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DESCRIPTION JPH10282073

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DESCRIPTION JPH10282073
[0001]
The present invention relates to a bonding method of metal, ceramic and the like, and a bonding
structure between an ultrasonic transducer, an acoustic lens and a ultrasonic absorbing material
in a sound wave probe manufactured by this bonding method. About.
[0002]
2. Description of the Related Art Electronic parts and optical parts are often composed of a
multilayer structure in which metals and ceramics are joined to one another. As a method of
mutually joining such metals and ceramics, for example, a method using an organic adhesive
such as an epoxy resin is used. However, when using an electrically insulating organic adhesive
such as an epoxy resin to mutually bond metals and ceramics, various problems have occurred
because the epoxy resin adhesive used for bonding changes with time.
[0003]
For example, there are joints of metal, ceramic, etc. in an incident window of EDX (Energy
Dispersion X-ray) provided in a vacuum chamber of an electron microscope (SEM), a viewing
window having a vacuum chamber such as a deposition apparatus, etc. When an organic
adhesive is used for the bonding portion, there is a problem that a gas is generated due to timedependent change, which contaminates the vacuum chamber or causes a vacuum degree defect
due to peeling or the like.
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[0004]
Furthermore, in a semiconductor device or the like, when a chip is bonded to a substrate, solder
bonding is performed using a flux, but with the miniaturization of the device, blow holes in the
solder and the like also become problems.
In addition, the same problem arises when bonding the electrode terminal of an optical
component (for example, an optical-electrical conversion element or the like) to a ceramic
substrate.
[0005]
Further, as a method of joining an ultrasonic transducer, an acoustic lens, and an ultrasonic
absorber for assembling an ultrasonic probe, a method using an organic adhesive such as an
epoxy resin has been mainly adopted. However, when using an electrically insulating organic
adhesive such as an epoxy resin to bond the ultrasonic oscillator to the acoustic lens and the
ultrasonic absorbing material, the epoxy resin adhesive changes with time, so the ultrasonic
probe There is a possibility that the acoustic characteristics of the feeler may be deteriorated
with time, and there is a problem that the reliability of the measurement is impaired.
[0006]
Also, in general, the difference between the acoustic impedances of the epoxy resin-based
organic adhesive and the ultrasonic oscillator and the acoustic lens is extremely large, so the
epoxy resin-based organic adhesive is used to join the ultrasonic oscillator and the acoustic lens.
The organic adhesive then forms an acoustic boundary layer, as a result of which the ultrasound
is reflected. For this reason, there is also a problem that the ultrasonic wave does not sufficiently
propagate from the ultrasonic wave generator to the acoustic lens, and the acoustic wave does
not exhibit good acoustic characteristics.
[0007]
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In order to solve this problem, the inventor of the present invention first joins the ultrasonic
wave oscillator, the ultrasonic wave absorbing material and the acoustic lens by physical
pressure welding without using the electrical insulator, and also the ultrasonic wave oscillator
and the acoustic wave. The inventors of the present invention have invented and filed a patent
application for a method of manufacturing an ultrasonic probe which consists of irradiating an
ion beam or an atom beam to a bonding surface in vacuum and pressing the bonding surface for
bonding the lens. In particular, in the prior invention, quartz is used as the material of the
acoustic lens, and the Au / Cr vapor deposition film is disposed on the bonding surface of the
acoustic lens with the ultrasonic wave oscillator. This invention is disclosed in Japanese Patent
Application Laid-Open No. 8-223695. The ultrasonic probe by the pressure bonding method has
good acoustic characteristics because it does not have an acoustic boundary layer such as an
adhesive between the ultrasonic oscillator and the acoustic lens. In addition, according to this
method, since it is possible to perform strong pressure welding without using an organic
adhesive which may change with time during bonding, an ultrasonic probe which does not
change in performance for a long time is obtained. be able to.
[0008]
In the prior invention disclosed in JP-A-8-223695, an Au / Cr deposited film having a thickness
of 3 μm or more is used for pressure bonding. However, forming an Au / Cr deposited film of
this thickness is expensive and time-consuming, and is not inexpensive from the viewpoint of
manufacturing cost. In addition, since the film thickness is too thick, there is a problem in film
quality. Furthermore, since the film thickness is too thick, there is also a problem that the sound
pressure reciprocation rate is low and the sensitivity is poor.
[0009]
Japanese Patent Application Laid-Open No. 63-194879 discloses a bonding method using an
insert material. According to this method, the melting point is lower than the bonding material
such as metal or ceramic, and a high melting point metal insert material (for example, Sn foil) and
a low melting point metal insert material (for example, In-Sn eutectic alloy) The composite insert
material configured by combining a plurality of metal insert materials having different melting
points is disposed between the materials to be joined, and the low melting point metal insert
material of this composite insert material melts, but the high melting point metal insert material
melts Heat the joints at a temperature that does not
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[0010]
However, in this method, the thickness of the composite insert material to be used becomes
relatively thick, and the production of the composite insert material itself has the disadvantages
of being troublesome.
[0011]
SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a
bonding method which minimizes the adverse effects of bonding and an ultrasonic probe
manufactured by the method.
[0012]
[Means for Solving the Problems] When the objects to be joined of ceramic are joined together,
the Au / Cr deposited film is provided on the joining surface of each joined object, and the
surface of one Au / Cr deposited film is provided. In the case where a Pb deposited film is
provided on the surface and an object to be joined made of ceramic and an object to be joined are
bonded, a Au / Cr deposited film is provided on the bonding surface of the ceramic object to be
joined. Alternatively, in the case where a Pb vapor deposition film is provided on the bonding
surface of the metal bonding object and the metal bonding objects are bonded to each other, the
Pb vapor deposition film is provided on the bonding surface of at least one metal bonding object
to press the both materials It is solved by joining.
[0013]
In this case, it is preferable that the Au / Cr deposited film have a thickness in the range of 0.3 to
0.5 μm, and the Pb deposited film has a thickness in the range of 3 to 8 μm.
[0014]
DETAILED DESCRIPTION OF THE INVENTION As noted above, the present invention is applicable
to bonding between ceramic and metal, ceramic and ceramic, or metal and metal.
As one of the embodiments of the present invention, an ultrasonic probe is specifically described
as an example of bonding between ceramic and metal.
[0015]
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FIG. 1 is a cross-sectional view of an ultrasonic oscillator 1 in an ultrasonic probe according to
the present invention.
An upper electrode 2 is provided on one surface of the ultrasonic wave oscillator 1 and a lower
electrode 3 is provided on the other surface.
The upper electrode 2 can be formed of an Au / Cr deposited film.
The Au / Cr vapor deposition film is formed by providing a Cr vapor deposition film 2a on the
surface side of the ultrasonic oscillator, and providing an Au vapor deposition film 2b on the
surface of the Cr vapor deposition film 2a. Similarly, the Au / Cr vapor deposition film of the
lower electrode 3 is formed by providing a Cr vapor deposition film 3a on the surface side of the
ultrasonic oscillator and providing an Au vapor deposition film 3b on the surface of the Cr vapor
deposition film 3a.
[0016]
Although the method of forming the upper electrode 2 and the lower electrode 3 is not
particularly limited, for example, the upper electrode 2 and the lower electrode 3 can be formed
by a method such as vapor deposition such as sputtering or vacuum evaporation. The thickness
of the upper electrode 2 and the lower electrode 3 is not particularly limited, but in general, it is
preferably in the range of 0.3 μm to 0.5 μm. If it is less than 0.3 μm, the surface roughness of
the ultrasonic oscillator 1 causes problems such as the absence of the upper electrode 2 and the
lower electrode 3, and if it exceeds 0.5 μm, there is no particular problem. It is only
uneconomical.
[0017]
A Pb (lead) film 40 is provided on the surface of the Au deposited film 2 b of the upper electrode
2 and the surface of the Au deposited film 3 b of the lower electrode 3. The Pb film is effective to
flatten the surface roughness of the Au film of the Au / Cr deposited film derived from the
bonding surface of the object to be bonded. In addition, lead has an acoustic impedance close to
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that of an ultrasonic wave generator, and thus is effective in improving the acoustic
characteristics. The Pb film 40 can be formed, for example, by a method such as sputtering or
vapor deposition such as vacuum evaporation. Such deposition methods are well known to those
skilled in the art. The film thickness of the Pb vapor deposition film 40 is not particularly limited
due to the roughness of the vapor deposition surface and the like, but in general, the film
thickness is preferably 3 μm or more. If it is less than 3 μm, it is not only insufficient to fill the
surface roughness, but also there is a possibility that a sufficient bonding effect can not be
obtained. On the other hand, although the upper limit of the film thickness of the Pb vapor
deposition film 40 depends on the thickness of the ultrasonic wave oscillator used, it is
preferable to be about 1/10 of the thickness of the ultrasonic wave oscillator 1. For example, in
the case of 25 MHz, the upper limit is about 8 μm. It is not preferable to use a Pb vapor
deposition film 40 thicker than this because problems such as interface reflection waves occur.
In general, the film thickness of the Pb vapor deposition film is preferably in the range of 3 to 5
μm.
[0018]
As a piezoelectric element constituting the ultrasonic oscillator 1, PZT (Pb (Zr, Ti) 03 series
ceramics) or PbTiO3 (lead titanate) can be used. Such materials are well known to those skilled in
the art.
[0019]
FIG. 2 is a cross-sectional view of an acoustic lens 5 in an ultrasound probe according to the
present invention. An Au / Cr vapor deposition film 4 is provided on the side of the acoustic lens
5 in contact with the lower electrode 3. The Au / Cr deposited film 4 is chemically stable because
Au is exposed on the surface. The Au / Cr vapor deposition film 4 can be formed by vapor
deposition such as sputtering or vacuum evaporation. Such film formation methods are known to
those skilled in the art. First, a Cr film is formed, and an Au film is formed thereon. The Cr film
promotes bonding between the lens and the metal. The Au / Cr deposited film 4 preferably has a
film thickness equivalent to that of the lower electrode 3 and is generally in the range of 0.3 μm
to 0.5 μm. If it is less than 0.3 μm, there may be a place where no film exists due to surface
roughness. On the other hand, if it exceeds 0.5 μm, there is no particular problem but it is only
uneconomical.
[0020]
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The electrode connecting lead wire 6 is connected to one end of the Au / Cr vapor deposition film
4 of the acoustic lens 5. This connection can be performed, for example, by using a silver paste
or a room temperature curable conductive resin.
[0021]
The acoustic lens 5 is formed of quartz. Quartz is chemically very stable and excellent in
corrosion resistance. Thus, the corrosion problems that occur with metallic acoustic lenses do not
occur at all.
[0022]
FIG. 3 is a schematic view illustrating one step of the method of manufacturing an ultrasonic
probe according to the present invention. In FIG. 3, reference numeral 1 is an ultrasonic
oscillator made of a piezoelectric element, 5 is an acoustic lens made of quartz, 13a and 13b are
beam sources for generating an atom beam, and 14a and 14b are pressing jigs. These are
disposed in the vacuum processing chamber 20. At an appropriate position of the vacuum
processing chamber 20, a duct 22 connected to an evacuation means (not shown) is provided.
[0023]
By irradiating an ion beam or an atom beam to the bonding surface of the ultrasonic oscillator
and the acoustic lens in a vacuum, a contamination layer such as an oxide film or water adhering
to the bonding surface is removed. As a result, the bonding surface becomes a clean and active
surface, and if it is pressurized and brought into close contact, a very good pressure bonding can
be formed. The term "pressure welding" as used throughout this specification means cleaning the
surfaces to be joined and bringing them into contact at high pressure to create diffusion and
bonding on the surfaces.
[0024]
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First, the ultrasonic oscillator 1 and the acoustic lens 5 are mounted on the pressure jigs 14 a
and 14 b respectively, and the atmosphere in the vacuum processing chamber 20 is evacuated
from the duct 22. Next, an atom beam of argon is generated from the beam sources 13a and 13b,
and the same beam is irradiated to the bonding surface of the ultrasonic wave oscillator 1 and
the acoustic lens 5, respectively, and the contamination layer present on these bonding surfaces
(for example, natural oxidation Remove substances or physically adsorbed water). Since the
bonding surface becomes a clean and active surface by this operation, the bonding surfaces of
both members are closely attached using the pressure jigs 14a and 14b, and by continuing
pressing for a predetermined time, diffusion is caused at the bonding surfaces of both members.
As a result, the ultrasonic oscillator 1 and the acoustic lens 2 can be pressure-bonded. The
pressing jig is for performing pressure welding between the respective members, and can be
constituted by a hydraulic cylinder or the like.
[0025]
When the pressure welding of the ultrasonic oscillator 1 and the acoustic lens 5 is completed, the
ultrasonic oscillator 1 and the pressing jig 14a are separated. Then, as shown in FIG. 4, the
ultrasonic absorbing material 7 is attached to the pressing jig 14 a. While maintaining the
vacuum pressure at the time of pressure welding of the ultrasonic oscillator 1, the beam source
13a and the joint surface of the other joint surface of the ultrasonic oscillator 1 not jointed to the
acoustic lens 5 and the ultrasonic absorption material 7 The atom beam of argon generated from
13b is irradiated to remove the contamination layer (eg, native oxide or physisorbed water, etc.)
present on these bonding surfaces. Since the bonding surface becomes a clean and active surface
by this operation, the bonding surfaces of both members are closely attached using the pressure
jigs 14a and 14b, and by continuing pressing for a predetermined time, diffusion is caused at the
bonding surfaces of both members. As a result, the ultrasonic wave oscillator 1 and the ultrasonic
wave absorbing material 7 can be press-bonded to each other. Thus, the acoustic lens 5 and the
ultrasonic absorbing material 7 are integrally press-bonded integrally with the ultrasonic
oscillator 1 interposed therebetween without using the conventional epoxy resin-based organic
adhesive. it can.
[0026]
In the present invention, an ion beam or an atom beam is used as a means for cleaning the
bonding surfaces of the ultrasonic wave generator 1, the acoustic lens 5 and the ultrasonic wave
absorbing material 7. The reason is that the surface active under vacuum conditions. In the same
chamber while maintaining the state. The surface cleaning means may be plasma, organic solvent
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or ultrapure water, but it is most preferable to use ion beam or atom beam to carry out surface
activation and bonding in the same chamber. For example, a beam of argon or the like can be
suitably used as the ion beam or the atom beam.
[0027]
The vacuum processing chamber 20 is used to efficiently perform the ion beam or atom beam
cleaning process. The vacuum pressure suitable for this purpose is not particularly limited, but
generally, it is preferably about 10 −6 Torr. If the vacuum pressure in the vacuum processing
chamber 20 is lower than this, recontamination of the bonding surface can not be prevented, and
if it is higher than this, the effect of the cleaning processing itself can be further enhanced. It is
only uneconomical because it can not be done.
[0028]
As the beam sources 13a and 13b, for example, an apparatus known to those skilled in the art
such as a beam gun commercially available from ATOMTECH can be used. The power of the ion
beam or atom beam required for the cleaning process of the bonding surface is not particularly
limited. It may be an output that can obtain a degree of cleanliness sufficient to establish
pressure welding between members. As a general index, it is preferable that the output of the ion
beam or atom beam be about 1 keV, 25 mA. If the output is less than 1 keV, 25 mA, the junction
surface may be poorly cleaned. On the other hand, when the output greatly exceeds 1 keV and
25 mA, it is not preferable because a disadvantage such as formation of a large void or the like
occurs in the junction surface. The beam irradiation time is not particularly limited as long as it
has a sufficient length for cleaning the bonding surface. The beam power and the beam
irradiation time have an inverse relationship to obtain the desired degree of interface cleaning.
For example, if a high power beam is used, the irradiation time will be short, while if a low power
beam is used, the irradiation time will be long. As a mere general index, the irradiation time is
about 600 seconds when using a beam with an output of about 1 keV and 25 mA.
[0029]
The pressing pressure and pressing time of each member by the pressing jigs 14a and 14b may
be any size and length as long as they are necessary and sufficient to form the pressure welding
between the members, and is not particularly limited. Generally, when a pressure of 12.5 MPa or
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more is used, the pressure time is about 30 seconds. If the pressure is too high, the quartz
acoustic lens 5 may be damaged. Generally, the upper limit of the applied pressure is determined
by the object to be bonded.
[0030]
In the present embodiment, although the members to be joined, ie, the piezoelectric element 1,
the acoustic lens 5 and the ultrasonic wave absorbing member 7 are all joined at room
temperature, the temperature of the joining surface is obtained by heating the members to be
joined using a heater or the like. When bonding is performed after raising to a range, bonding
strength further increases. Moreover, an ultrasonic welder etc. can be used as needed.
[0031]
Although bonding is performed in vacuum in this embodiment, bonding may be performed after
the atmosphere is filled with an inert gas such as argon or nitrogen after irradiation with an atom
beam. The formation of an inert gas atmosphere can prevent re-oxidation and re-contamination
of components.
[0032]
Next, an assembled structure of an ultrasonic probe manufactured using the present invention
will be described with reference to FIG. In FIG. 5, reference numeral 1 is an ultrasonic oscillator,
5 is an acoustic lens, 6 is a lead for connecting the lower electrode, 7 is an ultrasonic absorbing
material, 8 is a lead for connecting the upper electrode, 9 is a filler, and 10 is a protection Case
and 11 show a terminal, respectively. The basic components themselves are roughly the same as
ultrasound probes using conventional epoxy resin based adhesives. For example, as described
above, the ultrasonic wave generator 1 can use a piezoelectric element and PT (lead titanate)
which are known to those skilled in the art. Quartz is used as the acoustic lens 5. Lead, tin or the
like can be used as the ultrasonic absorbing material 7. The ultrasonic absorber performs the
function of suppressing ultrasonic vibration. The lower electrode lead wire 6 is connected to the
inner wall surface of the protective case 10. The upper electrode connecting lead wire 8 is
connected to the upper surface of the ultrasonic absorbing material 7. You may connect to the
lower surface of an ultrasonic absorption material. The lead wire 8 is insulated by the insulating
material 12 and taken out of the protective case 10. For example, epoxy resin can be used as the
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filler 9. The protective case 10 is made of metal and doubles as a conductor of the acoustic lens
side electrode.
[0033]
Next, the operation of the ultrasonic probe of the present invention will be described. When a
pulse voltage generator (not shown) applies a pulse voltage to the ultrasonic oscillator 1 via the
terminal 11, an ultrasonic pulse is generated. The generated ultrasonic waves are incident on a
not-shown object via the acoustic lens 5 to perform ultrasonic flaw detection.
[0034]
Also, assuming that the acoustic impedances of the three substances joined in a plane are Z1, Z2,
and Z3, the sound pressure reciprocation pass rate of these is expressed by the following
equation. Tl ′ = 4 (Z1 / Z3) / [{(Z1 / Z3) +1} 2 cos2θ + {(Z1 / Z2) + (Z2 / Z3)} 2 sin 2θ] where
θ = (2π / λ) · l, where Where l is the film thickness of Z2.
[0035]
In Table 1, Z1 is the acoustic impedance (x106 g / cm 2 · s) of a piezoelectric element (PbTiO 3 based ceramic) representative of materials for ultrasonic oscillators, and Z 3 is a quartz used as a
material for acoustic lenses It is an acoustic impedance, Z2 is an acoustic impedance of the vapor
deposition film by the side of a piezoelectric element, (lambda) is a wavelength in the said vapor
deposition film. The wavelength λ is a value at 25 MHz. In both the conventional example and
the present invention, l was 3 μm.
[0036]
When the numerical values shown in Table 1 are substituted into the above equation, the sound
pressure reciprocation rate of the conventional example is 0.797, whereas the sound pressure
reciprocation rate of the present invention is 1.349. Therefore, according to the present
invention, the sound pressure reciprocation rate is improved by about 70%.
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[0037]
FIG. 6 is a schematic cross-sectional view showing the case where the objects to be bonded are
ceramics. The bonding surfaces of the ceramics 30a and 30b are metallized with a deposited Au /
Cr film. A Pb film 40 is vapor deposited on the surface of either the Au film of 2b or 3b.
Optionally, a Pb film 40 can be deposited on the surface of both Au films. The Pb film is used to
fill the surface roughness derived from the ceramic surface. The film thickness of the Au / Cr
vapor deposition film to be used is preferably in the range of 0.3 to 0.5 μm. Similarly, the film
thickness of the Pb film is in the range of 3 to 8 μm, preferably 3 to 5 μm.
[0038]
FIG. 7 is a schematic sectional view showing the case where the objects to be joined are metals. A
Pb film 40 is deposited on the bonding surface of either of the metals 32a and 32b. If desired,
the Pb film 40 can be deposited on both metal bonding surfaces. In the case of metals, the Pb
film not only functions to bury the surface roughness of the metal but also functions as a
bonding material itself. The film thickness of the Pb film is in the range of 3 to 8 μm, preferably
3 to 5 μm. The advantage of using a Pb film as a bonding material for pressure bonding between
metals is that Pb films are very inexpensive compared to Au / Cr deposited films, and
furthermore, they have a short deposition time per hour, so they are short. It is possible to form a
film in time, and as a result, it contributes to the improvement of the throughput. In the case of
both ceramic-to-ceramic bonding and metal-to-metal bonding, the same surface cleaning
treatment as the ceramic-to-metal bonding can be applied. The pressure welding process itself is
also performed according to roughly the same method.
[0039]
As described above, according to the present invention, it is possible to obtain a pressure welding
method in which the adverse effect of bonding is minimized. In particular, the ultrasonic probe
manufactured by the pressure bonding method of the present invention exhibits excellent
acoustic characteristics because it does not have an acoustic boundary layer such as an adhesive
between the ultrasonic oscillator and the acoustic lens. Further, according to the present
invention, since it is possible to perform strong pressure bonding without using an organic
adhesive which may change with time during bonding, an ultrasonic probe whose performance
does not change for a long time is provided. can do.
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[0040]
Brief description of the drawings
[0041]
1 is a schematic cross-sectional view of an example of an ultrasonic oscillator in the ultrasonic
probe of the present invention.
[0042]
2 is a schematic cross-sectional view of an example of an acoustic lens in the ultrasonic probe of
the present invention.
[0043]
3 is a schematic view illustrating one step of the method of manufacturing an ultrasonic probe of
the present invention.
[0044]
4 is a schematic view illustrating another step of the method of manufacturing an ultrasonic
probe of the present invention.
[0045]
5 is a schematic cross-sectional view of an example of the assembly structure of the ultrasonic
probe of the present invention.
[0046]
6 is a schematic cross-sectional view of the ceramics joined by the pressure welding method of
the present invention.
[0047]
7 is a schematic sectional view of metals joined by the pressure welding method of the present
invention.
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[0048]
Explanation of sign
[0049]
DESCRIPTION OF SYMBOLS 1 ultrasonic oscillator 2 upper electrode 2a Cr vapor deposition film
2b Au vapor deposition film 3 lower electrode 3a Cr vapor deposition film 3 b Au vapor
deposition film 4 Au / Cr vapor deposition film 5 acoustic lens 6 lead wire for lower electrode
connection 7 ultrasonic wave absorbing material 8 upper Electrode connection lead wire 9 Filler
10 Protective case 13a, 13b Beam source 14a, 14b Pressure jig 20 Vacuum treatment chamber
22 Exhaust duct 30a, 30b Ceramic member 32a, 32b Metal member 40 Pb vapor deposition film
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