JP2003133460A - Airtight sealing type electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic component that copes with lead-free condition without deteriorating airtightness after press fit, and carries out airtight sealing with excellent heat resistance. SOLUTION: A base 1 comprises a metallic shell 10, insulating glass 13 that is filled in the shell, and lead terminals 11 and 12 that pass through the insulating glass 13 for fixing. On the Kovar surface of the shell and lead terminal, a nickel layer or a copper layer 101 is formed to a thickness of 2 to 5 μm. On the upper surface, silver layer 102 is formed by a thickness of 5 to 15 μm. In addition, on the upper surface, a gold layer 103 is formed by a thickness of 0.05 to 1 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic component such as a crystal oscillator, and more particularly to a hermetically sealed electronic component which is lead-free and has excellent heat resistance.

[0002]

2. Description of the Related Art An airtight sealing structure in which a metal shell is filled with insulating glass and a lead terminal is fixed through the insulating glass and a cylindrical cap is press-fitted into the airtight base is known. Japanese Patent Publication 58-47083
As is disclosed in Japanese Patent No. 3,849,865, it is commonly used in tuning fork type crystal oscillators and the like. The airtight seal is formed by forming a soft metal on either or both of the base and the cap, and by pressing the cylindrical cap into the approximately cylindrical base with a relatively large diameter, the plasticity of the soft metal is improved. Sealing is performed by deformation.

In the conventional structure, for example, the base material of the base metal shell is made of Kovar, a nickel or copper layer is formed on the surface by means such as plating, and a tin layer is further formed on the surface. is there. Further, the cap was made of iron-nickel alloy such as nickel silver, and at least a region of pressure contact with the base was formed with solder having a lead: tin9 ratio. With the above configuration, since the tin layer on the base side and the solder layer on the cap side are soft, they are plastically deformed by being press-fitted in a state where both metals are strongly adhered to each other, facilitating press-fitting.

By the way, in recent years, it has become necessary to support a reflow soldering environment. That is, in reflow soldering, since mounting on a mounting board is performed in a high temperature environment of 240 to 260 ° C., the metal structure of this press-fitted portion is also required to have heat resistance.

In order to meet such a demand, solder having a solder composition of, for example, lead 9: tin 1 and an increased lead content and an increased melting point has been used. However, since lead is a harmful substance to the human body, its use tends to be suppressed or prohibited worldwide. The above-mentioned solder composition is against the trend of lead-free, and a substitute product has been demanded.

[0006] A structure in consideration of such lead-free is disclosed in Japanese Patent Laid-Open No.
No. 001-68194, and a tin-silver alloy or a tin-bismuth alloy is exemplified as the lead-free brazing filler metal. However, in such an alloy, an oxide layer is easily formed on the surface, and the airtightness of the soft metal may be extremely deteriorated. This publication also discloses that a tin film for oxidation prevention is formed on the surface of the brazing material, but the melting point of the tin film is 220 ° C., which is lower than the reflow soldering temperature described above. However, there is a possibility that airtightness may be deteriorated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object thereof is to cope with lead-free without reducing airtightness after press fitting, and heat resistance Another object is to provide an electronic component that is highly airtight and sealed.

[0008]

According to a first aspect of the present invention, a metal shell is filled with insulating glass, and lead terminals are fixed through the insulating glass, and the base is mounted on the base. In the electronic component including an electronic element and a cap that hermetically seals the electronic element by being pressed into the base, a nickel layer or a copper layer is formed on at least the outer circumference of the metal shell, and a nickel layer or a copper layer is formed on the layer. And a gold layer is formed on the silver layer.

The nickel layer or the copper layer improves the film forming strength of the silver layer formed on the nickel layer or the copper layer, and improves the stability of the film. Although the silver layer is inferior to tin which has been used conventionally in softness, it has a certain degree of softness and can generate necessary plastic deformation at the time of press fitting. Further, as is well known, silver has a high melting point, and in an electronic component using silver as a sealing material at the time of press fitting, even when it is exposed to a reflow soldering environment under relatively high temperature conditions (for example, 260 to 280 ° C.), Problems such as melting of the sealing material do not occur. Further, the gold layer formed on the silver layer can prevent the oxidation of the silver layer below, and can smoothly press fit due to good ductility and improve airtightness.

As mentioned above, silver is inferior in softness to the conventionally used tin, but this can prevent the occurrence of defects by improving the manufacturing accuracy when the cap is press-fitted into the base. . For example, using a high-precision jig that eliminates the microscopic tilt and displacement of the base into which the cap is press-fitted, or a high-precision device that eliminates microscopic displacement in the press-fitting direction on the cap side, By using a jig, it is possible to eliminate problems during press fitting.

Further, as described in claim 2, in the structure of claim 1, the structure of the tin layer, the silver layer and the gold layer may be formed in the lead terminal. Oxidation of the lead terminals can be prevented by the uppermost gold layer, and solderability to the mounting board can be improved.

As described in claim 3, in each of the above structures, the gold layer may be formed to a thickness of 0.05 μm to 1 μm. If the gold layer is 0.05 μm or less,
When the antioxidizing action of silver becomes difficult to function and the silver oxide layer is formed, the softness of silver is lowered and the smoothness of the surface is also impaired. When press-fitting is performed in such a surface state, the airtightness due to plastic deformation of silver is reduced. For example, when applied to a tuning fork type crystal resonator that needs to maintain a vacuum inside, the airtightness is reduced, resulting in CI (crystal impedance). The reliability deteriorates as the value deteriorates and the function as the vibrator extremely decreases. When the thickness of the gold layer is 1 μm or more, the airtight performance is not so much improved, and the cost increase due to the use of gold becomes remarkable. Also, when the gold layer becomes thick, when joining the lead terminal part with a joining material such as solder,
It is known that gold diffuses into the bonding material and the bonding material becomes brittle. Therefore, also from this point of view, it is not preferable to make the gold layer too thick, and in consideration of performance versus price or performance quality, the thickness of the gold layer is preferably 0.05 μm to 1 μm.

Further, as described in claim 4, the thickness of the silver layer is preferably 5 μm to 15 μm. The silver layer has a certain degree of softness as described above, and has the advantage that it can generate the necessary plastic deformation at the time of press fitting to enhance the hermetic sealing performance and is also excellent in heat resistance. 5 μm silver layer
If it is less than the above, the plastic deformation area (thickness) due to silver is reduced, and if the state of the lower metal layer is not smooth, etc., the silver layer is affected by the metal layer, and even if it is pressed in accurately as described above. Even if the above is performed, the hermetic sealing performance may not be sufficient. When the thickness is 5 μm or more, the lower metal layer is less affected, and the hermetic sealing performance becomes stable.

It is also not preferable to make the silver layer too thick. That is, when, for example, a silver layer is formed by plating or the like, as shown in FIG.
1, the corner portion t2 has an increased thickness, and this phenomenon becomes more remarkable as the film thickness is increased. Note that FIG. 3 is a cross-sectional view of the base portion, and is a schematic diagram in which the above phenomenon is emphasized and described. If the press-fitting is performed in such a surface state, the cap may be distorted or damaged at the time of press-fitting, and as a result, the hermetic sealing performance may be deteriorated. The thickness of the silver layer is 15μ
By setting m or less, it is possible to prevent the deterioration of the hermetic sealing performance due to such a phenomenon. From the above, it can be said that the preferable range of the thickness of the silver layer is 5 to 15 μm.

Next, the performance of the product of the present invention and that of the conventional product were compared and confirmed. The samples used were 50 pieces each of the following conventional products, invention products, and comparative products, and the confirmed performances were airtightness, solderability, and heat resistance (reflow soldering resistance) performance. The airtightness was confirmed by a helium leak test. That is, a quartz resonator (electronic element) was mounted on each plated base, and a quartz resonator hermetically sealed (press-fitted) with a cap was confirmed to have hermetic performance by a helium leak test. Characteristic change (frequency change,
Goods with a CI value change etc. within the predetermined standard (○), those that are on average within the predetermined standard but are out of the standard depending on the manufacturing conditions are boundary products (△), and are outside the predetermined standard. The product was regarded as a defective product (x).

The solderability was confirmed by a solder wettability test. The external lead terminal of the crystal unit was immersed in a solder bath under predetermined conditions, and the wetted portion (wet area ratio) of the immersed portion was observed. A product having a wetting rate of 85% or more was regarded as a good product (◯), and a product having a wetting ratio of 95% or more was regarded as a good product (⊚). If the wetting ratio is 75% or less, it is a defective product (x).
And

Further, heat resistance (anti-reflow soldering) performance is required under predetermined conditions (for example, 240 in a reflow soldering environment).
Characteristic change (frequency change, CI
The change was confirmed by the presence or absence of value change. Goods with a characteristic change within the predetermined standard before and after the test were evaluated as good products (◯), and those with a property change outside the predetermined standards were evaluated as defective products (x).

The test results are shown in Table 1.

[Table 1]

Any metal film was formed on the shell of the base and the lead terminal. Conventional product 1 is Pb9: Sn1 containing heat-resistant solder formed to 12 μm, Conventional product 2 is Sn to 5 μm, Ag is formed on it to 3 μm, Conventional product 3
Is Sn having a thickness of 5 μm and Ag having a thickness of 8 μm formed thereon. Further, the product 1 of the present invention has Ni of 3 μm and Ag on top of it.
Having a thickness of 5 μm and Au formed thereon with a thickness of 0.05 μm,
The product 2 of the present invention has Ni of 3 μm, Ag of 5 μm formed thereon, and Au of 1 μm formed thereon. The product 3 of the present invention has Ni of 3 μm, Ag of 8 μm on it, and Au of 0.0 on it.
5 μm formed, Inventive product 4 has Ni of 3 μm, Ag of 8 μm formed thereon, and Au of 1 μm formed thereon. Invented product 5 has Ni of 2 μm formed thereon and Ag of 15 μm formed thereon.
m, Au having a thickness of 0.05 μm formed thereon, and the product 6 of the present invention has Ni having a thickness of 2 μm, Ag having a thickness of 15 μm formed thereon, and Au having a thickness of 1 μm formed thereon. Comparative product 1 had Ni of 5 μm, Ag of 2 μm on it, and Au of 0.0 on it.
5 μm, Comparative product 2 has Ni of 5 μm, Ag of 2 μm formed thereon, and Au of 1 μm formed thereon.
Comparative product 3 has Ni of 5 μm, Ag of 5 μm formed thereon, and Au of 0.03 μm formed thereon, and Comparative product 4 of Ni
Of 2 μm, Ag of 18 μm formed thereon, and Au of 0.05 μm formed thereon. Comparative product 5 has Ni of 3 μm,
5 μm of Ag is formed thereon, and 2 μm of Au is formed thereon.

From the above experimental results, the conventional products are inferior in solderability or heat resistance and are not suitable for practical use. In contrast, the product of the present invention is airtight, solderability,
Good heat resistance and good test results have been obtained, and especially solderability shows a solder wettability of 95% or more, showing that it is extremely good. Further, it can be understood that Comparative Examples 1 to 4 all have good solderability and heat resistance, but have a large variation in airtightness, and are somewhat lacking in reliability. Although the comparative product 5 is good in each of the above-mentioned characteristics, as described above, the cost of gold is high and the possibility that gold will adversely affect the bonding material is high.

[0021]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an exploded internal structure of a tuning fork type crystal unit, and FIG. 2 is a partially enlarged view of a base portion of FIG.

The base 1 comprises a metallic shell 10, an insulating glass 13 filled in the shell, and lead terminals 11 and 12 penetratingly fixed to the insulating glass 13. The shell 10 has, for example, a Kovar or iron-nickel-based alloy as a base, and has a cylindrical shape that penetrates vertically. The lead terminals 11 and 12 are formed into a linear shape using, for example, Kovar as a base, and are arranged through the shell at a predetermined interval. The insulating glass 13 is made of, for example, borosilicate glass, and includes the shell 10 and the lead terminal 1.
1 and 12 are integrally molded by a glass firing technique in an electrically independent state.

This integrally molded base is subjected to acid cleaning or the like to clean the metal surface or remove the carburized portion, and then the next metal coating is formed. On the surface of the Kovar of the shell and the lead terminal, the nickel layer or the copper layer 101 is 2-5.
The thickness of the silver layer 102 is 5 μm, and the silver layer 102 has a thickness of 5-5 μm.
It is formed with a thickness of 15 μm. Moreover, a gold layer 1 is formed on the upper surface thereof.
03 is formed with a thickness of 0.05 to 1 μm. Barrel plating is preferably used for forming each of these metal coatings. Barrel plating is excellent in mass productivity because it is possible to perform electrolytic plating efficiently by immersing the barrel into which the film-forming target is placed in the plating bath and rotating the barrel, and batch processing is also possible. ing.

By such a plating treatment, the above metal layers are formed on the surface of the base and the lead terminals. The tuning fork type crystal resonator element 2 which is an electronic element is joined to the inner sides 11a and 12a of the lead terminals by soldering or the like. Although not shown, a pair of excitation electrodes are formed on the main surface and the side surface of the tuning fork type crystal unit 2, and each of the electrodes is drawn out to a lead terminal portion, and the inner lead terminals 11a, 12a are formed. And conductively joined.

The cap 3 is made of nickel silver (Cu-Ni-Zn alloy) and has a bottomed cylindrical shape. A nickel layer 31 is formed on the outer and inner peripheral surfaces of the cap by means such as plating. The metal layer formed on the cap may use copper, silver, or gold instead of nickel, or may have a multi-layer structure in which nickel, copper, silver, and gold are appropriately combined. The inner diameter of the cap is designed to be slightly smaller than the shell portion of the base, and is set to, for example, 2 to 5% smaller. By covering such a cap with the tuning-fork type crystal oscillator piece which is the electronic element in a vacuum atmosphere and press-fitting the cap opening into the base, the base and the cap are firmly adhered to each other, and the inside of the cap is kept in a vacuum state. Airtight sealing can be performed.

From the above, the outer side 11 of the lead terminal
It is possible to obtain an electronic component in which a thin gold layer is formed on the surfaces b and 12b, so that the soldering to the mounting board can be performed smoothly without lowering the solderability. In addition, the solder that joins the electronic element to the lead terminal and the solder that joins the electronic component to the mounting board are lead-free, and by using a material with excellent heat resistance, the total electronic component can be lead-free and heat resistant. The electronic parts of can be obtained.

In the above structure, an alloy layer of nickel or copper may be formed between the silver layer and the silver layer. To form the alloy layer, for example, a nickel or copper layer and a silver layer are sequentially formed by plating, and then diffusion treatment may be performed by heating for several hours in a vacuum atmosphere at 210 ° C., for example. The alloy layer region can be controlled by the diffusion treatment time.

By forming the alloy layer, the film forming strength between the nickel or copper layer and the silver layer is improved, and the airtight sealing performance at the time of press fitting can be improved. The gold layer may be formed after the above diffusion process.

In the above embodiment, the tuning fork type crystal unit for vacuum sealing is shown as an example. However, the present invention can be applied to those which are hermetically sealed in an inert gas atmosphere, or for crystal units of other vibration modes. It is also possible to apply. Furthermore,
It is also possible to apply to hermetically sealing piezoelectric elements other than the crystal oscillator or other electronic elements.

[0030]

According to the present invention, the silver layer is firmly formed on the base, and the silver layer is plastically deformed at the time of press fitting, so that the required hermetic sealing performance is secured. Further, the gold layer prevents the silver layer from being oxidized, and the airtightness at the time of press-fitting effectively functions, and the good ductility allows the press-fitting to proceed smoothly. Further, all the metal materials have excellent heat resistance, and are relatively high temperature conditions (for example, 260 to 280).
(° C) reflow soldering can also be applied, and the applicable temperature range can be greatly expanded. Further, since the metal layer for the base is made of a material that does not use any lead, it is possible to deal with lead-free. Therefore, it is possible to obtain an electronic component that can be lead-free without lowering the airtightness after press-fitting and that has an excellent heat resistance and is hermetically sealed.

According to the second aspect, in addition to the above effect, the uppermost gold layer can prevent the lead terminals from being oxidized, and the solderability to the mounting substrate can be improved.

According to the third aspect, it is possible to obtain an electronic component which is preferably hermetically sealed in consideration of ensuring airtightness and cost.

Furthermore, according to the fourth aspect, it is possible to obtain an electronic component which is preferably hermetically sealed so that the necessary hermeticity can be surely obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an exploded internal structure of a tuning fork type crystal unit.

FIG. 2 is a partially enlarged view of a base portion of FIG.

FIG. 3 is a partial cross-sectional view of a base showing a defective state of film formation.

[Explanation of symbols]

1 base 10 shell 11,12 Lead terminal 13 insulating glass

Claims (4)

[Claims] 1. A base in which a metal shell is filled with insulating glass, and lead terminals are fixed through the insulating glass, an electronic element mounted on the base, and the electronic device by being press-fitted into the base. In an electronic component including a cap for hermetically sealing an element, a nickel layer or a copper layer is formed at least on the outer circumference of the metal shell, a silver layer is formed on the nickel layer or the copper layer, and a silver layer is formed on the silver layer. A hermetically sealed electronic component, wherein a gold layer is formed on the. 2. The hermetically sealed electronic component according to claim 1, wherein the nickel layer or the copper layer and the silver layer and the gold layer are also formed on the lead terminals. 3. The thickness of the gold layer is 0.05 μm to 1 μm.
The hermetically sealed electronic component according to claim 1 or 2, wherein 4. The hermetically sealed electronic component according to claim 1, 2 or 3, wherein the thickness of the silver layer is 5 μm to 15 μm.