Abstract:
The invention relates a wiring structure of a vibrator and a piezoelectric pump. On the basis of the recognition that it is difficult to obtain sufficient reliability of connecting parts with a conductive adhesive material only while attention is paid to using the conductive adhesive material instead of soldering, a wiring structure is obtained in which a connecting terminal and a film-like electrode are adhered to each other by a conductive adhesive material, and a pressing member which applies a force in a direction in which the connecting terminal is pressed against the film-like electrode is caused to abut on the connecting terminal.

Description:
[0001]     This application claims the benefit of Japanese Patent Application No. 2005-361151, filed on Dec. 15, 2005, the contents of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a wiring structure of a vibrator and a piezoelectric pump having the wiring structure.  
         [0004]     2. Description of the Related Art  
         [0005]     As an apparatus having a vibrator, there is, for example, a piezoelectric pump. In the piezoelectric pump, a pumping action is obtained by forming a variable volume chamber between a flat plate-like piezoelectric vibrator and a housing, and by vibrating the piezoelectric vibrator to change the volume of the variable volume chamber. More specifically, a pair of flow channels connected with the variable volume chamber is provided with a pair of check valves (a check valve which allows flow of fluid to the variable volume chamber and a check valve which allows flow of fluid from the variable volume chamber) having different flow directions. When the volume of the variable volume chamber changes by vibration of the piezoelectric vibrator, a pumping action is obtained from repetition of the operation that one of the pair of check valves is opened and the other valve is closed is repeated. Such a piezoelectric pump is used as, for example, a cooling water circulating pump of a water-cooling notebook computer or a water-cooling desktop computer by making full use of characteristics which can be obtained from a thin pump.  
         [0006]     The piezoelectric vibrator is obtained by stacking a piezoelectric body on at least one of the front and back sides of a shim (conductive sheet metal). Polarization characteristics are given to the piezoelectric body in the front and back directions. Thus, the piezoelectric body has a property that, when positive or negative polarity in the same direction as or in a direction opposite to the polarization direction is given between the front and back sides, one surface area increases and the other surface area decreases. For this reason, when positive and negative polarities to be given to the front and back sides of the piezoelectric body are alternately inverted, the cycles that one of the front and back sides expands and the other one shrinks are repeated, and thereby the shim vibrates.  
         [0007]     Conventionally, wiring to a piezoelectric vibrator is performed by soldering lead wires to a shim and piezoelectric bodies (film-like electrodes formed on the surfaces thereof) as can be seen from Japanese Unexamined Patent Application Publication Nos. 2006-105027 and 2006-144761. Meanwhile, in a piezoelectric vibrator in which vibrations having an amplitude of 1 mm or less (in the order of 100 μm) are repeated, it was found that poor connection occurs in soldered portions between the film-like electrodes on the piezoelectric vibrator and the lead wires due to long-term use. It is considered that that, since solder is fixed to the film-like electrodes and the lead wires, repetition of fine vibrations causes peel off in the interfaces between the electrodes and lead wires. This problem also applies to a flat plate-like crystal vibrator, etc. having electrodes on the surfaces thereof without being limited to the piezoelectric vibrator.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention has been made on the basis of the recognition of the above problem, and it is an object of the invention to obtain a wiring structure having high connection reliability and/or durability between a vibrator and lead wires. It is another object of the invention to obtain a piezoelectric pump having high connection reliability and/or durability between a piezoelectric vibrator and lead wires.  
         [0009]     The inventors have conceived the invention on the basis of the recognition that it is difficult to obtain sufficient reliability of connecting parts with a conductive adhesive material only while paying attention to using the conductive adhesive material instead of soldering.  
         [0010]     Specifically, according to an aspect of the invention, in a wiring structure for electrically connecting a connecting terminal at a tip of a lead wire to a film-like electrode formed on a surface of a vibrator, the connecting terminal and the film-like electrode are adhered to each other by a conductive adhesive material, and a pressing member which applies a force in a direction in which the connecting terminal is pressed against the film-like electrode is caused to abut on the connecting terminal.  
         [0011]     As the conductive adhesive material, for example, a conductive double-sided adhesive tape in which conductive metal powder (for example, Ni powder) is mixed into an adhesive layer can be used. A conductive metal foil (Cu foil) double-sided adhesive tape having a metal foil (for example, Cu foil) at the center thereof may be used. These adhesive materials are available from commercialized products. Moreover, the term ‘adhesion’ means a property capable of adhering again even after peel off, and is distinguished from ‘bonding,’ which means having no re-adhesiveness after peel off. The conductive adhesive material as described above appropriately absorbs the vibration of a piezoelectric vibrator by using elasticity of an adhesive layer thereof to prevent concentration of a stress, thereby improving connection reliability between the piezoelectric vibrator and lead wires.  
         [0012]     Preferably, materials having excellent elasticity are used for the pressing member. Among these, ethylene-propylene-diene rubber (EPDM) is desirable.  
         [0013]     Preferably, an FPC having high flexibility is used as the lead wire.  
         [0014]     According to another aspect of the invention, in a piezoelectric pump including a piezoelectric vibrator, a housing which forms a variable volume chamber between the housing and the piezoelectric vibrator, and a lead wire which feeds power to a film-like electrode formed on a surface of the piezoelectric vibrator, and obtaining a pumping action by feeding power to the piezoelectric vibrator via the lead wire to vibrate the piezoelectric vibrator, a connecting terminal at a tip of the lead wire and the film-like electrode are adhered to each other by a conductive adhesive material, and a pressing member which applies a force in a direction in which the connecting terminal is pressed against the film-like electrode is provided on the side of the housing.  
         [0015]     In this aspect, the pressing member can be made of a resin material formed integrally with the housing.  
         [0016]     As the piezoelectric vibrator, any one of a unimorph-type piezoelectric vibrator in which a piezoelectric body is provided only on either the front side or back side of the middle shim, and a bimorph-type piezoelectric vibrator in which piezoelectric bodies are provided on both the front and back sides can be used. In a more preferred embodiment, it is desirable that a bimorph-type piezoelectric element is used, and the lead wire is an FPC which is connected in the same potential to the film-like electrode formed on each of the surfaces of the front and back piezoelectric bodies.  
         [0017]     Moreover, the bimorph-type piezoelectric element formed in a circular shape in plan view is provided at a peripheral edge thereof with a spacer insulating ring made of a rubber material which determines the total thickness of the bimorph-type piezoelectric element. In such a piezoelectric element, when the pressing member is made of the same rubber material as the spacer insulating ring, the design to avoid concentration of a stress (stress is dispersed to both the piezoelectric bodies) is easy, which is preferable. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a longitudinal sectional view showing the principle of a piezoelectric pump to which a piezoelectric vibrator is to be applied;  
         [0019]      FIG. 2  is a schematic exploded perspective view showing an embodiment in which a wiring structure of the invention is applied to a bimorph-type piezoelectric vibrator;  
         [0020]      FIG. 3  is an exploded perspective view showing a specific embodiment of a piezoelectric pump having the piezoelectric vibrator to which the wiring structure is applied;  
         [0021]      FIG. 4  is a plan view of principal parts of the wiring structure;  
         [0022]      FIG. 5  is a sectional view taken along line V-V of  FIG. 4 ; and  
         [0023]      FIG. 6  is an enlarged view of principal parts of  FIG. 5 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]     The illustrated embodiment is an embodiment in which the invention is applied to a piezoelectric pump, and the principle of the piezoelectric pump is shown in  FIG. 1 . A housing  10  is composed of an upper housing  10   a  and a lower housing  10   b . Both the housings  10   a  and  10   b  are formed with recessed parts  11   a  and  11   b  and seal ring grooves  12   a  and  12   b  along the recessed parts  11   a  and  11   b  in their facing surfaces, respectively. A piezoelectric vibrator  20  is sandwiched between the upper housing  10   a  and the lower housing  10   b  by causing the front and back sides thereof to abut on seal rings  13   a  and  13   b  inserted into the seal ring grooves  12   a  and  12   b , respectively, and a variable volume chamber P is formed between the recessed part  11   a  and the piezoelectric vibrator  20 . Although a variable volume chamber is also formed between the recessed part  11   b  and the piezoelectric vibrator  20 , this chamber does not have a pumping action. Although the thickness of the piezoelectric vibrator  20  is drawn exaggeratingly, the actual thickness of the piezoelectric vibrator may be less than 1.5 mm. The shape of the recessed parts  11   a  and  11   b  is also a shallow shape along which the piezoelectric vibrator  20  can extend.  
         [0025]     In the lower housing  10   a , a liquid inlet port  14 A and a liquid outlet port  14 B are opened. The inlet port  14 A communicates with an inlet-side liquid reservoir chamber  15 A, and the outlet port  14 B communicates with an outlet-side liquid reservoir chamber  15 B. A partition wall  16 A is located between the inlet-side liquid reservoir chamber  15 A and the variable volume chamber P, and a partition wall  16 B is located between the outlet-side liquid reservoir chamber  15 B and the variable volume chamber P. Umbrellas (e.g., check valves)  17 A and  17 B are provided in the partition walls  16 A and  16 B, respectively. The umbrella  17 A is a check valve which allows flow of fluid from the inlet port  14 A (inlet-side liquid reservoir chamber  15 A) to the variable volume chamber P and does not allow the reverse flow of the fluid, and the umbrella  17 B is a check valve which allows flow of fluid from the variable volume chamber P to the outlet port  14 B (outlet-side liquid reservoir chamber  15 B) and does not allow the reverse flow of the fluid.  
         [0026]     In the above-described piezoelectric pump, when the piezoelectric vibrator  20  is elastically deformed forward or backward (vibrated), the umbrella  17 A is opened and the umbrella  17 B is closed in a stroke where the volume of the variable volume chamber P increases. Therefore, liquid flows into the variable volume chamber P from the cooing water inlet port  14 A (inlet-side liquid reservoir chamber  15 A). On the other hand, the umbrella  17 B is opened and the umbrella  17 A is closed in a stroke where the volume of the variable volume chamber P decreases. Therefore, liquid flows out to the outlet port  14 B (outlet-side liquid reservoir chamber  15 B) from the variable volume chamber P. Therefore, a pumping action can be obtained by continuously and elastically deforming (vibrating) the piezoelectric vibrator  20  forward and backward.  
         [0027]     FIGS.  2  to  6  show a more specific embodiment of the piezoelectric pump having the above-described principle of operation. The piezoelectric vibrator  20  of the present embodiment, as shown in  FIG. 2  (and  FIGS. 5 and 6 ), is a bimorph-type piezoelectric vibrator including a middle circular shim  111  and piezoelectric bodies  112  formed so as to be stacked on the front and back sides of the shim. The shim  111  is made of a conductive sheet metal material, for example, a 42-alloy sheet metal having a thickness of about 0.2 mm. The piezoelectric bodies  112  are made of, for example, PZT(Pb(Zr, Ti)0 3 ) having a thickness of about 0.3 mm, and are subjected to polarization treatment in the thickness directions.  
         [0028]     This polarization treatment is performed in the same direction on the pair of piezoelectric bodies  112  located on the front and back sides of the shim  111 . Specifically, referring to  FIG. 2 , when the polarization direction of the pair of piezoelectric bodies  112  are indicated by arrows ‘a’ or ‘b’, polarization treatment in the same direction as the thickness direction of the shim  111  is performed. In other words, the pair of front and back piezoelectric bodies which contact the shim show polarization characteristics of different polarities, respectively, and the exposed surfaces of the pair of piezoelectric bodies show different polarities, respectively. If the polarization characteristics of the front and back piezoelectric bodies are made the same direction as such, the displacement of the shim can be increased when positive and negative voltages are alternately applied between the shim, and the exposed surfaces of the pair of front and back piezoelectric bodies.  
         [0029]     The surfaces of the pair of piezoelectric bodies  112  on the side of the shim  111  are bonded to the shim  111  so as to be electrically connected to the shim over the entire surface thereof, and film-like electrodes  113  are formed on the entire exposed surfaces of the piezoelectric bodies opposite to the surfaces thereof on the side of the shim  111 . Each film-like electrode  113  is formed, for example, by performing printing (e.g., screen baking) with conductive paste (e.g., gold paste) or by sputtering good conductive metal. The shim  111  is formed with a wiring connecting projection  114  which protrudes in a radial direction. By making the film-like electrode  113  of a gold material, it is possible to avoid a migration problem which may be caused when an electrode is made of, for example, a silver material.  
         [0030]     Spacer insulating rings  115  which surround the piezoelectric bodies  112  annularly are respectively located above and below the circular shim  111 . Each spacer insulating ring  115  defines the total maximum thickness of the piezoelectric vibrator  20 , and is made of a rubber material (for example, EPDM).  
         [0031]     In the above-described circular bimorph-type piezoelectric vibrator  20 , an alternating electric field is applied using the shim as one electrode and using the exposed surfaces (film-like electrodes  113 ) of the pair of piezoelectric bodies  112  as the other common electrodes. In the present embodiment, a connecting terminal  23   a  at a tip of a lead wire  23  (see, e.g.,  FIG. 4 ) within a flexible printed circuit (FPC)  22  is adhered to each piezoelectric body  112  (film-like electrode  113 ) for wiring thereto by a conductive double-sided adhesive tape (conductive adhesive material)  21 . As the conductive double-sided adhesive tape  21 , commercialized products (for example, conductive double-sided adhesive tape T4420W made by Sony Chemical Corp. and conductive copper foil double-sided adhesive tapes 8321 and 8322 made by Teraoka Seisakusho KK) can be used. Since the lead wires  23  electrically connected to the front and back piezoelectric bodies  112  (film-like electrodes  113 ) are electrically connected to each other, they have the same potential. Moreover, a lead wire  24  which makes a pair with the lead wire  23  within the FPC  22  is soldered to the wiring connecting projection  114 . The wiring connecting projection  114  may be soldered because it does not vibrate.  
         [0032]     Insulating films  116  (e.g., polyphenylene sulfide (PPS)) (see  FIG. 2 ) are bonded on the surfaces of the piezoelectric vibrator  20  (piezoelectric bodies  112 ) after the lead wires  23  are adhered thereto by the conductive double-sided adhesive tapes  21  as described above. These insulating films  116  are not drawn in  FIGS. 3 and 4 .  
         [0033]     Pressing rubbers (pressing members)  25  are respectively supported by the housings  10   a  and  10   b  correspondingly to the positions where the lead wire connecting terminals  23   a  and the conductive double-sided adhesive tapes  21  adhere to each other. Specifically, recessed parts  26  are formed in the housings  10   a  and  10   b , respectively, and the pressing rubbers  25  are fitted into the recessed parts  26 , respectively. In a state where the housings  10   a  and  10   b  are closed, each pressing rubber  25  applies a force in a direction in which the connecting terminal  23   a  of the lead wire  23  is pressed against the piezoelectric body  112  (film-like electrode  113 ). The pressing rubbers  25  are made of the same rubber material (for example, EPDM) as the spacer insulating rings  115  of the piezoelectric vibrator  20 . The piezoelectric vibrator  20  is supported by the housing  10  with the spacer insulating rings  15  and the pressing rubbers  25 . Therefore, since the spacer insulating rings  115  and the pressing rubbers  25  have equal elasticity, a stress can be concentrated on any one of the spacer insulating rings  115  and the pressing rubbers  25 , thereby preventing a bad effect from being exerted on the vibration of the piezoelectric vibrator  20 . Therefore, it is easy to set stresses occurring in (caused by) the pressing rubbers  25  and the spacer insulating rings  115  in determining various dimensions.  
         [0034]     According to the wiring structure of the connecting terminals  23   a  of the lead wires  23  to the piezoelectric bodies  112  (film-like electrodes  113 ) of the above-described piezoelectric vibrator  20 , since the connecting terminals  23   a  are adhered by the conductive double-sided adhesive tapes  21 , and the connecting terminals  23   a  always are elastically pressed towards the piezoelectric bodies  112  (conductive double-sided adhesive tapes  21 ) by the pressing rubbers  25 , stable electrical connection can be established. In other words, various dimensions are set such that the connecting terminals  23   a  always are pressed towards the conductive double-sided adhesive tapes  21  with appropriate forces in consideration of the amplitude of the piezoelectric vibrator  20  and the elasticity of the pressing rubbers  25 .  
         [0035]     Moreover, in the present embodiment, the piezoelectric vibrator  20  has a circular shape in plan view as its basic shape. In contrast, as shown in  FIGS. 3 and 4 , the shape of the variable volume chamber P, that is, the recessed parts  11   a  and  11   b  of the housing and sealing members  130  (they corresponds to the seal rings  13   a  and  13   b  of  FIG. 1 , and are denoted by single reference numeral  130  in FIGS.  3  to  6 ) are formed in a non-circular shape (a portion of the piezoelectric vibrator  20  is cut away in an arcuate shape) which is smaller than the piezoelectric vibrator  20 , and the connecting terminals  23   a  are connected to the piezoelectric bodies  112  (film-like electrodes  113 ) of the piezoelectric vibrator  20  outside the variable volume chamber P.  
         [0036]     Specifically, each of the sealing members  130  defining the variable volume chamber P is formed in a modified D-shape having a large circular-arc section  130 (C) composed of a partial circle exceeding a semicircle, and a straight section  130 (L) connecting both ends of the larger circular-arc section with a straight line. The straight section  130 (L) is positioned so as to be outside to the maximum and make the large circular-arc section  130 (C) as large as possible within a range in which the areas for wiring to the piezoelectric bodies  112  can be ensured outside the straight section  130 (L). By locating the straight section outside to the maximum, a decline in the pump efficiency can be minimized. Moreover, from another viewpoint, the straight section  130 (L) is determined in a position where permanent distortion is not left in the straight section when the piezoelectric vibrator  20  vibrates reciprocally. That is, when the above-described circular bimorph-type piezoelectric vibrator  20  is vibrated by applying an alternating electric field between the shim  111  and the exposed surfaces (film-like electrodes  113 ) of the pair of piezoelectric bodies  112  thereof, the amplitude of the piezoelectric vibrator  20  is the greatest in its center and is reduced toward its peripheral edge. In this connection, the straight section  130 (L) is positioned such that permanent distortion is not left in the straight section  130 (L). Also, when a lead wire  23  is wired to the outside of the straight section  130 (L), it is not necessary to cause the lead wire  23  to intersect the sealing member  130  and there is no case that the sealing member  130  deforms locally. Thus, the durability of the sealing member can be improved. In addition, the amplitude of the piezoelectric vibrator  20  outside the straight section  130 (L) is around 100 μm. According to the wiring connection structure of the present embodiment, even if the vibrator experiences such large displacement, a stress caused by the displacement can be absorbed appropriately, thereby ensuring electrical connection between the lead wire  23  and the piezoelectric body  112  (film-like electrode  113 ).  
         [0037]     In the illustrated embodiment, the pressing rubbers  25  made of a rubber material are provided separately from the housings  10   a  and  10   b . However, it is also possible to adopt an aspect in which pressing members are integrally provided in the housings  10   a  and  10   b  made of, for example, a resin material. Moreover, the structure of the illustrated piezoelectric vibrator  20  is an example and has the degree of freedom, and the configuration of the umbrellas (e.g., check valves)  17 A and  17 B does not matter. As the piezoelectric vibrator  20 , in addition to a unimorph-type piezoelectric vibrator, a piezoelectric vibrator in which a driving voltage is lowered by a stacked structure of the piezoelectric bodies  112  is known. It is natural that these piezoelectric vibrators can also be used in the invention. Furthermore, the invention can be similarly applied to a flat plate-like vibrator (for example, a crystal vibrator) having film-like electrodes on the surfaces thereof. The pressing members can be provided in fixing members facing such a vibrator, or they can support the fixing members.  
         [0038]     According to the invention, it is possible to obtain a wiring structure having high connection reliability between a vibrator and lead wires. When the invention is applied to a wiring structure for a piezoelectric vibrator of a piezoelectric pump, a piezoelectric vibrator with high reliability and long service life is obtained.