JP2011244226

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DESCRIPTION JP2011244226
PROBLEM TO BE SOLVED: To detect a defective element from a plurality of elements arranged in
an array in a package in a manufacturing process of a transducer. A method of manufacturing a
transducer in which a plurality of capacitive type conversion elements each having a stationary
electrode and a vibrating electrode are disposed and connected in parallel with each other,
wherein a transducer chip having a plurality of the conversion elements disposed therein is
packaged. After the step of die bonding inward, before the step of closing the lid of the package,
the conversion element in a state where a predetermined voltage determined in advance is
applied to the conversion element, and the predetermined voltage is applied to the conversion
element The planar view image is taken, and a reference pattern image prepared in advance as a
planar view image of the conversion element when the predetermined voltage is applied to the
non-defective conversion element is compared with the planar view image, The defective
conversion element is detected based on the comparison result of the reference pattern image
and the planar view image. [Selected figure] Figure 1
Method of manufacturing a transducer
[0001]
The present invention relates to a method of manufacturing a transducer, and more particularly
to a method of manufacturing a transducer in which capacitive MEMS (Micro Electro Mechanical
Systems) conversion elements are arranged in an array and connected in parallel.
[0002]
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Patent Document 1 describes that voice can be detected with high sensitivity in one continuous
frequency region by providing a plurality of condenser microphones having different resonance
frequencies.
Patent Document 2 describes that in a pressure sensor unit in which a plurality of capacitive
pressure sensors are connected in parallel, the ineffective area is reduced to reduce parasitic
capacitance.
[0003]
JP, 2005-110204, A JP, 2001-235382, A
[0004]
In a transducer provided with a plurality of transducer elements in an array, if a defective
product is mixed in the transducer elements, the performance as a transducer becomes unstable.
The present invention has been made in view of the above problems, and in the process of
manufacturing a transducer, a defective element is detected after die bonding of a transducer die
chip in which a plurality of conversion elements are arranged in an array shape into a package.
An object of the present invention is to improve the yield of transducers by electrically cutting
elements.
[0005]
(1) The manufacturing method of a transducer (a transducer in which a plurality of capacitive
type conversion elements having a stationary electrode and a vibrating electrode are arranged
and connected in parallel with each other) for achieving the above object is a plurality of the
conversion elements A step of applying a predetermined voltage determined in advance to the
conversion element before the step of closing the lid of the package after the step of die-bonding
the arrayed transducer chips into the package; An imaging step of capturing a planar view image
of the conversion element in a state where a voltage is applied to the conversion element, and
preparing in advance a planar view image of the conversion element when the predetermined
voltage is applied to the conversion element that is not defective. Analysis step of comparing the
determined reference pattern image with the planar view image; the reference pattern image and
the planar view image Including a defective element detecting process of detecting the
transducer failure based on the comparison result.
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[0006]
According to the present invention, performance inspection can be performed on individual
conversion elements after die bonding.
When a predetermined voltage determined in advance is used as the conversion element, the
vibrating electrode is drawn to the stationary electrode, and if the conversion element is nondefective, any conversion element is similarly deformed. When the vibrating electrode is
deformed, the pattern or color tone in plan view of the conversion element is changed as
compared to when it is not deformed. An image of a planar view of the conversion element when
a predetermined voltage (a voltage having the same value as the voltage applied at the time of
inspection) is applied to the non-defective conversion element is prepared in advance as a
reference pattern image. And the planar view image image ¦ photographed in the state which
applied the predetermined voltage to the conversion element of the transducer of test object is
compared with the reference ¦ standard pattern image prepared beforehand. When the similarity
between the planar view image and the reference pattern image is lower than a predetermined
reference, the conversion element corresponding to the planar view image lower than the
reference can be detected as a defective product. The algorithm for determining the degree of
similarity between images may employ a known algorithm.
[0007]
In the predetermined voltage application step, a voltage value determined in advance as a voltage
value to which the vibrating electrode is deformed is applied, and the voltage value is not raised
stepwise to search for the pull-in voltage. The transducer of the present invention may be any
transducer provided with a plurality of capacitive type conversion elements, and, for example, a
pressure sensor, a microphone, etc. are assumed.
[0008]
(2) The method of manufacturing a transducer for achieving the above object may include a
wiring opening step of opening an independent wiring of the conversion element detected as a
defect among the plurality of conversion elements connected in parallel.
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[0009]
Here, in a circuit in which a plurality of capacitors (having a capacitor formed by a vibrating
electrode and a stationary electrode) connected in parallel, a wire directly connected to a power
supply is called a main wire, and is connected to the main wire at an intersection point The
wiring connecting the main wiring and the individual capacitors is called independent wiring.
Opening the main wiring can affect other capacitors, but even if the independent wiring is open,
it has no effect other than the capacitor directly connected to the independent wiring. In such a
configuration, by opening the independent wiring directly connected to the defective conversion
element, the non-defective conversion elements connected in parallel are left as they are, and
only the defective conversion element is electrically disconnected from the parallel connection
circuit. be able to. By electrically disconnecting defective conversion elements from the parallel
connection circuit, the number of conversion elements connected in parallel is reduced.
Therefore, the performance of a transducer with a smaller number of transducing elements is
reduced as compared to a transducer having no transducing elements at all. However, for
example, the transducers may be graded according to the proportion of defective transducer
elements that can be counted up to the total number of the plurality of transducer elements
arranged in one transducer, and the price may be set according to the grade for sale.
[0010]
(3) In the method of manufacturing a transducer for achieving the above object, the
predetermined voltage may be less than a pull-in voltage. By applying a voltage higher than the
pull-in voltage, the possibility of stiction between the vibrating electrode and the stationary
electrode is increased. Therefore, by applying a predetermined voltage less than the pull-in
voltage to identify a defective conversion element, inspection can be performed in a state in
which stiction hardly occurs.
[0011]
(1A) is a top view which shows the transducer chip concerning embodiment of this invention,
(1B) is sectional drawing of a conversion element. FIG. 2 is a top view showing a transducer chip
and an LSI chip housed in a package. (3A) is a circuit diagram according to an embodiment of the
present invention, (3B) is a circuit diagram to be compared. The flowchart which shows the
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manufacturing process concerning embodiment of this invention. (5A) is a cross-sectional view
showing a non-defective conversion element at the time of inspection according to the
embodiment of the present invention, (5B) is a plan view image of (5A), (5C) and (5D) are not at
the inspection Sectional drawing which shows the non-defective conversion element.
[0012]
Hereinafter, embodiments of the present invention will be described in the following order with
reference to the attached drawings. The same reference numerals are given to corresponding
components in the respective drawings, and the overlapping description will be omitted.
[0013]
1. First embodiment 1-1. Configuration FIG. 1 is a diagram showing a transducer according to
a first embodiment. The transducer of the present embodiment has a function as a microphone
that converts acoustic vibration into an electrical signal. As shown in FIG. 2, the transducer chip
1 is housed in a box-shaped package together with the LSI chip 2 and is fixed to the bottom of
the box-shaped package body 3. The package comprises a box-shaped package body 3 and a lid
not shown. The lid is formed with an acoustic hole connecting the inner space of the package and
the outer space. FIG. 2 shows a state in which the lid of the package is not attached. As shown in
FIG. 1, nine transducer elements M1 to M9 are arranged in the transducer chip 1 of the present
embodiment. The configuration of the conversion elements M1 to M9 is a laminated structure
including a stationary electrode P and a vibrating electrode D. Each transducer element is
simultaneously formed through the MEMS process so as to be integrated with the transducer
chip 1. A charge pump circuit, a C / V conversion circuit, a gain circuit and the like are formed in
the LSI chip 2, and the LSI chip 2 controls the transducer chip 1. In FIG. 2, the conversion
elements and wires of the transducer chip 1 and the various circuits of the LSI chip 2 are not
shown.
[0014]
FIG. 1B is a schematic cross-sectional view of line 1B-1B of FIG. 1A. That is, the figure shows the
cross section of one conversion element. The stationary electrode P and the vibrating electrode D
are opposed via the spacer S of the insulator. A plurality of through holes h are formed in the
stationary electrode P. The vibrating electrode D is supported by the wall W. When a sound wave
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propagates from the external space of the package to the internal space of the package through
the acoustic hole, the vibrating electrode D is vibrated through the through hole h. The
capacitance between the vibrating electrode D and the stationary electrode P changes due to the
vibration of the vibrating electrode D, and the potential difference between the vibrating
electrode D and the stationary electrode P changes.
[0015]
Wiring is formed on the transducer chip 1. The stationary electrode P of each conversion
element Mn (n is 1 to 9) is directly connected to the stationary electrode side main wiring 50 by
the independent wiring 500. The vibrating electrode D is directly connected to the vibrating
electrode side main wire 51 by the independent wire 510. That is, as shown in FIG. 3A,
capacitors Cn configured by the vibrating electrode D and the stationary electrode P of each
conversion element Mn are connected in parallel. In addition, although there exists a method of
connecting one electrode in series as shown to FIG. 3B in parallel connection of a capacitor ¦
condenser, the direction of FIG. 3A is employ ¦ adopted in embodiment of this invention.
[0016]
The voltage application electrode pad 51 a connected to the vibration electrode side main wiring
51 is wire-bonded to the voltage application electrode pad 61 a formed on the LSI chip 2.
Further, the signal extraction electrode pad 50 a connected to the stationary electrode side main
wiring 50 is connected by wire bonding to the signal extraction electrode pad 60 a formed on the
LSI chip 2.
[0017]
A fine microphone can be manufactured by using MEMS technology. If the microphone is made
smaller, the resonance frequency can be raised as a characteristic of the microphone. Thus, it is
also possible to produce microphones in the ultrasound range. By using a plurality of conversion
elements for converting sound into an electric signal, the S / N ratio as a microphone can be
improved.
[0018]
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1−2. Manufacturing Method FIG. 4 is a flowchart showing the manufacturing process of the
transducer described with reference to FIGS. 1 and 2. Steps S1 to S3 are steps for forming the
transducer chip 1 including the conversion element, and steps S4 to S6 are steps for forming the
LSI chip 2. Step S7 and subsequent steps are steps subsequent to their assembly. Steps S1 to S3
and steps S4 to S6 may be completed by the start of step S7.
[0019]
In the substrate process S1, a plurality of transducer chips 1 including a structure to be the
conversion element Mn described above (see FIG. 1B) are formed on the wafer. The wires 50, 51,
500, 510 and the electrode pads 50a, 51a are also formed in the substrate process S1. In the
inspection step S2, an open / short inspection, a pull-in voltage inspection, and the like are
performed on the plurality of transducer chips 1 formed on the wafer. In the dicing step S3, laser
dicing is performed to form the above-described transducer chip 1.
[0020]
In the substrate process S4, a plurality of circuits to be the above-mentioned LSI chip 2 are
formed on the wafer later. In the inspection step S5, open / short inspection of circuits formed on
a plurality of wafers and inspection of functional characteristics of circuits are performed. In the
dicing step S6, each LSI chip is separated by blade dicing to form the LSI chip 2.
[0021]
In the assembly process (first half) S7, the transducer chip 1 and the LSI chip 2 formed in the
processes S4 to S6 are die-bonded to the bottom surface of the package body 3.
[0022]
Since the conversion element Mn has a fine mechanical structure, it may be broken in the middle
of any of the above-described steps.
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Defective portions generated in the substrate process S1 can be detected and eliminated in an
inspection process S2 after the substrate process S1. In order to be able to detect the conversion
element Mn that has been broken and becomes defective in the fragmentation step S3 and the
assembly step S7, inspection is also performed after the attachment of the transducer chip 1
(assembly step S7). If the inspection is performed after closing the lid of the package, it is only
possible to detect a defect, and it is impossible to electrically separate the defective portion as
described later. For this purpose, after the die bonding of the transducer chip 1, the conversion
element is inspected again before the lid of the package is closed (array inspection step S8).
[0023]
In the array inspection step S8, a predetermined voltage determined in advance is applied
between the electrode pad 50a and the electrode pad 51a to the transducer chip 1 in which the
conversion elements Mn are arranged in an array and connected in parallel. As a result of
applying a predetermined voltage to the electrode pads 50a and 51a, a potential difference
occurs between the vibrating electrode D and the stationary electrode P of the conversion
elements M1 to M9, and the vibrating electrode D bends to the stationary electrode P side. Since
the outer peripheral portion of the vibrating electrode D is fixed, the normal conversion element
stops in a state where the center of the vibrating electrode D is closest to the stationary electrode
P (see FIG. 5A). When the center of the vibrating electrode D is deformed so as to be closest to
the stationary electrode P, the conversion element in plan view is in a state where the color
density changes concentrically (see FIG. 5B). In the case of a defective product, for example, as
shown in FIG. 5C, even if the same predetermined voltage is applied, the distance between the
stationary electrode P and the vibrating electrode D at the closest position is different from that
of the non-defective product. In some cases, concentric color changes may differ from nondefective products. Alternatively, as shown in FIG. 5D, since the position at which the stationary
electrode P and the vibrating electrode D are closest to each other is shifted from the center
position of the vibrating electrode D, the shape of concentric circles in the image in plan view is
distorted There is also a case that has become. The test can be performed in a situation where
stiction of the vibrating electrode D and the stationary electrode P is hard to occur by applying a
voltage less than the pull-in voltage as the predetermined voltage. Further, the planar view means
a case where the plane is viewed from a direction perpendicular to a plane parallel to the bottom
surface of the package body 3, the main surface of the transducer chip die 10, and the main
surface of the stationary electrode P.
[0024]
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A planar view image of the conversion element Mn disposed on the transducer chip 1 is
photographed in a state where a predetermined voltage is applied. A reference pattern image
showing a planar view image of the conversion element when a predetermined voltage is applied
to the non-defective conversion element is prepared in advance, and the reference pattern image
is compared with the planar view images of the individual conversion elements Mn captured. Do.
For example, the similarity with the reference pattern image is calculated by image processing
using a known algorithm, and a conversion element corresponding to a planar view image whose
similarity is lower than a predetermined reference is determined to be defective. As the index for
determining the degree of similarity, various feature amounts such as color, texture, and shape of
figure can be used. For example, the degree of change in concentric color change (the distance
between figures (concentric circles connecting pixels of the same color, the distance from the
center of the concentric circles)), the center of the concentric circles and the centers of the
stationary electrode P and the vibrating electrode D Alternatively, the positional deviation
between the pixels, the shape of a figure connecting pixels of the same color (whether circular or
not, etc.) may be used.
[0025]
As described above, defective conversion elements are detected. If there is a failure in the
plurality of capacitors connected in parallel, the performance as a microphone becomes unstable.
[0026]
Therefore, in the present embodiment, the independent wiring of the defective conversion
element is released so as not to affect the normal conversion element. Both the independent
wiring 500 and the independent wiring 510 directly connected to the defective conversion
element Mn are cut by a laser or the like. Since each conversion element is not connected in
parallel as shown in FIG. 3B, it is only necessary to cut the independent wires 500 and 510
directly connected to the electrodes of the defective capacitors. As shown in FIG. 3B, when one of
the electrodes of the capacitor is connected in series to form a parallel connection circuit of
capacitors, if the wire connected to the defective capacitor is cut, the voltage is applied to the
non-defective capacitor as well. It may not be applied. In the present embodiment, as shown in
FIG. 3A, since they are connected in parallel, even if the number of defective conversion elements
is n, (9-n) normal conversion elements slightly reduce the function as a transducer. Can be
realized.
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[0027]
In the assembly step (second half) S9, after the transducer chip 1, the LSI chip 2, and the package
body 3 are wire-bonded, the lid of the package is closed. In the completion inspection step S10,
an acoustic characteristic inspection is performed. Further, based on the result of the array
inspection in step S8 and the result of the acoustic characteristic inspection in step S10, the
grade of the transducer is classified according to the performance. By electrically disconnecting
defective conversion elements from the parallel connection circuit, the number of conversion
elements connected in parallel is reduced. Compared to a transducer without any bad transducer
element, the performance of the transducer with less number of transducer elements functioning
as a microphone due to the defect being electrically disconnected from the circuit is degraded.
However, for example, the transducer can be graded according to the proportion of defective
transducer elements which can be determined by the total number of transducer elements
arranged in one transducer, and can be priced according to grade and sold (for example, Grades
such as high grade products, high grade products, medium grade products, popular products,
rejected products etc. Thereafter, through the packing process S11, the transducers are shipped
by grade.
[0028]
2. Other Embodiments The technical scope of the present invention is not limited to the abovedescribed embodiment, and it goes without saying that various modifications can be made
without departing from the scope of the present invention. In the above embodiment, it has been
described that the array inspection is performed before the wire bonding with the LSI chip 2
after the die bonding of the transducer chip 1. However, for example, an electrode pad dedicated
to the array inspection process may be provided in addition to the electrode pads 50a and 51a
connected to the LSI chip, and the array inspection may be performed after wire bonding with
the LSI chip 2.
[0029]
1: Transducer chip 2: LSI chip 3: Package main body 50: Still electrode side main wiring 50a:
Signal extraction electrode pad 51: Vibrating electrode side main wiring 51a: Voltage application
electrode pad 60a: Signal Takeout electrode pad 61a: voltage application electrode pad 500:
independent wiring 510: independent wiring Cn: capacitor D: vibrating electrode h: through hole
M1 to M9 (Mn): conversion element P: stationary Electrode, S: Spacer, W: Wall.
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