JP7312060B2 - Circuit board with surface mount crystal oscillator - Google Patents

Description

The present invention relates to a circuit board with a surface-mounted crystal oscillator in which terminal electrodes of a surface-mounted crystal oscillator and a surface-mounted crystal oscillator are joined to a circuit board using a conductive adhesive.

Patent Literature 1 describes a method of joining terminal electrodes of a surface-mounted crystal oscillator to a circuit board by melting solder. However, according to Patent Document 1, generally speaking, alumina or the like is used as a package material for a surface-mounted crystal resonator from the viewpoint of mechanical strength, dielectric constant, airtightness, and moisture resistance. many. On the other hand, as a material for the circuit board, for example, a glass epoxy board is used from the viewpoint of cost, ease of manufacture and processing, and the like. Since the package and the circuit board of the surface-mounted crystal unit are made of different materials, the coefficients of thermal expansion of each are different. This mechanical stress is transmitted to the crystal vibrating piece housed in the surface mount type crystal unit and the electrode film formed on the surface of the crystal vibrating piece, and affects the aging characteristics of the vibrator characteristics. presumed to give.

According to Patent Document 2, when terminal electrodes of a surface-mounted crystal oscillator are soldered onto a circuit board having electronic components, mechanical stress that affects oscillator characteristics is transmitted from the circuit board to the surface-mounted crystal oscillator. Therefore, it is described that the mechanical stress transmitted to the crystal vibrating piece housed in the surface mount type crystal resonator can be reduced by bonding with a silicone-based conductive adhesive having a Young's modulus of less than 1 GPa instead of soldering. there is

JP-A-2008-41858 JP 2016-633229 A

However, in Patent Document 2, although the Young's modulus of the silicone-based conductive adhesive that joins the terminal electrodes of the surface-mounted crystal oscillator and the circuit board is considered, The Young's modulus of the conductive adhesive used to bond the crystal resonator element to the package, the Young's modulus of the silicone-based conductive adhesive used to bond the terminal electrodes and the circuit board of the surface-mounted crystal resonator, and the surface-mounted type. The crystal vibrating piece and the crystal contained in the surface mount type crystal vibrator because the relationship with the Young's modulus of the conductive adhesive for bonding the crystal vibrating piece contained in the crystal vibrator to the package is not taken into consideration. Reduction of the mechanical stress transmitted to the electrode film formed on the surface of the vibrating bar was insufficient.

The present invention has been made in view of the above-described problems, and the crystal vibrating piece housed in the surface-mounted crystal oscillator and the surface-mounted crystal oscillator and the electrode film formed on the surface of the crystal vibrating piece. An object of the present invention is to provide a circuit board with a surface-mounted crystal oscillator in which mechanical stress is sufficiently reduced.

A circuit board with a surface-mounted crystal oscillator, in which a terminal electrode of the surface-mounted crystal oscillator is joined with a conductive adhesive A to a mounting land pattern formed on the circuit board, wherein the surface-mounted crystal oscillator is , a crystal vibrating piece, a supporting member having a mount electrode for bonding the crystal vibrating piece, and a lid member, the crystal vibrating piece being bonded to the mount electrode with a conductive adhesive B, and the lid member further comprising the support member. The conductive adhesive A has a Young's modulus of 2 to 4 GPa, and the conductive adhesive B has a Young's modulus of 2 GPa .

The conductive adhesive A and the conductive adhesive B are used for a circuit board with a surface-mounted crystal oscillator made of silicone, epoxy, or urethane resin.

According to the circuit board with a surface-mounted crystal oscillator of the present invention, sufficient mechanical stress is transmitted to the crystal vibrating piece housed in the surface-mounted crystal oscillator and the electrode film formed on the surface of the crystal vibrating piece. A circuit board with a lightened surface mount type crystal oscillator is obtained.

1 is a cross-sectional view of a surface-mounted crystal oscillator; FIG. 1 is a cross-sectional view of a circuit board with a surface-mounted crystal oscillator according to an embodiment of the present invention in which a surface-mounted crystal oscillator is bonded to a circuit board; FIG. FIG. 4 is a diagram showing aging characteristics in an example of the present invention; FIG. 3 is a conceptual diagram of a C section in FIG. 2;

A circuit board with a surface-mounted crystal oscillator according to an embodiment of the present invention will now be described with reference to the drawings. The scope of the present invention is not limited to the following embodiments, and can be arbitrarily changed within the scope of the technical idea of the present invention. Also, in the drawings, in order to make each configuration easy to understand, the actual structure and each structure may be different in scale, number, and the like.

FIG. 1 is a cross-sectional view of a surface mount crystal oscillator 2 bonded to a circuit board 1a.

The surface-mounted crystal resonator 2 includes, for example, a thickness-shear crystal resonator plate 3, a support member 4, and a lid member 5. As shown in FIG. The crystal vibrating piece 3 is not limited to the thickness-shear crystal vibrating piece 3, and a tuning-fork type crystal piece may be used.

The thickness-shear crystal vibrating piece 3 is formed by subjecting a piezoelectric wafer to a well-known cutting technique, a polishing technique, and a vacuum vapor deposition technique. do. The electrode film 6 is composed of an excitation electrode film 6a and a junction electrode 6b, and the junction electrode 6b is electrically connected to the excitation electrode film 6a.

The support member 4 is provided with a recess 7 for accommodating the crystal vibrating piece 3 by stacking thin plates of ceramic or the like. A pair of mount electrodes 8 are formed near one end of the recess 7 . This mount electrode 8 is electrically connected to a terminal electrode 9 formed on the bottom surface of the support member 4 .

The bonding electrode 6b formed on the surface of the crystal vibrating piece 3 and the mounting electrode 8 are mechanically and electrically bonded with a conductive adhesive B11 made of a silicone resin containing a conductive filler containing Ag, for example. . The resin used for the conductive adhesive B11 is not limited to silicone resin, and epoxy resin and urethane resin may be used. The Young's modulus of the conductive adhesive B11 is 2 GPa.

The lid member 5 is made of a thin plate such as metal, and a frame-shaped bonding material is formed on one surface of the lid member 5 .

By joining the cover member 5 to the upper end of the support member 4 to which the crystal vibrating piece 3 is joined, the surface-mounted crystal oscillator 2 whose inside is sealed is obtained.

FIG. 2 is a cross-sectional view of a circuit board with a surface-mounted crystal oscillator according to the present invention, in which a surface-mounted crystal oscillator is joined to a circuit board.

The circuit board 1a has a mounting land pattern 1b formed on the surface of a board such as a glass epoxy board (FR-4) using a well-known photolithographic technique. The land pattern 1b for mounting of the circuit board 1a and the terminal electrode 9 of the surface mount type crystal unit 2 are mechanically and electrically bonded together by a conductive adhesive A10 made of a silicone resin containing a conductive filler containing Ag, for example. is joined to The resin used for the conductive adhesive A10 is not limited to the silicone resin, and may be an epoxy resin or a urethane resin. The Young's modulus of the conductive adhesive A10 is 2 to 4 GPa. An electronic component other than the surface-mounted crystal unit 2 may be bonded to the mounting land pattern 1b of the circuit board 1a. A circuit board 1 with a surface-mounted crystal oscillator is fixed to a housing of an electronic device or the like.

FIG. 3 shows the mounting land pattern 1b of the circuit board 1a and the terminal electrode 9 of the surface-mounted crystal resonator 2 in the embodiment of the present invention after bonding with a conductive adhesive A10 (Young's modulus: 2 to 4 GPa). Aging characteristic E1 is shown. The crystal vibrating piece 3 housed in the surface-mounted crystal vibrator 2 is fixed to the mount electrode 8 with the aforementioned conductive adhesive B11 (Young's modulus: 2 GPa). In order to make a comparison with the aging characteristic E1 of the present invention, the Young's modulus of the conductive adhesive A10 that joins the terminal electrode 9 of the surface-mounted crystal oscillator 2 to the mounting land pattern 1b and the surface-mounted crystal oscillator 2 Aging characteristics are also shown with the Young's modulus of the conductive adhesive B11 that joins the crystal vibrating piece 3 housed to the mount electrode 8 as follows.
Aging property E2 The Young's modulus of the conductive adhesive A10 is 5 GPa, and the Young's modulus of the conductive adhesive B11 is 2 GPa.
Aging property E3 Young's modulus of conductive adhesive A10: 40 GPa, Young's modulus of conductive adhesive B11: 2 GPa.
Aging property E4 The Young's modulus of the conductive adhesive A10 is 2 GPa, and the Young's modulus of the conductive adhesive B11 is 5 GPa.
The horizontal axis of the figure showing the aging characteristics is the elapsed time after the terminal electrode 9 of the surface-mounted crystal oscillator 2 is joined to the mounting land pattern 1b, and the vertical axis is the change in the oscillation frequency.

With each aging characteristic, the oscillation frequency after bonding the terminal electrode 9 of the surface-mounted crystal oscillator 2 to the mounting land pattern 1b changes to the positive side with the passage of time. The aging characteristic E1 has almost no change in oscillation frequency two days after bonding, but the aging characteristics E2, E3, and E4 show changes in oscillation frequency even two days after bonding. This is because the residual stress of the mechanical stress transmitted to the crystal vibrating piece 3 accommodated in the surface mount type crystal vibrator 2 and the electrode film 6 formed on the surface of the crystal vibrating piece 3 decreases with the lapse of time. It's for.

FIG. 4 is a conceptual diagram of part C in FIG. Using this conceptual diagram, the mechanism of the aging characteristics described above will be described.

When the land pattern 1b for mounting on the circuit board 1a and the terminal electrode 9 of the surface-mounted crystal oscillator 2 are joined with the conductive adhesive A10, mechanical damage occurs due to the difference in material between the surface-mounted crystal oscillator 2 and the circuit board 1a. stress D is generated. The mechanical stress D may also include mechanical stress generated from members constituting the package such as the support member 4 and the lid member 5 . This mechanical stress D is transmitted from the circuit board 1a to the mounting land pattern 1b and the conductive adhesive A10. A portion of the mechanical stress D is absorbed by the conductive adhesive A10. The mechanical stress D' that could not be absorbed is transmitted to the terminal electrode 9, the mount electrode 8, and the conductive adhesive B11. The conductive adhesive B11 absorbs part of the mechanical stress D'. Although it is transmitted to the excitation electrode film 6a and the crystal vibrating piece 3 via the bonding electrode 6b, the excitation electrode film can Good aging characteristics can be obtained by reducing the mechanical stress D' transmitted to the crystal vibrating piece 6a and the crystal vibrating piece 3.

The elastic conductive adhesive A10 absorbs a part of the mechanical stress D from the mounting land pattern 1b, but because of its high Young's modulus, the force ( Therefore, the mechanical stress D is transmitted to the conductive adhesive B11 via the terminal electrode 9 and the mount electrode 8 in a slightly reduced state.

The elastic conductive adhesive B11 absorbs a portion of the mechanical stress D' transmitted through the terminal electrode 9 and the mount electrode 8, and acts as a force ( force acting on the opposite side to the mechanical stress D' is generated, the mechanical stress D' from the mount electrode 8 is greatly reduced, and the mechanical stress D ' also becomes smaller. That is, since the residual stress of the excitation electrode film 6a and the crystal vibrating piece 3 is also small, good aging characteristics can be obtained. The Young's modulus of the conductive adhesive A10 is equal to or greater than the Young's modulus of the conductive adhesive B11 used for bonding the mount electrode 8 and the crystal vibrating piece 3. For example, the Young's modulus of the conductive adhesive A10 is 2. ~4 GPa, and the Young's modulus of the conductive adhesive B11 is preferably 2 GPa. If the Young's modulus is small, the elasticity is high, so a force that offsets the mechanical stresses D and D' is likely to occur. In addition, when the Young's modulus is large, the elasticity is low, so that the force that offsets the mechanical stresses D and D' is less likely to occur.

If the Young's modulus of the conductive adhesive A10 is greater than 4 GPa, the elasticity of the conductive adhesive drops and the amount of absorption of the mechanical stress D from the mounting land pattern 1b decreases. Therefore, the conductive adhesive B11 cannot fully absorb the mechanical stress D' transmitted through the mount electrode 8, and the mechanical stress D' is transmitted to the excitation electrode film 6a and the crystal vibrating piece 3, deteriorating the aging characteristics. . Further, when the Young's modulus of the conductive adhesive B11 is increased, the elasticity of the conductive adhesive B11 decreases, and the force that cancels the mechanical stress D' from the mount electrode 8 (acting on the opposite side to the mechanical stress D' force) is reduced and the aging properties are deteriorated. If the Young's modulus of the conductive adhesive A10 and the conductive adhesive B11 is less than 2 GPa, the bonding strength will decrease, and the bonding strength will be weak even if the surface mount type crystal resonator 2 is bonded to the circuit board 1a. Moreover, the crystal vibrating piece 3 bonded to the mount electrode 8 is also peeled off. If the Young's modulus of the conductive adhesive A10 is greater than 4 GPa, almost no force acts against the mechanical stress D, and the mechanical stress D hardly decreases. If the Young's modulus of the conductive adhesive B11 is made larger than 2 GPa, almost no force acts on the opposite side of the mechanical stress D', so that the mechanical stress D' hardly decreases.

Although the surface-mounted crystal oscillator 2 has been described as an example, a surface-mounted crystal oscillator in which an integrated circuit or the like is mounted on the support member 4 can also provide the same effect.

A similar effect can be obtained with respect to mechanical stress generated when the circuit board 1 with a surface-mounted crystal oscillator is fixed to a housing of an electronic device or the like.

REFERENCE SIGNS LIST 1 circuit board with surface-mounted crystal resonator 1a circuit board 1b land pattern for mounting 2 surface-mounted crystal resonator 3 crystal resonator element 4 support member 5 lid member 6 electrode film 6a excitation electrode film 6b junction electrode 7 concave portion 8 mount electrode 9 terminal electrode 10 conductive adhesive A
11 Conductive adhesive B

Claims (2)

A circuit board with a surface-mounted crystal oscillator in which a terminal electrode of the surface-mounted crystal oscillator is joined to a mounting land pattern formed on the circuit board with a conductive adhesive A,
The surface-mounted crystal resonator includes a crystal vibrating piece, a support member having a mount electrode that joins the crystal vibrating piece, and a lid member,
The crystal vibrating piece is bonded to the mount electrode with a conductive adhesive B, and the lid member is bonded to the support member,
A circuit board with a surface mount crystal oscillator, wherein the Young's modulus of the conductive adhesive A is 2 to 4 GPa, and the Young's modulus of the conductive adhesive B is 2 GPa . 2. The circuit board with a surface mount type crystal unit according to claim 1 , wherein said conductive adhesive A and said conductive adhesive B are silicone-, epoxy- or urethane-based resins.

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