JP2540972B2 - Sensor - Google Patents

Description

The present invention relates to mounting an acceleration sensor.

(Prior Art) Conventionally, a semiconductor acceleration sensor has been manufactured by making full use of micromachining technology called micromachining of single crystal silicon. The acceleration sensor has a beam structure having a weight having a scoop-like shape at its tip. When acceleration is applied to the structure, a force proportional to the acceleration is generated in the weight, and thus a beam supporting the weight is also subjected to stress proportional to the force. Therefore, a piezoresistor, which is a so-called pressure-sensitive element, is formed at the base of the beam, and changes in the generated stress are converted into changes in the electrical resistance value to detect acceleration. Early accelerometer structures include i Triple E Transactions on Electron Devices, Vol.ED
-26, P1911, 1979, and even today, the approximate structure is similar to this sensor. The present applicant has applied for an invention of a sensor having a structure opposite to this structure, that is, a semiconductor sensor (hereinafter referred to as a peripheral weight type sensor) in which the periphery is a weight and the center is a support portion and the beams are connected to each other (hereinafter referred to as a peripheral weight sensor). Wish sho 63-248058, 248066, 2480
No. 67).

The outline will be described with reference to FIGS. 4 and 5. In both figures, (a) is a view seen from slightly above, and (b) is a view seen from the side. As shown in (a), the center is a fixed portion 43, the periphery is a weight 41, and both are connected by a cantilever 42. The aluminum pad 44 is formed on the fixed portion 43. By doing this, the weight ratio can be increased compared to the case of being in the center.
Therefore, the measurement sensitivity is significantly improved. As for mounting, as shown in FIG. 2B, a pedestal 46 is interposed below the fixed portion 43 to secure a space for vibration, and then the package is housed in a package (only part of which is shown). The weight 41 is slightly etched to make it thinner
May be made relatively thick, and the lower portion of the fixed portion may also serve as the pedestal. Both the acceleration sensors shown in FIGS. 4 and 5 can measure the acceleration in the thickness direction of the beam. That is, the acceleration of rotation in the Z direction in FIG. 4 and the X direction in FIG. 5 and in the xy plane can be measured. The number of beams is not limited to this, and may be as many as two or four. The acceleration sensor has a characteristic that is significantly different from other semiconductor electronic devices in that the weight provided in the sensor chip vibrates in response to a mechanical signal of externally applied acceleration. The acceleration sensor uses a piezoresistor built into the Wheatstone bridge to detect acceleration. An aluminum pad is provided at the end of the Wheatstone bridge as a terminal for external connection. The acceleration signal converted into an electric signal in the acceleration sensor is connected to the terminal provided on the package from the aluminum pad by wire bonding as shown in FIG. The external connection technology by wire bonding is the method most often used in ordinary semiconductor production sites. Usually for wire material,
Aluminum or gold can be brought. The principle of connection is
By pressing down the wire and aluminum pad, applying violent vibration and heat by ultrasonic waves, and mixing and bonding metal members together.

On the other hand, in an acceleration sensor of a type in which the weight for detecting acceleration is located in the central portion of the sensor chip (herein referred to as central weight type sensor), since the aluminum pad is located in the peripheral portion of the chip, it is the same as a normal semiconductor chip. Although it can be connected to the package with a length of wire, it is shown in Fig. 2 because the aluminum pad is in the central part of the chip in the acceleration sensor of the character that uses the periphery of the chip as a weight for detecting acceleration. As you can see, very long wires are laid all over the air.

(Problems to be Solved by the Invention) Since an acceleration sensor measures vibrations, the sensor itself is always exposed to a violent vibration environment and needs to have a structure that can withstand a bad environment. Conventionally, an acceleration signal converted into an electric signal by an acceleration sensor chip is taken out as an electric signal to the outside through a wire,
In this structure, the wire floats in the air, so if vibration is applied from the outside for a long period of time, the wire acts like a guitar string, causing resonance with a large amplitude at a specific frequency, There was a drawback that the connection could be lost.

In the wire bonding method used in the conventional semiconductor acceleration sensor, an aluminum wire having a small diameter is used. Such aluminum wire is light and has poor mechanical strength.
When it is regarded as one structure, it easily resonates in a relatively low frequency region. Therefore, the wire vibrates with a large amplitude, and a large force is applied to the wire connecting portion, which is a major cause of disconnection of the wire connecting portion.

Furthermore, in the peripheral weight type semiconductor acceleration sensor described above, the wire becomes long because the aluminum pad is located in the center of the sensor. Then, compared with the case where the wire is short, even if the same vibration is applied, the amplitude of the vibration of the wire becomes large and the wire is easily broken. As described above, the connection reliability was extremely low.

On the other hand, in the case of an acceleration sensor that has a weight for detecting acceleration around it, in order to apply it to the vibration space of the weight,
It was necessary to provide a special pedestal, and it was necessary to accurately adjust the height of the pedestal. Fabrication of the pedestal complicates the fabrication process of the sensor and is not so preferable.

Although the semiconductor acceleration sensor has been described above as an example, a sensor using a material other than a semiconductor, such as an acceleration sensor in which a metal strain gauge is attached to a beam, a vibration sensor, an impact sensor, or the like, is electrically connected to the sensor element and the outside. A similar problem occurs in a sensor that uses wires for various connections. In this specification, the acceleration sensor, the vibration sensor, and the impact sensor are collectively referred to as an acceleration sensor.

An object of the present invention is to overcome the above problems and provide a semiconductor acceleration sensor that is strong against vibration. further,
Conventionally, in the peripheral weight type semiconductor acceleration sensor, a support pedestal was separately used to provide a vibration space for the weight, but by supporting it with a straight beam, the purpose is to avoid using it. I am trying.

(Means for Solving the Problem) The present invention is an acceleration sensor characterized in that an acceleration sensor element and a package are connected to each other by a beam that connects the two to each other by floating them in the air. The beam may have conductivity. A protrusion may be attached to the tip of the beam.

(Operation) In the present invention, a beam is used instead of a wire. Since the beam has higher mechanical strength than the wire, the strength of the structure can be made significantly higher than that of the wire, the resonance frequency can be set high, and the structure is extremely strong against vibration. You can

Furthermore, when applied to a peripheral weight type semiconductor acceleration sensor, by providing a protrusion at the tip of the beam,
The sensor vibrating portion can be floated in the space, and the area required for the vibration of the sensor can be easily provided. Further, the beam itself used for the connection also works as an excessive input prevention device because it works so as to prevent the sensor from causing the same when it occurs too much.

(Example) FIG. 1A is a perspective view showing a peripheral weight type acceleration sensor element 10 mounted on a package 3. The package 2 has terminals 2 for electrical connection to the outside.
The terminals 2 are provided with mounting beams 1 as shown in the plan view of FIG. 1 (b). The mounting beam 1 is connected to an aluminum pad (not shown in FIG. 1; the same as 44 in FIG. 4) provided on the fixed portion 43 of the acceleration sensor element 10. The mounting beam is made of stainless steel and has a length of 1 mm, a thickness of 100 μm, and a width of about 200 μm. In this embodiment, the projection 5 as shown in FIG.
Is provided and the projection 5 and the aluminum pad are connected to each other to secure a space in which the acceleration sensor element 10 vibrates.
The protrusion 5 is a cube having a length, width, and thickness of about 100 μm. The protrusion 5 is manufactured by the following steps. First, a resist pattern is formed on one surface of a stainless steel plate having a total thickness of beams and protrusions, the pattern being the shape of the protrusions 5. The substrate is turned over and aligned with the projection-shaped resist pattern provided on the front surface to form a resist pattern in the shape of the mounting beam 1. In this state, etching is performed on each side using an appropriate etching solution.
The height of the protrusion can be changed by changing the etching time from the surface having the pattern of the protrusion.

After the acceleration sensor element 10 is connected to the practical layer beam 1, the cap 4 is covered as shown in FIG. 1 (c). The implementation is completed in this way. FIG. 1D shows a cross section of the acceleration sensor at the end of mounting.

If plastic is used as the material of the package, the sensor becomes lighter, which is advantageous, and if it is ceramic, it is possible to obtain extremely high strength. It is also possible to insulate the surface of metal or the like for use. In the structure shown in FIG. 1, since the mounting beam 1 is closely attached to the package, the strength of the beam can be improved by the package.

Although the peripheral weight type semiconductor acceleration sensor is shown in the above embodiments, the present invention is not limited to this, and the present invention can be applied to a central weight type semiconductor acceleration sensor. In the case of the center weight type, the projection 5 is not always necessary because the aluminum pad is in the peripheral portion of the chip, but if the weight vibrates and goes out from the chip surface, the projection may be provided. When the protrusion is not provided, the chip surface and the package 3 contact each other when the mounting beam 1 and the terminal 2 are on the same plane as shown in FIG. Bring it closer to your side). In addition to semiconductor acceleration sensors, sensors that use materials other than semiconductors, such as acceleration sensors where metal strain gauges are attached to beams, vibration sensors, shock sensors, etc., are used to connect sensor elements to the outside. It can be applied to sensors that have

Although stainless steel was used as the material of the mounting beam 1 in the embodiment, other metals may be used, or a non-material material such as silicon or ceramics or a material material may be used. When a non-conductive material is used, the surface may be coated with a conductive material by a suitable method. Further, the mounting beam 1 may not have conductivity if an LED, a semiconductor laser or the like for converting an electric signal into an optical signal is mounted on the chip and the signal is transmitted to the outside of the chip by light.

(Effect of the Invention) According to the present invention, a mechanically very strong connection can be obtained as compared with the wire bonding method conventionally used for mounting a sensor. Therefore, it is strong against vibration and high reliability can be obtained. Further, when applied to a peripheral weight type semiconductor acceleration sensor, it is possible to provide a space for vibrating the sensor without using a support pedestal, and there is an effect that the production of the sensor pedestal can be omitted. Further, when the projection 5 at the tip of the beam is formed, the width of the vibration space of the sensor can be determined by the etching time, that is, the thickness of the projection, and there is an effect that the dynamic range of the sensor can be set at the time of mounting. Further, the mounting beam also has a role as a stopper for preventing the sensor from being destroyed when an excessive acceleration is applied to the sensor.

Since the characteristics of the acceleration applied to the sensor body can be changed by changing the strength of the beam in various ways, it is possible to prevent the sensor from being destroyed in the event of a collision.

When the beam is made conductive, electricity passes through a conductor having a wide cross-sectional area, and electrical connection can be made with a lower resistance than wire bonding.

In a dynamic sensor such as an acceleration sensor, conventionally, the entire back surface of the sensor element is connected to the package, but due to a difference in thermal expansion coefficient between the two, strain is applied to the sensor, and temperature characteristics are significantly deteriorated. In the present invention, since the sensor element is connected to the package only at the mounting beam portion, it is not affected by the difference in the coefficient of thermal expansion between the sensor element and the package. Therefore, the temperature characteristics can be significantly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an acceleration sensor according to an embodiment of the present invention. FIG. 2 is a structural diagram of a conventional semiconductor acceleration sensor. FIG. 3 is an enlarged view of the tip portion of the embodiment of the present invention. 4 and 5 are schematic views of a peripheral weight type acceleration sensor. 1 ... Mounting beam, 2 ... Terminal, 3 ... Package, 4 ...
… Cap, 10 …… Periphery weight type acceleration sensor element, 5
...... Beam tip projection part, 21 …… Bonding wire, 22
...... Acceleration sensor chip, 23 ...... Aluminum pad, 24 ......
External terminal, 25 …… terminal, 26 …… package

Claims (3)

(57) [Claims] 1. A sensor, characterized in that an acceleration sensor element and a package are connected to each other by a beam that connects the acceleration sensor element and the package in a hollow manner. 2. The sensor according to claim 1, wherein the beam is electrically conductive. 3. The sensor according to claim 1, wherein a projection is provided on a tip portion of the beam.