US3385647A - Method of making a hydrogen flame visible - Google Patents

Description

May 28, 1968 c. F. MILLER ETAL METHOD OF MAKING A HYDROGEN FLAME VISIBLE Filed Aug. 50, 1965 s RmR OLE m m W K QD mm On 2 W 5H E m a Z M w a c United States Patent 3,385,647 METHOD OF MAKING A HYDROGEN FLAME VISIBLE Charles Frederick Miller, Anaheim, and Howard L. Spicer,

La Habra, Calif., assignors to Basic Products Corporation, a corporation of Wisconsin Filed Aug. 30, 1965, Ser. No. 483,647 4 Claims. (Cl. 431-4) ABSTRACT OF THE DISCLOSURE Hydrogen is supplied to an alcohol-hydrogen torch through a sealed container of alcohol. The amount of alcohol is thereby limited to the saturation point ofalcohol vapor in hydrogen. The burning alcohol insures a visible hydrogen-alcohol flame.

This invention relates to a method for making a hydrogen flame visible and, more particularly, to the imparting of visibility to a fine hydrogen flame used in the cutting and balling of the ends of fine gold wire in ball bonding operations on semi-conductor devices such as transistors.

In bonding conductors to semi-conductor assemblies, such as transistors, one of the methods commonly employed is so-called ball bonding. In this method a fine gold wire on the order of .0007" to .003" in diameter is fed through a capillary needle and bonded by the needle to terminal posts and to conductor areas on semi-conductor wafers. After the last bond in a connection is formed, the capillary needle is raised to expose the wire and the wire is severed and formed into balls on its ends by passing a fine hydrogen flame across it. When the needle is again moved down for another bonding operation, it engages the ball on the end of the wire to feed the wire against the surface to which it is to be bonded and to press the ball against the surface to bond it thereto.

One of the major problems in this operation has been control of the hydrogen flame to form a uniform sized ball on the end of the wire in each cutting operation. The size of the ball is dependent upon the size and character of the flame and its position relative to the wire as well as upon the effect on the wire of inert atmosphere gas commonly used to envelop the cutting area. However, since a hydrogen flame is invisible its size and character could only be judged by observing its action on the wire during a cutting and balling operation, which made adjustment of the flame extremely diflicult.

It is accordingly one of the objects of the present invention to provide a method by which the hydrogen flame is made visible so that its size, character and position relative to the wire to be out can easily be observed and adjusted.

Another object is to provide a method in which alcohol vapor in automatically controlled quantities is added to hydrogen being supplied to a torch to give the flame from the torch an easily visible color.

According to a feature of the invention the hydrogen supplied to the torch is passed through the upper part of a sealed container containing alcohol to pick up alcohol vapor. The quantity of alcohol vapor picked up is automatically limited to the saturation of alcohol vapor in hydrogen so that the quantity is accurately and automatically controlled. Furthermore, since alcohol adds only carbon to the flame, it does not introduce troublesome impurities which might affect the cutting and balling operations.

The above and other objects and features of the invention will be more readily apparent from the following description when read in connection with the accompanying drawing in which:

FIG. 1 is a diagrammatic view of a ball bonding apparatus illustrating only the cutting portions of the apparatus; and

FIG. 2 is a sectional view of the alcohol container of FIG. 1.

As shown in FIG. 1 a fine gold wire indicated at 10 is to be bonded between a semi-conductor wafer 11 and terminal posts 12 carried by a base 13 and forming a part of a transistor assembly. As illustrated, short lengths of the wire are bonded between conductive areas on the outer face of the wafer 11 and the respective terminal posts 12 to form electrical connections therebetween.

The operation is performed in a known type of wire bonding apparatus which includes a small capillary needle 14 through which the wire 10 is threaded. When the wire 10 is cut by a flame as, for example, the hydrogen flame 15 emitted from a torch 16, the wire will be melted where it is contacted by the flame and the ends thereof will form into generally spherical balls as shown at 17. These balls are larger than the bore in the needle 14 so that when the needle is moved down the end of the needle will engage a ball and carry the wire down until the ball is pressed against either the conductive surface on the wafer or one of the terminal posts 12 to be bonded thereto. After a connection has been completed the needle is raised to approximately the position shown and the torch is moved so that-the flame will sweep across the wire between the last bonding point and the needle to sever the wire and to cause balls to be formed on the severed ends thereof.

As shown, the torch is supplied with hydrogen from a tank 18 through a suitable pressure regulating valve 19 and a conduit 21. The torch may be movably mounted for swinging across the wire and is carried by a portion of the wire bonding apparatus and is moved synchronously with movement of the needle or under the control of an operator to effect the severing of the wire at the desired times.

In order to impart visibility to the hydrogen flame 15 so that the size, character and position of the flame relative to the wire can readily be adjusted, the hydrogen supplied to the torch has alcohol vapor added to it according to the present invention. For this purpose a container 22 is provided. As shown in detail in FIG. 2, the container comprises a cylindrical wall 23 which may be welded to a base plate 24 which preferably extends beyound the container and is formed in its extended area with one or more openings 25 to receive mounting screws. The top of the container is closed by a flat top plate 26 welded to the upper edge of the cylindrical wall 23 and formed with spaced conduit connections 27 and 28. Preferably also a removable filler plug 29 is provided in the side wall through which alcohol may be inserted into the container to a maximum level approximately as indicated at 31.

With the container filled with alcohol and preferably with iso-propyl alcohol to approximately the level 31, and with the filler plug 29 secured in place to seal the container, the conduit connection 27 may be connected to the conduit 21 leading to the hydrogen tank 18 while the conduit connection 28 is connected to a conduit 32 leading to the torch 16. The conduit 21, as shown in FIG. 2, extends into the container to a point near the bottom thereof so that hydrogen entering the container will be introduced below the liquid level to bubble up through the liquid thereby to insure saturation of the hydrogen with liquid vapor. The container is preferably relatively heavy to withstand any pressures which may develop therein during use without leakage. In use of the apparatus, the alcohol in the container will vaporize so that the upper part of the container will be filled with alcohol vapor. As the hydrogen from the tank flows through the upper part of the container to the torch, it will pick up alcohol vapor to the extent permitted by saturation of the hydrogen by the alcohol vapor. At the flame both the hydrogen and the alcohol vapor will burn simultaneously and the alcohol vapor present is sufficient to give the flame a strong blue color which is readily visible to the eye. Therefore, since the flame can easily be observed, its size, character and position can easily be adjusted to perform the cutting and balling operation in the desired and most eflicient manner.

While one embodiment of the invention has been shown and described in detail, it will be understood that this is for the purpose of illustration only and is not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

1. The method of making a hydrogen flame from a torch visible which comprises supplying a stream of hydrogen to the torch to burn in a flame and adding alcohol vapor to the hydrogen stream before it reaches the torch.

2. The method of claim 1 in which the alcohol vapor is iso-propyl alcohol.

3. The method of making a hydrogen flame from a torch visible which comprises supplying a stream of hydrogen to the torch to burn in a flame, confining alcohol in a closed space, and passing the hydrogen stream through the closed space to pick up alcohol vapor therefrom before the hydrogen stream reaches the torch.

4. The method of claim 3 in which the hydrogen is introduced into the closed space below the level of the alcohol therein.

References Cited UNITED STATES PATENTS 1,325,116 12/1919 Sebilk 158-1175 1,718,732 6/1929 Danforth 158117.5 2,003,864 6/1935 Nock 1581l X FOREIGN PATENTS 486,170 3/1912 France.

JAMES W. WESTHAVER, Primary Examiner.

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