JP2008193357A - Ultrasonic probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the increase of attenuation due to an acoustic lens by securing close contact between an ultrasonic probe formed by using a cMUT and an object to be probed. <P>SOLUTION: The ultrasonic probe includes a semiconductor substrate, on which a cMUT type vibrator placed on a backing layer is formed, and a wiring board for external wiring, and electrode terminals of the vibrator and lead electrodes of the wiring board are bonded in order from the terminal side having higher height from a placing face of the backing layer to the terminal side having lower height. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic probe used in an ultrasonic diagnostic apparatus.

  An ultrasound probe used in an ultrasound diagnostic apparatus is formed with a plurality of transducers, and the transducers are driven by ultrasonic frequency electrical signals (drive signals) to be converted into ultrasound and sent to the subject. The reflected echo of the ultrasonic wave reflected and reflected in the subject is received by the vibrator and converted into an electrical signal.

  For example, as described in Patent Document 1, it has been proposed to use a vibrating element called a cMUT (Capacitive Micromachined Ultrasound Transducer) for the vibrator constituting the ultrasonic probe. The cMUT is a capacitive vibrator, in which one electrode is formed on a film body made of an insulating material, the other electrode is disposed facing the space, and a drive signal is applied between the pair of electrodes. The film body is vibrated to generate ultrasonic waves. In particular, by superimposing a DC bias voltage on the drive signal to control the tension of the film body, the ultrasonic transmission / reception sensitivity, that is, the electromechanical coupling coefficient can be changed according to the magnitude of the bias voltage. ing. Moreover, since it can be manufactured by a semiconductor microfabrication process, development has been advanced.

  When an ultrasonic probe is formed using such a cMUT, usually, a single transducer is formed by a plurality of cMUTs, and a plurality of transducers are arranged in one or two dimensions on the same semiconductor substrate. Formed. The electrodes on the vibration film side arranged on the ultrasonic transmission / reception surface side of each cMUT are individually connected to the electrode terminals of the vibrator provided on the edge of the semiconductor substrate. Further, when one vibrator is constituted by a plurality of cMUTs, the plurality of cMUTs may be divided into a plurality of groups and an electrode terminal may be provided for each group. Each electrode terminal is connected to a lead terminal formed on an external wiring board such as a flexible wiring board by wire bonding, and is configured such that a drive signal is applied from the outside via the lead terminal (Non-Patent Document 1).

US Patent Publication US2005 / 0203409 A1 Omer Oralkan, et. a1. “Volumetric Ultrasound Imaging Using 2-D CMUT Arrays,” IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND CONTROL, VOL. 50, N0.19, PP. 1581-1594, NOVEMBER 2003

  However, in the above prior art, depending on the size of the space that accommodates the bonding wire that connects the electrode terminal and the lead terminal, a concave portion is formed on the contact surface of the ultrasonic probe that is used in contact with the body surface of the subject. There is a problem that it is not taken into consideration.

  That is, an ultrasonic probe formed using a cMUT is configured such that a semiconductor substrate on which a cMUT is formed is fixed to the upper surface of a backing layer via an adhesive layer, and the ultrasonic transmission / reception surface side of the cMUT is interposed via an adhesive layer. The acoustic lens is directly fixed. The acoustic lens has a convex curvature in the short axis direction orthogonal to the arrangement direction of the plurality of transducers, and is formed in a shape that covers the ultrasonic transmission / reception surface of the cMUT excluding the electrode terminals of the semiconductor substrate. In addition, the electrode terminals are formed on the surface of the semiconductor substrate adjacent to both ends of the acoustic lens in the short axis direction, and a lead terminal is disposed near the electrode terminals, and the terminals are bonded with wires. Therefore, the protective member, which is integrally formed of the same material as the acoustic lens, is extended from both ends in the short axis direction of the acoustic lens to the probe casing, and wire bonding is performed in the space between the protective member and the electrode terminal surface. The structure which accommodates a part is employ | adopted, and the contact surface which contacts the body surface of a test subject is formed with the outer surface of an acoustic lens and a protection member.

  By the way, on the ultrasonic transmission / reception surface side of the cMUT, an acoustic lens is directly bonded without providing an acoustic matching layer, and the semiconductor substrate on which the cMUT is formed tends to be formed thinner and thinner. Therefore, the height of the space between the protective member and the chip electrode surface is reduced, so that the thickness of the acoustic lens is reduced in order to secure a height space for housing the bonding wire formed with a loop shape. It is necessary to increase the thickness or to bend the protective member to the outer surface side.

  However, increasing the thickness of the acoustic lens leads to a problem that the ultrasonic wave is attenuated, and if the protective member is bent to the outer surface side, a concave portion is formed on the contact surface with the subject. Adhesion with the subject is reduced due to the presence of the air layer, which leads to a problem in that the sensitivity and frequency characteristics are deteriorated and obstruct the ultrasonic measurement.

  The problem to be solved by the present invention is to secure adhesion between an ultrasonic probe formed using a capacitive transducer and a subject and to suppress an increase in attenuation by an acoustic lens.

  In order to solve the above problems, an ultrasonic probe of the present invention includes a semiconductor substrate on which a capacitive vibrator is formed, a backing layer on which the semiconductor substrate is placed, and ultrasonic transmission / reception of the semiconductor substrate. An acoustic lens placed on a surface; an electrode terminal of a transducer connected to the transducer and formed in a region outside the ultrasonic wave transmitting / receiving surface of the semiconductor substrate; and a mounting surface of the semiconductor substrate on the backing layer A wiring board connected to an external wiring having a mounted lead terminal; and a wire bonding part formed by connecting the electrode terminal and the lead terminal, the electrode terminal of the wire bonding part and the lead terminal The bonding is characterized in that bonding is performed from the terminal side having a low height from the mounting surface of the backing layer to the terminal side having a high height. In this case, the protection member may be provided so as to cover the wire bonding portion and extend from both ends of the short axis direction of the acoustic lens to the probe casing.

  Usually, in wire bonding, a spark is formed on the tip of the wire to form a spherical body, the spherical body is pressed against the electrode terminal of the semiconductor substrate to form a bump, and the tip of the wire is welded through the bump. Thereafter, a method is employed in which the wire is stretched and the side surface of the wire is pressed against the lead electrode and welded. That is, since the electrode terminals of the semiconductor substrate are vulnerable to mechanical shock during wire bonding, the impact is absorbed by welding via spherical bumps. According to this, since the wire on the electrode terminal side rises in the vertical direction with respect to the electrode terminal to form a loop portion, a space high enough to accommodate the loop portion is required above the electrode terminal. Become.

  Therefore, in the present invention, the height of the loop portion from the semiconductor substrate surface can be suppressed by the amount of the step by bonding from the low terminal side to the high terminal side. As a result, the height of the space between the protective member and the semiconductor substrate surface can be reduced, so that the protective member can be avoided from being bent to the outer surface side. Thereby, it is possible to prevent the concave portion from being formed on the contact surface with the subject, to secure the close contact with the subject, and to prevent deterioration of sensitivity and frequency characteristics. Moreover, since it can suppress that the thickness of an acoustic lens is thickened, attenuation | damping of an ultrasonic wave can be suppressed.

  Specifically, in the ultrasonic probe of the present invention, when the electrode terminal is higher than the lead terminal, the bonding wire has the wire tip welded to the lead terminal via the bump, and the side surface of the wire is connected to the electrode terminal via the bump. It can be set as the structure welded to. When the lead terminal is higher than the electrode terminal, the bonding wire can have a structure in which the wire tip of the electrode terminal is welded via the bump and the wire side surface is welded to the lead terminal via the bump.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesiveness of the ultrasonic probe formed using a capacitive vibrator | oscillator and a test object can be ensured, and the increase in attenuation | damping by an acoustic lens can be suppressed.

  Hereinafter, an embodiment of a method for manufacturing an ultrasonic probe of the present invention will be described.

(Embodiment 1)
FIG. 1 shows a short-axis cross-sectional view of the main part of an ultrasonic probe using a cMUT manufactured by the manufacturing method of one embodiment of the present invention, and FIG. 2 schematically shows a cross-section of a vibration element of the cMUT. FIG. 3 is a perspective view showing a part of the transducer group formed by the cMUT.

  As shown in FIG. 2, the vibration element 1 of the cMUT is formed by fine processing by a semiconductor process, and an insulating layer 4 having a void layer 3 inside is formed on the substrate surface of a semiconductor substrate 2 such as silicon. Has been. A driving electrode 5 is formed on the upper surface of the insulating layer 4 so as to correspond to the gap layer 3, and the upper surface of the driving electrode 5 is covered with a film body 6. A common electrode 7 is provided on the back surface of the semiconductor substrate 2 so as to face the drive electrode 5 with the gap layer 3 interposed therebetween.

  The insulating layer 4 is made of, for example, a semiconductor compound such as plasma tetraethoxysilane (PTEOS), tetraethoxysilane (TEOS), or silicon nitride (SiN). The film body 6 is made of a semiconductor compound such as a silicon compound, for example. In the drawing of the film body 6, the upper surface is an ultrasonic wave transmitting / receiving surface. Between the drive electrode 5 and the common electrode 7, a transmission means 8 including a power source for supplying a drive signal and a bias means 9 for applying a DC bias voltage are connected in series. The gap layer 3 is filled with a vacuum state or a predetermined gas. For example, the element described in cMut (Captive Micromachined Ultrasonic Transducer: IEEE Trans. Ultrason. Ferrolect. Freq. Contr. Vol 45 pp. 678-690, May 1998) can be applied to the vibration element 1 of the cMUT.

  When a DC bias voltage is applied between the drive electrode 5 and the common electrode 7 of the vibration element 1 of the cMUT configured as described above, an electric field is formed between both electrodes, which causes the film body 6 to be strained. It becomes an electromechanical coupling coefficient corresponding to the bias voltage. When a drive signal is applied between the electrodes from the transmission unit 8, ultrasonic waves are emitted from the film body 6 based on the electromechanical coupling coefficient. When the bias voltage is changed, the electromechanical coupling coefficient is changed, and ultrasonic waves corresponding to the electromechanical coupling coefficient are emitted from the film body 6 from the film body 6. Similarly, when receiving an ultrasonic wave, the film body 6 is excited by the reflected echo signal generated from the subject, whereby the capacitance of the air gap layer 3 changes, and the electric signal corresponding to the change is generated by both signals. Output from between electrodes.

  By forming the cMUT vibration element 1 shown in FIG. 2 on the same semiconductor substrate 10, for example, as shown in FIG. One ultrasonic probe is formed by arranging in the direction. A plurality of m (six in the illustrated example) cMUT vibration elements 12-1 to 12-m are formed on each transducer 11. In the figure, the Y-axis direction is the major axis direction of the ultrasonic probe, and the X-axis direction is the minor axis direction.

  In the embodiment of FIG. 3, the driving electrodes 5 of the cMUT vibrating elements 12-1 to 12-m forming each vibrator 11 are common electrodes formed on the upper surface of the semiconductor substrate 10 by internal wiring (not shown). The terminals 15-1 to 15-n are connected. In addition, although not illustrated, the common electrodes 7 of the vibration elements 12-1 to 12-m are appropriately divided and connected to the common electrodes provided at both ends in the major axis direction.

  In each vibrator 11 configured in this way, the electromechanical coupling coefficient, that is, the transmission / reception sensitivity changes depending on the magnitude of the DC bias potential applied by the bias means 9. Then, the driving signal supplied from the transmission means 8 vibrates according to the electromechanical coupling coefficient, and the film body 6 is converted into ultrasonic waves and transmitted to the subject. Further, the ultrasonic wave received from the subject is converted into a reflection echo signal of an electric signal by the film body 6.

  At this time, if the tension of the film body 6 is controlled by changing the magnitude of the bias voltage applied to the vibrators 11-1 to 11-n, the vibrator 11-1 can be used even when drive signals having the same amplitude are input. Sound pressure (for example, amplitude) of ultrasonic waves emitted from ˜n can be changed.

  Here, with reference to FIG. 1, the structure of the ultrasonic probe manufactured by one Embodiment of the manufacturing method of the ultrasonic probe which is the characteristics of this invention is demonstrated. In the present embodiment, an example of the linear array type ultrasonic probe 20 is shown, but the present invention is not limited to this, and the present invention is also applicable to a convex type or two-dimensional array type ultrasonic probe. Can be applied.

  As shown in FIG. 1A, the semiconductor substrate 21 on which the plurality of cMUT vibrators shown in FIG. 3 is formed is placed on one surface of the backing layer 22 with an adhesive layer 23 interposed therebetween. An acoustic lens 24 is placed on the ultrasonic wave transmitting / receiving surface of the semiconductor substrate 21 via an adhesive layer 25. The acoustic lens 24 is formed to have a convex curvature in the minor axis direction of the ultrasonic transmission / reception surface, and a protection member 26 is provided to extend from both ends of the acoustic lens 24 in the minor axis direction. A plurality of electrode terminals 27 are provided corresponding to the plurality of vibrators in the region of the edge portion in the minor axis direction that is off the ultrasonic wave transmitting / receiving surface of the semiconductor substrate 21.

  In addition, flexible wiring boards 28 connected to external wirings are disposed on both side surfaces of the backing layer 22 in the minor axis direction. The lead terminal 29 provided at the end of the flexible wiring board 28 is placed on the surface of the backing layer 22 on which the semiconductor substrate 21 is mounted, and is fixed by the adhesive layer 30. The electrode terminal 27 and the lead terminal 29 are connected by a bonding wire 31. The protection member 26 extending from both ends of the acoustic lens 24 is provided so as to cover the wire bonding portion that connects the electrode terminal 27 and the lead terminal 29, and the end portion is fixed to the inner surface of the casing 33 by the adhesive layer 32. Has been. Instead of the flexible wiring board 28, a hard wiring board may be used.

  The height of the electrode terminal 27 of the present embodiment from the upper surface of the backing layer 22 is formed higher than the height of the lead terminal 29 from the upper surface of the backing layer 22. That is, the semiconductor substrate 21 is formed thicker than the flexible wiring substrate 28. As a result, as shown in FIG. 1B, the electrode terminal 27 and the lead terminal 29 are arranged with a height difference d between the leads.

  In this embodiment, as shown in FIG. 1B, bonding is performed from the lead terminal 29 side having a low height from the mounting surface of the semiconductor substrate 21 of the backing layer 22 toward the electrode terminal 27 side. By bonding, the height of the loop portion 34 formed at the rising portion of the bonding wire from the upper surface of the semiconductor substrate 21 is suppressed. Accordingly, the wire bonding portion can be accommodated in the space formed between the protection member 26 and the semiconductor substrate 21 without bending the protection member 26 outward, so that the outer surfaces of both ends of the acoustic lens 24 and the protection member 26 are accommodated. Can be connected smoothly, and adhesion to the subject can be secured. In addition, an increase in the thickness of the acoustic lens 24 can be suppressed and attenuation of the ultrasonic wave can be suppressed.

  On the other hand, when wire bonding is performed first from the electrode terminal 27 side as in the comparative example shown in FIG. 4, a loop portion of the bonding wire is formed on the electrode terminal 27 side, and the lead terminal 29 to be wire bonded later. The side of the bonding wire is welded to the side. That is, if the height of the loop portion formed by wire bonding from the upper surface of the semiconductor substrate 21 is high, the loop portion cannot be contained in the space between the inner surface of the protective member 26 and the upper surface of the semiconductor substrate 21. In order to accommodate the loop portion, it is conceivable to provide the protection member 26 with a bent portion 35 and connect it to the acoustic lens 24. However, the bent portion 35 causes a depression on the contact surface with the subject. There is a problem in that the adhesiveness of the ultrasonic wave is lowered, the sensitivity and the frequency characteristics are deteriorated, and the ultrasonic measurement becomes an obstacle. Instead of this, it is conceivable to increase the overall thickness of the acoustic lens 24 to reduce the depression by the bent portion 35. However, increasing the thickness of the acoustic lens 24 increases the attenuation of the ultrasonic wave. .

  Here, with reference to FIG. 5, the procedure of the wire bonding of this embodiment is demonstrated concretely.

  Step 1: A wire 41 such as gold is held by a clamp 42 and a capillary 43, and an electric spark or the like is blown to the tip of the wire 41 to form a spherical ball 44.

  Step 2: In this state, the clamp 42 is opened, the capillary 43 is lowered toward the electrode terminal 27, the ball 44 is brought into contact with the target electrode terminal 27, and heating and pressurization are performed while the ball 44 is captured by the capillary 43. In this state, an ultrasonic wave is applied to the ball 44 to form a bump.

  Step 3: After raising the capillary 43 to a certain height, the capillary 43 is again lowered onto the joint portion of the bump and the tip of the wire 41 is pressed. Also at this time, an ultrasonic wave is applied to the ball 44 in a heated and pressurized state, and the wire 41 is bonded onto the electrode terminal 27 to form the bump 45.

  Step 4: The capillary 43 tears the wire 41 from the joint portion while leaving the bump 45. A high voltage is applied to the tip of the wire 41 secured at the tip of the capillary 43 to spark a spark, and a ball is formed at the tip of the capillary. The bump 45 is formed on the electrode terminal 27 by the above process.

  Step 5: With the ball captured at the tip of the wire 41, the clamp 42 is opened and the capillary 43 is lowered to the lead terminal 29. The capillaries 43 apply ultrasonic waves to the balls 44 in a heated and pressurized state while capturing the balls 44 to weld the tips of the wires 41 to the lead terminals 29 via the bumps 46 on the target.

  Step 6: The capillary 43 is raised to a certain height (loop height), the wire 41 is stretched and moved onto the bump 45 formed on the electrode terminal 27, and lowered again to bump the side surface of the wire 41. Press on 45. Also at this time, ultrasonic waves are applied to the bumps 45 in a heated and pressurized state to bond the wires 41 on the target.

  Step 7: The capillary 43 tears the wire 41 from the joint while leaving the wire 41. A high voltage is applied to the tip of the wire 41 secured at the tip of the capillary 43 to spark a spark, and a ball is formed at the tip of the capillary.

  By performing reverse bonding in this manner, as shown in FIG. 1B, a rising portion of the wire is formed on the lead terminal 29 side, so that (loop height) = (rising portion height) − (electrode terminal) 27 and the lead terminal 29). As a result, the height of the loop portion (loop height) can be reduced without reducing the height of the rising portion. In the case of reverse bonding, it is necessary to previously form bumps 45 on the electrode terminal 27 side in order to avoid damage due to mechanical impact on the electrode terminal 27.

(Embodiment 2)
FIG. 6 is a short-axis cross-sectional view of the main part of an ultrasonic probe using a cMUT manufactured by the manufacturing method according to another embodiment of the present invention. Components having the same configurations as those of the embodiment of FIG. The present embodiment is different from the first embodiment in that the present invention is applied when the height of the electrode terminal 27 is equal to the height of the lead terminal 29 or the height of the electrode terminal 27 is lower than the height of the lead terminal 29. There is.

  In the case of this embodiment, as shown in FIG. 6A, the electrode terminal 27 and the lead terminal 29 are connected by normal bonding. That is, it corresponds to the case where the thickness of the semiconductor substrate 21 is formed to be equal to the thickness of the flexible wiring substrate 28 or thinner than the thickness of the flexible wiring substrate 28 due to progress in manufacturing technology or the like. In this case, since the loop height is controlled by the lead terminal 29 having a high height from the upper surface of the backing layer 22, bonding is performed from the electrode terminal 27 side having a low height from the upper surface of the backing layer 22. In this case, since the side surface of the wire is not directly bonded to the electrode terminal 27, it is possible to omit a step of previously forming a bump for alleviating mechanical shock.

  In the case of the present embodiment, the acoustic lens 50 is increased in overall thickness, and the protective member 51 is disposed away from the upper surface of the semiconductor substrate 21 to secure a space for storing the bonding wire portion. Thereby, both ends of the acoustic lens 50 and the outer surface of the protective member 51 can be smoothly connected, and no depression is formed, so that adhesion to the subject can be ensured. Although the thickness of the acoustic lens 50 is slightly increased, an increase in the attenuation amount of the ultrasonic wave can be sufficiently suppressed.

It is sectional drawing of the principal part of the ultrasonic probe manufactured by the manufacturing method of one Embodiment of this invention. It is a figure which shows typically the cross section of the vibration element of cMUT. It is a perspective view which shows a part of vibrator | oscillator formed by cMUT. It is sectional drawing of the principal part of the ultrasonic probe manufactured with the manufacturing method of the comparative example. It is process drawing explaining the specific procedure of the bonding of FIG. 1 embodiment. It is sectional drawing of the principal part of the ultrasonic probe manufactured by the manufacturing method of other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Semiconductor substrate 22 Backing layer 23 Adhesive material layer 24 Acoustic lens 25 Adhesive material layer 26 Protection member 27 Electrode terminal 28 Flexible wiring board 29 Lead terminal 30 Adhesive material layer 31 Bonding wire 34 Loop part

Claims (4)

A semiconductor substrate on which a capacitive vibrator is formed, a backing layer on which the semiconductor substrate is placed, an acoustic lens placed on an ultrasonic wave transmitting / receiving surface of the semiconductor substrate, and the semiconductor connected to the vibrator A wiring board connected to an external wiring having an electrode terminal of a vibrator formed in a region off the ultrasonic wave transmitting / receiving surface of the substrate and a lead terminal mounted on the mounting surface of the semiconductor substrate of the backing layer; A wire bonding portion formed by connecting the electrode terminal and the lead terminal;
The ultrasonic probe, wherein the electrode terminal and the lead terminal of the wire bonding portion are bonded from a low terminal side to a high terminal side from the mounting surface of the backing layer. . The ultrasonic probe according to claim 1,
An ultrasonic probe characterized in that a protective member is provided so as to cover the wire bonding portion and extend from both ends in the short axis direction of the acoustic lens to a probe casing. The ultrasonic probe according to claim 1,
When the electrode terminal is higher than the lead terminal, the bonding wire has a wire tip welded to the lead terminal via a bump, and a wire side surface welded to the electrode terminal via the bump. Ultrasonic probe. The ultrasonic probe according to claim 1,
When the lead terminal is higher than the electrode terminal, the bonding wire is formed by welding the wire tip of the electrode terminal via a bump and welding the side surface of the wire to the lead terminal via the bump. Ultrasonic probe.

Images