Procedure For Fabricating Ultra-small Gold Wire

Abstract

The procedure for fabricating ultra-small precious metal or metal alloy wire comprising the steps of fabricating and annealing a copper sleeve with an axially aligned opening formed therein, forming and annealing a precious metal core and inserting the core into the opening, the sleeve and the core having outer dimensions preferably formed in the ratio of ten to one, mechanically binding the core to the sleeve to produce a bi-metallic wire combination, reducing the size of the wire combination on suitable wire drawing dies and then chemically removing the sleeve from the precious metal wire.

Description

BACKGROUND OF THE INVENTION

This invention relates in general to the field of manufacturing fine wire, and more particularly, is directed to a procedure for fabricating ultra-small gold wire.

In the production of ultra fine wire, prior workers in the art have previously achieved the desired small wire diameter by drawing processes whereby the metal or metal alloy is drawn through a hole in a plate or a block of harder material which is known as a die. This operation converts the configuration of the starting material, for example a rod, to an elongated wire of reduced cross section. The drawing process is repeated as often as necessary by using dies with successively smaller holes until the desired reduction in cross sectional area is obtained. When working in the ultra fine wire area, for example wires having a diameter of one one-thousandths of an inch, it has been the common practice to employ diamond dies. Such dies are relatively expensive in manufacture and in use, thus resulting in a greater cost for the ultra fine wire thereby produced. When the desired final wire size is greater than four one-thousandths of an inch, it is possible to employ carbide dies and not diamond dies to thereby reduce equipment costs. The carbide dies can be economically and practically used in wire drawing down to four one-thousandths of an inch. With smaller wire diameters, it is the usual practice always to utilize diamond dies.

In the case of drawing ultra fine gold wire, it has been found that the physical strength of the gold element was such that the wire drawing procedure could only be utilized to draw gold wire down to two one-thousandths of an inch by utilizing conventional wire drawing equipment due to the weakness of the material itself. Accordingly, at the present time, there is no inexpensive method or apparatus capable of drawing gold wire as fine as one one-thousandths of an inch.

SUMMARY OF THE INVENTION

The present invention relates generally to the field of forming fine wires, and more particularly, is directed to a procedure for fabricating ultra-small, pure gold wire of one one-thousandths of an inch diameter or less in size.

The present invention features a method which starts with a copper sheath of square cross sectional configuration which has a square axial bore provided therein. A square gold or other precious metal bar of suitable cross sectional dimensions to easily slide within the axial bore is formed and placed in position within the axial bore. The geometry of the initial components is such that the ratio of measurements of the copper sheath to the gold bar is initially a ratio of at least 5 to 1, and preferably is precisely at the ratio of 10 to 1.

The assembled copper clad gold bar is entered into suitable square shaped wire reduction rolls and is reduced sufficiently to mechanically bond the gold bar to the copper sleeve, thereby creating a composite wire having a ratio of ten to one, copper to gold. Continued reduction of the assembled product is achieved by employing conventional wire reducing rolls. Steps are taken to change the configuration from square to round in well known manner.

By continued reduction, any desired gauge, for example 30 A.W.G., can be reached so that the copper sheath will measure 0.010 inches outside diameter. Wires of this diameter can be conveniently drawn by employing carbide dies. The gold core diameter will remain in the same ratio of 10 to 1, thereby resulting in a gold wire diameter of 0.001 inches. At 31 A.W.G., the sheath diameter will be 0.0089 inches and a gold core of 0.00089 inches will result. At 32 gauge, the sheath will measure 0.008 inches and a gold core of 0.0008 inches will result. At 33 gauge, the sheath diameter will be 0.0071 inches and the gold core will be reduced to 0.00071 inches. At 34 gauge, the sheath will measure 0.0063 inches and a gold core of 0.00063 inches will result. At 35 gauge, the sheath will measure 0.0056 inches and the gold core of 0.00056 inches will result. At 36 gauge, the sheath diameter will be 0.005 inches and a gold core of 0.0005 inches will result.

When the desired gold wire is achieved, the composite material can be cut into lengths and the lengths can be placed in a glass container for etching or removing the copper sheath from the finish gold core wire by employing a suitable acid, for example, nitric or sulphuric acid. The ultra-small pure gold wire thus produced will meet known gold wire standards, for example ASTM Designation: F72-69 entitled "Gold Wire For Semi-conductor Head-Bonding" as published by the American Society For Testing and Materials.

It is therefore an object of the present invention to provide an improved procedure for fabricating ultra-small pure gold wire of the type set forth.

It is another object of the present invention to provide an improved method for fabricating ultra-small pure gold wire by employing a copper sheath and a gold core in an initial ratio of 10 to 1.

It is another object of the present invention to provide a novel method for fabricating ultra-small pure gold wire wherein a gold bar is placed within a copper sheath having an initial ratio of ten to one, copper to gold, and wherein the components are simultaneously reduced by wire drawing in the same ten to one ratio until the ultra fine wire size is achieved.

It is another object of the present invention to provide a novel method for fabricating ultra-small pure gold wire wherein a gold bar is inserted into a copper sheath and the assembly is reduced by drawing to the ultra fine range, wherein the strength of the copper sheath is employed to permit gold to be drawn to diameters of 0.001 inches or less.

It is a further object of the present invention to provide a novel method of fabricating ultra-small gold wire of 0.001 inches diameter or less wherein the need for diamond dies can be completely eliminated.

It is another object of the present invention to provide a novel method for fabricating ultra-small pure gold wire of 0.001 diameter or less in size wherein gold wire is copper clad and the copper cladding has a tendency to increase the working characteristics of the composite structure through increased strength.

As used in this specification, the term "ultra-small" may be considered as those wires having a diameter of 0.001 inches or less.

It is a further object of the present invention to provide a novel method for fabricating ultra-small pure gold wire that is simple in procedure, inexpensive in equipment costs and trouble free in operation.

Other objects and a fuller understanding of the invention will be had by referring to the following description and claims of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, wherein like reference characters refer to similar parts throughout the several views and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, perspective view of the end of an initial square copper sheath in accordance with the present invention.

FIG. 2 is a view similar to FIG. 1 showing a gold bar in the process of being inserted into the central opening of the sheath.

FIG. 3 is a cross sectional view taken along Line 3--3 of FIG. 2, looking in the direction of the arrows.

FIG. 4 is an enlarged schematic, elevational view showing a reduction in wire gauge size of the composite material.

FIG. 5 is a schematic, elevational view showing one method of removing the copper sheath from the gold wire.

FIG. 6 is a perspective view of a spool upon which the ultra-small pure gold wire produced in accordance with the present method is being wound.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of my invention selected for illustration in the drawings and are not intended to define or limit the scope of the invention.

The invention will be described with the sheath to core dimensional relationship of 10 to 1. It will be appreciated however, that other relationships such as 5 to 1 or over can be similarly utilized. In order to practice the present invention, a gold or other precious metal or metal alloy ingot should be prepared by melting pure gold in a clay-graphite crucible in an oxidizing atmosphere. The melting precious metal or alloy is then poured into a graphite split mold at preferably approximately 50.degree. F. above the melting point of gold, or approximately at a temperature in the 1,950.degree. to 2,000.degree. F range. The mold should preferably be preheated and an oxidizing atmosphere should be employed during the melting and pouring operations. Slow pouring is advisable to reduce the dangers of cold shuts and surface imperfections. The gold is then conventionally rolled to reduce the size, but great precautions should be taken to guarantee the cleanliness of the rolls from any metallic objects. Cleaning must be done every fourth reduction on the wire reducing rolls. At no time should the wire be permitted to rub on the metallic plate, either when entering or exiting the rolls. This cleaning process is necessary to remove very small micro particles which may be carried over from the rolling process. In the preferred embodiment, the rolling and cleaning processes should be continued until the gold wire bar 14 has been reduced to approximately 0.320 inches square. The gold wire is then cleaned and annealed at 970.degree. F. for 15 minutes.

Separately, a copper sleeve 10 is prepared by either casting or machining to a square configuration having outside dimensions of precisely 31/4 inches with a longitudinally extending, central, square opening 12 machined or otherwise provided therein. The square opening 12 is formed to a configuration whereby each of the sides measures precisely 0.375 inches. The copper sleeve 10 is then annealed in a reducing atmosphere such as nitrogen at 1,000.degree. F. for 15 minutes. It is noteworthy that at no time is the composite gold-copper assembly ever annealed together. In this manner, by separately annealing the gold and copper components, it is possible to avoid any diffusion whatsoever of gold into copper or copper into gold when the gold bar 14 and copper sheath 10 are brought into contact. Thus, the copper can be readily removed by acid treatment as hereinafter more fully set forth when the composite article is finished to the desired final size diameter. The annealed gold bar 14 is then inserted into the square opening 12 of the separately annealed sheath 10. It will be noted that the side dimensions of the gold bar 14 are precisely 0.320 inches and the dimensions of the opening 12 are 0.375 inches, thereby permitting an easy, sliding fit without the need for employing any tools or other mechanical devices.

The assembled copper clad gold bar is then entered into conventional, square shaped wire reduction rolls (not shown) and is reduced from the original outside measurement of 3.250 inches square to 3.200 inches square. In this manner, the dimensions of the opening 12 will be reduced to 0.320 inches to mechanically bond the copper sleeve 10 to the gold bar 14 at a ratio of 10 to 1, copper to gold. The outside dimensions of the copper sleeve 10 will then be 3.200 inches on each side and the dimensions of the hole 12 and the gold bar 14 will be precisely 0.320 inches on each side, causing a tight mechanical bond.

With the composite material thus bonded, continued reduction on carbide wire reducing rolls 18 can conventionally proceed by standard reductions in a manner well known to those skilled in the art, until the size of 0.325 inches outside measurement is obtained. One end of the assembled, reduced unit can then be forged or otherwise pointed and rounded for a length of approximately 4 inches to a size slightly less than a conventional carbide wire drawing die 18, for example 0.290 inches diameter so as to permit the mechanical pull of the elongated wire combination 16 through the die 18 for its entire length. This operation will change the shape of the wire 16 from square cross-sectional configuration to a partially round cross-sectional configuration 20.

The assembled, partially round unit 20 is then again forged or pointed for a length of approximately 4 inches to a size slightly less than the next round shaped carbide wire drawing die, namely a die of 0.257 inches diameter. At this stage, the shape of the wire will be changed from its original square shaped cross-sectional configuration to a perfectly round shaped copper clad gold wire 22 after having been mechanically, conventionally pulled through the die 18.

The composite round wire 22 is then reduced from the 0.257 inches (No. 2 A.W.G.) by A.W.G. reductions on a conventional wire machine (not shown). When 30 A.W.G. is reached by the carbide wire drawing dies (not shown), the copper sheath will measure 0.010 inches outside diameter and a gold core diameter of 0.001 inches will result. At 31 A.W.G., the outside diameter of the copper sleeve will measure 0.0089 inches and the gold core diameter of 0.0089 inches will result. At 32 gage, the outside diameter will measure 0.008 inches and the gold core will measure 0.0008 inches, as shown in the following table:

SIZE DIAMETER DIAMETER A.W.G. COPPER SLEEVE GOLD CORE ______________________________________ 30 0.0100 0.0010 31 0.0089 0.00089 32 0.0080 0.0008 33 0.0071 0.0007 34 0.0063 0.00063 35 0.0056 0.00056 36 0.0050 0.0005 ______________________________________

When the desired final diameter of gold core is reached, the gold wire 24 will be finished with the copper sheath 26 still intact. The spooled end is then fed at a rate of approximately 10 feet or more per minute to a conventional, miniature wire straightening machine (not shown) that runs in a rotary motion to straighten the wire. If desired, the composite copper clad gold wire 22 of reduced diameter can be cut into lengths as required and then placed into a glass or other suitable container 28 for etching or otherwise removing the copper sheath 26 from the gold core wire 24 by employing a bath 30 such as nitric acid. The cut lengths remain in the nitric acid bath 30, a sufficient length of time until all of the copper sheath 26 has been removed. Optionally, the composite copper clad wire 22 may be continuously fed into the bath 30 by employing suitable rolls 32, 34, 36 in a manner to automatically and continuously remove the copper sheath 26 from the gold wire 24. If necessary, the pure gold, ultra-fine wire 24 can be thoroughly rinsed in conventional manner to remove any etchents and then dried by air prior to use. If desired, the gold wire 24 may be conventionally wound upon a finished wire spool 38 for storage purposes prior to use.

Although I have described the present invention with reference to particular embodiments therein set forth, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction may be resorted to without departing from the spirit and scope of the invention. Thus, the scope of the invention should not be limited by the foregoing specification, but rather by the scope of the claims appended hereto.

Claims

I claim:

1. The method of fabricating ultra-small precious metal or metal alloy wire comprising the steps of

A. forming a copper sleeve having a first cross-sectional size and annealing the sleeve,

1. said copper sleeve being formed with an axially aligned opening having a second cross-sectional size;

B. forming a core of precious metal or metal alloy having a third cross sectional size and annealing the core, said annealing being carried out separately from annealing the sleeve,

1. the ratio of the first cross-sectional size to the third cross-sectional size being at least five to one,

2. the second cross sectional size being formed slightly larger than the third cross-sectional size;

C. inserting the previously annealed core into the opening and then reducing the second cross-sectional size to equal the third cross-sectional size to mechanically bond the core to the sleeve;

D. reducing the cross-sectional size of the sleeve and the cross sectional size of the core in the same ratio as the initial sizes by successive size reductions until the core is reduced to the ultra-small wire size range, and

E. removing the sleeve chemically from the core to produce an ultra-small precious metal wire.

2. The method of claim 1 wherein the ratio of sleeve to core is ten to one.

3. The method of claim 1 wherein the copper sleeve, the opening and the core are all initially formed to square cross-sectional configurations.

4. The method of claim 3 wherein the sleeve and core combination is introduced to successively smaller sized carbide wire drawing dies to achieve smaller wire sizes.

5. The method of claim 4 wherein the sleeve and core combination is drawn to 36 A.W.G. without employing diamond wire drawing dies.

6. The method of claim 5 and the additional step of cleaning the sleeve and core combination at least as often as every fourth reduction on the wire drawing dies.

7. The method of claim 1 wherein the reduction of the second cross sectional size is carried out simultaneously throughout the length of the copper sleeve to provide overall bonding.