JP2008193357

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DESCRIPTION JP2008193357
An object of the present invention is to secure adhesion between an ultrasonic probe formed
using cMUT and a subject, and to suppress an increase in attenuation by an acoustic lens. A
semiconductor substrate having a cMUT-type vibrator mounted on a backing layer and a wiring
board for external wiring are provided, and bonding of electrode terminals of the vibrator and
lead electrodes of the wiring board is performed using the backing layer. The terminal is bonded
to the high terminal side from the terminal side where the height from the mounting surface is
low. [Selected figure] Figure 1
Ultrasound probe
[0001]
The present invention relates to an ultrasound probe used in an ultrasound diagnostic apparatus.
[0002]
An ultrasonic probe used in an ultrasonic diagnostic apparatus is formed to have a plurality of
transducers, and the transducer is driven by an electric signal (drive signal) at an ultrasonic
frequency to be converted into ultrasonic waves and transmitted to a subject The echoes of the
ultrasonic waves that are waved and reflected in the object are received by the transducer and
converted into electrical signals.
[0003]
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For example, as described in Patent Document 1, it has been proposed to use a vibrator element
called cMUT (Capacitive Micromachined Ultrasound Transducer) as a vibrator that constitutes an
ultrasound probe.
The cMUT is a capacitive vibrator, in which one electrode is formed on a film made of an
insulating material, the other electrode is disposed to face the other across a space, and a drive
signal is applied between the pair of electrodes The membrane is vibrated to generate an
ultrasonic wave.
In particular, by superimposing a DC bias voltage on the drive signal to control the degree of
tension of the film, the ultrasonic transmission / reception sensitivity, that is, the
electromechanical coupling coefficient can be changed according to the magnitude of the bias
voltage. ing. In addition, development is in progress because it can be manufactured by a
semiconductor microfabrication process.
[0004]
When forming an ultrasonic probe using such cMUT, usually, one cMUT forms one transducer,
and the transducers are arrayed in one or two dimensions on the same semiconductor substrate
It is formed. The electrodes on the vibrating film side disposed on the ultrasonic wave
transmitting / receiving surface side of each cMUT are individually connected to the electrode
terminals of the transducers provided at the edge of the semiconductor substrate. When one
vibrator is configured by a plurality of cMUTs, the plurality of cMUTs may be divided into a
plurality of groups, and electrode terminals 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 a drive signal is applied from the outside through the lead
terminal (Non-Patent Document 1).
[0005]
US Patent Publication US 2005/0203409 A1 Omer Oralkan, et. a1. Volumetric Ultrasound
Imaging Using 2-D CMUT Arrays, IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS,
AND CONTROL, VOL. 50, N 0.19, PP. 1581-1594, NOVEMBER 2003
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[0006]
However, in the above-mentioned prior art, depending on the size of the space for
accommodating the bonding wire connecting the electrode terminal and the lead terminal, the
contact surface of the ultrasonic probe used in contact with the body surface of the subject may
have a recess. There is a problem that it is not taken into consideration about
[0007]
That is, the ultrasonic probe formed by using cMUT fixes the semiconductor substrate on which
the cMUT is formed on the upper surface of the backing layer through the adhesive layer, and
the adhesive layer on the ultrasonic transmitting / receiving surface side of the cMUT It has a
structure in which an 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 covering the
ultrasonic transmission / reception surface of the cMUT excluding the electrode terminal of the
semiconductor substrate. The electrode terminals are formed on the surface of the
semiconductor substrate adjacent to both ends in the minor axis direction of the acoustic lens,
and lead terminals are disposed near the electrode terminals to bond the two terminals with a
wire. Therefore, a protective member integrally formed of the same material as the acoustic lens
is extended from both ends in the minor axis direction of the acoustic lens to the probe casing,
and wire bonding is performed in the space sandwiched between the protective member and the
electrode terminal surface. A structure for housing the portion is adopted, and the contact
surface that contacts the body surface of the subject is formed by the acoustic lens and the outer
surface of the protective member.
[0008]
By the way, an acoustic lens is directly adhered to the ultrasonic transmitting / receiving surface
side of the cMUT without providing an acoustic matching layer, and the semiconductor substrate
on which the cMUT is formed tends to be thinner and thinner. Therefore, since the height of the
space sandwiched between the protective member and the chip electrode surface is reduced, the
thickness of the acoustic lens is set to secure the space of the height for accommodating the
bonding wire formed in a loop shape. It is necessary to thicken or to form the protective member
by bending it to the outer surface side.
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[0009]
However, increasing the thickness of the acoustic lens leads to the problem that the ultrasonic
waves are attenuated, and bending the protective member to the outer surface side forms a
recess in the contact surface with the subject, so the contact surface with the subject The air
layer intervenes to lower the adhesion with the subject, which leads to the problem that the
sensitivity and frequency characteristics are deteriorated to cause an obstacle to ultrasonic
measurement.
[0010]
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.
[0011]
In order to solve the above problems, in the ultrasonic probe according to the present invention,
a semiconductor substrate on which a capacitive vibrator is formed, a backing layer on which the
semiconductor substrate is mounted, and ultrasonic transmission / reception of the
semiconductor substrate An acoustic lens placed on the surface, an electrode terminal of the
transducer connected to the transducer and formed in a region out of the ultrasonic wave
transmitting / receiving surface of the semiconductor substrate, and a mounting surface of the
backing substrate on the semiconductor substrate A wiring substrate connected to an external
wiring having lead terminals mounted thereon; and a wire bonding portion formed by connecting
the electrode terminal and the lead terminal, the electrode terminal of the wire bonding portion
and the lead terminal The bonding is characterized in that the bonding is performed from the
terminal side where the height from the mounting surface of the backing layer is low to the
terminal side where the height is high.
In this case, the wire bonding portion may be covered and extended from both ends in the minor
axis direction of the acoustic lens to the probe casing to provide a protective member.
[0012]
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In general, wire bonding is performed by forming an electric spark or the like at the tip of the
wire to form a spherical body, pressing the spherical body against the electrode terminal of the
semiconductor substrate to form a bump, and welding the tip of the wire through the bump After
that, a method is employed in which the wire is stretched and the side of the wire is pressed
against the lead electrode for welding.
That is, since the electrode terminal of the semiconductor substrate is weak to mechanical impact
at the time of wire bonding, the impact is absorbed by welding through bumps of spherical
bodies. According to this, the wire on the electrode terminal side rises in the vertical direction
with respect to the electrode terminal to form a loop portion. Therefore, a space having a height
sufficient to accommodate the loop portion is required above the electrode terminal. Become.
[0013]
Therefore, in the present invention, by bonding from the lower terminal side to the higher
terminal side, the height of the loop portion from the semiconductor substrate surface can be
suppressed by the difference in level. As a result, since the height of the space sandwiched
between the protective member and the semiconductor substrate surface can be reduced,
bending and forming the protective member to the outer surface side can be avoided. As a result,
it is possible to prevent the formation of a recess on the contact surface with the subject, ensure
the adhesion to the subject, and prevent the deterioration of sensitivity and frequency
characteristics. In addition, since the increase in thickness of the acoustic lens can be suppressed,
the attenuation of ultrasonic waves can be suppressed.
[0014]
Specifically, in the ultrasonic probe according to the present invention, when the electrode
terminal is higher than the lead terminal, the bonding wire is welded to the lead terminal at the
wire tip through the bump and the wire side surface is the electrode terminal Can be welded to
the When the lead terminal is higher than the electrode terminal, the bonding wire may 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.
[0015]
According to the present invention, the adhesion between the ultrasonic probe formed using the
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capacitive vibrator and the object can be secured, and the increase of the attenuation by the
acoustic lens can be suppressed.
[0016]
Hereinafter, an embodiment of a method of manufacturing an ultrasonic probe according to the
present invention will be described.
[0017]
(First Embodiment) FIG. 1 shows a short-axis cross-sectional view of the main part of an
ultrasonic probe using cMUT manufactured by the manufacturing method according to one
embodiment of the present invention, and FIG. The cross section is schematically shown, and a
part of the transducer group formed by the cMUT is shown in FIG. 3 by a perspective view.
[0018]
As shown in FIG. 2, the cMUT vibration element 1 is formed by microfabrication by a
semiconductor process, and an insulating layer 4 having an air gap layer 3 inside is formed on
the substrate surface of a semiconductor substrate 2 such as silicon. It is done.
A drive electrode 5 is formed on the upper surface of the insulating layer 4 corresponding to the
air gap layer 3, and the upper surface of the drive electrode 5 is covered with the film 6.
Further, 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 air gap layer 3 interposed therebetween.
[0019]
The insulating layer 4 is formed of, for example, a semiconductor compound such as plasma
tetra-ethoxysilane (PTEOS), tetra-ethoxysilane (TEOS), silicon nitride (SiN) or the like.
The film body 6 is formed of, for example, a semiconductor compound such as a silicon
compound. The upper surface in the drawing of the film body 6 is the ultrasonic transmission /
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reception surface. Between the drive electrode 5 and the common electrode 7, transmission
means 8 including a power supply for supplying a drive signal and bias means 9 for applying a
DC bias voltage are connected in series. In addition, the space layer 3 is filled with a vacuum or a
predetermined gas. The vibrating element 1 of the cMUT is, for example, cMut (Capative
Micromachined Ultrasonic Transducer: IEEE Trans. Ultrason. Ferroelect. Freq. Contr. Vol 45 pp.
678-690, May 1998) and the like can be applied.
[0020]
When a direct current bias voltage is applied between the drive electrode 5 and the common
electrode 7 of the cMUT vibrating element 1 configured as described above, an electric field is
formed between the two electrodes, whereby the film body 6 is strained. It becomes an
electromechanical coupling coefficient corresponding to the bias voltage. Then, when a drive
signal is applied between the electrodes from the transmitting means 8, an ultrasonic wave is
emitted from the film body 6 based on the electromechanical coupling coefficient. Further, when
the bias voltage is changed, the electromechanical coupling coefficient is changed, and an
ultrasonic wave corresponding to the electromechanical coupling coefficient is emitted from the
film body 6 from the film body 6. Similarly, when ultrasonic waves are received, the film body 6
is excited by the reflection echo signal generated from the subject, whereby the capacitance of
the air gap layer 3 is changed, and the electric signals corresponding to the change are both It is
output from between the electrodes.
[0021]
By forming the vibration element 1 of the cMUT shown in FIG. 2 on the same semiconductor
substrate 10, for example, as shown in FIG. One ultrasound probe is formed by arranging in the
direction. In each of the vibrators 11, a plurality of (six in the illustrated example) cMUT
vibrating elements 12-1 to 12m are formed. In the figure, the Y-axis direction is the major axis
direction of the ultrasound probe, and the X-axis direction is the minor axis direction.
[0022]
In the embodiment of FIG. 3, the drive electrodes 5 of the vibrator elements 12-1 to 12-m of the
cMUT forming the respective vibrators 11 are common electrodes respectively formed on the
upper surface of the semiconductor substrate 10 by internal wiring not shown. It is connected to
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the terminals 15-1 to n. Further, although not shown, the common electrodes 7 of the vibrating
elements 12-1 to 12-m are appropriately divided and connected to common electrodes provided
at both end portions in the long axis direction.
[0023]
The electromechanical coupling coefficient, that is, the transmission / reception sensitivity of
each vibrator 11 configured as described above changes depending on the magnitude of the
potential of the DC bias applied by the bias unit 9. Then, the film body 6 vibrates according to the
electromechanical coupling coefficient, converts the driving signal supplied from the transmitting
means 8 into an ultrasonic wave, and transmits the ultrasonic wave to the subject. Further, the
ultrasonic wave received from the subject is converted by the film body 6 into a reflection echo
signal of the electric signal.
[0024]
At this time, if the degree of tension of the film body 6 is controlled by changing the magnitude
of the bias voltage applied to the vibrators 11-1 to n, even when drive signals of the same
amplitude are input, the vibrator 11-1 is obtained. The sound pressure (for example, amplitude)
of the ultrasonic wave emitted from 〜 n can be changed.
[0025]
Here, with reference to FIG. 1, the structure of the ultrasound probe manufactured by one
Embodiment of the manufacturing method of the ultrasound 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 it is also possible to use a convex type or a twodimensional array type ultrasonic probe. It can apply.
[0026]
As shown in FIG. 1A, the semiconductor substrate 21 on which the plurality of transducers of the
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cMUT of FIG. 3 are formed is mounted on one surface of the backing layer 22 with the adhesive
layer 23 interposed therebetween. An acoustic lens 24 is mounted 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 wave transmission / reception surface, and is extended from both ends in the minor
axis direction of the acoustic lens 24 to be provided with protective members 26. A plurality of
electrode terminals 27 are provided corresponding to a plurality of transducers in the region of
the edge in the minor axis direction which is out of the ultrasonic wave transmitting / receiving
surface of the semiconductor substrate 21.
[0027]
In addition, flexible wiring boards 28 connected to external wiring are disposed on both side
surfaces of the backing layer 22 in the short axis direction. The lead terminals 29 provided at the
end of the flexible wiring board 28 are mounted on the surface of the backing layer 22 on which
the semiconductor substrate 21 is mounted, and fixed by the adhesive layer 30. The electrode
terminal 27 and the lead terminal 29 are connected by the bonding wire 31. Protective members
26 extended from both ends of the acoustic lens 24 are provided to cover wire bonding portions
connecting the electrode terminals 27 and the lead terminals 29, and the end portions thereof
are fixed to the inner surface of the casing 33 by the adhesive layer 32. It is done. In place of the
flexible wiring board 28, a hard wiring board may be used.
[0028]
The height from the upper surface of the backing layer 22 of the electrode terminal 27 of the
present embodiment is formed higher than the height from the upper surface of the backing
layer 22 of the lead terminal 29. That is, the thickness of the semiconductor substrate 21 is
formed to be thicker than the thickness of the flexible wiring substrate 28. As a result, as shown
in FIG. 1B, the electrode terminal 27 and the lead terminal 29 are disposed with a height
difference d between leads.
[0029]
In this embodiment, as shown in FIG. 1B, so-called reverse bonding is performed from the lead
terminal 29 side where the height of the backing layer 22 from the mounting surface of the
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semiconductor substrate 21 is low toward the electrode terminal 27 side. By bonding, the height
from the upper surface of the semiconductor substrate 21 of the loop portion 34 formed at the
rising portion of the bonding wire is suppressed. Thus, the wire bonding portion can be
accommodated in the space formed between the protective member 26 and the semiconductor
substrate 21 without bending the protective member 26 outward, so the outer surfaces of both
ends of the acoustic lens 24 and the protective member 26 can be accommodated. Can be
connected smoothly, and adhesion with the subject can be secured. Further, the attenuation of
ultrasonic waves can be suppressed by suppressing the increase in the thickness of the acoustic
lens 24.
[0030]
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 is wire-bonded later. On the side, the wire
side of the bonding wire is welded. That is, when the height of the loop portion formed by wire
bonding from the top surface of the semiconductor substrate 21 is high, the loop portion does
not fit in the space between the inner surface of the protective member 26 and the top surface of
the semiconductor substrate 21. In order to accommodate the loop portion, it is conceivable to
provide the bent portion 35 in the protective member 26 and connect it to the acoustic lens 24,
but since the dent is generated on the contact surface with the subject by the bent portion 35
There is a problem that the adhesion of the above is deteriorated, and the sensitivity and the
frequency characteristic are deteriorated to become an obstacle of the ultrasonic measurement.
Instead of this, it is conceivable to increase the overall thickness of the acoustic lens 24 and
reduce the depression due to the bent portion 35. However, increasing the thickness of the
acoustic lens 24 causes a problem that the attenuation of ultrasonic waves increases. .
[0031]
Here, the procedure of the wire bonding of the present embodiment will be specifically described
with reference to FIG.
[0032]
Step 1: A wire 41 of gold or the like 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.
[0033]
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Step 2: In this state, the clamp 42 is opened, the capillary 43 is lowered toward the electrode
terminal 27, and the ball 44 is brought into contact with the electrode terminal 27 of the target.
In the state, an ultrasonic wave is applied to the ball 44 to form a bump.
[0034]
Step 3: After raising the capillary 43 to a certain height, the capillary 43 is lowered again onto
the bump joint to press the tip of the wire 41.
Also at this time, an ultrasonic wave is applied to the ball 44 in a heated and pressurized state to
bond the wire 41 onto the electrode terminal 27 to form a bump 45.
[0035]
Step 4: The capillary 43 tears off the wire 41 from the joint while leaving the bumps 45.
A high voltage is applied to the tip of the wire 41 secured at the tip of the capillary 43 to blow
sparks to form a ball at the tip of the capillary.
The bumps 45 are formed on the electrode terminals 27 through the above steps.
[0036]
Step 5: With the ball captured at the tip of the wire 41, the clamp 42 opens to lower the capillary
43 to the lead terminal 29. While capturing the ball 44, the capillary 43 applies an ultrasonic
wave to the ball 44 in a heated and pressurized state to weld the tip of the wire 41 to the lead
terminal 29 via the bump 46 on the target.
[0037]
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Step 6: The capillary 43 ascends to a certain height (loop height), stretches the wire 41 to move
onto the bump 45 formed on the electrode terminal 27, and redrops to bump the side of the wire
41 45 Press on. Also at this time, ultrasonic waves are applied to the bumps 45 in a heated and
pressurized state to bond the wires 41 onto the target.
[0038]
Step 7: The capillary 43 tears off 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 blow sparks to
form a ball at the tip of the capillary.
[0039]
By performing reverse bonding in this manner, as shown in FIG. 1B, the rising portion of the wire
is formed on the lead terminal 29 side, so (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 lowered without lowering the height of the rising portion. In the case of reverse bonding,
in order to avoid damage to the electrode terminal 27 due to mechanical impact, it is necessary
to form a bump 45 on the side of the electrode terminal 27 in advance.
[0040]
Second Embodiment FIG. 6 shows a short-axis cross-sectional view of a main part of an ultrasonic
probe using cMUT manufactured by the manufacturing method of another embodiment of the
present invention in FIG. The components having the same configuration as 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 smaller than the height of the lead terminal 29. It
is.
[0041]
In the case of the present embodiment, as shown in FIG. 6A, the electrode terminal 27 and the
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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 by the
progress of the manufacturing technology and the like. In this case, since the loop height is
controlled by the lead terminal 29 whose height from the top surface of the backing layer 22 is
high, bonding is performed from the side of the electrode terminal 27 whose height from the top
surface of the backing layer 22 is low. In this case, since the side surface of the wire is not
directly bonded to the electrode terminal 27, it is possible to omit the step of forming in advance
a bump for alleviating mechanical impact.
[0042]
In the case of the present embodiment, the entire thickness of the acoustic lens 50 is increased,
and the protective member 51 is disposed away from the upper surface of the semiconductor
substrate 21 to secure a space for housing the bonding wire portion. Thereby, the outer surfaces
of the both ends of the acoustic lens 50 and the protective member 51 can be smoothly
connected, and no depression is formed, so that the adhesion with the subject can be secured.
Although the thickness of the acoustic lens 50 is slightly increased, the increase in attenuation of
the ultrasonic wave can be sufficiently suppressed.
[0043]
It is sectional drawing of the principal part of the ultrasound 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 of cMUT. It is sectional drawing of the principal part of the ultrasonic
probe manufactured by the manufacturing method of a comparative example. It is process
drawing explaining the concrete procedure of bonding of FIG. 1 embodiment. It is sectional
drawing of the principal part of the ultrasound probe manufactured by the manufacturing
method of other embodiment of this invention.
Explanation of sign
[0044]
Reference Signs List 21 semiconductor substrate 22 backing layer 23 adhesive layer 24 acoustic
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lens 25 adhesive layer 26 protective member 27 electrode terminal 28 flexible wiring board 29
lead terminal 30 adhesive layer 31 bonding wire 34 loop portion
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