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The present invention relates to a method for bonding a piezoelectric element plate to a
diaphragm of a piezoelectric acoustic transducer. Prior Art FIG. 3 shows the structure of a
piezoelectric acoustic transducer. This piezoelectric acoustic transducer has a configuration in
which a vibrating plate 3 is interposed between a front cover 1 and a substrate 2 and a
piezoelectric element plate 4 is joined to the back surface of the vibrating plate 3. The substrate
2 is made of an electrically insulating material, and the diaphragm 3 is made of a metal such as
brass. The lead terminals 5 and 6 of two trees are planted on the substrate 2, and these lead
terminals 56 and 6 are formed on the substrate 2 via a printed wiring path or the like (not
shown). It is connected to one side and the other side respectively. When an electric signal of a
predetermined frequency is input between the lead terminals 5.6, the piezoelectric element plate
4 resonates, and as a result, the diaphragm 3 vibrates to produce a sound wave. (Problems to be
Solved by the Invention) In order to bond the piezoelectric element plate 4 to the vibration plate
3, conventionally, a liquid or paste-like adhesive is previously attached to the central portion of
the bonding surface of the diaphragm 3 The piezoelectric element plate 4 is brought into
restraining contact with the bonding surface. The thickness of the adhesive layer formed between
the diaphragm 3 and the piezoelectric element plate 4 affects the resonant frequency of the
piezoelectric element plate 4. The thickness depends on the coating layer of the adhesive, so that
if this coating amount is not properly managed, a product having the intended performance can
not be obtained. However, it is practically difficult to precisely control the amount of application
of the liquid or paste adhesive, and this has conventionally caused the disadvantage that the
product performance varies and the yield is lowered. SUMMARY OF THE INVENTION An object
of the present invention is to provide a method of bonding piezoelectric element plates in which
the bonding of the piezoelectric element plates can be favorably performed without variation in
the bonding result. (Structure of the Invention) (Means for Solving the Problems) In the present
invention, a film-like adhesive having a heat melting property is interposed between a diaphragm
constituting a piezoelectric acoustic transducer and a piezoelectric element plate, The
piezoelectric element plate is bonded to the vibrating plate by heating and melting the film-like
adhesive. (Operation) According to the present invention, the piezoelectric element plate is joined
to the diaphragm by the thermally melted film adhesive. The present invention will be described
in detail below with reference to the drawings. FIG. 1 shows an embodiment of a method of
bonding piezoelectric element plates according to the present invention. In the figure, the same
components as those shown in FIG. 3 are assigned the same reference numerals.
As shown in the figure, in this embodiment, first, the film-like adhesive 7 having a diameter
slightly larger than the diameter of the piezoelectric element 4 is disposed on the diaphragm 3,
and then the piezoelectric element is provided on the film-like adhesive 7. The board 4 is placed.
The film-like adhesive 7 is formed of a thin film of synthetic resin having heat melting property
and having excellent adhesion when melted. In this embodiment, a polyamide-based resin is used
as the material of the film-like adhesive, but it is of course possible to apply other resins such as
a varnish-based resin. After the film adhesive 7 and the piezoelectric element plate 4 are
disposed on the diaphragm 3 as described above, a pressing force is applied from above the
piezoelectric element plate 4 and heating is simultaneously performed until the film adhesive 7 is
melted. Be done. That is, for example, when the melting point of the film adhesive 7 is 80 ° C.,
about 281 / CI! Since the piezoelectric element plate 4 is pressed with a certain pressure, heat of
about 120 ° C. is applied to the film-like adhesive 7 for a predetermined time (for example,
several seconds). The adhesive 7 melted by the heating forms a uniform and very thin adhesive
layer at the time of heat-hardening solidification, and the piezoelectric element plate 4 is strongly
joined to the diaphragm 3 through the adhesive layer. The adhesive layer always has a constant
thickness by appropriately setting the pressure applied to the piezoelectric element plate 4 and
the heating temperature and heating time of the adhesive 7. The pressing of the piezoelectric
element plate 4 and the heating of the film-like adhesive 7 can be easily carried out using an
apparatus as shown in FIG. The apparatus comprises a table 8 and a lift 9 positioned directly
above the table 8. The elevating body 9 has an upper portion connected to an elevating
mechanism such as a fluid pressure cylinder, and a heater 10 for heating the lower surface to a
predetermined temperature is disposed on the lower surface side. The diaphragm 3 on which the
film-like adhesive 7 and the piezoelectric element plate 4 are previously mounted is placed on
the table 8 by a manipulator or the like (not shown). Thereafter, the elevating body 9 is lowered
and pressed by the lower surface of the piezoelectric element plate 4 with a predetermined
pressure. At this time, since the film-like adhesive 4 is heated and melted through the
piezoelectric element plate 4 by heating the lower surface of the elevating body 9 in the heated
state, the elevating body 9 is lifted after a predetermined time to solidify the adhesive 4. The
piezoelectric element plate 4 can be strongly bonded to the diaphragm 3. The control of the
manipulator and the elevating body 9 is automatically performed by control means (not shown).
(Effects of the Invention) According to the present invention, since the film-like adhesive in which
the piezoelectric element plate and the diaphragm are interposed is bonded by heating and
melting, a-like contact white layer is obtained. And there is no variation in the bonding result.
Therefore, the quality and yield of the piezoelectric acoustic transducer can be improved.
Brief description of the drawings
FIG. 1 is a perspective view conceptually showing an embodiment of a bonding method according
to the present invention, and FIG. 2 is a conceptual view showing an example of an apparatus
used in practicing the method of the present invention.
3 ... diaphragm, 4 ... piezoelectric element plate, 7 ... film-like adhesive. Figure 1 Figure 2
procedure Ne r) 7 letter book (scheme), display of the case 1988 patent application No. 271599,
the title of the invention Piezoelectric acoustic transducer Relationship with the person who
makes method correction Patent applicant (307) Toshiba Corporation, agent (〒 104) Tokyo
Ginza, Chuo-ku, Ginza 2-chome 11-2, February 13, 1990 (starting port 1) 7th month) 6, 1/7 of
the brief description of the drawing of the target specification of correction, contents of
correction, 7th page and line 8 described in the specification. R figure.
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description, jph02117298
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