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Oct. 15, 1968 E. E Conrad 3,406,041
METHOD AND APPARATUS FOR DEPOSITING PARTICLES ONTO AN OBJECT Filed March 8, 1965 2 Sheets-Sheet 1
Oct. 15, 1968 E. E. Conrad 3,406,041
METHOD AND APPARATUS FOR DEPOSITING PARTICLES ONTO AN OBJECT Filed March 8, 1965 2 Sheets-Sheet 2
United States Patent Office
Patented Oct. 15, 1968
METHOD AND APPARATUS FOR DEPOSITING
PARTICLES ONTO AN OBJECT
Ernest E. Conrad, Clinton Corners, N.Y., assignor to In-
ternational Easiness Machines Corporation, Armonk,
N.Y., a corporation of New York
Filed Mar. 8,1965, Ser. No. 437,805
14 Claims. (CI. 117—101)
ABSTRACT OF THE DISCLOSURE
A method and apparatus for depositing particles onto an object which involves centrifuging the object and an enveloping fluid containing the particles to be deposited on the object for a period of time and with a force sufficient to deposit particles in the fluid onto the object. The object is supported so as to be movable relative to the fluid depending upon the centrifugal force on the object. The centrifugal force on both the object and the fluid is reduced after the deposition process is completed which causes the object, with the particles uniformly deposited thereon, to move out of the fluid before termination of the centrifuging force.
This invention is directed generally to a method and apparatus for depositing particles onto an object and, more particularly, to a method and apparatus for depositing glass particles onto an object and subsequently forming a thin, hole-free, glass film thereon.
It is often desirable to deposit particles of a particular substance onto an object to create a new or improved product which has enhanced qualities. In manufacturing cathode ray tubes, for example, it is often desirable to form the screen by depositing fluorescing powdered material sensitive to electron beam bombardment on the face of a cathode ray tube. The deposited powdered material is generally deposited with a binder substance to adhere the powdered material to the face of the cathode ray tube, however, the binder material can be applied to the powdered material after its deposition on the face of the cathode ray tube.
In many situations it is desirable to deposit particles onto an object and fuse or join the deposited particles to form a coating on or about the object. In the manufacture of various electrical components such as resistors, capacitors and semiconductor devices, it is often necessary to provide a tightly adherent protective jacket which serves as a hermetic seal and prevents the contamination of the components by foreign or noxious materials which may impair the electrical characteristics of the device or may physically damage them so as to render them unsatisfactory or worthless. A wide variety of coating materials such as plastic and glass have been employed with some success and some of these coating materials have been formed by fusing or joining particles deposited on the components.
The present trend in the electronic computer fields is toward the miniaturization of semiconductor or solid state components, i.e., integrated or monolithic circuits. Accordingly, only thin protective coatings are practical since thick protective coatings undesirably increase the bulk of such components and often such thick jackets are subject to cracking during use over a range of operating temperatures.
Two U.S. patent applications entitled "Method of Forming a Glass Film on an Object and the Product Produced Thereby" and "Method of Forming a Glass Film on an Object," whose respective serial numbers and filing dates are S.N. 141,668, now Patent No. 3,212,921, and S.N. 181,743, now Patent No. 3,212,929, filed Sept. 29,
1961, and Mar. 22, 1962, and assigned to the same assignee of this invention, relate to techniques for forming thing lass films on an object for the purpose of providing a hermetic seal or coating therefor. Both of these aboveidentified applications use centrifuging techniques for depositing glass particles onto the object and a glass film is then formed on the object by fusing or joining the deposited glass particles.
The essential step in forming a uniform, hole-free, thin glass film on an object is to deposit a smooth layer of particles onto the object and maintain the smooth deposited layer during the entire centrifugation process. In prior art centrifuging operations for depositing particles onto an object, it was the common practice to decant the liquid from the centrifuged container which caused the liquid to flow over the surface of the object located at the bottom of the container and thereby caused some of the deposited particles to flow with the liquid. This action is termed "running" and produces an uneven coating of glass particles. Hence, it was a problem to retain a smooth deposited layer on the object after the centrifuging process because of the "running" effect caused by decanting the liquid.
In addition, during the slowing down of the centrifuging apparatus after the particles had been smoothly deposited on the object, the container, housing the object upon which the particles had been deposited, attains a centrifuging position which is, for a period of time, at an angle with respect to both the horizontal and vertical planes. Consequently, with the container in this position, the level of the fluid in the container is not perpendicular to the side wall of the container but is at an angle with respect to the side wall of the container so that a vortex motion of the fluid, due to the position of the container between horizontal and vertical planes and the angle of the fluid level, disturbs the smooth coating of deposited particles on the object. Therefore, the smooth deposited particle layer that was initially created in the beginning of the centrifuging process was not consistently achieved by the end of the process because of the vortex effect naturally caused by the centrifuging arrangement and also because of the "running" effect from decanting the fluid.
Furthermore, in past centrifuging operations for depositing particles onto an object, the object was generally dropped into the centrifuging container so that on occasion, the object turned over before resting on the bottom of the container which necessitated removal of the object from the container since particle deposition would not occur on the desired surface of the object. After the object was properly located at the bottom of the centrifuging container and after decanting the fluid from the container, when the centrifuging process was terminated, it was generally necessary to heat the bottom of the container so as to evaporate a film of fluid which formed between the object and the bottom of the container. This heating step was time consuming, but was essential for removing the object from the container since the surface tension of the film of fluid caused the object to adhere to the btotom of the container.
Accordingly, it is an object of this invention, therefore, to produce a new and improved method for depositing particles onto an object.
It is another object of this invention to provide an improved centrifuging apparatus for depositing particles onto an object.
It is a further object of this invention to provide an improved method and apparatus for depositing glass particles onto an object for the purpose of producing a hermetically sealed glass coating that would prevent contamination of the object.
It is an additional object of this invention to provide an arrangement for keeping an object that particles are
to be deposited thereon out of the fluid containing the particles both before the beginning and ending of a centrifuging particle depositing process and thereby avoid the effect of vortex fluid motion and eliminate decanting of the fluid to reach the object. 5
It is a still further object of this invention to provide an arrangement which permits rapid removal of an object, on which particles have been deposited, from a container after a centrifuging process.
In accordance with'a particular form of the invention, ^ the method of depositing particles onto an object comprises centrifuging the Object and an enveloping fluid containing the particles to be deposited on the object for a period of time and with a force sufficient to deposit particles in the fluid onto the object. The object is unique- j 5 ly supported so as to be movable relative to the fluid depending upon the centrifugal force on the object. The centrifugal force on both the object and the fluid is reduced after the deposition process is completed which causes the object, with the particles uniformly deposited 2n thereon, to move out of the fluid before termination of the centrifuging force.
Also in accordance with the invention there is provided an apparatus for depositing particles onto an object which includes a container having a fluid containing the particles 25 suspended therein. Support means are located in the container for supporting the object from the bottom of the container. The support means are resilient and adapted to move within the container relative to the fluid depending upon the centrifugal force on the resilient support means. 30 Means are provided for centrifuging the container to deposit particles from the fluid onto the object supported by the support means. The centrifuging means cause the resilient support means to be compressed and thereby move the object into a position in the container for receiv- 3g ing particles from the fluid. The object is suspended above the fluid by the resilient support means before the beginning and the ending of the centrifuging of the container.
The foregoing and other objects, features and advantages of the invention will be apparent from the following ^.q more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.
In the drawings:
FIG. 1 is a diagrammatic representation of a centrifuging apparatus employed in depositing glass particles on objects with parts of one container broken away to show the arrangement of smaller containers therein; 45
FIG. 2 is a cross sectional view of one of the smaller containers of FIG. 1 showing the object located on a spring supported platform;
FIG. 3 is a view similar to FIG. 2 showing the object and spring supported platform during particle deposition 50 from centrifuging;
, FIG. 4 is a top view of the platform and container of FIG. 2 with most of the object broken away to show the platform configuration; and
FIGS. 5 and 6 are top views similar to FIG. 4 with 55 objects removed to show other platform configurations.
In practicing the present invention, a suitable glass is comminuted as by ball milling to form a powdered glass. Many different types of glasses are suitable for use in accordance with the method of the present invention. The 60 type of glass selected may depend upon the particular application at hand. For example, the object to receive a thin, hole-free, glass film of uniform thickness may require a chemical resistive glass such as borosilicate type glass for protective purposes and for withstanding high 65 operating temperature. Also the object may be a device such as a transistor which may dictate that, for protective purposes, the coefficient of thermal expansion of the semiconductor material of the device and that of the glass film be substantially equal so as to minimize stresses which 70 might otherwise crack the glass during temperature cycling. For example, silicon has a coefficient of expansion per degree centigrade of 32X10-7, which is closely matched by that of. a borosilicate glass available to the trade as Corning 7740 or Pyrex and having a coefficient 75
of expansion of 32.6 X 10-7. The ball milling operation produces small particles of glass of varying size. The powdered glass from the ball milling procedure is then introduced and dispersed in a suitable fluid suspending medium. An organic fluid such as methyl alcohol is one of many which are satisfactory for this purpose. Other appropriate fluids are ethyl alcohol, isopropyl alcohol, acetone and water. Ultrasonic agitation is particularly useful in dispersing particles in this suspending medium.
Next it is now desirable to remove the larger glass particles from the suspension since they are ordinarily too large for use in subsequent filming operations. This may be accomplished with a centrifuging apparatus 10 such as that represented diagrammatically in FIG. 1. To that end, the suspension of glass particles is placed in twenty-eight containers 12, seven of which are mounted in each of four carriers 14 that are supported by trunnions 16 in slots 18 in a transverse member 29 that is mounted in a horizontal plane at the end of a drive shaft 21 of a variable speed motor 22. Rotation of the motor for a few minutes at a relatively low speed develops a centrifugal force of from about 15 to 100 times the force of gravity g which swings the carriers 14 and their containers 12 to the broken-line positions represented in FIG. 1 and separates out the larger glass particles in the suspension by depositing them on the bottoms of the containers. When the machine comes to rest, the containers 12 may be removed and the suspension decanted leaving behind the undesirable larger particles. The suspension is then placed in other containers and again centrifuged at a higher speed to develop say 500 g. to separate out the desired finely divided glass particles. It will be appreciated that these speeds of rotation may be varied from that indicated depending upon the particle size separations which are desired. The last-mentioned suspending fluid is decanted leaving the desired finely divided glass particles. The suspension which had been decanted in this last step contains extra fine glass particles which are not always desirable in subsequent operations and may contain unwanted impurities that were picked up in the ball-milling operation.
The desired glass particles are removed from their containers and may be dried on a hot plate to which mild heat is applied or they may be dried in a desiccator at room temperature. Then a suspension is made by ultrasonically mixing the dried glass particles in a fluid suspending medium. 0.02 to 0.1 gram of the glass particles in 100 cc. of the suspending medium has proved to be a useful concentration although other concentrations may be employed. The glass particles are probably irregular in shape and may have a selected mean particle size in the range of 0.1 to 2 microns. Better results may be obtained by using the smaller particle sizes. A selected mean particle size in the range of 0.1 to 0.7 micron has been employed with particular success in forming glass films having uniform thicknesses in the range of 0.8 to 10 microns on substrates of semiconductor and insulating material.
The suspending medium is an organic fluid having a dielectric constant in the range of 3.4 to 20.7. Various suspending media which have proved satisfactory are methyl alcohol, ethyl acetate, isoamyl acetate, tertiary butyl alcohol mixed with a slight amount of secondary butyl alcohol to maintain the former fluid at room temperature, isopropyl alcohol, acetone and methyl ethyl ketone. Various mixtures of the recited fluids and also mixtures of those fluids with one or more of the fluids benzene, hexane, petroleum ether and methyl alcohol may be employed. Also mixtures of methyl alcohol and either benzene, hexane and/or petroleum ether have also proved satisfactory. A few examples of appropriate such mixtures are 73 cc. of normal hexane and 27 cc. of acetone producing a dielectric constant of about 7. 69 cc. of normal hexane and 31 cc. of isopropyl alcohol producing a dielectric constant of 7 have also given good results. A mixture of 9 cc. of isopropyl alcohol and 91 cc. of isoamyl acetate producing a dielectric constant of 6 has been satisfactory. 5-15 parts of isopropyl alcohol and 95-85 parts of ethyl