JP2010103249A - Piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein tensile stress generated by a lead wire is not relaxed and is propagated to an external electrode when a piezoelectric element itself to which an application voltage is applied is displaced since lead-free solder is hard if the external electrode of the piezoelectric element is soldered to the lead wire by lead-free solder, and hence an arc-shaped crack is generated with a part of a termination section where the external electrode and the lead wire are subjected to lead-free soldering as a boundary and hence the piezoelectric element may be damaged. <P>SOLUTION: In a piezoelectric actuator, a plurality of piezoelectric elements where the external electrode is formed on the side are connected in series, the external electrode of each piezoelectric element and the lead wire are soldered by lead-free solder, and the end faces of adjacent piezoelectric elements are adhered by an adhesive. In the piezoelectric actuator, those other than a part soldered to the external electrode of the piezoelectric element in the lead wire are in a curved shape, and length to the end of a part where the closest lead wire has been soldered from the end face of the piezoelectric element is not more than 0.5 mm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric actuator mounted on a positioning apparatus such as an XYZ stage such as a semiconductor exposure apparatus or processing apparatus or a measurement apparatus.

  In the conventional piezoelectric actuator, as shown in FIG. 1, a plurality of piezoelectric elements (in FIG. 1, piezoelectric element 3, piezoelectric element 4, piezoelectric element 5, and piezoelectric element 6) are connected in series, and are shown in FIG. As described above, the external electrodes 11 on the side surfaces of the piezoelectric elements are electrically connected by soldering with the metal lead wires 12, respectively, and the end faces of the adjacent piezoelectric elements are bonded with an adhesive. Here, FIG. 1 is a sectional view of a positioner in which the piezoelectric actuator 1 is sealed. FIG. 2 is a schematic view of the inside of the positioner. Then, the piezoelectric actuator 1 is fixed on the base 9, the hemisphere 2 is bonded to the end surface opposite to the base 9 of the piezoelectric actuator 1, and the piezoelectric actuator 1 is fitted with a metal cap 8 that applies a compressive force. As a result, the piezoelectric actuator 1 is stretched and used in a sealed state.

  When a voltage is applied to the piezoelectric actuator, each piezoelectric element expands, and when the voltage application is stopped, each piezoelectric element returns to its original length. In addition, there is a method of reinforcing the external electrode of the piezoelectric actuator with a metal wire as one method for preventing fatigue failure due to expansion and contraction of the piezoelectric element. By reinforced with a metal wire, the displacement amount of the external electrode portion is suppressed, and fatigue failure is prevented. Here, since the lead wire soldered to the external electrode of the piezoelectric actuator is not displaced when a voltage is applied, a tensile stress is generated at the end of the external electrode of the piezoelectric actuator. When soldering with lead solder, the Young's modulus of the solder is as low as about 30 GPa, so that the solder acts as a buffer layer to relieve the stress generated in the piezoelectric actuator.

JP 2001-148521 A

  However, the actuator having such a structure has the following problems. That is, in recent years, lead-free soldering has progressed, and solder used for piezoelectric elements has also become lead-free. FIG. 3 is a cross-sectional view of a piezoelectric element soldered to a lead wire with conventional lead-free solder. In general, lead-free solder has a high Young's modulus of about 60 GPa as compared with solder containing lead. Therefore, as shown in FIG. 3, when the external electrode 11 and the lead wire 12 of the piezoelectric element 3 are soldered with lead-free solder, the piezoelectric element 2 to which an applied voltage is applied due to the fact that the lead-free solder is hard. The tensile stress generated by the lead wire 12 when it is displaced is transmitted to the external electrode without being relaxed. Then, a crack is generated in an arc shape at the end portion where the external electrode 11 and the lead wire 12 are lead-free soldered, such as the crack portion 13, and the piezoelectric element 2 is destroyed as a result. In particular, in a piezoelectric actuator in which a plurality of piezoelectric elements are connected in series, a crack occurs near the surface where the end faces of the piezoelectric elements are bonded together.

  Therefore, the present invention relates to such a problem, even when a piezoelectric element is soldered by lead-free solder, the piezoelectric element is subjected to the same stress as that generated by a piezoelectric actuator in which the piezoelectric element is soldered with lead-containing solder. An object of the present invention is to provide a piezoelectric actuator having a performance equivalent to that of a piezoelectric actuator in which a piezoelectric element is soldered with a lead-containing solder.

  That is, a plurality of piezoelectric elements having external electrodes formed on the side surfaces are connected in series, the external electrodes of each piezoelectric element and lead wires are soldered with lead-free solder, and the end surfaces of adjacent piezoelectric elements are Is a piezoelectric actuator bonded with an adhesive, and the lead wire has a curved shape except for the portion to be soldered to the external electrode of the piezoelectric element, and the lead wire closest to the end face of the piezoelectric element is The length between the end of the soldered portion is 0.5 mm or less.

  Preferably, the end surfaces of the adjacent piezoelectric elements are bonded to each other by applying an adhesive to the center portion of the end surfaces.

  According to the present invention, the piezoelectric element is not damaged by the stress generated when the applied piezoelectric element itself is displaced, and the yield is the same as that of the piezoelectric actuator obtained by soldering the piezoelectric element with lead-containing solder. Yield and contributes to reduction of product cost and inspection man-hours.

  Hereinafter, embodiments of a piezoelectric actuator of the present invention will be described with reference to the drawings.

  FIG. 4 is a sectional view of a piezoelectric element constituting a piezoelectric actuator according to an embodiment of the present invention. The piezoelectric element 3 is formed by alternately stacking piezoelectric layers and internal electrodes, and inactive portions are formed above and below these stacked bodies. The external electrode 11 on the side surface of the piezoelectric element 3 is soldered to the lead wire 12 with lead-free solder. Here, by changing the length ΔX from the end face of the piezoelectric element 3 to the shortest end of the external electrode 11, in any case, an arc shape is formed with the terminal portion of the external electrode and the lead wire soldered as a boundary. We compared whether cracks would occur in the case.

  In FIG. 4, both end surfaces of the piezoelectric element are formed with a length ΔX from both end surfaces of the piezoelectric element 3 to the shortest end portion of the external electrode 11. Here, the external electrode is located at an intermediate position from both end faces of the piezoelectric element. FIG. 5 corresponds to the case where ΔX = 0 in FIG. In general, the lead wire 12 has a semicircular arc-shaped elastic portion in addition to the portion soldered to the external electrode 11 as shown in FIG. The elastic portion is formed from the vicinity of the end of the external electrode 11 to the vicinity of the end of the external electrode of the adjacent piezoelectric element. The lead wire 12 is composed of alternating straight portions soldered to the external electrodes of the piezoelectric element and semi-circular curved elastic portions.弾 性, the semicircular arc-shaped elastic part is not necessarily formed from the vicinity of the end of the external electrode 11 to the vicinity of the end of the external electrode of the adjacent piezoelectric element, but from the vicinity of the center of the external electrode of the piezoelectric element. There is no problem even near the center of the external electrode of the adjacent piezoelectric element. The semicircular arc-shaped elastic part is preferably made of a spring or a metal having a high elastic force designed to have a deflection. This is because fatigue damage of the lead wire does not occur.

  First, three types of 6 mm × 6 mm × 10 mm, 10 mm × 10 mm × 10 mm, and 6 mm × 6 mm × 5 mm were prepared as piezoelectric elements having different dimensions. The lead wire made of phosphor bronze is soldered with lead-free solder so that the length ΔX from the end face of the piezoelectric element 2 to the shortest end of the external electrode 11 is 0.75 mm, 0.5 mm, and 0 mm. did. There were prepared 200 each of these dimensions and lengths ΔX (for example, piezoelectric elements of 6 mm × 6 mm × 10 mm, ΔX = 0.5 mm, 9 patterns in total). Then, 300 V corresponding to twice the general rated voltage was applied to each of these piezoelectric elements.

  Table 1 is a table that describes whether or not each piezoelectric element is cracked when a voltage of 300 V is applied to all the piezoelectric elements having different dimensions and different ΔX. As shown in Table 1, when the length ΔX is 0.75 mm, 2 to 4 of 200 cracks are generated regardless of the dimensions of the piezoelectric elements. On the other hand, when the length ΔX was 0.5 mm and 0 mm, no crack occurred in all the piezoelectric elements regardless of the dimensions of the piezoelectric elements.

Further, two piezoelectric elements having the same dimensions were bonded to each end face with an epoxy adhesive using three types of piezoelectric elements of 6 mm × 6 mm × 10 mm, 10 mm × 10 mm × 10 mm, and 6 mm × 6 mm × 5 mm. At that time, the adhesive between the end faces is applied by applying an adhesive to the entire end face of the piezoelectric element, and a circular adhesive of about φ5 is applied to the center part of the end face of the piezoelectric element, and the outer edge part of the end face is applied. Was carried out by two methods of adhesion without coating. Then, two piezoelectric elements having the same dimensions were bonded to each other by changing the bonding method, and 50 pieces each were formed. At that time, the lead wire made of phosphor bronze was soldered with lead-free solder so that the length ΔX from the end face of the piezoelectric element to the shortest end of the external electrode was 0.5 mm.
Then, a voltage of 300 V was applied to all the two piezoelectric elements bonded together. Then, in the case of bonding the end faces to each other by applying an adhesive to the entire end face of the piezoelectric element, one or two of the 50 cracks occurred regardless of the dimensions of the piezoelectric element. On the other hand, when the adhesive was applied only to the central portion of the end face of the piezoelectric element, no cracks occurred in all the piezoelectric elements regardless of the dimensions of the piezoelectric elements.

As described above, when the length ΔX from the end face of the piezoelectric element to the shortest end of the external electrode is 0.5 mm or less, the possibility of cracking the piezoelectric element is extremely low.
Furthermore, in addition to the length ΔX from the end face of the piezoelectric element to the shortest end of the external electrode being 0.5 mm or less, the adhesive is applied only to the center part of the end faces of the adjacent piezoelectric elements and bonded. It was confirmed that the piezoelectric actuator operated normally without cracking the piezoelectric element even when 300 V corresponding to twice the rated voltage was applied.

  The lead wire 12 is soldered by the external electrode of the piezoelectric element. From the place where the lead wire 12 and the external electrode of the piezoelectric element are soldered to the place where the external electrode of the adjacent piezoelectric element is soldered. It is a spring part composed of a spring. Therefore, in the lead wire 12 of the piezoelectric actuator that connects a plurality of piezoelectric elements, the locations where the lead wires 12 and the external electrodes of the piezoelectric elements are soldered and the spring portions are alternately configured.

  Since the present invention has a higher Young's modulus compared to lead solder, the piezoelectric actuator in which the piezoelectric element and the lead wire are soldered with lead-free solder is cracked near the soldered part as the piezoelectric element expands and contracts. In addition, it was possible to prevent fatigue failure at the soldering location of the piezoelectric element and lead wire due to lead-free solder.

It is sectional drawing of the positioner which sealed the piezoelectric actuator which is one Example of this invention inside. It is the schematic inside the positioner which is one Example of this invention. It is sectional drawing of the piezoelectric element soldered with the lead wire with the conventional lead free solder. It is sectional drawing of the piezoelectric element which comprises the piezoelectric actuator which is one Example of this invention. It is sectional drawing of the piezoelectric element which comprises the piezoelectric actuator which is one Example of this invention.

Explanation of symbols

1: Piezoelectric actuator 2: Hemisphere 3, 4, 5, 6: Piezoelectric element 7: Lead wire 8: Cap 9: Base 10: Terminal 11: External electrode 12: Lead wire 13: Cracked portion

Claims (2)

  A plurality of piezoelectric elements having external electrodes formed on the side surfaces are connected in series, the external electrodes of each piezoelectric element and lead wires are soldered with lead-free solder, and the end faces of adjacent piezoelectric elements are bonded to each other A piezoelectric actuator bonded with an agent, and the lead wire has a curved shape except for the portion to be soldered to the external electrode of the piezoelectric element, and the lead wire closest to the end face of the piezoelectric element is soldered The piezoelectric actuator is characterized in that the length between the end portions of the formed portions is 0.5 mm or less.   2. The piezoelectric actuator according to claim 1, wherein the end surfaces of the adjacent piezoelectric elements are bonded by applying an adhesive to a central portion of the end surfaces.

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