JP2013201646A - Ultrasonic probe and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a conventional ultrasonic probe in that, with a piezoelectric element used as an oscillation element, a plate-like piezoelectric element is stacked together with a member such as a backing, a matching layer, and an electrode, and then they are diced and divided into individual elements, and in that case, dicing is made in hundred or more elements with a width about 100-200 μm normally, however, a tact time thereof is long and a water stream is jetted in order to reduce friction heat of a rotary blade, which can cause damage such as element breaking or layer peeling.SOLUTION: In an ultrasonic probe of the present invention, those obtained by processing PZT into balls are precisely arrayed, and electrode and wiring are formed mainly by screen printing, painting, and transfer, to allow transmission/reception of signals.

Description

  The present invention relates to an ultrasonic probe or an ultrasonic sensor used for ultrasonic diagnosis.

  First, a conventional general ultrasonic probe will be described with reference to FIG. FIG. 1 is a longitudinal sectional view showing a configuration of a conventional ultrasonic probe. 1, the acoustic lens 3, the matching layer 2, the piezoelectric vibrator 1, and the backing material 4 are stacked. In FIG. 1, the thickness direction of each member is illustrated, and the upper part is the living body side. It is.

  In a general ultrasonic diagnostic apparatus, an ultrasonic wave transmitted from the piezoelectric vibrator 1 passes through the matching layer 2 and the acoustic lens 3 and is radiated to the living body, and the ultrasonic wave reflected in the living body follows a route opposite to the forward path. The signal is received by the piezoelectric vibrator 1 again, and a signal in accordance with the received intensity and response time is converted into luminance information and visualized.

  The above is an example in which elements are arranged one-dimensionally. However, a probe having this one-dimensional structure can obtain a planar image by moving the probe body. On the other hand, by arranging these elements in a two-dimensional arrangement (matrix arrangement), a planar image can be obtained without moving the probe body, and a three-dimensional image (3D image) can be obtained by moving it. There is a so-called two-dimensional array type probe.

  In the process of manufacturing an ultrasonic probe, a piezoelectric element is overlaid on the backing material 4 in FIG. 1, and an electrode and a matching layer 2 are overlaid and bonded, followed by dicing at a predetermined width (for example, at 100 μm intervals). A plurality of transmitting / receiving elements arranged independently of each other are obtained.

  Similarly, the two-dimensional array probe can obtain an element structure arranged in a matrix by dicing piezoelectric elements vertically and horizontally. By applying signals to the elements arranged in the vertical and horizontal directions in order, transmitting ultrasonic waves, and receiving the sound waves returned from the subject, the structure of the subject can be visualized.

  The explanation here is described in the above-mentioned ultrasonic probe for medical use, but it is not only used for transmitting the ultrasonic wave into the body and knowing the state of the internal organs, but also radiating it in the air, It can be similarly functioned as a sensor for detecting an object existing in space. In that case, in order to match the acoustic impedance, it is necessary to change the design of the matching layer 2 to one corresponding to air.

  Basically, since a high-definition image is required for medical use, the element size is as small as 200 μm or less, but the element size may be larger if a large object located in a space is detected. The larger the probe size, the wider space sensing is possible.

  The matching layer design is the same even if the medium through which the ultrasonic wave passes is concrete or water.

JP 2011-110111 A JP 2005-101748 A

  As a prior example of a two-dimensional array probe, reference 1 is given as an example. In order to produce a two-dimensional array probe, it is necessary to dice the piezoelectric element vertically and horizontally and cut it into a state as shown in FIG.

  However, for example, in order to obtain the number of elements of a general one-dimensional array probe, about 100 elements, in order to carry out dicing 100 times, it is necessary to cut while taking approximately 1 hour. This is because increasing the cutting speed causes breakage of the piezoelectric layer such as cracks and element breaks, separation between layers, and the like, resulting in a decrease in yield. When dicing elements vertically and horizontally to obtain a two-dimensional array probe in such a state, to obtain an array of 100 × 100 elements, not only simply doubles the time but also the size of the upper surface is small. As a result, chipping of the surface layer (mainly the matching layer) is likely to occur, and furthermore, the backing-piezoelectric element-matching layer laminate cut into a biaxial shape into a rod shape itself is physically folded. It becomes easy.

  In the dicing process, the cutting operation is performed while reducing the frictional heat with the workpiece by applying the fountain flow to the rotating blade. For this reason, the rod-shaped element that is easy to be broken will follow the load from the outside more and more, and it will not be a problem of simply taking time. This is as illustrated by the cross-sectional area of FIG.

  In addition, it is difficult to increase the area of the piezoelectric element, and if a plurality of elements are used in a large format, the reliability of the element is affected, and unevenness in the thickness between elements occurs, resulting in loss of stability.

  In reference to such a decrease in yield, Document 1 also “generally, as the aperture diameter (number of vibrators) increases, the yield of the vibrator group tends to deteriorate and the cost tends to increase. Is recognized.

  As described above, in the transition from one dimension to two dimensions, due to the above-described problems, the yield is drastically reduced, and a conventional piezoelectric element is obtained by a precise process using semiconductor technology such as cMUT or pMUT. The current situation is that it is impossible to compete with the process of two-dimensionally arranging elements at high density.

  An object of the present invention is to solve the problem in manufacturing tact and the problem of reliability in construction method, and to provide an inexpensive two-dimensional array probe.

  The present invention solves the above-described conventional problems, and provides a technique capable of stably forming a large number of elements without using a dicing process that requires manufacturing tact.

  According to the ultrasonic probe and sensor of the present invention, an element made of PZT that forms an element is processed into a spherical shape.

  As an example of using a spherical element, for example, in Document 2, a heat-meltable resin coated with a uniform thickness on the surface of a spherical body is integrated so that the elements touch each other, and then the resin is heated and melted. A method of bringing them into close contact with each other is disclosed.

  When this method is adopted, a process technology that stabilizes the distortion and dimensional change after bonding by controlling the film thickness on the element and tightening the bonding conditions is indispensable. High technology and accuracy are required for the manufacturing process, such as partial removal of the coating film in the previous stage, and high costs associated with manufacturing are expected to be realized in order to realize it.

  Further, in Reference 2, there is a description that the two-dimensional and three-dimensional arrangement of the spherical elements is possible, but it is not clear how to form the electrode after the arrangement and how to use it. Lack of practicality.

  Furthermore, when this method is used, there is a high possibility that the film thickness of the resin coated on the element is non-uniform, or that there is a deviation between elements due to uneven heating or uneven pressure.

  A technique for forming a uniform film thickness on a minute sphere is not particularly disclosed in Document 2, but it is technically difficult to form a uniform thin film on a minute sphere by an element alone, and this accuracy is low. This also affects the accuracy of element placement.

  Further, when the elements are joined by melting, since they are spheres, there is naturally a space without resin between the spheres. In the case of fusion bonding, these are confined in a space, but the presence of air between elements causes reflection due to an extreme difference in impedance, which is a big problem in actual use.

  In addition, although not described, it is necessary to form an electrode necessary for driving the piezoelectric element on the element, but from the element once coated with the resin, a part of the coated resin Is difficult to peel off without affecting the resin between the elements, and it is essential to cause distortion in the arrangement between the elements.

  All of the above issues affect the accuracy of the ultrasonic beam, but not only a very high level of technology is required to realize the idea of Document 2 by solving these process issues, High costs are expected to occur.

  In the present invention, unlike the technique found in Document 2, elements are arranged by a simpler method to form electrodes.

  A basic structure is a structure obtained by arranging PZT (5) processed into a true sphere having a diameter of approximately 200 μm in each hole of the substrate (6) provided with a plurality of holes in a predetermined arrangement.

  Further, a resin (7) is poured into the gaps between the piezoelectric elements, and the respective elements are fixed. Then, electrodes (8) are provided on the upper and lower sides of the piezoelectric elements with conductive paste, and wiring is applied by screen printing or the like.

  Furthermore, the matching layer is bonded, and the device is polarized by applying a predetermined voltage to the piezoelectric electrode.

  The reason why the piezoelectric body polarized from the beginning is not used is that the polarization directions of the individual cut element pieces are not aligned at the time of arrangement. The reason why the elements are made spherical is that it is not necessary to consider the shape directionality when the individual element pieces are arranged.

  As for PZT spheres, those that have been once formed in bulk in a flat shape are cut into a predetermined block size and then physically processed into spheres (sphere polishing). If there is an efficient method of forming the process, it does not stick to the process.

  The material of the sphere is required to obtain the required sensitivity and can be processed into a sphere, and PZT does not necessarily have to be a material as long as these conditions are satisfied.

  In the case of functioning not as a medical ultrasonic probe but as a spatial sensor, it is desirable that the element has a larger size, for example, about 1 mm, instead of 200 μm. This is because the output sensitivity is increased and the reach of sound waves can be obtained more. This size may be determined in consideration of the sensing accuracy and sensitivity of the target object.

  Even for medical use, it is not necessary to stick to 200 μm, and the size may be designed based on the required sensitivity and accuracy.

  The resin material (7) filled between the elements for fixing the sphere also has an effect of attenuating crosstalk between the elements, so that it has an excellent support effect (that is, has rigidity) and an excellent attenuation effect. It is desirable to use a high internal loss material.

  As a method of holding individual elements before filling the resin (7) between the spherical elements (5), a method of vacuuming from the opposite direction of the substrate (6) and temporarily fixing them to the holes by suction force is available. desirable.

  As for wiring, it is necessary to provide electrodes (8) above and below each spherical piezoelectric element and to apply a plus / minus reverse phase potential to each of them. It is desirable to implement a three-dimensional wiring when these wirings intersect. The three-dimensional wiring may be formed inside the backing material or may be formed on the front side of the piezoelectric. In addition, so-called “solid wiring” may be performed by using one electrode as a ground that is shared by all elements (or a unit in which a plurality of elements are grouped). If this electrode material is on the piezoelectric side, it may form part of the matching layer.

  As a method for forming the wiring, it is desirable to use screen printing or an ink jet type printing machine using a conductive paste. As for the conductive paste, it is desirable to use nano silver paste, nano copper paste, nano gold paste, etc. with a resistance component as small as possible to prevent breakdown due to voltage load. This is also desirable because it does not apply thermal load.

  In addition, if there is a wiring material having a small resistance component, the above-mentioned materials are not particular.

  As for the matching layer, it is desirable to adopt a formation method in which a material that provides the function of the matching layer is applied and laminated together with the element substrate, but the film material that forms the matching layer is pasted on the substrate as in the conventional method. It doesn't matter.

  With respect to the holes in the substrate provided for arranging the elements, a mortar-shaped hole can be precisely formed by using the microblast method. However, a precise hole such as etching or processing using a drill is predetermined. Any method can be used if it can be formed.

  According to the ultrasonic probe according to the present invention, a spherical piezoelectric element is arranged on a substrate provided with predetermined pores, and electrodes, wiring, element emphasis elements and matching layers are formed by screen printing or precision coating. This is an inexpensive method that shortens the tact time compared to making a flat plate made of piezoelectric material into an element by dicing, and prevents the destruction of the element due to dicing and the yield. Can also contribute to the cost reduction of products.

Cross-sectional view of a conventional ultrasonic probe Sectional drawing which arrange | positioned the spherical piezoelectric material in this invention in the base which provided the hole Cross-sectional view in which the spherical piezoelectric element according to the present invention is fixed by a priority resin and wiring is provided.

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

(Embodiment)
A 300-micron-thick PZT piezoelectric element formed on a flat plate was diced into a vertical, horizontal, and 300-micron height and polished to obtain a spherical piezoelectric body having a diameter of 200 microns.

  In addition, holes with a diameter of 150 microns are separately formed on a ceramic substrate with a thickness of 100 microns by a microblast manufacturing method, and element intervals are 10 rows vertically and horizontally at a pitch of 250 microns. A total of 100 pores were provided. Two substrates having predetermined holes provided at exactly the same position were prepared as substrate A and substrate B, respectively.

  A vacuum was attached to the back surface of the substrate A provided with the pores, and suction was performed to hold the spherical piezoelectric element of 100 elements in the pores.

  From the surface side of another substrate B, the conductive paste was filled into the holes using a squeegee. All conductive paste adhering to the periphery was wiped off.

  While the substrate A was vacuumed and the element was held, the surfaces of the substrate A and the substrate B were aligned and inserted into the pores of the spherical piezoelectric substrate B of the substrate A.

  In this state, the conductive paste was sufficiently cured at 200 ° C. for 1 hour to fix the particles in the holes and to form electrodes on the “southern hemisphere portion” of the sphere.

  Thereafter, a UV curable polymer resin was filled in the gaps between the elements, and cured by UV irradiation to fix the elements.

  Next, a silver nano paste was applied to the piezoelectric element side, that is, the entire surface of the “northern hemisphere”, and baked at 150 ° C. for 10 minutes to obtain an electrode.

  A backing using a laminated substrate with three-dimensional wiring was attached to the back surface while accurately aligning.

  Thereafter, polarization was performed by applying a voltage of 1 kv to the front and back electrodes (7). The polarization was performed in silicon oil heated to about 200 ° C. so as to exceed the Curie temperature of the piezoelectric material.

  Finally, a predetermined amount of the matching layer material was applied to the piezoelectric element side, dried and fired to obtain an ultrasonic probe transducer.

  Ultrasonic waves could be transmitted by applying a pulse potential to the backing side and the piezoelectric element side of the ultrasonic probe transducer obtained in this example through electrodes formed of silver paste and silver nanopaste.

  The ultrasonic probe according to the present invention is formed by precisely arranging PZT processed into a spherical shape, wiring, and forming a predetermined member mainly by screen printing or coating, thereby enabling transmission and reception of signals. It is a thing. This eliminates the time required for dicing, leading to a reduction in tact time. In addition, it is possible to improve the yield in the assembly process due to element destruction due to dicing, and it is possible to develop a probe with excellent cost performance. This structure and manufacturing method are particularly effective in a two-dimensional array probe in which elements are arranged in a matrix and the number of elements is significantly increased.

  Furthermore, this structure can increase the area regardless of the plate size of the piezoelectric element, and can be applied not only for ultrasonic medical diagnosis but also in many fields such as an object sensor for space.

DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 2 Matching layer 3 Acoustic lens 4 Backing 5 Spherical piezoelectric element 6 Substrate 7 Filling material between piezoelectric elements 8 Electrode material

Claims (9)

PZT is processed into a sphere, with the equator position of the sphere as the boundary, electrodes are provided on all or part of the surface of the hemisphere located in the southern and northern hemispheres, and an element in which an insulating area not coated with an electrode is provided near the equator An ultrasonic probe formed as a result. Two elements are formed by processing PZT into a sphere, providing electrodes on all or part of the surface of the hemisphere located in the southern and northern hemispheres with the equator position of the sphere as the boundary, and providing an insulating area near the equator where no electrode is applied. The ultrasonic probe according to claim 1, wherein the ultrasonic probe is arranged in a dimension. The ultrasonic probe according to claim 1, wherein the PZT sphere has a size between 100 and 1000 μm. The processing hole of the base material on which the element is arranged is a through hole forming a predetermined taper, and the diameter of the hole on the upper surface on which the element is arranged is a diameter at which the sphere is not completely embedded in the hole. The ultrasonic probe according to claim 1, wherein the aperture is a size equal to or smaller than the diameter of the sphere. 5. The ultrasonic probe according to claim 1, wherein the processing hole in which the element is arranged is filled with a conductive paste having adhesiveness in advance to fix the arranged element and form an electrode. 6. The ultrasonic probe according to claim 5, wherein the filling amount is controlled so that the conductive paste pushed out to the back surface by the arranged sphere forms a bump for the electrode. The filling amount of the resin is controlled so that the same diameter as the aperture provided in the base material remains on the upper surface of the sphere while filling the space between the plurality of spherical elements arranged on the base material with resin. 5 ultrasonic probes. The ultrasonic probe according to claim 7, wherein the conductive paste is uniformly applied to the upper surface of the arranged sphere, and the formation of the electrodes and the wiring are performed simultaneously. The ultrasonic probe according to claim 1, wherein a plurality of arranged spheres are connected by electrodes.

Images