Metal fusion bonding – Process – Using high frequency vibratory energy
Reexamination Certificate
1999-11-12
2001-08-14
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Using high frequency vibratory energy
C228S180500, C428S544000
Reexamination Certificate
active
06273322
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to connections of the amorphous wire with terminal and their production method.
DESCRIPTION OF THE PRIOR ART
The MI effect of amorphous wire is a phenomena to show a large change of the impedance proportional to external magnetic field when a high frequency current is applied. Recently all MI sensor based on the MI effect has been watched with a keen interest. Because the MI sensor works with a small dimension the same as a hall sensor or MR sensor and never the less the small dimension it has a superior sensitivity to magnetic field 100 times larger than the MR sensor or hall sensor which are popular magnetic sensors. This sensitivity means to be as same as that of flux gate sensor.
An MI sensor consists of an amorphous wire for detecting magnetic field, a pickup coil bounding the amorphous wire and an electronic circuit for measuring a current running in the pickup coil. The amorphous wire used is made from cobalt alloy with a diameter of 20 &mgr;m to 130 &mgr;m. This amorphous wire has a recrystallization temperature of about 500° C. If the recrystallization occurs, MI effect of the amorphous wire drastically decreases. Therefore the soldering temperature must be kept below 300° C.
As is well known, the amorphous wires are stronger than piano wire. 60% Sn-40% Pb solder is not mixed with cobalt alloy of the amorphous wire. After soldering, the contact with 60% Sn-40% Pb solder and the amorphous wire shows appears to be only mechanical and not chemical.
As usual the amorphous wire is soldered according to the following procedures. At first the oxide film on the surface is removed by polishing it with emery paper. Then contamination on the surface is removed by flax. After that, sufficient mass of molten solder alloy is placed on the terminals produced on the substrate. These terminals are made from copper. The amorphous wire is inserted into the molten solder and the solder is then harden by cooling. In this manner, the amorphous wire is connected electrically with the terminals.
Another way to connect the amorphous wire with the terminal is a resistance welding method in which electricity is turned on while the amorphous wire is pressed to the terminal under some pressure after the wire is in contact with electrode.
Moreover, Japanese Examined Patent Application Publication (koukai) No.2-32077 discloses a method to connect the amorphous wire with the terminal using ultrasonic vibration. In the method, the amorphous wire is placed on the terminal and then ultrasonic vibration produced by the ultrasonic machine is loaded under some pressure.
THE PROBLEMS TO BE SOLVED BY THE INVENTION
However the above methods can not make a good contact between the amorphous wire and the terminal because the Co alloy type amorphous wire has a poor wettability in soldering metal. When soldering with them, the solder would be repelled from the amorphous wire by a surface force of melting solder. In fact the observation of the boundary with them is shown in
FIG. 9
in which the solder contacts partially to there is a amorphous wire and the lack of the solder remaing on the wire.
The MI sensor having the above poor contact can not pass a heat cycle test in which the test samples undergo heat shock from −40° C. to +80° C. with repeated numbers of 100 in oil bath. Although many trials to solve this problems has been made so far, they have not come to success.
The MI sensor needs two coils wound around the amorphous wire for improving the linearity or extending the measuring range. But the coils are wound not directly to the amorphous wire because the amorphous wire is too fine in the diameter of 30 &mgr;m to 120 &mgr;m. They are inevitably offered as hollow coils so that assembly with the amorphous wire and the coils is so weak to vibration or shock. That means that this kind of MI sensor could not apply to automobile use which requires a strong structure to mechanical vibration or heat shock.
The above resistance welding method meets with a problem that the amorphous state changes to a crystal structure when subjected to the heat of welding. The soldering method can give only a poor mechanical contact because the solder would be repealed from the amorphous wire by a surface force of molten solder on soldering. The amorphous wire has only a poor wettability to the molten solder.
Moreover it is difficult for the above ultrasonic vibration method to make a good connection of the amorphous wire with the terminal. The reason is that the round wire placed on the terminal has a point contact, which can not easily form a strong connection. Although the present inventors made many trials using this method, they could not pass a heat cycle test or environment tests for automobile.
The amorphous wire is so hard and poor in elasticity that it is easily broken by mechanical vibration brought with ultrasonic energy. When the ultrasonic vibration method applies to a fine amorphous wire, this problem happens very often.
The purpose of the present invention is to offer solutions of the above problems. A connection of the amorphous wire with the terminal which is made through the present invention possesses a good mechanical strength and the amorphous state to suppress crystallization. Also their production method is offered in the present invention.
SUMMARY OF THE INVENTION
The present invention recited in claim
1
is a method to connect the amorphous metal with the terminal using a mass of soft bonding metal in which the amorphous metal is sandwiched between the terminal and the mass of the soft bonding metal. A bonding energy is supplied on the mass of soft bonding metal.
Soft bonding metals used should be aluminum, gold, solder and so on. The amorphous metal coated with the soft bonding metal can be used in stead of the mass of the soft bonding metal. In this case it is better that a mass of soft bonding metal can be applied on the coated amorphous metal in bonding. A reason is that the long time is needed to produce a thick enough coating layer of the bonding metal by the coating, CVD method and PVD method.
In this way the head of a bonding tool is not contacted with the amorphous metal which is so hard and very brittle and the bonding energy is not directly transferred to the amorphous metal. The bonding energy is transferred through the soft bonding metal so that the amorphous metal is protected with a buffer effect of the soft bonding metal. As a result the amorphous metal does not meet with any trouble, and is not broken, or not bent by the bonding energy.
In other words, the direct contact of the hard bonding tool to the hard and brittle amorphous metal is apt to bring about a problem to break or deform the metal. The buffer effect of soft bonding metal placed between the bonding tool and the amorphous metal can solve this problem.
The present method can transfer the bonding energy to the amorphous metal and the terminal more effectively than the method to contact the tool to the amorphous metal. Because the contact area with the amorphous metal and the soft bonding metal becomes large and the powerful bonding energy is transferred to the amorphous metal. Then its energy is transferred to the terminal through the amorphous metal and can make a good connection with the amorphous metal and the terminal.
In the present method only a little stress, is given to the amorphous metal compared with the conventional soldering method. Because solidification from the molten solder is accompanied with shrinkage of the volume and the shrinkage cause the internal stress in the amorphous metal.
The present invention recited in claim
2
is a method with the usage of ultrasonic bonding.
In the present method the ultrasonic vibration under some pressure generates heat only on the boundaries among the soft bonding metal, the amorphous metal and the terminal. The vibration inevitably makes the boundaries clean due to ultrasonic friction. The heat melts the soft bonding metal and forms the connection through the clean surface. The heat generates only
Honkura Yoshinobu
Mouri Kaneo
Yamamoto Michiharu
Aichi Steel Corporation
Dunn Tom
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Stoner Kiley
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