JPH10256409A - Fabrication of packages for piezoelectric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for fabricating low-cost and mass-producible packages adapted for use as piezoelectric devices for industrial products without inviting deterioration of a bonding agent caused by heating at the time of sealing, the rise of cost, and frequency variation caused by the evolution of gasses and moisture from a sealing means, keeping frequency variation after drop and impact tests within the range of 1-2ppm. SOLUTION: In this package fabrication method, a piezoelectric element 14 is fixed by bonding on a base 11 through a conductive bonding agent 15, and the base 11 and a cap 17 are jointed together through a sealing agent 18 which has a melting point higher than the deterioration temperature of the bonding agent 15. The cap 17, after being applied with the sealing agent 18 onto the lower surface, is solely heated by a heating means at a temperature higher than the melting point of the sealing agent 18 to permit the sealing agent 18 to melt. The base 11 and the cap 17 are jointed together via the melted sealing agent 18, and then the heating means is removed from the cap 17 after passage of a required time to complete sealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method of manufacturing a package for a piezoelectric device, and more particularly, to a method for bonding a piezoelectric element in a ceramic package using a highly flexible silicon-based conductive adhesive excellent in impact resistance. The present invention relates to a method for manufacturing a package of a piezoelectric device, which enables use of a sealing means such as glass having a melting point higher than the deterioration temperature of a ciolin-based conductive adhesive as a sealing means between a package base and a cap while being used. .

[0002]

2. Description of the Related Art As a conventional package of a piezoelectric device, a ceramic base supporting a piezoelectric element such as a quartz oscillator is sealed with a ceramic cap.
Alternatively, a ceramic base having an upper surface sealed with a metal cap is known. As a package of a piezoelectric device in which a piezoelectric element such as a quartz oscillator supported on a ceramic base is hermetically sealed with a ceramic cap, there is, for example, a type shown in a vertical sectional view of FIG. The package has one end of a piezoelectric vibrator 4 such as a crystal element bonded and fixed on a pedestal 3 in a recess 2 formed on the upper surface of the ceramic base 1 using a conductive adhesive 5. The upper surface of the part 6 and the ceramic cap 7 are joined by using sealing means (sealant) 8 to seal the inside. As the conductive adhesive 5, for example, a hard polyimide adhesive or a soft adhesive such as a silicon adhesive, an epoxy adhesive, or a urethane adhesive is used. Polyimide-based adhesives have a characteristic that, while the deterioration temperature is high, the hardness after the adhesive is hardened increases. As the sealing means 8, low melting point glass, solder, resin, and the like have been generally used.

[0003] Among these sealing means, low melting point glass and solder provide advantages in terms of sealing workability and cost, but have a melting point of about 320 ° C. In this case, it is necessary to heat at a high temperature of, for example, about 330 to 350 ° C. For this reason, as the conductive adhesive 5 for bonding the piezoelectric element in the package, an adhesive having a lower deterioration temperature than the heating temperature at the time of sealing, for example, a silicon-based conductive adhesive (deterioration temperature of about 300 ° C.) is used. An adhesive having a deterioration temperature exceeding the heating temperature at the time of sealing, for example, a polyimide-based conductive adhesive cannot be used. However, the polyimide-based conductive adhesive has a high hardness after curing, so that the piezoelectric element is rigidly supported. Piezoelectric devices used in the field of mobile phones, etc., are required to have high drop impact resistance.However, when a rigid adhesive such as a polyimide adhesive is used to fix the piezoelectric element to a rigid base, a drop impact test There is a problem that the frequency is shifted and the standard cannot be satisfied, or the piezoelectric element is damaged and cannot be used at all. In addition, when the piezoelectric element is rigidly fixed on the base, there is a problem that thermal distortion is applied to the piezoelectric element and a shift occurs in its frequency. In addition, since the piezoelectric element is exposed to a high temperature for a long time, a component of the electrode film deposited on the piezoelectric element, for example, Ag is sublimated by heat generated at the time of sealing the package, and the mass of the electrode is reduced. This causes a problem that the frequency of the piezoelectric element deviates from an expected value. As a result, in a package using a polyimide conductive adhesive as a bonding means for the piezoelectric element, the frequency variation before and after sealing becomes large, for example, 30 ppm. The overall specification including the test could not satisfy f ₀ ± 10 ppm), and was exclusively used for consumer goods having the total specification of approximately ± 50 ppm.

Therefore, in place of the polyimide-based conductive adhesive, the piezoelectric element can be supported non-rigidly because it can maintain a sufficient degree of softness when cured. A silicon-based adhesive that has the advantage that it can sufficiently satisfy industrial specifications such as, and has the advantage of reducing the frequency shift of the piezoelectric element because of its flexible thermal strain Attempts have been made to use it as an adhesive. But,
Soft adhesives 5 such as a silicon-based conductive adhesive have a common property that the deterioration temperature is low. Therefore, while the piezoelectric element is adhered with a silicon-based conductive adhesive, when solder, glass, or the like having a high melting temperature is used as the sealing means 8 for the ceramic package, the position inside the ceramic package is increased by high-temperature heating during sealing. There is a problem that the flexibility and adhesive strength of the adhesive 5 having a low deterioration temperature deteriorate, and the frequency stability decreases. For this reason, as the adhesive 5 used for bonding the piezoelectric elements in the ceramic package, a polyimide-based conductive adhesive still had to be used. That is, the melting point of the low melting point glass is 320. C and the degradation temperature (30
0. C), it is 330-35 in a sealed furnace.
It is common knowledge in the art that heating at a high temperature of 0 ° C. causes deterioration of the adhesive 5 having a low deterioration temperature, and that the combination of the silicon-based adhesive and the like and the low melting point glass is impossible. Was. Specifically, when a package is conventionally sealed using low-melting glass, the entire package is 330 to 340 with a ceramic cap over a ceramic base. Since it is necessary to heat at C for 10 minutes, the internal silicon-based adhesive is 300. As described above, it was not possible to avoid the problem that the adhesive was exposed to a temperature exceeding C for a long time and the flexibility and the adhesive strength of the adhesive were deteriorated. The deterioration temperature of the epoxy adhesive is about 220 to 230 ° C, and the deterioration temperature of the urethane adhesive is about 180 to 200 ° C.

[0005] Therefore, a device using a resin as a sealing means has been proposed. Resin has advantages in workability and cost, and its degradation temperature is as low as about 150 to 180 ° C. Therefore, if resin is used as the sealing means, a soft silicone adhesive with a low degradation temperature can be used as a piezoelectric. It can be used for bonding elements, and can sufficiently secure the impact resistance of the piezoelectric element after curing. It also has the effect of reducing thermal distortion. However, in addition to the resin having the disadvantage of generating gas, the interior of the package should be kept in a dry nitrogen atmosphere.Because the resin has water absorption, the moisture that penetrates through the resin causes Since the frequency gradually changes due to, for example, adhesion to the electrodes of the piezoelectric element, it is not suitable for piezoelectric devices for industrial products that require high frequency stability, and for piezoelectric devices for consumer products that are mass-produced at low cost. Could only be applied. For the above reasons, a package of a piezoelectric device in which a ceramic cap is sealed on a ceramic base is considered to be unsuitable for a piezoelectric device used for industrial products. A metal cap sealed on a base by seam welding, gold tin, or resistance welding is used. According to these sealing methods, the package can be sealed at a temperature not higher than the deterioration temperature of the silicon-based adhesive or the like. Therefore, a soft adhesive such as a silicon-based adhesive is used as the bonding means of the piezoelectric element. it can. Therefore, the above-mentioned problems caused by the deterioration of the flexibility and the adhesive force of the silicon-based adhesive and the like, and the problems such as sublimation of the components constituting the electrode film and frequency shift due to generation of moisture are less likely to occur. Since it is possible to keep the concentration within the range of ２2 ppm, this is a sealing method suitable for a piezoelectric device for industrial use. However, the method of sealing the metal cap by seam welding or the like has a problem in that it is disadvantageous in terms of facilities, workability, parts cost, and the like.

[0006]

As described above, in the conventional method for manufacturing a package of a piezoelectric device, a package structure is formed while using a silicon-based adhesive or the like as a conductive adhesive for bonding a piezoelectric element. A base and cap made of ceramic cannot be used, and as a result, there is a problem that an inexpensive ceramic base and cap package having excellent sealing workability cannot be used for industrial products. The present invention has been made in view of the above, and in a package having a structure in which a ceramic cap is sealed on a ceramic base, a silicon-based adhesive having a low deterioration temperature is used as an adhesive for supporting the piezoelectric element in the base. However, the package is sealed using a sealing means having a melting point exceeding the degradation temperature of the adhesive, and the adhesive deteriorates and the price increases due to heating during sealing, and gas and moisture from the sealing means Provide a method of manufacturing a low-cost, mass-productive package that can be used as a piezoelectric device for industrial products by keeping the frequency fluctuation after drop impact test within the range of 1 to 2 ppm without causing frequency fluctuation due to generation of cracks. It is intended to be.

[0007]

To achieve the above object, according to the present invention, there is provided a base having a recess for accommodating a piezoelectric element on an upper surface, and an upper surface of an annular projection surrounding the recess of the base. And a cap that seals the recess in close contact with
A package in which the piezoelectric element is bonded and fixed on a pedestal in a recess with a conductive adhesive, and the annular protrusion and the cap are joined with a sealant having a melting point higher than the deterioration temperature of the conductive adhesive. A method of manufacturing, a step of heating the base on which the piezoelectric element is adhered and fixed on the pedestal with a conductive adhesive for a short time at a temperature lower than the deterioration temperature of the conductive adhesive alone,
A step of applying a sealant to the lower surface of the cap and then heating the cap alone at a temperature equal to or higher than the melting point of the sealant to melt the sealant; And bonding the cap holding the molten sealing agent thereto, followed by pressurizing to seal the cap. According to a second aspect of the present invention, there is provided a base for accommodating a piezoelectric element on an upper surface, and a cap for sealing the base by closely contacting the periphery of the base, and bonding the piezoelectric element to the base with a conductive adhesive. A method for manufacturing a package, wherein the package is fixed and the base and the cap are joined together with a sealing agent having a melting point higher than the deterioration temperature of the conductive adhesive,
A step of preheating the base on which the piezoelectric element is adhered and fixed by the conductive adhesive alone at a temperature not higher than the deterioration temperature of the conductive adhesive, and applying a sealant to the lower surface of the cap, and then heating by a heating means Heating the cap alone at a temperature equal to or higher than the melting point of the sealant to melt the sealant; joining the base and the cap via the melted sealant; Sealing the means by separating the means from the cap.
According to a third aspect of the present invention, there is provided a ceramic base having a concave portion for accommodating a piezoelectric element on an upper surface, and a ceramic cap for sealing the concave portion by closely contacting an upper surface of an annular protrusion surrounding the concave portion of the ceramic base. A method for manufacturing a package in which the piezoelectric element is bonded and fixed on a pedestal in a recess with a silicon-based conductive adhesive, and the annular projection and a ceramic cap are joined with low-melting glass, Heating a ceramic base having a piezoelectric element bonded and fixed on a pedestal with a silicon-based conductive adhesive at a temperature lower than the deterioration temperature of the silicon-based conductive adhesive alone for a short time; Coating the ceramic cap alone at a temperature equal to or higher than the melting point of the low melting point glass to melt the low melting point glass; After joining the ceramic cap holding the low melting point glass described above melt in the base of the annular projection top surface, characterized in that and a step of sealing by pressing.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing an example of a package structure of a piezoelectric device manufactured by the method of the present invention. The characteristic structure of this package is a pedestal 1 in a recess 12 formed on the upper surface of a ceramic base 11.
One edge of a piezoelectric element 14 such as a quartz crystal plate is bonded and fixed on silicon 3 with a silicon-based conductive adhesive 15 and
The upper surface of the annular projection 16 of the base 11 surrounding the base 2 and the ceramic cap 17 are joined by sealing means (sealant) made of low-melting glass 18 to thereby obtain the piezoelectric element 1.
4 is hermetically sealed. The silicon-based adhesive is obtained by mixing fine silver particles in a binder containing silicon as a main component, and the low-melting glass is supplied in a form in which glass powder is mixed in a resin paste. The cap 17 is previously screen-printed.
The binder is removed by pre-baking after printing on the application surface 17a, and the glass component is fixed.

As the conductive adhesive 15, an epoxy-based adhesive, a urethane-based adhesive, or the like can be used in addition to a silicon-based adhesive. Since the piezoelectric element can be maintained rigidly, the piezoelectric element can be rigidly supported and the impact resistance can be increased. However, the deterioration temperature of these adhesives is lower than the melting point of the low-temperature glass 18 (32
0-380. C), it was difficult to maintain the frequency stability after the impact resistance test at the heating temperature in the conventional sealing method, and it was difficult to maintain the frequency stability after the impact resistance test. By adopting the method, it is possible to seal the package using the low melting point glass without extremely heating the adhesive in the base 11.
As described above, in the conventional package structure and the method of manufacturing the same, while using a silicon-based adhesive having a low deterioration temperature as a conductive adhesive for bonding a piezoelectric element, a low melting point is used as a sealing means for bonding a base and a cap. There is no one using glass, and this package structure has been established as having practicality for the first time by the establishment of a manufacturing method described later, and therefore this structure itself is a novel structure.

Next, an example of a novel manufacturing method for manufacturing a package having the above structure will be described with reference to the process charts of FIGS. 2 (a) and 2 (b). In FIG. 2A, a heater (heating means) 2 which supports the outer surface of the cap 17 and raises and lowers the cap.
0 to cap 17 at 360 to 400 ° C. for about 5 to 1
Heat for 0 second to melt the low melting point glass 18 applied to the application surface of the cap. That is, since the low-melting glass 18 does not melt unless the cap 17 exceeds 330 ° C., the heater temperature is determined so that the cap 17 reaches about 330 ° C. Further, for example, the base 11 is preheated by a heater (heating means) 21 to a temperature range from room temperature to 250 ° C. This is because if the temperature of the upper surface of the annular projection 6 of the base 11 is sufficiently raised, the time required for sealing is shortened accordingly. Further, since the base 11 is merely preheated to a temperature lower than 300 ° C., which is the deterioration temperature of the silicon-based adhesive, the adhesive does not deteriorate. In addition, an epoxy-based adhesive (deterioration temperature 220 to 230 ° C),
Alternatively, when using a urethane-based adhesive (deterioration temperature of 200 ° C.), the base 11 is pre-heated at a temperature that does not cause each deterioration.

The respective heating means for the cap 17 and the base 11 are separate, and the cap 17 and the base 11 are sufficiently separated at the time of heating, so that the conductive adhesive on the base adversely affects the heat on the cap side. There is no fear of receiving it. It is apparent from the above description that the base 11 does not need to be heated (the heating temperature is from room temperature to 250 ° C.). Both the heating operation and the sealing operation described below are performed in an N ₂ atmosphere. The heaters (heating means) 20 and 21 can be variously selected from those using a heating wire, those using pulse heating, and the like. When the cap 17 and the base 11 are sufficiently heated, respectively, the cap 17 coated with the low melting glass 8 on the upper surface of the annular projection 6 of the base 11 as shown in FIG.
Is pressed, and an appropriate load, for example, 0 to 500 g, is applied thereto and held for about 0 to 20 seconds. Thereafter, the heater 20 releases the support of the cap and rises as shown in (c), so that the package remains in the heater 21. Here, the presence or absence of deterioration of the conductive adhesive is determined by a tensile strength test by pulling the piezoelectric element bonded on the base with the conductive adhesive. For example, when a silicon-based adhesive is left in an atmosphere of 330 ° C., which is the temperature at which it is sealed with low-melting glass, the tensile strength is significantly reduced in about 4 minutes, and the adhesive is not used. This has been found experimentally. Therefore, at the worst, the heating and pressing time is preferably within 4 minutes, practically 2 minutes or less, more preferably 20 seconds or less.

The structure and shape of the heater shown in the figures are merely examples. Further, in FIG. 2, the cap may be arranged on the lower side, and the base may be moved up and down on the cap. Note that the base and the cap constituting the package of the present invention are not limited to ceramic, and the annular projection 16 and the cap 17 of the base 11 are sealed with a melting point higher than the deterioration temperature of the conductive adhesive. All packages joined and sealed with an agent fall within the scope of the present invention. According to the manufacturing method of the package of the present invention configured as described above, the sealing agent for the base and the cap is formed using a material having a melting point higher than the deterioration temperature of the internal conductive adhesive. The cap is held separately from the base while it is kept separate from the base, and the two are quickly bonded and sealed in a state where the sealant is sufficiently melted. It is possible to perform sealing using low-melting glass, etc. while using it, and while maintaining sufficient impact resistance in the drop impact test, which is an advantage of the silicone adhesive, gas from the sealing agent is maintained. A stable sealing structure without generation of water or moisture can be realized. In addition, since the piezoelectric element is not heated at an extremely high temperature by heating at the time of sealing, components of the electrode film, for example, Ag and the like deposited on the piezoelectric element are sublimated by heat generated at the time of sealing the package. As a result, the problem that the mass of the electrode is reduced and the frequency of the piezoelectric element deviates from the initial value does not occur. In the above-described embodiment, low-melting-point glass is exemplified as the sealing means. However, this is merely an example, and sealing means having a melting point higher than the deterioration temperature of the adhesive, for example, solder may be used. It is possible. In this case, in order to prevent gas generation from the solder, it is effective to reduce the amount of flux used, or to use a fluxless solder.

[0013]

As described above, according to the method of the present invention, the base (for example, a ceramic base) for accommodating the piezoelectric element on the upper surface and the upper surface of the base are brought into close contact with the peripheral edge (for example, the annular projection) of the base. A cap (for example, a ceramic base) for sealing, wherein the piezoelectric element is bonded and fixed to a top surface of the base with a conductive adhesive (for example, a silicon-based adhesive). Bonding and sealing were performed with a sealing agent having a melting point higher than the deterioration temperature of the conductive adhesive. For this reason, it is possible to seal the ceramic package with a low-melting glass or the like while using a silicon-based adhesive having a relatively low deterioration temperature as a bonding means for the piezoelectric element, and satisfy the standards in the drop impact test. In addition, it is possible to realize a sealing structure that satisfies the general specifications as an industrial product and has aging stability with no generation of gas or moisture from the sealing agent.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a package structure manufactured by a manufacturing method according to an embodiment of the present invention.

2 (a), (b) and (c) are views for explaining the steps of the method of the present invention.

FIG. 3 is a longitudinal sectional view showing the structure of a conventional package.

[Explanation of symbols]

11 ceramic base, 12 recess, 13 pedestal, 1
4 piezoelectric element, 15 conductive adhesive, 16 annular protrusion,
17 ceramic cap, 17a coated surface, 18 low melting point glass (sealing means, sealing agent), 20, 21 heater.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H03H 9/02 H01L 41/08 C

Claims (3)

[Claims] 1. A base for accommodating a piezoelectric element on an upper surface, and a cap for sealing the base in close contact with a peripheral edge of the base, wherein the piezoelectric element is bonded and fixed on the base with a conductive adhesive. A method of manufacturing a package in which the base and the cap are joined with a sealant having a melting point higher than the degradation temperature of the conductive adhesive, wherein the sealant is applied to the lower surface of the cap and then heated. Heating the cap alone at a temperature equal to or higher than the melting point of the sealant to melt the sealant, and joining the base and the cap via the melted sealant, and elapsing the required time And sealing the heating device by separating the heating device from the cap. 2. A base for accommodating a piezoelectric element on an upper surface, a cap for sealing the base in close contact with a periphery of the base,
And a method of manufacturing a package in which the piezoelectric element is adhered and fixed on a base with a conductive adhesive, and the base and the cap are joined with a sealant having a melting point higher than the deterioration temperature of the conductive adhesive. A step of preheating the base to which the piezoelectric element is adhered and fixed by the conductive adhesive alone at a temperature lower than the deterioration temperature of the conductive adhesive, and applying a sealant to the lower surface of the cap. Heating the cap alone at a temperature equal to or higher than the melting point of the sealant by a heating means to melt the sealant; and joining the base and the cap via the molten sealant, and After the lapse of time, a step of separating the heating means from the cap to seal the cap, and a method of manufacturing a package of a piezoelectric device. 3. A ceramic base having a concave portion for accommodating a piezoelectric element on an upper surface, and a ceramic cap sealingly sealing the concave portion by closely contacting an upper surface of an annular projection surrounding the concave portion of the ceramic base. A method of manufacturing a package comprising: bonding the piezoelectric element to a pedestal in a recess with a silicon-based conductive adhesive; and bonding the annular protrusion and the ceramic cap with low-melting glass. Heating the ceramic base to which the piezoelectric element is adhered and fixed with a silicon-based conductive adhesive for a short time at a temperature not higher than the deterioration temperature of the silicon-based conductive adhesive, and applying a low-melting glass to the lower surface of the ceramic cap Heating the ceramic cap alone at a temperature equal to or higher than the melting point of the low-melting glass to melt the low-melting glass; Bonding a ceramic cap holding the molten low-melting glass to the upper surface of the annular projection of the base, and sealing by pressing the ceramic cap.