates that the finally prepared bars, prior to their separation into individual units, are held together in groups, (i.e., such as in slabs 16) wherein adjacent bars are assured to have come from adjacent regions in the original mass from which they have been produced. The resulting slabs containing multiple bars are convenient to handle, and minimize the chance of the individual bars inadvertently becoming separated.

It will be apparent to those skilled in the art that the steps of the invention may readily be practiced on masses of various different configurations and sizes to produce different shapes and sizes of bars. Thus, while a preferred method of practicing the invention has been described herein, it is appreciated that variations and modifications may be made without departing from the spirit of the invention.

tis laim d d ired tos cureb Lette P tent: A? metliod of pi' eparing from a inass o piezoresistive material multiple smaller units of such material, and of positively maintaining in close proximity to each other, during and throughout such preparing, units which come from adjacent regions in the mass, said method comprising dividing said mass into one set of substantially planar and generally parallel slabs,

releasably joining said slabs to form an assembly wherein the slabs have substantially the same positions relative to each other that they had in the mass,

dividing said assembly along planes disposed at angles to the planes of said first-mentioned slabs to form another set of substantially planar slabs, each containing plural adjacent releasably joined separable units, and

until separating of adjacent units in said second-mentioned slabs, preserving the spacial and configurational relationships of such units in such slabs.

2. The method of claim 1, wherein said joining is accomplished through adhering adjacent ones of said first-mentioned slabs with a dissolvable adhering agency.

3. The method of claim 1, wherein said first-mentioned dividing step is performed along one set of substantially parallel planes, and said second-mentioned dividing step is performed along another set of planes which are substantially at right angles to the planes of said first-mentioned slabs.

4. The method of claim 1, wherein said dividing steps are performed by slicing operations.

5. The method of claim 1, wherein said mass comprises an elongated cylinder, said first-mentioned dividing step is performed generally lengthwise of said cylinder and said second-mentioned dividing step is performed generally lengthwise of said assembly.

Claims

1. A method of preparing from a mass of piezoresistive material multiple smaller units of such material, and of positively maintaining in close proximity to each other, during and throughout such preparing, units which come from adjacent regions in the mass, said method comprising dividing said mass into one set of substantially planar and generally parallel slabs, releasably joining said slabs to form an assembly wherein the slabs have substantially the same positions relative to each other that they had in the mass, dividing said assembly along planes disposed at angles to the planes of said first-mentioned slabs to form another set of substantially planar slabs, each containing plural adjacent releasably joined separable units, and until separating of adjacent units in said second-mentioned slabs, preserving the spacial and configurational relationships of such units in such slabs.