JP2000081471A - Magnetic impedance element excellent against thermal shock and mechanical vibration and magnetic impedance sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amorphous wire magnetic impedance(MI) element allowing easy junction such as solder joint. SOLUTION: A MI element 1 has an amorphous wire 11 and metal solder 12 formed on two surface parts of the amorphous wire 11 which are spaced apart at a predetermined interval. This MI sensor has a base part, having a placement surface and conducting parts located in positions across the placement surface, and the amorphous wire supported at its center part on the placement surface and joined to each conducting part via the metal solder formed on the surface parts leading to the center part. Since the metal solder is applied to the surface parts, wettability is so well that firm welding with other metals is made possible with the use of the solder or the like. Thus, a junction resistant to mechanical vibration and thermal distortion such as temperature cycles is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic impedance element (hereinafter, referred to as MI element) used for a magnetic impedance sensor (hereinafter, referred to as MI sensor) for an automobile or the like.

[0002]

2. Description of the Related Art There has been proposed an MI sensor using a magnetic-impedance (MI) effect in which the impedance of an amorphous wire is greatly changed by an external magnetic field. This MI sensor can be as small as a Hall element or an MR element, has a magnetic field detection sensitivity of 100 times or more that of a Hall element or an MR element, and is known as a sensor similar to a flux gate sensor. .

[0003] The MI sensor includes an amorphous wire as a detection body and an electronic circuit for measuring a high-frequency impedance of the amorphous wire. Amorphous wire is
Usually, a Co-based amorphous wire having a thickness of about 20 to 130 microns is used. The Co-based amorphous wire is recrystallized at a temperature of several tens of degrees Celsius, and when recrystallized, the MI effect completely disappears. For this reason, the upper limit of the soldering temperature is 30 when soldering or the like.
0 ° C.

[0004] Such an amorphous wire is harder than a piano wire, and furthermore, a general solder material such as Sn
There is a property that an alloy layer is not formed between a solder material of 60% -Pb40%. Thus, in soldering, the solder merely comes into mechanical contact with the amorphous wire. Conventionally, in the case of soldering a Co-based amorphous wire, first, the surface of the amorphous wire is finished to a rough surface with emery abrasive paper or the like to remove an oxide film, and further, a surface is removed using a flux. Thereafter, as shown in FIG. 13, a relatively high amount of molten solder 4 is applied to a joint of a conductive pattern made of a conductor 21 such as copper formed on the surface of the base 2 such as a printed circuit board. Then, the amorphous wire 11 is inserted into the molten solder 4 to cool and solidify the molten solder 4. Thereby, the amorphous wire 11 is electrically connected to the joint.

However, in such a soldering method, since the Co-based amorphous wire has poor wettability to the solder, the solder is repelled from the surface of the amorphous wire by surface tension during soldering. Become. Therefore, when soldering is performed as described above, when the interface between the amorphous wire 11 and the solder 6 is observed, the solder 6 partially contacts the surface of the amorphous wire 11 as shown in FIG. And a missing portion 61 of the solder 6 is generated.

[0006] In a cooling / heating cycle test for examining the durability of the MI sensor thus obtained as to whether or not it can be mounted on a vehicle, a liquid tank test in which the MI sensor is immersed in a liquid tank under the conditions of -40 ° C to + 80 ° C When repeated, there was a problem that solder joints failed in 100 thermal cycle tests. Various approaches have been considered to solve the problem of poor contact, but have not been solved yet.

In order to improve the linearity of the MI sensor and to expand the detection range, a coil is wound around the amorphous wire which is the detection object. However, since the diameter of the amorphous wire is as small as 30 to 120 μm, It could not be wound directly, the coil was provided in a hollow state, and had a structure that was extremely weak against vibration. By these things, MI
The device was vulnerable to thermal shock and mechanical vibration, and was difficult to be mounted on a vehicle.

An object of the present invention is to overcome these problems, and an object of the present invention is to provide an MI element which is resistant to thermal shock and mechanical vibration and has durability that can be mounted on a vehicle.

[0009]

The present inventor has made various studies to improve the wettability of the amorphous wire. As a result, the wettability to the solder was improved while the MI effect was maintained by slightly applying a plating to the amorphous wire. I discovered that it would be. Further investigation was further conducted, and it was confirmed that the wettability was improved without sacrificing the MI effect by plating only the surface portion to be joined, and the MI device of the present invention was completed.

Further, the present inventor has proposed that M
It is possible to obtain an MI sensor that can be easily handled by confirming that it can be integrated into the base without giving any distortion to the amorphous wire by fixing it to the base while supporting the center of the amorphous wire that exhibits the I function with the base supported on the base. Thus, the MI sensor of the present invention is completed. That is, the MI element of the present invention is characterized by having an amorphous wire and metal plating formed on two surface portions of the amorphous wire separated by a predetermined distance. Further, the MI sensor of the present invention includes a base having a mounting surface and a conductive portion at a position separated from the mounting surface, a central portion supported on the mounting surface and connected to the central portion, the conductive portion And an amorphous wire bonded to each of the conductive portions via metal plating formed on a surface portion in contact with the conductive portion.

The MI element of the present invention has two surface portions plated with metal. Since this surface portion has good wettability, it is possible to perform strong welding with another metal using solder or the like. Therefore, it is possible to form a joined body that is resistant to mechanical vibration and thermal distortion such as a thermal cycle. In the MI sensor of the present invention, the amorphous wire is supported on the mounting surface of the base. Therefore, distortion due to gravity does not occur in the amorphous wire. Therefore, the magnetism can be measured stably and accurately. Also,
The amorphous wire is joined to the conductive portion of the base via metal plating formed on the surface portion. For this reason, this MI sensor is resistant to mechanical vibration and thermal distortion such as cooling and heating cycles.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The MI element of the present invention has an amorphous wire and metal plating formed on two surface portions of the amorphous wire separated by a predetermined distance. As the amorphous wire, a conductive amorphous wire can be used as it is. A typical amorphous wire is FeCoSiB. Amorphous wire diameter is 10μm ~ 100μm
It may be of the order. The length is 0.3mm to 30mm
It may be of the order. Usually, those having a diameter of 30 μm and an effective length (distance between joints) of about 1 mm are used.

The surface portion on which the plating is formed has improved wettability. Therefore, the plated surface portion can be joined to another metal. The portion between the two plated surface portions is a portion exhibiting the MI function. The plated surface portion needs at least two portions separated by a predetermined distance. However, the surface portion on which plating is formed may be three or more for various purposes. Further, extremely thin plating can be formed on the entire surface of the amorphous wire. When the plating is thin, for example, a usable output voltage can be obtained even with a plating thickness of 0.5 μm.

For reference, FIG. 1 shows the relationship between the plating thickness and the MI function. In this case, plating of various plating thicknesses is uniformly applied to the front surface of the amorphous wire. Plating is electroless plating, electrolytic plating, chemical vapor deposition (CV
D), which can be formed by physical vapor deposition (PVD).
Transition metal elements such as Au, Ag, Cu, and Ni are preferable as the plating metal.

It is not clear how the bonding between the amorphous wire and the plating is achieved. It can be considered that the metal element adheres to the surface of the amorphous wire, and the plating metal enters the recesses on the surface of the amorphous wire and is fixed in a wedge shape. The bonding of the MI element of the present invention will be specifically described with reference to FIG. In FIG. 2, the MI element 1 includes an amorphous wire 11 and metal platings 12 formed on the surface portions at both ends. The substrate 2 is made of a glass epoxy plate and has a conductive portion 21 formed on the upper surface thereof by metal plating. Bonding is performed on the substrate 2
The metal plating 12 of the MI element 1 is brought into contact with the conductive part 21 of the MI element 1, and the molten part is brought into contact between the conductive part 21 and the plating 12 to be joined. That is, the plating 12 improves the solder wettability of the amorphous wire 11 and forms an alloy layer between the plating layer 12 and the solder material. It can be easily joined without being repelled from the surface.

Further, as shown in FIG. 3, a preferred bonding method is to perform solder bonding between the plating 12 on the end of the amorphous wire 11 of the MI element 1 and the conductive portion 21 via the metal pad 3 having a high heat removal effect. Do. In the solder joining, more heat is required than melting the solder. However, if heat is applied more than necessary, the plating 12 will be destroyed due to an excessive amount of heat, and the heat input to the amorphous wire 11 will increase. Of the MI effect due to the recrystallization.

Therefore, it is necessary to prevent excessive heat from being transmitted to the amorphous wire 11 as much as possible. Therefore, the solder bonding of the amorphous wire 11 is performed through a metal pad having a high heat removal effect, and heat more than necessary at the time of solder bonding is stored in the metal pad 3 so as not to be transmitted to the amorphous wire 11. The metal pad 3 is plated with Ni or N to improve the wettability with solder.
It is preferable to perform i-B plating, Au plating, or Ni-Au plating.

Further, preferably, as shown in FIG. 4, the amorphous wire 11 having the plating 12 is soldered by being sandwiched between two highly heat-dissipating plated metal pads 3 and 3. As a result, it is not necessary to pile the solder high, and soldering can be performed with a minimum necessary amount of solder as shown in FIG. Therefore, the amount of heat required for soldering can be reduced. Therefore, it is possible to suppress the destruction of the plating or the plating and the solder alloy layer due to an excessive amount of heat, and it is also possible to suppress the heat input to the amorphous wire 11 to be low. .

Further, it is preferable that the MI element 1 having plating as shown in FIG.
When soldering is performed by inserting the solder 3 or 3, the solder 4 or the solder foil or the solder paste plated on the pads 3 and 3 is used as a method of supplying solder, and the solder is inserted between the pads 3 and 3 to apply heat. The amount of solder required for this soldering is originally small, and unlike wire solder supplied in a linear form, the amount of solder can be kept constant from the beginning, so there is no need to melt more solder than necessary. The amount of heat required for attachment can be kept small. Therefore, it is possible to suppress the destruction of the plating or the plating and the solder alloy layer due to an excessive amount of heat, and it is also possible to suppress the heat input to the amorphous wire 11 to be low. .

As shown in FIG.
When soldering by sandwiching between the metal pads 3 and 3 having high heat removal action, a solder 4, a plating foil and a solder paste plated on the pads 3 and 3 are used as a method of supplying solder in the soldering. This is inserted between the pads 3 and 3, and a laser, an infrared ray, and a soldering iron 5 are used as a heat supply method. As a result, a constant amount of heat can be applied to the metal pad 3 in a spot manner, so that it is possible to suppress the plating or the destruction of the plating and the solder alloy layer due to an excessive amount of heat, and also to suppress the heat input to the amorphous wire low. This makes it difficult for the MI effect to disappear due to the recrystallization of the amorphous wire.

The MI sensor of the present invention has at least a base and an amorphous wire. The base is formed of a non-magnetic electric insulator, and has a mounting surface on which the amorphous wire is supported and conductive portions formed at positions separated from the mounting surface. Synthetic resins and ceramics can be used as the electric insulator. The mounting surface formed on the base supports the amorphous wire without giving any deformation. Usually, since the amorphous wire is linear, the mounting surface can be a flat surface having a length substantially equal to the length of the amorphous wire and a width corresponding to the diameter of the amorphous wire, and a cylindrical inner peripheral surface having an arc-shaped cross section.

The mounting surface is a U-shaped groove or a concave groove,
It can be formed on a bottom surface such as a groove. Side wall portions on both sides of these grooves serve as protection walls for protecting the amorphous wires supported on the mounting surface at the bottom. The conductive portion serves as a terminal for fixing the amorphous wire to the base and for incorporating the amorphous wire into an electric circuit. The conductive portion may be formed on the surface of the base by plating or the like, or may be fixed by bonding a metal piece to the base mechanically or by using an adhesive or the like. Also,
A lead wire, a metal pad, or the like may be used as the metal piece.

It is preferable that the surface of the conductive portion and the surface of the mounting surface are flush with each other. As a result, the amorphous wire including the surface portion on which the plating is formed is continuously supported by the base conductive portion and the mounting surface. Thereby, deformation of the amorphous wire due to gravity acting on the amorphous wire can be avoided. Bonding of the amorphous wire at the conductive portion is achieved through metal plating formed on a surface portion of the amorphous wire.
A low melting point solder can be used for this joining. Also, bonding can be performed by using ultrasonic bonding without using solder. The metal plating formed on the surface portion of the amorphous wire and the metal on at least the surface portion of the conductive portion are preferably transition metals such as Au, Ag, Cu, and Ni.

When the conductive portion and the plating on the surface portion of the amorphous wire are joined by soldering, it is preferable to solder via a metal pad. Further, it is preferable that the solder bonding is performed in a state where the plating on the surface portion of the amorphous wire is held between the two metal pads. Preferably, the metal pad is plated with Ni, Ni-B, Au, or Ni-Au on the side to be soldered.

In the case of performing ultrasonic bonding, it is preferable that both the plating on the surface portion of the amorphous wire and the metal on the surface portion of the conductive portion are made of the same Au, Al, or the like.
The MI sensor of the present invention preferably has a bias coil and / or a feedback coil. It is preferable that the bias coil and the feedback coil have a part of the base on which the amorphous wire is supported as a bobbin around which the coil is wound, and the conductor is wound around the amorphous wire together with the bobbin. Note that it is necessary to prevent the coil from contacting the amorphous wire.

The bias coil and the feedback coil are preferably molded with resin and integrated with the base. Further, the MI sensor of the present invention preferably has a radio wave shielding case that covers at least the amorphous wire. The magnetic shield case needs to be formed of a nonmagnetic conductive material such as Al, Cu and a resin containing these metals. Note that the entire sensor may be housed in a magnetic shield case.

[0027]

The MI element of the present invention has metal plating formed on two surface portions of the amorphous wire separated by a predetermined distance. This metal plating is firmly fixed on the surface of the amorphous wire. In addition, since the metal plating has good wettability, it can be easily bonded to solder or the like.
For this reason, what has been joined by solder welding, ultrasonic bonding, or the like can be firmly joined because an alloy layer is formed between the plating and the solder material. For this reason, the thermal cycle characteristics of the joined products are improved.

Further, since the soldering is facilitated, the soldering time can be reduced, and the amount of heat required for the soldering can be reduced. Therefore, the destruction of plating due to excessive heat can be suppressed, and the heat input to the amorphous wire can be suppressed low, and the MI effect due to recrystallization due to the heat of the amorphous wire is less likely to occur.

In the bonding by ball bonding, the effective amorphous length can be bonded to the entire length with an accuracy of 3% or less. That is, the resistance value proportional to the effective amorphous wire length of the MI sensor can be manufactured without variation. This makes it possible to easily adjust the gain and the zero point on the circuit side. In the MI sensor of the present invention, the amorphous wire is supported on the mounting surface of the base. Therefore, distortion due to gravity does not occur in the amorphous wire. Therefore, the magnetism can be measured stably and accurately. Further, the amorphous wire is joined to the conductive portion of the base via metal plating formed on the surface portion. For this reason, this MI sensor is resistant to mechanical vibration and thermal distortion such as cooling and heating cycles. Further, since the soldering is facilitated, the joining can be performed at a lower temperature and a shorter time. Therefore, crystallization due to heating can be suppressed,
It becomes a highly sensitive sensor.

[0030]

(Embodiment 1) An MI element 1 according to an embodiment of the present invention is shown in FIG. This MI element 1 has a diameter of 30 μm and a length of 1.
An amorphous wire 11 having a composition of 2 mm FeCoSiB and an Au plating 12 having a thickness of 0.5 μm formed on a surface portion of 0.2 mm at both ends. This Au
The plating 12 is formed by electrolytic plating.

In order to check the bondability of the MI element 1, a bonding test was performed by two kinds of methods: solder bonding and ultrasonic bonding. Solder joint is made of A of MI element with two metal pads.
A method of supplying heat with a soldering iron across u-plating was adopted. Specifically, this was performed by pressing the tip of the soldering iron against the surface of one pad for 3 seconds as shown in FIG. The solder plated on the pad melts and the M
Au plating of the I element and an alloy layer were formed and joined.
In addition, since the amount of heat required for soldering can be reduced, the destruction of the solder alloy layer due to excessive heat can be suppressed.

In the ultrasonic bonding, as shown in FIG. 9, the Au plating 12 of this MI element 1 is placed on a metal plate 2 made of Au-plated Cu, and a gold ball 6
, And pressed by an ultrasonic bonding terminal to apply ultrasonic waves to perform gold ball ultrasonic bonding. For comparison, the same metal pad, the same solder, and the same gold ball ultrasonic bonding as described above were performed using the same amorphous wire that had not been Au-plated to obtain two types of samples of comparative examples.

One cycle of heating these four types of joined body samples from -40 ° C. to + 85 ° C. and returning to -40 ° C. was repeated 5 times.
The shock shock thermal cycle test was performed by putting the sample into an oil liquid tank. In each of the two types of samples using the MI element 1 of the example, no inconvenience such as loosening or falling off of the junction was observed even after the cycle test of 4000 times. On the other hand, two kinds of samples directly bonded to the amorphous wire of the comparative example
The junction was broken before the cycle reached 0, and the metal plate and the amorphous wire were separated.

Further, the vibration resistance of the same four kinds of samples was examined. This vibration test is a test for evaluating the durability by applying a vibration having an acceleration of 54 m / s ² and a frequency of 10 to 400 Hz. The two types of samples of the embodiment of the present invention are:
It was able to withstand more than one million vibrations required for vehicle mounting. On the other hand, the two samples of the comparative example were damaged before reaching 10,000 times.

For reference, the cross-sectional micrographs of the sample of the embodiment, which was soldered between two metal pads after the thermal shock cycle test was performed 3,500 times, and the comparative example 1
FIG. 10 shows a cross-sectional micrograph after the thermal shock test of 00 times. In the case of the example, the wire and the solder are integrally joined, while in the case of the comparative example, a gap is formed at the boundary between the wire and the solder, so that the wire and the solder are separated.

As described above, it was confirmed that the MI device of Example 1 had excellent bonding properties. Embodiment 2 FIG. 11 is a perspective view of an MI sensor according to Embodiment 2 of the present invention. This MI sensor has a height of about 2.5 mm, a width of about 3 mm, and a width of about 1.8 mm. The base 2 whose partial view is shown in FIG. It comprises a coil 8 and a mold 9.

The base 2 is made of an acrylic resin by cutting, and has a columnar support portion 210 having a V-shaped cross-section groove 201 opening on the upper surface and having a constant cross section, and formed integrally with the support portion 210 on both sides thereof. And a conductive part 230 having an Au plating layer on a total of six surfaces, three at a distance, integrally joined to the upper surface of each leg 220. The bottom of the V-shaped groove 201 forms a support surface, and the bottom and the upper surface of the conductive portion 230 are formed to have the same height, that is, the same surface.

In this MI sensor, the MI element 1 has a base 2
Of the amorphous wire of the MI element 1 at the both ends of the amorphous wire of the MI element 1.
Each of the i-plates is in contact with the upper surface of the central conductive portion 230. Then, as shown in FIG. 9, the Ni plating at both ends and the upper surface of the conductive portion 230 at the center respectively correspond to the Ni plating at both ends.
The gold ball placed on the plating is pressed by an ultrasonic bonding terminal to apply ultrasonic waves, and the gold ball is subjected to ultrasonic bonding.

In this state, the bias coil 7 and the feedback coil 8 are wound around the support portion 210 of the base 2,
The end of each coil applies the same gold ball ultrasonic bonding to the remaining four conductive portions 230. Thereafter, a liquid resin is impregnated and cured on the bias coil 7 and the feedback coil 8 to form a mold 9.

Although no case is used in the MI sensor of this embodiment, this MI sensor is used by being housed in an aluminum case. The same thermal shock cycle test and vibration test as in Example 1 were also performed on the MI sensor of this example. This MI sensor withstands a thermal shock cycle test of 4000 times and a vibration of 1 million times, and shows no deterioration of the MI function even after these tests.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between plating thickness and MI function.

FIG. 2 is a perspective view showing a bonding method of the MI element of the present invention.

FIG. 3 shows a MI soldered in one metal pad.
It is a perspective view which shows an element.

FIG. 4 shows an MI soldered in two metal pads
It is a perspective view which shows an element.

FIG. 5 shows the MI soldered in two metal pads
It is sectional drawing which shows an element.

FIG. 6 is a cross-sectional view showing the supply of solder in two metal pads.

FIG. 7 is a diagram showing a method of supplying heat in two metal pads.

FIG. 8 is a perspective view of the MI element according to the first embodiment.

FIG. 9 is a perspective view showing an arrangement of gold balls of the ultrasonic bonding.

FIG. 10 is a photomicrograph showing a bonded cross section after a thermal shock cycle test.

FIG. 11 is a perspective view of an MI sensor according to a second embodiment.

FIG. 12 is a perspective view of a part of a base used in the MI sensor according to the second embodiment.

FIG. 13 is a perspective view showing a conventional amorphous wire solder joint.

FIG. 14 is a cross-sectional view showing a joining state of a conventional amorphous wire solder joint.

[Explanation of symbols]

1: MI element 2: Base 3: Metal pad
4: Solder 5: Ultrasonic vibration terminal 7: Bias coil 7 8:
Feedback coil 9: Mold 11: Amorphous wire 1
2: Plating 21: Conductive part

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshiaki Kotani 1 Aomachi Wanowari, Tokai City, Aichi Prefecture Inside Aichi Steel Co., Ltd. (72) Inventor Yoshinobu Honkura 1 Aramachi Town Wanowari, Aichi Prefecture Aichi Product Steel Co., Ltd.

Claims (18)

[Claims] 1. A magneto-impedance element comprising: an amorphous wire; and metal plating formed on two surface portions of the amorphous wire separated by a predetermined distance. 2. The metal plating is made of Au, Ag, Cu, N
2. The magneto-impedance element according to claim 1, wherein the element is a plating of a transition metal element such as i. 3. The magneto-impedance element according to claim 1, wherein said amorphous wire is an amorphous Co alloy wire. 4. The magneto-impedance element according to claim 1, wherein the two surface portions are surface portions at both ends of the amorphous wire. 5. The magneto-impedance element according to claim 1, wherein said metal plating is formed only on said two surface portions. 6. A base having a mounting surface and a conductive portion at a position separated from the mounting surface, and a surface which is supported on the mounting surface and has a central portion connected to the central portion and in contact with the conductive portion. A magnetic impedance sensor comprising: an amorphous wire bonded to each of the conductive portions via metal plating formed on the portion. 7. The metal plating is made of Au, Ag, Cu, N
7. The magneto-impedance sensor according to claim 6, which is a plating of a transition metal element such as i. 8. The magneto-impedance sensor according to claim 6, wherein the joining is performed by soldering. 9. The magneto-impedance sensor according to claim 8, wherein said soldering connection is made via a metal pad. 10. The magneto-impedance sensor according to claim 9, wherein the solder joint is soldered while being held between the two metal pads. 11. The metal pad may be provided with Ni plating, Ni-B plating, Au plating or N
The i-Au plating is performed.
The magnetic impedance sensor according to any one of the preceding claims. 12. The magneto-impedance sensor according to claim 6, wherein the bonding is performed by ultrasonic bonding. 13. The magneto-impedance sensor according to claim 6, wherein the mounting surface is formed as a bottom surface of the groove of the base. 14. The magneto-impedance sensor according to claim 6, further comprising a bias coil wound around the amorphous wire in a non-contact manner with the amorphous wire. 15. The magneto-impedance sensor according to claim 6, further comprising a feedback coil wound around the amorphous wire in a non-contact manner with the amorphous wire. 16. The magneto-impedance sensor according to claim 6, further comprising a bias coil and a feedback coil wound around the amorphous wire in a non-contact manner with the amorphous wire. 17. The magnetic impedance sensor according to claim 16, wherein the bias coil and the feedback coil are molded with a resin. 18. The magnetic impedance sensor according to claim 6, further comprising a radio wave shielding case covering at least the amorphous wire.