JP2011049493A - Piezoelectric body module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To take effective pyroelectric measures in a process of mounting a piezoelectric body on a circuit board etc. <P>SOLUTION: A piezoelectric transformer 10 as a piezoelectric body module has a piezoelectric ceramic 12 stored in a case body 14 and in this state, a primary-side electrode 12a and a secondary-side electrode 12 are connected via conductors 16 to a primary-side terminal 18a and a secondary-side terminal 20, respectively. The piezoelectric ceramic 12 has a conductive film 24 formed on its outer surface, and the conductive film 24 connects two primary-side electrodes 12a to each other. Especially, a resistance value imparted by the conductive film 24 between the primary-side electrodes 12a is set within a range of predetermined resistance values. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric module suitable for applications such as a piezoelectric transformer, a piezoelectric actuator, and a piezoelectric motor.

  Conventionally, when the ambient temperature of a piezoelectric body (piezoelectric element) used for a piezoelectric transformer, a piezoelectric actuator, a piezoelectric motor, or the like changes, a so-called pyroelectric effect works to generate electric charges between the electrodes or easily cause discharge. The problem is known. As a countermeasure against this pyroelectricity, for example, prior art for connecting in parallel between the input terminals of a piezoelectric transformer element, an impedance having a magnitude that is greater than or equal to the impedance value between the drive electrodes at the resonance frequency of the piezoelectric transformer element and less than its insulation resistance value Is known (for example, see Patent Document 1).

  The above prior art pays attention to a change in ambient temperature when a piezoelectric body (element) is used as a piezoelectric transformer, and takes measures against the pyroelectric effect generated at that time. That is, the pyroelectric countermeasure impedance (resistance) is soldered between the input electrodes in a state of being incorporated in, for example, a circuit formed on the substrate, separately from the piezoelectric body itself. For this reason, it is considered that the prior art technique is effective as a countermeasure against pyroelectricity generated in the actual use environment in a state where the piezoelectric body is completed as a practical device.

JP 2000-307166 A JP-A-11-330578

  However, the pyroelectric effect does not occur only when the piezoelectric material is applied to a practical device as a piezoelectric transformer or the like and the ambient temperature changes in the mounted state, but can also occur in the previous manufacturing process. That is, when storing the piezoelectric body (piezoelectric element) in a state where the ambient temperature changes, or when mounting the piezoelectric body (piezoelectric element) on a circuit board by reflow or flow technology, the temperature of the piezoelectric body during soldering The pyroelectric effect may occur due to the change. The pyroelectric voltage generated in such a manufacturing process not only deteriorates the piezoelectric body itself, but also may cause damage to the peripheral circuit formed on the mounting circuit board and its circuit elements due to discharge.

  In this respect, the above-described prior art method is useful only after the piezoelectric body is actually completed as a piezoelectric transformer and already mounted on a circuit board. This is not a countermeasure for pyroelectricity in the process (1).

  Therefore, an object of the present invention is to take effective pyroelectric countermeasures in the process of mounting a piezoelectric body on a circuit board or the like.

  In order to solve the above problems, the present invention employs the following solutions.

  Solution 1: The piezoelectric module of the present invention is such that at least two electrodes formed on the outer surface of a piezoelectric body are connected (directly or indirectly connected) by a conductive film. The conductive film is formed along the outer surface of the piezoelectric body, and the resistance value applied between the electrodes is not less than the resonance resistance value between the electrodes of the piezoelectric body and not more than 10% of the insulation resistance value between the electrodes. . In addition, as long as a resistance value is provided between electrodes within the above range, the conductive film may not be directly connected to the electrodes.

  The “resonance resistance value” corresponds to the minimum resistance value between the electrodes of the piezoelectric body (before formation of the conductive coating) in the resonance mode to be used. The above “insulation resistance value” is a value of resistance between electrodes of the piezoelectric body (before formation of the conductive film), and includes both internal resistance and surface resistance.

  According to the piezoelectric module of the present invention, since the conductive film is formed along the outer surface of the piezoelectric body, even if the piezoelectric module alone is used, other parts are not interposed between the electrodes of the piezoelectric body. It is in a state of being connected via a resistor (= conductive film). For this reason, when a piezoelectric module is incorporated into a product for any purpose (eg, piezoelectric transformer, piezoelectric actuator, piezoelectric motor), even if the ambient temperature changes during the manufacturing process, the charge generated by the pyroelectric effect is quickly consumed. It does not damage other circuit components.

  In particular, the present invention has the following advantages because the resistance value of the conductive film is set within the range of the resonance resistance value of the piezoelectric body and 10% or less of the insulation resistance value. In other words, if the lower limit of the resistance value between the electrodes provided by the conductive film is set to the resonance resistance value, the resistance will not be excessively lowered, so the input voltage when the piezoelectric module is used (when the input voltage is applied). Will not be inadvertently divided.

  On the other hand, since the upper limit of the resistance value between the electrodes provided by the conductive film is suppressed to 10% of the insulation resistance value, the upper limit of the resistance value is simply set within a wide range such as “less than the insulation resistance value”. Compared with the case where it sets, it can suppress that resistance value becomes large too much. Of course, when some resistance is connected between the electrodes as a countermeasure against pyroelectricity, it is common knowledge that, if the resistance value is “less than the insulation resistance value”, it is theoretically difficult to generate a discharge during pyroelectricity. However, even if it is “below the insulation resistance value”, if the actual resistance value between the electrodes is set excessively with respect to the pyroelectric voltage, in most cases, the loss of electric charge (consumption) is practical. May not be obtained and may not function effectively as an actual pyroelectric countermeasure.

  The inventors of the present invention pay attention to the fact that if the upper limit of the resistance value is set in a range that is theoretically considered as common sense in theory, it may not function as a countermeasure for pyroelectricity practically, and within the range of conventional common sense Inspired by new issues that were overlooked. As a result of extensive research, the inventors of the present invention are effective as a means for solving the problem to suppress the upper limit of the resistance value between the electrodes provided by the conductive film to 10% of the insulation resistance value. I found out.

  Thereby, the piezoelectric body module of this invention can exhibit a practical pyroelectric countermeasure with respect to the temperature change at the time of incorporating in the use as a certain product. In addition, it is possible to ensure normal piezoelectric operation during use as a product and to exhibit effective pyroelectric countermeasures against temperature changes in the usage environment.

  Solution 2: In Solution 1 described above, the conductive film is formed by applying a conductive paint mixed with a resin and a conductive material on the outer surface of the piezoelectric body. At this time, the range in which the conductive paint is applied is the application width when the minimum distance necessary to connect the electrodes formed in parallel with each other when viewed in the direction along the outer surface of the piezoelectric body is defined as the application width. It is preferable that the coating length is determined based on the initial unit resistance value per unit length applied between the electrodes when the conductive paint for the unit length is applied. If the electrodes are formed in parallel on the outer surface of the piezoelectric body, the minimum distance required for connection between them can be defined as a constant coating width. If the coating width is constant, the resistance value per unit length is constant, so that the resistance value applied between the electrodes can be easily adjusted by adjusting the coating length of the conductive paint. it can.

  According to the above aspect, when the resistance value between the electrodes provided by the conductive film is set within the above optimal range, the coating length of the conductive paint necessary to obtain the resistance value is the optimal resistance. It becomes obvious from the result of dividing the value by the initial unit resistance value. Therefore, in the manufacturing process of the piezoelectric body module, the resistance value given between the electrodes by the conductive film can be accurately determined by simply applying the conductive paint to the outer surface of the piezoelectric body by the required coating length. Can be managed.

  Further, when the conductive film is formed of a conductive paint, the conductive film can be easily formed along the outer surface even if the outer surface of the piezoelectric body is three-dimensional. In addition, since the conductive paint can be easily applied by a technique such as printing or transfer, the conductive film forming operation is suitable for automation. Thereby, the workability | operativity at the time of forming a conductive film can be improved, and the production efficiency of a piezoelectric body module can be improved. Furthermore, if it is a conductive paint, it is easy to visually inspect and confirm the appearance (inspection and confirmation of whether or not the conductive film is formed correctly) by the color development, and thus contribute to the efficiency of quality control. Can do.

  Solution 3: In Solution 1, 2, the piezoelectric module of the present invention is held in a state in which the piezoelectric body is accommodated, and has an opening that exposes a part of the outer surface of the piezoelectric body in this held state. A case body is further provided. In this case, the conductive coating is preferably formed at a position exposed through the opening in a state where the piezoelectric body is held by the case body.

  Usually, a piezoelectric body generates vibration due to a piezoelectric effect during its operation. Therefore, when this is used for some applications (for example, a piezoelectric transformer, a piezoelectric actuator, a piezoelectric motor), the piezoelectric body is held in a case body. A form that absorbs vibration or protects a piezoelectric body is common. In addition, in the present invention, as described above, a part of the outer surface of the piezoelectric body is exposed through the opening of the case body, and a conductive coating is formed at the exposed position. There is an advantage that inspection and confirmation can be easily performed.

  Solution 4: The piezoelectric module of the present invention may have the following configuration. That is, the piezoelectric module includes a polarized piezoelectric body, at least two electrodes formed on the outer surface of the piezoelectric body, a case body that houses the piezoelectric body, and an electrode that is provided in the case body and houses the piezoelectric body. Are formed along the outer surface of the case body so as to connect the terminals to each other, and the resistance value applied between the electrodes via the terminals is equal to or greater than the resonance resistance value of the piezoelectric body. And a conductive film having an insulation resistance value of 10% or less.

  In the piezoelectric module of the present invention, the structure in which the piezoelectric body is accommodated in the case body covers the suitability as a mounting component by absorbing vibration during operation or protecting the piezoelectric body as described above. is there. Moreover, the terminal provided in the case body bears connection with a wiring pattern etc. at the time of mounting to a circuit board etc. In addition, if a conductive coating is formed along the outer surface of the case body, a visual inspection based on the appearance is further performed as compared with the case where the conductive coating is formed on the outer surface of the piezoelectric body (solution means 1 to 3). And confirmation can be performed easily. The other advantages are common to the solving means 1 to 3.

  Solution 5: In Solution 4, the piezoelectric module of the present invention may further include at least two conductive wires that connect each electrode and each terminal in a state where the piezoelectric body is accommodated in the case body. . In this case, the conductive coating is formed along the outer surface of the case body in a state where the conductive wires are connected to each other, and between the terminals, the conductive coating is connected to each terminal via each conductive wire. Preferably it is.

  Even if it is said aspect, by connecting each electrode and each terminal with a flexible conductive wire (for example, gold thread wire), these electrodes and each terminal can be made non-contact and these frictions can be eliminated. In addition, if the conductive wires are connected to each other through the conductive coating on the outer surface of the case body, the result is a state where the two electrodes are connected from the conductive coating through each conductive wire and each terminal. Therefore, the charge during pyroelectricity can be reliably eliminated.

  Solution 6: Alternatively, the piezoelectric module of the present invention may have the following configuration. That is, the piezoelectric body module of the present invention is a piezoelectric body that has a polarized body, at least two electrodes formed on the outer surface of the piezoelectric body, and an input signal or output of the piezoelectric body through each electrode in a state where the piezoelectric body is mounted. A circuit board on which a circuit for transmitting at least one of the signals is formed; a conductive pattern disposed in at least two locations on the circuit board to connect each electrode of the piezoelectric body and the circuit; and between the conductive patterns on the circuit board. Are formed along the outer surface of the circuit board so as to be connected to each other, and the resistance value provided between the electrodes via the conductive pattern is equal to or greater than the resonance resistance value of the piezoelectric body and equal to or less than 10% of the insulation resistance value. It is the structure provided with the adhesive film.

  If the piezoelectric module includes the configuration of the circuit board as described above, the conductive patterns on the circuit board are connected in advance with a conductive coating so that the piezoelectric body is accommodated in the case body. Even when electric charges are generated due to temperature changes when mounting the circuit board on the circuit board, it can be quickly eliminated. Further, since the conductive film remains even after the piezoelectric body is mounted on the circuit board, it effectively functions as a countermeasure against pyroelectricity even when the piezoelectric body module is used.

  Solution 7: In the present invention (all of Solution 1 to Solution 6), the conductive film preferably has a resistance value applied between the electrodes that is 10 times or more the resonance resistance value between the electrodes of the piezoelectric body.

  If the lower limit of the resistance value provided between the electrodes by the conductive film is set as described above, for example, when a driving voltage is applied to the piezoelectric body, the voltage is efficiently applied to the piezoelectric body. The efficiency as a module can be maintained.

  The piezoelectric module of the present invention can realize effective pyroelectric countermeasures with a simple configuration in which a conductive film is simply formed on the outer surface of a piezoelectric body, a case body, a circuit board or the like. In particular, since the resistance value applied between the electrodes by the conductive film is set to an optimum range, pyroelectric charge that can be generated in practice can be surely lost, and it effectively functions as a countermeasure against pyroelectricity. .

  In addition, since the resistance applied between the electrodes is formed by a conductive film, the cost can be reduced compared to the case where another resistance component is retrofitted, and the conductive film can be a piezoelectric body, a case body, or a circuit board. Therefore, it is possible to suppress an increase in the volume of the entire product as compared with a form in which another part is added.

It is the perspective view which decomposed | disassembled and showed the piezoelectric transformer of 1st Embodiment to the component. It is a perspective view which shows the completion state of a piezoelectric transformer. It is the characteristic view which showed the relationship between the ratio of the conductive resistance value with respect to the insulation resistance value between primary side electrodes, and the generated voltage at the time of pyroelectricity, and the relationship between the application length of a conductive coating material, and resistance value, respectively. It is a figure which shows concretely the characteristic part of the piezoelectric transformer of 2nd Embodiment. It is a figure which shows concretely the characteristic part of the piezoelectric transformer of 3rd Embodiment. It is a perspective view which shows the structural example of the piezoelectric transformer of 4th Embodiment. It is the perspective view which decomposed | disassembled and showed the piezoelectric transformer of 5th Embodiment into the component.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, an embodiment in which the piezoelectric module is applied to a piezoelectric transformer will be described. However, the piezoelectric module of the present invention is not limited to the piezoelectric transformer.

[First Embodiment]
FIG. 1 is an exploded perspective view showing the piezoelectric transformer 10 of the first embodiment as components. The piezoelectric transformer 10 includes, for example, a plate-shaped piezoelectric ceramic 12 (piezoelectric body) housed in a resin case body 14 and assembled. The piezoelectric transformer 10 is mounted on, for example, a circuit board (not shown) with the orientation shown in FIG. The structure to be implemented.

[Piezoelectric body]
The piezoelectric ceramic 12 mentioned here has, for example, a long and thin rectangular parallelepiped outer shape. And the primary side electrode 12a (electrode) is formed in a pair of outer surface which opposes the thickness direction of the piezoelectric ceramic 12, respectively. Although only one location is shown in FIG. 1, the primary electrode 12 a is formed on the surface opposite to the illustrated outer surface, and two primary electrodes 12 a are formed on the outer surface of the piezoelectric ceramic 12. Yes. The piezoelectric ceramic 12 has a secondary electrode 12b formed at an end located on the opposite side to the primary electrode 12a in the longitudinal direction. When the piezoelectric ceramic 12 is viewed in the longitudinal direction, the portion where the primary electrode 12a is formed functions as a drive unit. Moreover, the part in which the primary side electrode 12a is not formed functions as a power generation part.

[Case body]
The case body 14 has an outer shape larger than that of the piezoelectric ceramic 12, and a concave accommodating portion 14b is formed therein. In the state shown in FIG. 1 (upside down state), the case body 14 has an open upper surface, and the accommodating portion 14 b extends from the opening toward the inside of the case body 14. The accommodating portion 14b has a shape that is slightly larger than the piezoelectric ceramic 12, so that the accommodating portion 14b is accommodated so that the piezoelectric ceramic 12 is inserted from the opening in a posture in which the piezoelectric ceramic 12 is stood as shown in the drawing. can do.

  The case body 14 is integrally formed with projecting portions 14a on both side surfaces thereof, and the projecting portions 14a project from the side surfaces of the case body 14 to the side with a certain thickness. A conductive member 18 is inserted into each protrusion 14a, and each protrusion 14a has an insertion hole for the conductive member 18 (shown by a broken line on the front side in FIG. 1). ) Is formed. The insertion hole extends through the inside of each protrusion 14a in the vertical direction.

(Terminal)
In addition, the conductive member 18 is inserted into the protruding portion 14a, and one end thereof (the upper end portion in the illustrated state) is formed as the primary terminal 18a. The conductive member 18 forms a pair on both sides of the case body 14 according to the protruding portion 14a. For this reason, the case body 14 is provided with two primary terminals 18a on both sides thereof. . These primary side terminals 18a protrude upward from the upper surface of the case body 14 in the state shown in FIG.

  Each conductive member 18 protrudes downward from the lower surface of the case body 14 (projection 14a) with the other end 18b shown in FIG. 1, and from there toward one end of the case body 14 (in FIG. 1). Is bent at about 90 °. The tip of the other end 18 b protrudes from the outer surface (end surface) of the case body 14 in one end direction.

  The case body 14 is provided with a single secondary terminal 20 at one end opposite to the primary terminal 18a as viewed in the longitudinal direction. The secondary terminal 20 also protrudes upward from the upper surface of the case body 14 in the state shown in FIG. In this example, the other end of the secondary terminal 20 does not protrude from the lower surface of the case body 14 and is embedded in the case body 14 (may protrude).

[Conductive wire]
One end of a conductive wire 16 (for example, a gold thread wire) is soldered to each of the two primary side electrodes 12a of the piezoelectric ceramic 12 at a substantially central position. One end of a conductive wire 16 (also a gold thread wire) is soldered to the secondary electrode 12b. Then, with the piezoelectric ceramic 12 housed in the case body 14, the other end of each conductive wire 16 is soldered in a state of being entangled with the primary side terminal 18 or the secondary side terminal 20. Yes. As a result, the two primary side electrodes 12 a are connected to the primary side terminal 18, and the secondary side electrode 12 b is connected to the secondary side terminal 20.

  Further, the piezoelectric ceramic 12 is bonded and held by, for example, a silicone adhesive (not shown) in a state where the piezoelectric ceramic 12 is stored in the case body 14 (in the storage portion 14b). The case body 14 has, for example, two recesses 14c formed at the edge of the opening adjacent to the pair of protrusions 14a on both sides, and is filled (or coated) with silicone adhesive at the positions of these recesses 14c. It has become. The silicone adhesive is a material that exhibits an appropriate elasticity even when the piezoelectric ceramic 12 is adhered and held to the case body 14 and is fixed (fixed) after application. For this reason, the piezoelectric ceramic 12 can freely vibrate inside the case body 14 during driving, and the vibration is absorbed by the silicone adhesive. The silicone adhesive may be applied to a position other than the recess 14c (for example, a vibration node between the primary electrode 12a and the secondary electrode 12b).

[Conductive coating]
A conductive coating 24 is formed along the outer surface of the piezoelectric ceramic 12. For example, the conductive coating 24 extends to each side surface (each side surface on which the primary electrode 12a is formed) adjacent to both sides of the piezoelectric ceramic 12 across the small end surface along the longitudinal direction, and the primary side on each side surface. It is formed so as to overlap (overlap) the electrode 12a. Therefore, although not shown in FIG. 1, the conductive coating 24 is formed on the opposite side surface of the piezoelectric ceramic 12 so as to overlap the primary electrode 12 a.

  Such a conductive film 24 is formed, for example, by applying a conductive paint (a paint in which a conductive material is mixed with a resin) to the outer surface of the piezoelectric ceramic 12. In addition, as a method of applying the conductive coating, for example, a method of applying directly using a brush, or in a state where the conductive coating is infiltrated into the permeable support, the support is attached to the piezoelectric ceramic 12. There are a method of applying by temporarily pressing and transferring from there, a method of applying while spraying a conductive paint using an unillustrated injector (air brush), and the like. Moreover, what has a viscosity (fluidity) suitable for use of said application | coating method can be used for a conductive paint.

  In any case, the conductive coating 24 is formed by applying a conductive paint to the outer surface of the piezoelectric ceramic 12. The conductive coating 24 electrically connects the primary electrodes 12 a on both sides along the outer surface of the piezoelectric ceramic 12.

  FIG. 2 is a perspective view showing a completed state of the piezoelectric transformer 10. As described above, in the completed state of the piezoelectric transformer 10, the piezoelectric ceramic 12 is accommodated in the accommodating portion 14 b of the case body 14. At this time, the piezoelectric ceramic 12 as a whole is buried in the case body 14 in the height direction, and a small end surface (upper surface in the state shown in FIG. 2) along the longitudinal direction protrudes from the opening of the case body 14. Not. Further, as described above, each conductive wire 16 is soldered in a state where the other end is entangled with the primary side terminal 18a or the secondary side terminal 20, respectively.

[Countermeasures against pyroelectricity with conductive coating]
The completed piezoelectric transformer 10 is mounted on the circuit board by being soldered to a circuit board (not shown) using a flow tank or the like with the primary side terminal 18a and the secondary side terminal 20 facing downward. Is done. At this time, a charge due to the pyroelectric effect is generated in the piezoelectric ceramic 12 due to a temperature change (flow heat) during soldering, but the charge is mainly consumed through the conductive coating 24. For this reason, deterioration of the piezoelectric ceramic 12 due to the pyroelectric effect can be suppressed, and damage to the peripheral circuits (for example, an input circuit, an output circuit, a control circuit, etc.) formed on the circuit board can be prevented from being generated. it can. Further, the conductive coating 24 continues to function even after the piezoelectric transformer 10 is mounted, and is an effective countermeasure against pyroelectricity against changes in ambient temperature when the piezoelectric transformer 10 is used.

[Characteristics of conductive film]
Here, the conductive coating 24 has a resistance value applied between the primary side electrodes 12a that is equal to or higher than the resonance resistance value between the primary side electrodes 12a of the piezoelectric ceramic 12 (preferably 10 times or more), and the primary side electrode 12a. It is set within a range of 10% or less of the insulation resistance value. More preferably, in the use conditions of the first embodiment, the resistance value provided between the primary electrodes 12a by the conductive coating 24 is 100 GΩ or less. More preferably, the resistance value is in the range of 10 MΩ to 1 GΩ. Within such a range, damage due to pyroelectricity can be prevented in the process of mounting the piezoelectric transformer 10, and the conductive film 24 extremely divides the input voltage during operation of the piezoelectric transformer 10 after mounting. There is no end.

[Management of resistance value by application length]
In particular, in the first embodiment, the resistance value of the conductive coating 24 can be managed (adjusted) based on the length of the range in which the conductive paint is applied (reference symbol L in the figure). That is, since the conductive paint has a property that the overall resistance value (resistance value applied between the primary electrodes 12a) is determined according to the area of the applied range, the width of the applied range is constant. Then, the resistance value can be determined (substantially in proportion) according to the length to be applied.

  In the first embodiment, the range in which the conductive paint is to be applied is between the two primary electrodes 12a in the direction along the outer surface of the piezoelectric ceramic 12 (the direction from one side surface to the other side surface across the small end surface). The minimum distance necessary to connect the two can be considered as the coating width (thickness of the piezoelectric ceramic 12 + α). Then, assuming that the resistance value obtained when the conductive coating for the unit length is applied with the coating width at this time is “initial unit resistance value (Ω / mm)”, the resistance value provided as the entire conductive film 24 (Ω) is obtained by “initial unit resistance value (Ω / mm)” × “application length (mm)”.

  Therefore, if the initial unit resistance value (Ω / mm) is clarified from the physical properties of the conductive coating used and the required coating width, the resistance by the conductive coating 24 can be easily adjusted by simply adjusting the coating length L thereafter. The value can be managed.

  FIG. 3 is a characteristic diagram showing the relationship between the ratio of the conductive resistance value to the insulation resistance value between the primary electrodes 12a and the generated voltage during pyroelectricity, and the relationship between the coating length of the conductive paint and the resistance value. is there. This will be specifically described below.

[Relationship between the ratio of the conductive resistance value to the insulation resistance between the primary electrodes and the voltage generated during pyroelectricity]
In FIG. 3, (A): When the conductive resistance value applied between the primary side electrodes 12a is increased by the conductive coating 24, the ratio (%) to the insulation resistance value between the primary side electrodes 12a of the piezoelectric ceramic 12 as seen on the horizontal axis. ) Will increase.

  If the proportion of the conductive resistance value is almost 0% (resistance is very small), the generated voltage observed during pyroelectricity is also 0 (Vdc) because it is almost the same as when the primary electrodes 12a are short-circuited. It ’s close. However, setting such a conductive resistance value (a ratio of 0% with respect to the insulation resistance value) is not practical because the input voltage is greatly divided when the piezoelectric transformer 10 is actually used. Therefore, such extremely low resistance values are excluded from an appropriate numerical range. Usually, it is preferable that the resistance value at which the input voltage is not divided between the primary side electrodes 12a is equal to or higher than the resonance resistance value between the primary side electrodes 12a of the piezoelectric ceramic 12. Therefore, here, the resonance resistance value or higher is adopted as the lower limit of the numerical range.

  On the contrary, when the conductive resistance value is increased, as the ratio to the insulation resistance value is increased (resistance is increased), the primary side electrodes 12a are closer to being insulated. In this case, even if the conductive film 24 is formed, the electric charge due to pyroelectricity is hardly consumed in a short time, and as a result, the generated voltage increases. In the verification by the inventors of the present invention, a remarkable increase in the generated voltage starts to be observed when the ratio to the insulation resistance value exceeds 10%, and the generated voltage (value greater than V2) at that time is generated in the peripheral circuit. May cause some damage.

  On the other hand, when the ratio of the conductive resistance value is 10% or less (for example, Pa (%)), it can be seen that the generated voltage is suppressed to a value of V2 or less (for example, V1). From the above, the inventors of the present invention decided to set the lower limit as the resonance resistance value and the upper limit as 10% or less of the insulation resistance value as the optimum range of the resistance value provided by the conductive coating 24. . The generated voltage (V2) when the ratio of the conductive resistance value was 10% was an appropriate upper limit value that would not be affected by pyroelectricity.

[Relationship between coating length and resistance value]
In FIG. 3, (B): When the coating width (and coating film thickness) is assumed to be constant as described above, the conductive resistance value (in this example, simply conductive) is approximately proportional to the coating length of the conductive paint. The resistance value of the paint shall be indicated). Therefore, if an appropriate resistance value (Ra) is determined in advance within the above numerical range, the coating length (La) necessary to obtain the resistance value (Ra) can be easily determined.

  In addition, in the first embodiment, as shown in FIG. 2, the small end face of the piezoelectric ceramic 12 is exposed from the opening of the case body 14 even when the piezoelectric transformer 10 is completed, and the conductive coating 24 is formed on the small end face. Therefore, the coating length L can be easily visually inspected or confirmed. Further, since the conductive coating 24 is formed of a conductive paint, the conductive coating 24 stands out from the ground color of the piezoelectric ceramic 12 due to the color (for example, white, red, blue). Inspection and confirmation become easier. Furthermore, even if the resistance value varies depending on the color of the conductive paint, it can be easily confirmed whether the resistance value is appropriate from the color. In the first embodiment, for example, the following conditions are adopted for the piezoelectric ceramic 12 and the conductive paint.

First, use conditions of the piezoelectric transformer 10 of the first embodiment are as follows, for example.
Material of piezoelectric ceramic 12: PZT (lead zirconate titanate)
The longitudinal dimension of the piezoelectric ceramic 12 is about 20 mm × width (height) is about 5 mm, and the thickness is about 1 mm. Resonance frequency: 160 kHz
Resonance resistance between the primary side electrodes 12a of the piezoelectric ceramic 12: 100Ω
Insulation resistance between the primary electrodes 12a of the piezoelectric ceramic 12: 2 TΩ

Next, the conditions for the conductive paint are as follows.
Conductive material for conductive paint: zinc oxide (white)
Film thickness after coating (fixing): 20 μm
Initial unit resistance: 10 MΩ / mm
Application length: 1 mm to 10 mm
Resistance value: 10MΩ to 10GΩ

[Summary of First Embodiment]
In the first embodiment described above, the piezoelectric ceramic 12 is accommodated in the case body 14 to complete the piezoelectric transformer 10. However, the case body 14 is not essential for the minimum configuration as the piezoelectric transformer 10 (piezoelectric module). For this reason, the piezoelectric transformer 10 of the first embodiment is formed by forming the primary side electrode 12a and the secondary side electrode 12b on the piezoelectric ceramic 12 without using the case body 14, and forming the conductive coating 24 on the outer surface thereof. A minimum configuration may be used.

  In the first embodiment, the conductive coating 24 is formed on the small end surface along the longitudinal direction of the piezoelectric ceramic 12, but the conductive coating 24 may be arranged in other ways. For example, the conductive coating 24 may be formed on the small end face (the small end face in the vertical direction in FIG. 2) along the short side of the piezoelectric ceramic 12.

[Second Embodiment]
Next, the piezoelectric transformer 10 according to the second embodiment will be described. The piezoelectric transformer 10 of the second embodiment also has the same basic configuration as that of the first embodiment described above. However, in 2nd Embodiment, arrangement | positioning of the conductive film 24 differs from 1st Embodiment, and it has the characteristic in the point. Hereinafter, the piezoelectric transformer 10 according to the second embodiment will be described focusing on differences from the first embodiment. In the following description, items that are the same as those in the first embodiment are denoted by the same reference numerals including illustrations, and redundant descriptions thereof are omitted.

  FIG. 4 is a diagram specifically showing a characteristic part of the piezoelectric transformer 10 of the second embodiment. 4A is a partial plan view of the piezoelectric transformer 10, and FIG. 4B is a side view thereof. This will be specifically described below.

  4A: In the second embodiment, the conductive coating 24 is formed not on the outer surface of the piezoelectric ceramic 12 but on the outer surface (here, the upper surface) of the case body 14. FIG. That is, the conductive coating 24 is formed (applied) along the outer surface of the case body 14 so as to connect between the primary terminals 18 a located on both sides of the piezoelectric ceramic 12.

  In FIG. 4B, the conductive coating 24 is formed (applied) on the primary side terminal 18a so as to adhere to the one side surface of the case body 14 from the upper surface. As a result, the primary terminals 18a on both sides are electrically connected via the conductive coating 24. At this time, the resistance value provided between the primary side electrodes 12a by the conductive coating 24 via the primary side terminal 18a is set within the optimum range similar to the first embodiment.

  According to the piezoelectric transformer 10 of the second embodiment described above, since the primary side terminals 18a on both sides are connected via the conductive film 24, the two primary side electrodes 12a of the piezoelectric ceramic 12 are consequently connected. Are connected through the conductive coating 24, the primary terminals 18 a, and the conductive wires 16. Therefore, even when the pyroelectric effect occurs due to a temperature change due to the flow at the time of mounting, the charge is consumed in a short time through the conductive film 24. The damage to can be surely suppressed.

  In this example, the conductive film 24 is formed only on the upper surface of the case body 14. However, the conductive film 24 may be formed (applied) so as to wrap around the side surface of the case body 14. Alternatively, the conductive film 24 may be formed (applied) so as to go around the inner surface of the accommodating portion 14b.

[Third Embodiment]
Next, the piezoelectric transformer 10 of 3rd Embodiment is demonstrated. The piezoelectric transformer 10 of the third embodiment also has the same basic configuration as that of the first and second embodiments described above. However, in the third embodiment, the arrangement of the terminal portion of the conductive coating 24 is different from that of the second embodiment and is characterized in that respect. Hereinafter, the piezoelectric transformer 10 according to the third embodiment will be described focusing on differences from the second embodiment. In addition, the same code | symbol including illustration is attached | subjected here also about the matter which is common in 1st, 2nd embodiment, and the duplicate description shall be abbreviate | omitted.

  FIG. 5 is a diagram specifically showing the characteristic part of the piezoelectric transformer 10 of the third embodiment. 5A is a partial plan view of the piezoelectric transformer 10, and FIG. 5B is a side view thereof. This will be specifically described below.

  In FIG. 5A, also in the third embodiment, the conductive coating 24 is formed not on the outer surface of the piezoelectric ceramic 12 but on the outer surface (here, the upper surface) of the case body 14 as in the second embodiment. ing. That is, the conductive coating 24 is formed (applied) along the outer surface of the case body 14 so as to connect between the primary terminals 18 a located on both sides of the piezoelectric ceramic 12.

  However, in the case of the third embodiment, the end of the conductive coating 24 does not reach one side surface of each primary side terminal 18 a, and the end stops at the conductive wire 16.

  In FIG. 5, (B): That is, the coating range of the conductive coating 24 stops at the position in contact with the conductive wire 16 from the upper surface of the case body 14, and as described in the previous second embodiment, the primary side terminal It has not reached one side of 18a. However, since the primary side terminal 18a and the conductive line 16 are basically at the same potential, the primary side terminals 18a on both sides are electrically connected via the conductive film 24 in the third embodiment as well. It becomes a state. In addition, it is assumed that the resistance value provided between the primary side electrodes 12a by the conductive coating 24 via the primary side terminal 18a is set within the same optimal range as in the first embodiment.

  According to the piezoelectric transformer 10 of the third embodiment described above, since the conductive wires 16 (primary terminals 18a) on both sides are connected via the conductive film 24, the two primary electrodes 12a of the piezoelectric ceramic 12 are connected. As a result, the conductive film 24, the primary terminals 18a, and the conductive wires 16 are connected. Therefore, even when the pyroelectric effect occurs due to a temperature change due to the flow at the time of mounting, the charge is consumed in a short time through the conductive film 24. The damage to can be surely suppressed.

  Here, an example in which the conductive coating 24 is formed only on the upper surface of the case body 14 is described, but the conductive coating 24 may be formed (applied) so as to wrap around the side surface of the case body 14. Alternatively, the conductive film 24 may be formed (applied) so as to go around the inner surface of the accommodating portion 14b.

[Fourth Embodiment]
FIG. 6 is a perspective view illustrating a configuration example of the piezoelectric transformer 10 according to the fourth embodiment. In FIG. 6, the piezoelectric transformer 10 is shown in a completed state, and the posture thereof is shown upside down with respect to FIGS. 1 and 2. The piezoelectric ceramic 12 is not shown here because it is housed in the case body 14.

  The piezoelectric transformer 10 of the fourth embodiment also has a basic configuration in common with the first to third embodiments described above. However, the fourth embodiment is significantly different from the second and third embodiments in the arrangement of the conductive coating 24 and is characterized in that respect. Hereinafter, the piezoelectric transformer 10 according to the fourth embodiment will be described focusing on differences from the second and third embodiments. Here, the same reference numerals including those shown in the drawings are attached to the items common to the first to third embodiments, and the duplicate description thereof is omitted.

  In the fourth embodiment, a conductive coating 24 is formed (applied) on the upper surface of the outer surface of the case body 14 as viewed in the mounted state. That is, the conductive coating 24 extends along the outer surface of the case body 14 so as to connect the other end portions 18b of the conductive members 18 located on both sides of the piezoelectric ceramic 12 with the piezoelectric ceramic 12 interposed therebetween. It is formed (applied). In this case as well, it is assumed that the resistance value provided between the primary side electrodes 12a by the conductive coating 24 via the conductive member 18 is set within the same optimal range as in the first embodiment.

  According to the piezoelectric transformer 10 of the fourth embodiment described above, since the conductive members 18 (other end portions 18b) on both sides are connected via the conductive film 24, the two primary side electrodes of the piezoelectric ceramic 12 are used. As a result, the conductive film 24, the conductive members 18 (the other end 18 b and the primary terminal 18 a), and the conductive wires 16 are connected to each other. Therefore, even when the pyroelectric effect occurs due to a temperature change due to the flow at the time of mounting, the charge is consumed in a short time through the conductive film 24. The damage to can be surely suppressed.

  Here, an example in which the conductive coating 24 is formed only on the upper surface of the case body 14 is described, but the conductive coating 24 may be formed (applied) so as to wrap around the side surface of the case body 14.

[Fifth Embodiment]
Next, FIG. 7 is a perspective view showing the piezoelectric transformer 10 of the fifth embodiment in an exploded manner. The piezoelectric transformer 10 of the fifth embodiment includes a configuration mounted on the circuit board 30 in a completed state. However, in the case of the fifth embodiment, the conductive coating 24 is not formed on either the piezoelectric ceramic 12 or the case body 14, and the conductive coating 24 is formed (applied) on another circuit board 30. Has characteristics.

  An insertion hole (through hole) 30 a for inserting and mounting the piezoelectric transformer 10 is formed in the circuit board 30. Among these, for example, connection lands 30b made of conductive patterns or the like are formed around the through holes 30a at positions corresponding to the two primary-side electrodes 12a, respectively. In addition, although many insertion holes are formed in the circuit board 30 at other positions, they are omitted here because they are not particularly relevant. When the piezoelectric transformer 10 is inserted and mounted, the primary side terminal 18a and the secondary side terminal 20 are inserted into the insertion holes 30a, and soldered to a wiring pattern (not shown) on the back surface of the circuit board 30, or thermosetting. It is possible to connect using a conductive paste of a mold.

  Here, in the piezoelectric transformer 10 of the fifth embodiment, the conductive film 24 is formed (applied) at a position where the two connection lands 30b are connected before the piezoelectric transformer 10 is mounted on the circuit board 30. That is, the conductive coating 24 is formed (coated) on the upper surface (mounting surface) of the circuit board 30 so as to connect the connection lands 30b. The conductive coating 24 may be formed so as to cover the entire connection land 30b, or may overlap with only a part thereof. Also here, it is assumed that the resistance value provided between the primary-side electrodes 12a by the conductive coating 24 via the connection lands 30b is set within the same optimal range as in the first embodiment.

  According to the piezoelectric transformer 10 of the fifth embodiment described above, the two connection lands 30b are connected in advance via the conductive film 24 on the circuit board 30 which is the mounting destination (the other party). For this reason, when passing through the solder flow tank when the piezoelectric transformer 10 is mounted, for example, if the wiring pattern on the back surface of the circuit board 30 and each primary side terminal 18a are soldered, the two primary side electrodes of the piezoelectric ceramic 12 As a result, the conductive film 24, the connection lands 30 b, the primary terminals 18 a, and the conductive wires 16 are connected. Therefore, even when the pyroelectric effect occurs due to a temperature change in the solder flow tank, the charge is consumed through the conductive film 24 in a short time, so that the polarization characteristics deteriorate due to pyroelectricity and the surroundings. Damage to the circuit can be reliably suppressed.

  Here, an example in which the conductive film 24 is formed on the upper surface (mounting surface) of the circuit board 30 is described, but the conductive film 24 may be formed (coated) on the lower surface of the circuit board 30. In this example, the piezoelectric transformer 10 is inserted and mounted through the through hole 30a of the circuit board 30. However, the piezoelectric transformer 10 may be of a surface mount type.

  As described above, when the piezoelectric transformer 10 of each embodiment is passed through a solder flow tank or a reflow device when mounted on a circuit board (the circuit board 30 in the fifth embodiment), the piezoelectric ceramic is changed by the temperature change. Even if the pyroelectric effect is generated in 12, the primary-side electrodes 12a are connected through the conductive coating 24, so that the charge due to pyroelectricity immediately disappears (or the charge does not accumulate). Therefore, an excessive charge is not applied to other circuit components on the circuit board, and no discharge occurs around the piezoelectric transformer 10, and the quality of the product can be continuously guaranteed even after the completion of the mounting operation. .

  In addition, since the conductive coating 24 can be formed by applying a relatively low-viscosity conductive paint, the film thickness after application is reduced compared to a high-viscosity material such as a conductive adhesive. be able to. Therefore, the volume of the conductive coating 24 can be minimized while ensuring the necessary resistance value, so that the product dimensions do not increase carelessly.

Further, in each of the above embodiments, the following deformation elements can be employed.
The conductive film 24 can be formed by applying, for example, a conductive adhesive in addition to the conductive paint, or can be formed by a conductive adhesive tape. The conductive adhesive is obtained by mixing a conductive material into, for example, a silicone adhesive, and has conductivity (resistance) even in a fixed state. The conductive pressure-sensitive adhesive tape is obtained by mixing a conductive material into the pressure-sensitive adhesive layer, and also has conductivity (resistance) in a state where it is stuck. In addition, the resistance value in this case is appropriately set within the range mentioned in the first embodiment.

  Further, the component of the conductive paint may contain nickel, copper, carbon or the like in addition to the zinc oxide mentioned in the above example.

  The present invention is not limited to the above-described embodiments, and can be implemented with various modifications. For example, the shape of the piezoelectric ceramic 12 is not limited to the illustrated shape, and may be other shapes. Further, the shape of the case body 14 can be appropriately modified in accordance with the outer shape of the piezoelectric ceramic 12.

  In the first embodiment, the conductive coating 24 is formed in contact with each primary electrode 12a. However, the conductive coating 24 is applied between the primary electrodes 12a with the conductive coating 24 formed on the outer surface of the piezoelectric ceramic 12. If the resistance value is within the above-mentioned appropriate range, the conductive coating 24 may not be directly connected to the primary electrode 12a (the primary electrode 12a and the conductive coating 24 on the outer surface of the piezoelectric ceramic 12). And may be formed apart from each other.)

  In each embodiment, the piezoelectric transformer 10 is taken as an example, but the piezoelectric module of the present invention can be applied to, for example, a piezoelectric actuator or a piezoelectric motor (ultrasonic motor).

  In addition, the structure shown with illustration in each embodiment is a preferable example to the last, and it can be said that the present invention can be suitably implemented even if various elements are added to the basic structure or a part thereof is replaced. Not too long.

10 Piezoelectric transformer 12 Piezoelectric ceramics (piezoelectric material)
12a Primary side electrode 14 Case body 18a Primary side terminal 20 Secondary side terminal 24 Conductive coating

Claims (7)

A polarized piezoelectric body;
At least two electrodes formed on the outer surface of the piezoelectric body;
It is formed along the outer surface of the piezoelectric body to connect the electrodes to each other, and the resistance value applied between the electrodes is equal to or greater than the resonance resistance value between the electrodes of the piezoelectric body, and the insulation between the electrodes A piezoelectric module comprising a conductive film having a resistance value of 10% or less. The piezoelectric module according to claim 1,
The conductive coating is
It is formed by applying a conductive paint mixed with a resin and a conductive material on the outer surface of the piezoelectric body,
The range for applying the conductive paint is:
When the minimum distance necessary to connect the electrodes formed in parallel with each other when viewed in the direction along the outer surface of the piezoelectric body is defined as the coating width, the conductive paint for a unit length of the coating width A piezoelectric module, wherein the coating length is determined based on an initial unit resistance value per unit length applied between the electrodes when the coating is applied. In the piezoelectric body module according to claim 1 or 2,
In addition to holding the piezoelectric body, the case further includes a case body having an opening that exposes a part of the outer surface of the piezoelectric body in the holding state.
The conductive coating is
The piezoelectric body module is formed at a position exposed through the opening in a state where the piezoelectric body is held by the case body. A polarized piezoelectric body;
At least two electrodes formed on the outer surface of the piezoelectric body;
A case body for housing the piezoelectric body;
At least two terminals provided on the case body and respectively connected to the electrodes in a state in which the piezoelectric body is accommodated;
Formed along the outer surface of the case body to connect the terminals to each other, and a resistance value applied between the electrodes via the terminals is equal to or greater than a resonance resistance value between the electrodes of the piezoelectric body, and A piezoelectric module comprising a conductive film having an insulation resistance value between the electrodes of 10% or less. The piezoelectric module according to claim 4, wherein
In a state where the piezoelectric body is accommodated in the case body, the case body further includes at least two conductive wires connecting the electrodes and the terminals,
The conductive coating is
It is formed along the outer surface of the case body in a state in which the conductive wires are connected to each other, and the conductive coating is connected to the terminals via the conductive wires between the terminals. A piezoelectric module characterized by the above. A polarized piezoelectric body;
At least two electrodes formed on the outer surface of the piezoelectric body;
A circuit board on which a circuit for transmitting at least one of an input signal or an output signal of the piezoelectric body is formed through the electrodes in a state where the piezoelectric body is mounted;
A conductive pattern disposed on at least two locations on the circuit board to connect the electrodes of the piezoelectric body and the circuit;
A resistance value provided between the electrodes through the conductive pattern is formed along the outer surface of the circuit board so as to connect the conductive patterns to each other on the circuit board, and resonance between the electrodes of the piezoelectric body. A piezoelectric module comprising: a conductive film having a resistance value or more and 10% or less of an insulation resistance value between the electrodes. In the piezoelectric body module according to any one of claims 1 to 6,
The conductive coating is
A piezoelectric module, wherein a resistance value applied between the electrodes is 10 times or more a resonance resistance value between the electrodes of the piezoelectric body.

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