JPH0843431A - Acceleration sensor and its manufacture - Google Patents

Abstract

PURPOSE:To provide a small acceleration sensor wherein direct soldering is possible on a printed board, and improve its manufacturing method. CONSTITUTION:Relating to an acceleration sensor consisting of a piezoelectric caramics 1 cut out of a plate-like piezoelectric ceramics, the plate-like piezoelectric ceramics, polarized in advance in surface direction at an electorde surface provide on an end surface, terminals 8 and 9 wherein an electorde surface is electrically connected to a hole porocessed into a through hole, and additive mass bonded to the piezoelectric ceramics are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly to an improvement of a small acceleration sensor which can be directly soldered to a printed circuit board and a manufacturing method thereof.

[0002]

2. Description of the Related Art A fixed disk device generally called a hard disk is known. It has a higher recording density and a larger storage capacity than floppy disks, but
It has the drawback of being vulnerable to shock. For this reason, in order to read / write the data, it is essential to stop the read / write operation when there is a shock. An acceleration sensor mounted on the apparatus itself is used as an impact sensor that detects this impact and particularly issues a write stop command.

On the other hand, recently, it has been attempted to incorporate a sensor in the above-mentioned device and control the output of the sensor, and a small and inexpensive sensor has been required. For example, there is JP-A-64-41865. According to this, as shown in one embodiment of FIG.
A piezoelectric element 1 and an additional mass (weight) 2 are attached to the inside of 0. The housing 40 is mounted on a printed circuit board 41, and the output from the piezoelectric element 1 is taken out from one electrode through a lead wire 45 and the same substrate circuit 41, and the other electrode is grounded to the housing.

As another attempt, for example, FIG. 17 is one example thereof. The piezoelectric element 1 and the additional mass 2 bonded to the piezoelectric element 1 are covered with the housing 40, and the electrodes 43, 4
The substrate 42 made of alumina or the like to which No. 4 is attached is also fixed by an adhesive or the like. The electrode 43 is located on the slightly right half of the substrate in the figure, and is formed on a portion deviated from the lower surface of the piezoelectric element 1. The other electrode 44 is formed on the lower surface portion of the piezoelectric element 1 in the slightly left half of the substrate at a position where it does not contact the electrode 43. The lead wire 45 is connected to the electrode 43, and the housing 40 is connected to the substrate 42.
The electrodes 43 and 44 are soldered to the printed circuit board 41 with solders 46 and 47. Top and bottom of the figure (thickness)
The output from the piezoelectric element 1 polarized in the direction is taken out through the electrodes 43 and 44 by the vibration in the vertical direction and sent to the control circuit mounted on the printed board 41.

[0005]

The above-mentioned conventional acceleration sensor has a drawback that it is too large to be used for a vibrating body such as a hard disk as an object to be mounted. As a result, the shock of the vibrating body itself is not detected, and the vibration sensor is used as a shock sensor including an acceleration sensor.
For this reason, there are many problems to be solved, such as meeting the purpose of downsizing, having a small number of parts, labor saving to eliminate wiring work, and drastically reducing manufacturing cost.
The present invention has been made in view of the above conventional problems, and is different from the conventional handmade manufacturing method, and includes an acceleration sensor mounted on a miniaturized direct printed circuit board that can be mass-produced. The present invention relates to the provision of a new acceleration sensor suitable for detecting the temperature of a hard disk and ensuring the reliability of products with low impact resistance such as hard disks.

[0006]

The present invention relates to an acceleration sensor and a method for manufacturing the same, and more particularly, in an acceleration sensor made of a piezoelectric ceramic cut out from a plate-shaped piezoelectric ceramic, an electrode surface provided on an end surface of the acceleration sensor in advance in the surface direction. It is provided by an acceleration sensor comprising the polarized plate-shaped piezoelectric ceramic, a terminal having an electrode surface electrically connected to a through-hole processed hole, and an additional mass bonded to the piezoelectric ceramic. Further, in the case of the piezoelectric ceramic having electrode surfaces on the front and back and terminals electrically connected to the treated electrode surfaces on the end surfaces of the piezoelectric ceramic, the thickness slip and thickness polarized in the thickness direction are further included. The acceleration sensor for detecting a directional impact is provided.

Further, as a method of manufacturing the acceleration sensor, an end face electrode is provided on the plate-shaped piezoelectric ceramic to polarize between the end faces, an electrode face is provided in the thickness direction of the plate-shaped piezoelectric ceramic, a hole is provided, and It is provided by making through holes in the holes to form terminals that are electrically connected to the electrode surface, and then individually cutting out the piezoelectric ceramics and adhering the additional mass. Further, the present invention is also effectively provided when the polarization treatment in the thickness direction is added to the plate-shaped piezoelectric ceramic and further when the additional mass is bonded before the piezoelectric ceramic is cut out individually.

[0008]

The piezoelectric output depending on the polarization direction of the piezoelectric element and the additional mass is detected from the vibration of the piezoelectric element and the additional mass, and this is changed to the acceleration output by the control circuit or the like on the printed circuit board to perform the necessary control operation. By reducing the size of the element, a hard disk or the like as a mounted device can detect an acceleration close to that peculiar to the device, and operates as an acceleration sensor whose sensor itself has very little weight dependency.

[0009]

EXAMPLES Examples will be described with reference to the drawings.
FIG. 1 is a perspective view showing an embodiment of an acceleration sensor obtained by the present invention. In FIG. 1, an additional mass 2 is bonded to the upper surface of the piezoelectric ceramic 1 and a printed circuit board (not shown) is bonded to the lower surface of the piezoelectric ceramic 1, which is used. The acceleration sensor is polarized in the vertical direction of the drawing. Silver electrodes are screen-printed and printed on the top and bottom of the piezoelectric ceramic 1 in a fixed pattern. Electrodes 3 and 4 provided on both sides of the piezoelectric ceramic 1 are similarly brushed with a silver electrode paint and baked on each electrode. Electrodes 3 and 4 are piezoelectric ceramics 1
Are electrically connected between the upper and lower surfaces of the board and soldered to the printed circuit board. For the additional mass 2, a metal plate or an insulator such as alumina can be used. In the case of metal, it is possible to secure insulation between the electrodes 3 and 4 by interposing an insulating film between the piezoelectric ceramic 1 and the additional mass 2.

FIG. 2 shows a silver electrode 3 on the upper surface of the piezoelectric ceramic 1,
4 is a perspective view showing another example of the acceleration sensor in which the electrode 4 is formed with electrodes 6 and 7 on the lower surface. An additional mass is adhered to the upper surface and used as an acceleration sensor. Specifically, the acceleration sensor is mounted on a part of a circuit board of a vibrating body such as a hard disk or on the vibrating body and operates as a sensor via an interface or the like to output an operation command or the like to the vibrated body. 3 is a partially cutaway top view of the plate-shaped piezoelectric ceramic 12 before cutting out a large number of piezoelectric ceramics 1, and FIG.
FIG.

The plate-shaped piezoelectric ceramic 12 having a large number of holes prepared in advance is provided with through-hole processed portions 8, 9, 10 and silver electrodes 3, 4, 5, 6, 7. From this, one piezoelectric ceramic 1 is cut out from the dotted line portion in the drawing. Lead zirconate titanate is suitable as the plate-shaped piezoelectric ceramic material, and a piezoelectric ceramic having a thickness of about 0.6 mm was used. Although it depends on the measurement application and the difference in acceleration due to the degree of impact, due to the recent advances in circuit technology, it has been requested to cut out to an extremely thin piezoelectric ceramic 1, and a thickness of 0.2 to 0.5 mm is also possible, which is also applicable. Met. Further, the piezoelectric ceramic 1 can be similarly cut out into a small size, for example, a size of 3.4 to 5.0 mm square can be supported.

Next, a manufacturing example will be specifically described. In order to obtain the piezoelectric ceramics 1, first, the plate-shaped piezoelectric ceramics 12 are provided at the positions shown in FIG. 3 corresponding to the number of the piezoelectric ceramics 1 to be cut out in parallel with the holes 8, 9 and 10 having a diameter of about 1.2 mm. Prepare an opening. These can be prepared at the time of molding the plate piezoelectric ceramic or by post-processing. The upper surface of the piezoelectric ceramic 12 surrounds the periphery of the silver electrode 11
The silver electrodes 3 and 4 and the silver electrodes 5, 6 and 7 on the back surface are screen-printed and printed in a certain pattern except for the portions. Further, through the holes 8 and 9 provided on both sides of the piezoelectric ceramic 1 in each electrode shown in FIG.
As shown in FIG. 6, they are sequentially electrically connected. The through-hole treatment of each of these connections is performed by electroless nickel plating on the holes. Next, polarization treatment 21 was performed between the electrode 4 and the electrode 3 in the thickness direction of the piezoelectric ceramic 1 in FIG. 2 with a DC voltage of 1 kv / mm.

After that, the piezoelectric ceramic 1 was cut out at a portion surrounded by a dotted line in FIGS. Added mass 2 to this
An acceleration sensor was obtained by bonding (not shown). Alumina was used as the additional mass and the thickness was 1 mm. The completed acceleration sensor was soldered to the printed circuit board at the semi-circle portions of the through holes 8 and 9. In the case of a metal having a large specific gravity, the additional mass 2 can be formed into a thinner plate, which is preferable, but in the acceleration sensor of FIG.
It is also possible to cut out the piezoelectric ceramic 1 in a state in which the piezoelectric ceramic 1 is previously adhered to and finish it as an acceleration sensor. In such a case, an insulator such as alumina can be used, and when a metal is used, an insulating film forming treatment is appropriate on the metal surface, at least on the back surface. When the additional mass 2 is adhered to the surface of the piezoelectric ceramic 12 in advance, after the screen printing, the electrode baking process is performed, and then the through hole 8,
9, 10 and the additional mass is adhered to positions other than the electrode portion for polarization. Subsequent through-hole processing steps may be the same as before. A constant sensor was obtained without the need to subsequently bond additional mass to the resulting acceleration sensor.

FIG. 14 shows the output frequency characteristic of the acceleration sensor obtained in the embodiment. The horizontal axis is frequency 50Hz-50k
The sensor output is 10 db / scale on the vertical axis of Hz, and the sensitivity is 0.77 mV per 1 G of acceleration. Similarly, FIG. 15 shows ringing characteristics with respect to the impact force of the acceleration sensor. The horizontal axis represents time and the vertical axis represents the output of the sensor, and no ringing was observed.

From these, it is possible to obtain a sensor which is flat up to about 10 kHz and which is small and lightweight, so that it can be mounted on a printed circuit board. As a result, the vibration system is not disturbed and it can be expected to be used in a wide range of fields of use.

Also, this acceleration sensor can be used with a shock force of 0.1 G or more, which is considerably small, and is suitable for use with a hard disk or the like. Further, since the weight ratio of the acceleration sensor to the vibrating body such as the mounted device can be made extremely low, the resonance frequency also becomes high, and the acceleration sensor capable of measuring the acceleration of the mounted device without being conscious of sensor mounting was obtained. Therefore, it was clear that an acceleration close to the peculiar to the device can be detected, and that the sensor operates as an acceleration sensor having very small weight dependence of the sensor itself.

FIG. 5 shows electrodes 15 on the upper surface of the piezoelectric ceramic 1.
16 is a perspective view showing another embodiment of an acceleration sensor in which electrodes 16, 14 are formed on the side surfaces and electrodes 17 are formed on the lower surface. An additional mass is adhered to the upper surface, and the lower surface is soldered to printed circuit board 5 (not shown) from through holes 18 and 19 connected to electrodes 13, 14 and 17, respectively, and is used as an acceleration sensor. Here, the electrodes 13 and 14 are polarized in the rightward arrow direction in the drawing, and the electrodes 16 and 17 are polarized in the vertical direction in the drawing.

Further, the electrode 17 is connected to holes 18 and 19 formed on both sides of the piezoelectric ceramic 1 by through hole processing. The electrode 13 is electrically connected to the electrode 16, and the electrode 14 is electrically connected to the electrode 15. Next, a manufacturing process of this acceleration sensor will be described. FIG. 6 is a perspective view showing a part of the plate-shaped piezoelectric ceramic 12 before being cut into the piezoelectric ceramic 1 of FIG. Brushing silver paint on both sides of the piezoelectric ceramic 12 and baking electrodes 13,
14 is formed. Next, a polarization process 22 is performed between the electrodes 13 and 14 in the direction of the arrow in the figure.

FIG. 7 is a front view of FIG. 6, and FIG. 8 is a rear view of FIG. First, holes are formed at the positions of the through holes 18, 19, 20. This hole is a plate-shaped piezoelectric ceramic 1.
2 through-holes 18 and 1 in advance in the molding and firing process stages
Holes may be prepared at positions 9 and 20. On the front surface of the plate-shaped piezoelectric ceramic 12, silver electrodes 15 and 16 are formed in a fixed pattern as shown in FIG. 7, and on the back surface, electrodes 17 are formed as shown in FIG.
Are screen printed and baked. Through hole 1 is processed by electroless nickel plating in the hole.
8, 19, 20 are formed. The polarization is then electrodes 15,1
Between 7 and 7, the right half of the figure is polarized 23 in the vertical thickness direction.

The piezoelectric ceramic 1 is aa and b- in FIG.
The portion surrounded by the line b is cut out, and each through hole portion is divided into half and cut. After that, the additional mass 2 is adhered to the piezoelectric ceramic 1, and each electrode 13,
The through holes 18 and 19 connected to 14 and 17 are soldered to the printed circuit board. Since this acceleration sensor has polarization directions in the X-axis direction and the Z-axis direction as shown in FIG. 5, one acceleration sensor can detect vibrations in both axial directions at the same time, and can be formed in a small size. Note that X
Detection of vibration in the axial direction is output between the electrodes 17 and 14, and detection of vibration in the Z-axis direction is output between the electrodes 17 and 13.

Although the method of adhering the additional mass 2 to the individual piezoelectric ceramics 1 has been described, it may be manufactured by adhering it to the front surface at the stage of the plate-shaped piezoelectric ceramics 12. In this case, after the screen printing of the electrodes 15 and 16, the additional mass 2
And the through holes 18, 19,
It suffices to avoid the additional mass 2 from each of the 20 parts and bond them.

Next, another mass-production type acceleration sensor will be described with reference to the drawings. 9 is a top view of the acceleration sensor, FIG. 10 is a front view thereof, FIG. 11 is a top view of the piezoelectric ceramic 1, FIG. 12 is a bottom view thereof, and FIG. 13 is a schematic plan view showing a state before the piezoelectric ceramic is cut out. . The plate-shaped piezoelectric ceramic 12 is used as an acceleration sensor by cutting out a large number of piezoelectric ceramics 1. For example, it is possible to cut out about 5 × 5 piezoelectric ceramics 1 with a thickness of about 0.6 mm. In the ceramic 12, end face polarization is performed in advance between the silver electrodes applied to the end faces on the left and right sides. Next, a silver electrode is pattern-printed on both the front and back by screen printing and baked. The pattern is the electrode 35 in the area defined by the solid line on the front surface, and the electrodes 31, 32, 3 at the positions shown by the dotted lines on the back surface.
Bake 3, 34.

After that, the terminals 25 to 30 are subjected to through-hole treatment, and polarized between the electrodes 35 and 31 in the thickness direction. For the cutting, the piezoelectric ceramic 1 is cut out at a portion surrounded by aa, bb, cc, and d-d. The additional mass 2 uses alumina, which is slightly smaller than the piezoelectric ceramic 1, and the size is 5.8 mm.
The thickness was about 6.7 mm and the thickness was about 1.0 mm. The additional mass 2 was adhered to the positions shown in FIGS. About 7 x 7 mm as a whole
It was a sensor with high sensitivity and high reliability that could manufacture a micro angular acceleration sensor. As the acceleration sensor, the thickness slip is detected from the vibration in the X-axis direction in the left-right direction as shown by the arrow in FIG. Further, the thickness vibration can be detected from the vibration in the Z-axis direction which is the vertical direction in FIG. Therefore,
It can be used to detect lateral and vertical impact forces of an arm in a magnetic head of a hard disk device. The output performs acceleration detection on the Z axis between the electrodes 31 and 35 and on the X axis between the electrodes 32 and 35.

For use as an acceleration sensor, it is soldered to the printed circuit board by the terminals 25 to 30. Terminal 2
Reference numerals 5 and 28 denote the back surface electrode 32 of the piezoelectric ceramic 1 and the terminal 2
Reference numerals 7 and 30 are electrically connected to the back surface electrode 31 of the piezoelectric ceramic 1, respectively. Further, the terminal 26 is connected to the electrode 33 and the terminal 29 is connected to the electrode 34, and at the same time, is electrically connected to the surface electrode 35 of the piezoelectric ceramic 1. The acceleration sensor of the present invention is small and lightweight, can be surface-mounted on a printed circuit board, has a wide detection frequency range, and has other advantages .

[0025]

As described above, according to the present invention, it is possible to provide an acceleration sensor suitable for use in a hard disk or the like, which is unprecedented in size reduction and the number of parts is reduced, resulting in a large reduction in manufacturing cost. Furthermore, since the weight ratio of the acceleration sensor to the vibration body such as the mounted device is extremely low, the resonance frequency can be increased and the acceleration measurement closer to that of the vibration body itself can be achieved. In addition, sensor mounting is simple, shock resistance and reliability are high. The effect was recognized as a high acceleration sensor. Furthermore, the polarization can be easily performed in a plurality of directions, and the vibration generated in the X and Z axis directions can be expected to be used in a wider field of use.

[0026]

[Brief description of drawings]

FIG. 1 is a perspective view of an acceleration sensor according to the present invention.

FIG. 2 is a perspective view of an acceleration sensor according to the present invention.

FIG. 3 is a partially cutaway top view of a plate-shaped piezoelectric ceramic before cutting out the piezoelectric ceramic.

4 is a rear view of FIG.

FIG. 5 is a perspective view showing another embodiment of the acceleration sensor of the present invention.

FIG. 6 is a perspective view of a plate-shaped piezoelectric ceramic before the piezoelectric ceramic is cut out.

FIG. 7 is a front view of FIG.

FIG. 8 is a rear view of FIG.

FIG. 9 is a top view showing another embodiment of the acceleration sensor of the present invention.

FIG. 10 is a front view of FIG.

FIG. 11 is a top view of the piezoelectric ceramic with the added mass removed.

FIG. 12 is a bottom view of FIG.

FIG. 13 is a schematic plan view of a plate-shaped piezoelectric ceramic before the piezoelectric ceramic is cut out.

FIG. 14: Output frequency characteristic of the acceleration sensor

FIG. 15 is a ringing characteristic of the acceleration sensor with respect to impact force.

FIG. 16 is a sectional view of a conventional acceleration sensor.

FIG. 17 is a sectional view of another conventional acceleration sensor.

[Explanation of symbols]

 1 Piezoelectric Ceramic 2 Additional Mass 3 Electrode 8 Hole 12 Piezoelectric Ceramic Plate

Claims (6)

[Claims] 1. An acceleration sensor made of a piezoelectric ceramic cut out from a plate-shaped piezoelectric ceramic, wherein the plate-shaped piezoelectric ceramic is polarized in advance in a plane direction on an electrode surface provided on an end face, and an electrode is formed in a through-hole-processed hole. An acceleration sensor comprising terminals whose surfaces are electrically connected and an additional mass adhered to the piezoelectric ceramic. 2. An acceleration sensor made of a piezoelectric ceramic cut out from a plate-shaped piezoelectric ceramic, the piezoelectric ceramic having electrode surfaces on the front and back sides, and electrically connected to the processed electrode surface on the end surface of the piezoelectric ceramic. And an additional mass bonded to the piezoelectric ceramic. 3. The acceleration sensor according to claim 1, which detects a thickness slip and a thickness impact that are polarized in the thickness direction of the piezoelectric ceramic. 4. An acceleration sensor made of a piezoelectric ceramic cut out from a plate-shaped piezoelectric ceramic, wherein the plate-shaped piezoelectric ceramic is provided with end face electrodes and polarized between the end faces, and an electrode surface is formed in the thickness direction of the plate-shaped piezoelectric ceramic. And a hole is formed in the plate-shaped piezoelectric ceramic, and a through hole is processed in the hole to form a terminal electrically connected to the electrode surface,
A method for manufacturing an acceleration sensor, wherein piezoelectric ceramics are individually cut out from the plate-shaped piezoelectric ceramics, and an additional mass is adhered to the piezoelectric ceramics. 5. The method of manufacturing an acceleration sensor according to claim 4, wherein polarization treatment in the thickness direction is added to the plate-shaped piezoelectric ceramic. 6. The method for manufacturing an acceleration sensor according to claim 4, wherein an additional mass is adhered to the piezoelectric ceramics before they are individually cut out from the plate-shaped piezoelectric ceramics.