JP2002160089A - Airtight terminal and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an airtight terminal having heat resistance in reflow soldering, inexpensive and highly reliable, and using Pb-free solder. SOLUTION: A film of a non-eutectic Ag-Bi material having 30-80 at% Bi content is formed on a lead wire of the airtight terminal by plating or the like. The film and a quartz oscillator, a surface acoustic wave(SAW) resonator, etc., are melted and bonded to each other. Through these processes, the airtight terminal having heat resistance in reflow soldering, inexpensive and highly reliable, and using Pb-free solder is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hermetic terminal used for a quartz oscillator or the like, and more particularly to a highly reliable and inexpensive hermetic terminal for realizing Pb-free and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, when electronic components are discarded due to acid rain or the like, P in solder materials used for connecting substrates and terminals has been reduced.
Due to concerns about environmental problems that b melts out and contaminates the soil, the shift to electronic components using so-called Pb-free solder is being promoted. By the way, the crystal unit and the SAW resonator, which are the elements of the electronic parts, are airtight terminals with airtightness.
(Hermetic seal), which is often used as an important part. The hermetic terminal is soldered to a crystal resonator or a SAW resonator in a sealed package, and hermeticity is maintained by heat-pressing the can package and the stem.

[0003] For such a purpose, a solder plating film is preliminarily applied to a joint portion of the hermetic terminal, and the joint with the crystal oscillator is performed by this solder material. The melting of the solder plating film is generally performed by placing it in an electric furnace or the like and flowing hot air into the furnace. The lower limit of hot air temperature is
Temperature at which heat-resistant solder is completely melted, upper limit is crystal oscillator, S
The temperature is limited to a temperature at which the AW resonator does not deteriorate. Specifically, 3
50 ° C to 500 ° C. The hermetically packaged quartz resonator and SAW resonator are arranged on a substrate, and generally are subjected to reflow soldering.

The peak temperature of components during reflow soldering varies depending on the heat capacity of the components because the heating of the reflow furnace is mainly performed by hot air heating. In addition, the Pb-free reflow solder has a melting point higher than that of ordinary SnPb solder, and thus has a temperature of 220 ° C. to 260 ° C. Even at this reflow peak temperature, the crystal unit and the SAW resonator bonded to the solder in the hermetic terminal do not fall off. As described above, the solid-phase temperature (lower limit temperature at which the melting of the metal material starts) of the hermetic terminal solder plating film is set higher than that of ordinary SnPb solder. For this solder plating film, a solder material called heat-resistant solder is used. Furthermore, heat-resistant solder is generally Pb90 atomic% (hereinafter abbreviated as at%).
Heat resistance is realized by using the front and rear SnPb materials.

[0005]

As described above, the hermetic terminal provided with the heat-resistant solder plating film has a high Pb content, which is against the trend of the era of realizing Pb-free. There's a problem. AuSn is a Pb-free and heat-resistant bonding material, but the price of Au is very high, and when used for the production of hermetic terminals,
There is a problem that the hermetic terminal as an electronic component becomes very expensive.

It is an object of the present invention to provide an inexpensive and highly reliable P
An object of the present invention is to provide an airtight terminal on which b-free heat-resistant solder plating has been applied, and a method for manufacturing the same.

[0007]

According to the present invention, as a result of studying the adoption of a Pb-free plating film having heat resistance, Bi
This is based on the finding that an AgBi plating film having a content of 30 to 80 at% is suitable for a Pb-free heat-resistant solder.

According to the present invention, the thickness of the AgBi alloy film is not particularly limited, but is preferably about 5 to 20 μm. The reason for this is that when the content is less than the AgBi alloy, the amount of solder for joining the lead of the hermetic terminal and the crystal unit as the element decreases, and the bonding strength of the AgBi alloy decreases. On the other hand, when the thickness of the AgBi alloy is 20 μm or more, the effect of the solder flowability is not impaired, but the production of the film thickness becomes difficult, the economic efficiency is reduced, and it is almost impossible to implement. In the present invention, when the AgBi alloy film is formed on the soldering connection part of the hermetic terminal, the film is formed by blowing hot air, but the heat resistance temperature of the electronic component such as a quartz oscillator at the time of spraying is as follows. 500 ° C. or less is desirable. 500
° C or lower because the normal electronic component heat resistance temperature is 50 ° C.
This is because it is 0 ° C. or less. Meanwhile solidus temperature of AgBi alloy film when the吹着with the solid-liquid phase line S ₃ is composition region S ₂ in FIG. 2
From the lower limit temperature of 30 to 80 at% to 350 ° C., the lower temperature limit for forming a film by blowing hot air when forming a film on the soldering connection portion is 350 ° C. In the present invention, as a means for forming the AgBi alloy film, electrolytic plating, electroless plating, sputtering, vapor deposition, or the like may be appropriately selected. Further, depending on the conditions, an AgBi alloy foil may be used to form an airtight terminal. And the lead wire of
The bonding may be performed by sandwiching and bonding between the bonding pads. However, in the case of an irregular shape such as the hermetic terminal for a crystal unit, it is difficult to form a uniform film selectively only on a metal portion by a sputtering or vapor deposition method with current technology, and therefore, electrolytic plating is more preferable. Under the AgBi alloy film, Cu, Cr, Ni, T
It is preferable to appropriately set a base layer such as i.

[0009]

FIG. 2 is a phase diagram of an AgBi binary alloy. Alloy composition is eutectic composition (Bi 95.3at%)
Point, out of the _{S 0,} Bi amount a composition region _{S 2} is 30 to 80
By using an at% AgBi alloy or an AgBi + α (α: balance) alloy containing AgBi as a main component as an airtight terminal plating solder, the heat resistance at 262 ° C. can be secured.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An airtight terminal according to an embodiment will be described with reference to FIG. FIG. 1A shows an example of a lead-in terminal portion of a hermetic terminal for mounting a crystal resonator. Inside the metal outer ring 1, two external introduction leads 2 are molded in advance with glass 3 for hermetic sealing so as not to be electrically short-circuited and to maintain hermeticity. The metal portions of the metal outer ring 1 and the external lead 2 of the lead introducing terminal portion are plated with solder. FIG. 1B shows an embodiment in which the external lead 2 and the electrode of the crystal unit 4 are joined by melting a solder film plated on the external lead 2.

FIG. 1 (c) shows a case where the lead introducing terminal portion soldered to the quartz oscillator 4 is placed in a case 5 in a vacuum atmosphere.
Is cold-pressed into the metal outer ring 1 of the lead introducing terminal portion. The airtightness between the metal outer ring 1 and the metal case 5 is maintained by using the metal properties of the solder film applied around the relatively soft and ductile metal outer ring 1 to maintain the airtightness of the airtight terminal. I have.

In the present invention, electrolytic AgBi plating having reflow soldering heat resistance is used as a solder plating film applied to the metal outer ring 1 and the external lead 2. FIG.
(d) is a side view for explaining the solder bonding between the crystal unit 4 and the external lead 2. The external lead 2 solder-plated on the electrode 6 of the wiring board patterned on the crystal oscillator 4 is fixed by a jig or the like. In this state, hot air or the like is blown to the joint between the external lead 2 and the electrode 6 to melt the AgBi + α (α: remaining) alloy solder film 7 on the lead 2 and solder the lead 2 to the electrode 6.

As described above, FIG. 2 is a phase diagram of an AgBi binary alloy. The heat resistance of the AgBi alloy film will be described with reference to FIG. AgBi alloy films are typical eutectic alloys. The solid state temperature S ₁ is 262 ° C. and 2
Melting up to 62 ° C. is not possible. The hermetically packaged quartz resonator and SAW resonator are arranged on a substrate, and generally are subjected to reflow soldering. The component peak temperature during reflow soldering is 220 to 260 ° C. Even at this reflow peak temperature, the operating temperature range of the airtight terminal solder plating film is set so that the soldered crystal unit and SAW resonator in the airtight terminal do not fall off. 220-26
The temperature is 0 ° C., and heat resistance that can withstand this range is required.
The AgBi material of the present proposal has a solid state temperature S ₂ of 26 as described above.
It is 2 ° C., which indicates that it has heat resistance to the reflow temperature.

An ordinary SnPb solder material has a solidus temperature S
Since ₁ and liquidus temperature S ₂ soldering workability is deteriorated leaves are used in eutectic per composition solid phase temperature and the liquidus temperature are matched. In the case of the AgBi alloy film of the present embodiment, the eutectic composition point S ₀ is Bi 95.3 at%, and has heat resistance properties. However, with such a composition having a high Bi content, the alloy itself becomes very brittle, so that AgBi is used. The alloy was never used as a solder material.

The composition of the AgBi alloy film used in the present invention deviates from the eutectic composition (Bi 95.3 at%), and the Bi content region S ₂ is 30 to 80 at% AgBi alloy or AgBi of this composition as a main component. Ag-Bi-α (α:
(Remainder) alloy. AgBi alloy is the composition region of the Bi amount solidus temperature _{S 1} is 262 ° C. and heat resistance even if the above 80at% is ensured, AgB by Bi content is increased
The i-alloy becomes very brittle and the tensile strength is rapidly deteriorated, so that the bonding strength between the crystal unit and the hermetic terminal is weak and lacks reliability. Further, even if the Bi content of the composition area falls below 30 at%, but also solidus temperature S ₁ is 262 ° C. and heat-resistant temperature is ensured, the liquidus temperature S ₂ becomes too above 500 ° C., the electronic component Cannot guarantee the heat resistant temperature. This is because generally, the heat-resistant temperature of an electronic component such as a crystal oscillator is 500 ° C. or less. Bi at 500 ℃ or less soldering work
When an AgBi alloy having an amount of 30 at% or less is used,
Residual melting occurs in the i-alloy, and the bonding strength between the crystal unit and the hermetic terminal also rapidly deteriorates. In addition, this Bi amount (30
In to 80 at%) composition region _{S 2,} since the inclination of the solid-liquid phase line _{S 3} is relatively gentle, variations in characteristics deviate composition slightly is small amount Bi is 80at% or more, or less 30 at% so as can be seen from Figure 2, that since the inclination increases and the liquid phase temperature of the temperature gradient of the solid-liquid phase line S ₄ of the liquid phase becomes sensitive to compositional variations, it must be controlled strictly composition adjustment Problems arise.

As another embodiment, besides Cu for improving adhesion, for example, Cr, T
There may be an underlayer of i, Ni or the like. Further, a protective film for protection such as oxidation prevention may be provided on the AgBi surface. S based on Sn commonly used as solder material
For materials such as nPb, SnCu, and SnAg, when a compressive stress is applied to the material, a special recrystallization process called a whisker occurs due to stress relaxation, which causes troubles such as an electrical short. Does not use Sn, such a problem does not occur.

Although the material cost of Ag is slightly higher than that of Sn-based materials, it is not as high as that of AuSn.
The ratio of the cost of the alloy material to the cost of the hermetic terminal is not so high, and the cost can be reduced. Ag of the present invention
The thickness of the Bi film is not particularly limited.
Since the amount of melted gBi is too small, the bonding strength decreases. 2
Even when the thickness is 0 μm or more, the film formation time is increased and waste is increased, so that the thickness is preferably about 5 to 20 μm. AgB
i may be formed by plating, sputtering, vapor deposition, or the like, or may be made into a foil, sandwiched between a lead wire of an airtight terminal and a bonding pad, and fused to be joined.

Next, the relationship between the bonding strength of the crystal unit and the Bi composition dependency of the present invention will be described using experimental data. The diameter of the hermetic terminal lead wire used in the experiment was φ
0.3 mm, and a Cu 2 μm underlayer
/ AgBi (Bi: at%) 10 μm was formed by plating. On the other hand, the bonding pad is made of an Au-plated quartz oscillator having a size of 0.3 × 0.2 mm ² ,
AgBi was joined at a temperature of 50 ° C., and the joining strength was examined. FIG. 3 is an experimental graph of the bond strength dependence when the Bi amount composition region S ₂₂ (xat%) is changed. For the bonding strength standard of 700 g / mm ² or more, B deviated from the eutectic composition
It can be seen that the adhesion strength satisfying the standard can be obtained when i is 30 to 80 at%. When Bi is 30% (S ₂₀ ) or less, as is clear from the AgBi phase diagram, the liquidus temperature is 5%.
At a bonding temperature of 450 ° C., AgBi
Since the alloy does not completely melt, the adhesion strength decreases, while Bi8
At 0 at% or more (S ₉₀ ), the Bi amount increases and AgBi
It is considered that the adhesion strength was also lowered because the alloy itself became brittle. In addition, the Bi composition-adhesion strength characteristic diagram of FIG. 3 is a graph that considers the dispersion of the adhesion measured 50 by 50 for each Bi amount.

[0019]

As described above, according to the present invention, an airtight terminal using Pb-free solder having low heat resistance and high reliability can be produced.

[0020]

[Brief description of the drawings]

FIG. 1 is a perspective view of an airtight terminal for explaining an embodiment of the present invention.

FIG. 2 is an AgBi alloy phase diagram for explaining an AgBi alloy film according to an example of the present invention.

FIG. 3 is a Bi composition-adhesion strength characteristic diagram for an AgBi alloy film of an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal outer ring 2 External lead 3 Glass 4 Element (quartz oscillator) 5 Metal case 6 Electrode 7 AgBi plating film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03H 9/02 H03H 9/02 EF term (Reference) 5J108 BB02 CC04 CC06 EE02 EE07 EE19 FF15 GG04 GG15 GG17 GG20 KK03 KK04 MM06

Claims (4)

[Claims] A non-eutectic Ag-Bi alloy having a Bi composition ratio of 30 to 80 at% at a soldered connection portion of an airtight terminal for soldering an element of an electronic component to a lead wire led out.
And Ag-B whose main component is Ag-Bi of this composition ratio.
An airtight terminal, wherein an i-α (remainder) alloy is formed. 2. The method according to claim 1, wherein C is formed under the AgBi alloy film.
An airtight terminal, wherein an underlayer of u, Cr, Ti, Ni or the like is formed. 3. The hermetic terminal according to claim 1, wherein the AgBi alloy film is formed by electrolytic plating. 4. The hermetic terminal according to claim 1, wherein hot air of 350 to 500 ° C. is blown onto the soldered connection portion of the hermetic terminal to melt and join the AgBi alloy, and a method of manufacturing the hermetic terminal.