WO2021049643A1

WO2021049643A1 - Lead-free solder alloy

Info

Publication number: WO2021049643A1
Application number: PCT/JP2020/034572
Authority: WO
Inventors: 西村　哲郎; 貴利西村; 徹哉赤岩
Original assignee: 株式会社日本スペリア社
Priority date: 2019-09-12
Filing date: 2020-09-11
Publication date: 2021-03-18
Also published as: JPWO2021049643A1

Abstract

The purpose of the present invention is to provide a lead-free solder alloy and a solder bonded body that, despite no addition of "Ni", have solderability and bonding characteristics as with a "Ni"-added lead-free solder alloy.　This lead-free solder alloy is characterized in that Sn-Cu is used as a basic composition and that the basic composition contains one or more selected from the group consisting of Co, Mn, Pd, Rh, and Fe. By using the lead-free solder alloy, it is possible to achieve: a lead-free solder alloy that, as compared with a "Ni"-containing lead-free solder, is free from Ni sensitization, and exhibits excellent solderability and workability during soldering and excellent mechanical characteristics and bonding reliability; and a solder bonded body using the lead-free solder alloy.

Description

Lead-free solder alloy

The present invention relates to a lead-free solder alloy having excellent soldering characteristics and long-term reliability, and a solder joint using the alloy.

Lead-free solder is widely used as a bonding material for electronic parts in order to reduce the burden on the global environment, and Sn-Ag-Cu-based solder alloys and Sn-Cu-Ni-based solder alloys are typical compositions thereof.
In recent years, Sn-Cu-Ni-based solder alloys have excellent properties such as high mechanical strength, stability of joint strength against thermal history and impact, high fluidity and good mountability, and Sn-Ag. -The market is rapidly spreading due to the added cost advantage over Cu-based solder.

However, the Sn-Cu-Ni-based solder alloy contains a small amount of "Ni", which is recognized as a skin sensitizing substance. On the other hand, "Ni" is a substance that is also contained in 500-yen coins, and is a component that is also found in environments where many people often touch it with their bare hands.
Lead-free solder as a bonding material is often used in the manufacture of electronic parts and electronic devices, but the current situation is that it is used in extremely limited environments compared to the opportunities that ordinary people touch, such as 500-yen coins. Is.
Companies are required to provide safer products that do not contain skin sensitizers.

By the way, in lead-free solder, many advantages are known regarding the effect of adding "Ni". In particular, in a lead-free solder alloy containing Sn-Cu as a main component, the fluidity is improved by adding "Ni". Is disclosed in Patent Document 1.
Further, as an effect of adding "Ni", as disclosed in Patent Document 2, an intermetallic compound (hereinafter, IMC) having a composition of _{(Cu, Ni) 6} Sn _{5 is generated at the bonding interface with the copper substrate.} It is known to have excellent mechanical properties and joint reliability.

Therefore, there is a demand for a lead-free solder alloy composition that has the same excellent solderability and joining reliability as that of "Ni" addition, while having a lead-free solder alloy composition without adding "Ni".

Japanese Patent No. 3152945 International Publication No. 2009-051255

An object of the present invention is to provide a lead-free solder alloy and a solder joint that have the same solderability and joint reliability as that of the addition of "Ni" while not adding "Ni".

As a result of diligent studies on elements that replace "Ni" in Sn—Cu-based lead-free solder alloys, the inventors have conducted the same as lead-free solder alloys in which "Ni" is added to Co, Mn, Pd, Rh, and Fe. They have found that they have solderability and joining reliability, and have completed the present invention.

That is, the present invention comprises a lead-free solder alloy containing Sn—Cu as a basic composition and one or more selected from the group of Co, Mn, Pd, Rh and Fe in the basic composition. And a solder joint using the lead-free solder alloy.

Since the present invention can have solderability equal to or higher than that of a lead-free solder alloy containing "Ni" and high bonding reliability while not adding "Ni", it can be applied to electronic parts, electronic devices, and the like. It is a highly safe solder alloy that can be applied to soldering in a wide range of versatility and has little effect on the human body.

Graph comparing zero cross times SEM photograph of Example 2 SEM photograph of Comparative Example 1 SEM photograph of Comparative Example 2 Coagulation sample photograph of Example 2 Coagulation sample photograph of Comparative Example 1 Coagulation sample photograph of Comparative Example 2

Hereinafter, the present invention will be described in detail.
The lead-free solder alloy of the present invention is characterized by containing Sn—Cu as a basic composition and containing one or more selected from the group of Co, Mn, Pd, Rh, and Fe. It is a solder alloy and a solder joint using the lead-free solder alloy.
Further, by containing Ge, Ga, P, Si, Al, V, and Zr having an antioxidant effect, solderability and workability at the time of soldering are further improved.

The Sn—Cu-based lead-free solder alloy to which "Ni" is added is known to have excellent mounting performance with stability of joint strength and solderability. _{These factors include the formation of (Cu, Ni) 6} Sn ₅ IMC by the addition of "Ni" and the miniaturization of IMC particles.
_{Cu 6} Sn ₅ in the Sn—Cu based solder alloy has a stable crystal structure of monoclinic crystals (hereinafter, η'phase) and hexagonal crystals (hereinafter, η phase) at 186 ° C., respectively, and has an environmental temperature. It is known that the crystal structure on the stable side undergoes a phase transformation.
Furthermore, it is known that stress-strains may accumulate inside the crystal due to changes in the volume of the crystal during phase transformation, leading to the occurrence of cracks.
_{On the other hand, (Cu, Ni) 6} Sn ₅ formed in the Sn—Cu based solder alloy to which “Ni” is added has only the η phase, and the above phase transformation does not occur, and therefore the accumulation of stress strain inside the crystal and the accumulation of stress strain inside the crystal occur. Cracks do not occur and a stable bonding state can be maintained.
Further, the finely divided (Cu, Ni) ₆ Sn ₅ IMC particles disperse and strengthen the solder alloy, and its mechanical strength is improved.
Due to these excellent characteristics, when the cold environment is continuously repeated, even if the temperature environment changes such as heat cycle and aging that is maintained at high temperature for a long time, the decrease in joint strength is suppressed and it is stable for a longer period of time. The effect of maintaining a good bond can be obtained.

Further, the addition of "Ni" improves the fluidity of the solder alloy. Improving fluidity is a very important property in terms of improving mountability. When the fluidity is lowered, needle-like crystals are generated, bridges are generated to short-circuit the conductors, and protrusion-shaped horns are generated when the substrate on which the electronic component is attached separates from the molten layer, resulting in poor quality. Further, if the wettability of the solder alloy with respect to the base material or the electronic component is lowered, the through-hole rising property is deteriorated, resulting in poor quality. Products that have the phenomenon of bridges and horns and worsening through-hole rise are eliminated as defective products at the time of mounting, and the yield is reduced. The decrease in mountability greatly affects the decrease in efficiency in mass production work.

In the present invention, Co, Pd, Rh, Mn, and Fe were selected as the elements substitutable for "Ni" in order to have the same characteristics as when "Ni" was added. The selected element has the same effect of refining IMC particles as the effect of "Ni".

It is known that Sn—Cu-based lead-free solder alloys to which "Ni" is added have improved mechanical strength. Comparing the SEM photographs of the solder alloy with "Ni" added in Fig. 2 and the solder alloy with Co added in Fig. 3, the IMC particles have an elliptical shape and large dimensions, with a major axis of about 1.2 μm and a minor axis of about 0.8. An IMC of μm and the same shape and size is formed at the bonding interface. It can be seen that in the solder alloy to which Co is added, the IMC is miniaturized as in the case where "Ni" is added, and the shape and dimensions are the same. On the other hand, the fact that the IMC particles are made finer by the solder alloy to which Co is added and the shape and dimensions of the IMC particles are the same as those of the solder alloy to which "Ni" is added means that the solder alloy to which Co is added also has the same mechanical strength. It can be said that it is improving.
It is known that the IMC formed at the bonding interface has the property of being harder and more brittle than the solder alloy. Since the IMC, the substrate, and the electronic components have different coefficients of linear expansion, stress is generated by thermal shock, and if the stress is biased, the IMC cracks, the IMC in the brittle part is destroyed, and the bonding reliability of the solder alloy is impaired. .. By suppressing the growth of IMC and making it finer, it becomes a highly reliable solder alloy with stable joint strength that can withstand stress.

Similar to Ni and Co, by adding the elements Pd, Rh, Mn, and Fe, which refine the IMC particles, to the solder alloy, an IMC having the same shape as when "Ni" is added is formed mechanically. It is expected that the strength will be improved and the solder alloy will have stable joint strength and high reliability.

Next, in order to compare the fluidity that affects the mountability of the solder alloy, we measured and compared the wettability as an index. The wettability of the solder alloy in which "Ni" shown in Table 2 and FIG. 1 was replaced with another element was measured, and the results showed that the wettability was improved as compared with the solder alloy to which "Ni" was added. You can see that. In particular, the solder alloy to which Co is added has a value of 90 to 94% as compared with Comparative Example 1 to which "Ni" is added, and has an excellent effect of improving wettability as compared with Pd, Rh, Mn and Fe. It turned out that there was. From the measurement results of wettability, the solder alloy of the present invention has improved fluidity, suppresses the generation of bridges and horns, and improves the through-hole rise property, and is a solder alloy with excellent mountability. found.

The lead-free solder alloy of the present invention has Sn and Cu as basic compositions, and is characterized by containing one or more selected from the group of Co, Mn, Pd, Rh, and Fe.
The Cu content is preferably 0.1 to 1.0% by mass, more preferably 0.5 to 0.9% by mass.
The Co content is preferably 0.001 to 0.1% by mass, more preferably 0.01 to 0.05% by mass.
The Mn content is preferably 0.001 to 0.01% by mass, more preferably 0.003 to 0.008% by mass.
The content of Pd is preferably 0.01 to 1.0% by mass, more preferably 0.04 to 0.1% by mass.
The content of Rh is preferably 0.005 to 0.5% by mass, more preferably 0.01 to 0.1% by mass.
The Fe content is preferably 0.001 to 0.01% by mass, more preferably 0.003 to 0.008% by mass.
The Sn content is other than the above elements and unavoidable impurities.
Among the "Ni" substitution elements of Co, Mn, Pd, Rh and Fe, Co is preferable.

Further, as an element having an antioxidant effect that can be added to the lead-free solder alloy of the present invention, one or more selected from the group of Ge, Ga, P, Si, Al, V, Zr) can be used. The content thereof is not particularly limited as long as it has the effect of the present invention, but the following content is preferable.
The content of Ge is preferably 0.0001 to 0.1% by mass, more preferably 0.005 to 0.01% by mass.
The content of Ga is preferably 0.0001 to 0.1% by mass, more preferably 0.003 to 0.008% by mass.
The content of P is preferably 0.0001 to 0.1% by mass, more preferably 0.003 to 0.005% by mass.
The Si content is preferably 0.0001 to 0.1% by mass, more preferably 0.005 to 0.01% by mass.
The Al content is preferably 0.0001 to 0.05% by mass, more preferably 0.003 to 0.008% by mass.
The V content is preferably 0.0001 to 0.05% by mass, more preferably 0.005 to 0.01% by mass.
The Zr content is preferably 0.0001 to 0.05% by mass, more preferably 0.005 to 0.01% by mass.

The lead-free solder alloy of the present invention is characterized in that Sn and Cu are used as basic compositions, and one or more selected from the group of Co, Mn, Pd, Rh, and Fe is contained therein.
Furthermore, by containing one or more selected from the group of Ge, Ga, P, Si, Al, V, and Zr as an element having an antioxidant effect, excellent soldering characteristics and high bonding reliability are included. However, Ag, Sb, Bi, In, Zn, Ti and the like can also be contained within the range having the effect of the present invention.
In addition, the shape can be arbitrarily processed according to the application. For example, when soldering is performed by the dip soldering method, the solder shape is rod-shaped, and when soldering is performed by the reflow soldering method, a paste or ball is used. In the case of solder joining using a soldering iron in the shape and preform shape, it is possible to process and use it in a linear shape such as solder.

The present invention will be described in more detail with reference to Examples.
(Wetability evaluation)
Wetness evaluation was carried out to prove the effect of the present invention.
[Evaluation sample]
Evaluation sample: Solder alloy with the composition shown in Table 1.

〔Evaluation methods〕
-Solder alloys of Examples 1 to 25 and Comparative Examples 1 to 3, standard flux B, and phosphorus deoxidized copper plate (thickness: 0.3 mm, width: 10 mm, length) according to JISZ3197: 2012 "Wetting Balance Method". Dimension: 30 mm), and using a solder checker (SAT-5100) manufactured by Reska Co., Ltd., the immersion depth is 2 mm, the immersion speed is 20 mm / sec, the immersion time is 10 seconds, and the solder bath temperature is 35 ± 3 from the liquidus temperature. The measurement was performed under the condition of ° C. (according to JIS).
The results are shown in Table 2 and FIG.
The evaluations shown in Table 2 and FIG. 1 represent the values of Examples 1 to 25 and Comparative Examples 2 and 3 with the zerox time and the zero cross time of Comparative Example 1 as 100%.

As shown in Table 2 and FIG. 1, all the samples of Examples 1 to 25 showed a numerical value of less than 100%, and were wetted as compared with Comparative Example 1 to which "Ni" having an effect of improving wettability was added. It turned out to be excellent in sex. Among them, Examples 2, 6 to 8, 9, 12, 17, and 20 to 22 containing Co accounted for 90 to 94%, which was smaller than 94 to 98% of Examples to which other elements were added. , It can be seen that the effect of improving wettability is high.

Further, in Examples 6 to 25, as elements having an antioxidant effect, Ge0.0001 to 0.1% by mass, Ga0.0001 to 0.1% by mass, P0.0001 to 0.1% by mass, Si0.0001 to Si0.0001 to It contains one or more of 0.1% by mass, Al0.0001 to 0.05% by mass, V0.0001 to 0.05% by mass, and Zr0.001 to 0.05% by mass. The zero cross times of Examples 6 to 25 are all smaller than those of Comparative Example 1, and even if an element having an antioxidant content is contained, the element that does not hinder the wettability and refines the particles of the intermetallic compound is present. It can be seen that it is effective.

From the results shown in Table 2 and FIG. 1, it was found that all of the examples of the present invention were superior in wettability as compared with Comparative Example 1 to which "Ni" was added.
Further, when the state at the time of sample melting was visually observed, it was confirmed that Examples 1 to 25 were comparable in fluidity to Comparative Example 1.

(Evaluation of joint condition)
In order to evaluate the bonded state, the copper plates (phosphorylated copper plates) of Example 2, Comparative Example 1 and Comparative Example 2 in which the wettability was evaluated were surface-etched and the surface was observed.
[Observation sample preparation method]
Sodium hydroxide solution (concentration: 50 g / L) and ortho-nitrophenol solution (concentration: 3)
In a state where the solution mixed with 5 g / L) was heated to about 60 ° C., the soldered surface of the copper plate whose wettability was evaluated was immersed for about 5 minutes, polished with a cotton swab, washed with running water, and naturally dried for observation. It was used as a sample.
[Observation method]
It was observed and evaluated at a magnification of 7000 times using a scanning electron microscope (JSM-6360LA) manufactured by JEOL Ltd.

Comparing the IMC particles formed at the bonding interface in Example 2 and Comparative Example 1 from the SEM photographs of FIGS. 2 to 4, they both have an elliptical shape, a large particle size, a major axis of 1.2 μm, and a minor axis of 0.8. An IMC having the same shape and size, which is about μm, is formed at the bonding interface. It can be seen that in the solder alloy to which Co is added, the IMC is miniaturized as in the case of the solder alloy to which "Ni" is added, and the shape and dimensions are the same.
However, Comparative Example 2 containing no Ni or Co has a shape closer to a circle than Example 2 and Comparative Example 1, and has a large IMC particle size diameter of about 2.0 μm. It is about twice as much as that of Comparative Example 1 containing 2 or "Ni".

It is known that Sn—Cu-based lead-free solder alloys to which "Ni" is added have improved mechanical strength. The fact that the IMC particles of the solder alloy to which Co is added becomes finer and the shape and dimensions of the IMC particles are the same as those of the solder alloy to which "Ni" is added means that the mechanical strength of the solder alloy to which Co is added is also improved. Indicates that
Further, the IMC formed at the bonding interface is known to have a property of being harder and more brittle than a solder alloy. Since the IMC, the substrate, and the electronic components have different coefficients of linear expansion, stress is generated by thermal shock, and if the stress is biased, the IMC cracks, the IMC in the brittle part is destroyed, and the bonding reliability of the solder alloy is impaired. .. By suppressing the growth of IMC and making it finer, it becomes a highly reliable solder alloy with stable joint strength that can withstand stress.
Similar to Ni and Co, by adding the elements Pd, Rh, Mn, and Fe, which refine the IMC particles, to the solder alloy, an IMC having the same shape as when "Ni" is added is formed. It can be expected that the mechanical strength will be improved and the solder alloy will have stable joint strength and high reliability.

That is, the SEM photographs of FIGS. 2 to 4 show a comparison in which the lead-free solder alloy of the present invention containing Co in the composition based on Sn—Cu of Example 2 is a conventional composition containing “Ni”. Similar to Example 1, it shows that it is a highly reliable solder alloy with improved mechanical strength and stable bonding strength.
Similarly, since the IMC particles are also refined into the elements of Mn, Pd, Rh, and Fe, the IMC particles formed by adding Mn, Pd, Rh, and Fe improve the mechanical strength of the solder alloy. It is presumed that the solder alloy to which Mn, Pd, Rh, and Fe are added has the effect of stabilizing the bonding strength and is a highly reliable solder alloy.

(Evaluation of solderability)
Next, the solidification test result of the lead-free solder alloy of the present invention will be described.
[Coagulation test method]
About 50 g of the solder alloy as a sample was weighed, melted at 270 ° C., and then about 40 g was poured into a mold and allowed to cool at room temperature to prepare a solidified sample.
[Coagulation test evaluation method and results]
As an evaluation method, the gloss of the surface and the presence or absence of shrinkage cavities were visually evaluated.
FIG. 5 which is a coagulation sample of Example 2 of the present invention and FIG. 6 which is a coagulation sample of Comparative Example 1 containing "Ni" are excellent in surface gloss and no shrinkage cavities are observed, whereas Co is used. In FIG. 7, which is Comparative Example 2 not contained, although the surface is glossy, a shrinkage cavity is seen in the central part of the solidified sample.
Since the effect of adding "Ni" to the surface gloss is excellent and no shrinkage cavities are generated, the same effect can be seen in Example 2 in which Co is added, Co is a component of the lead-free solder alloy of the present invention. Is proof that it has a substitute effect of "Ni".

Although the present invention does not contain "Ni", the lead-free solder alloy containing "Ni" has excellent solderability, workability at the time of soldering, mechanical properties, and joining reliability of the same or higher. Since it is possible to provide a solder joint, it can be expected to be widely applied to the joining of electronic devices and electronic parts.

Claims

Sn and Cu are used as basic compositions, and one or more selected from the group of Co, Mn, Pd, Rh, and Fe is contained therein, and the content of each is 0.1 to Cu. 1.0% by mass, Co content 0.001 to 0.1% by mass, Mn content 0.001 to 0.01% by mass, Pd content 0.01 to 1.0% by mass , A lead-free solder alloy characterized in that the content of Rh is 0.005 to 0.05% by mass, the content of Fe is 0.001 to 0.01% by mass, and the balance is unavoidable impurities and Sn.
As an element having an antioxidant effect, one or more selected from the group of Ge, Ga, P, Si, Al, V, Zr is contained, and the content of each is 0. .0001 to 0.1% by mass, Ga content is 0.0001 to 0.1% by mass, P content is 0.0001 to 0.1% by mass, and Si content is 0.0001 to 0. 1% by mass, Al content is 0.0001 to 0.05% by mass, V content is 0.0001 to 0.05% by mass, and Zr content is 0.0001 to 0.05% by mass. The lead-free solder alloy according to claim 1, wherein the lead-free solder alloy is characterized by the above.
A solder joint body characterized by being solder-bonded using the lead-free solder alloy according to claim 1 and 2.