JP2020192600A - Solder alloy, solder powder, solder paste, and solder joint using them - Google Patents

Abstract

To provide a solder alloy, solder powder and the like which suppress changes with time of a solder paste, are excellent in wettability, have a small temperature difference between a liquidus line temperature and a solidus line temperature, have high mechanical characteristics and exhibit a high joint strength.SOLUTION: A solder alloy has an alloy composition of at least one of 0.55-0.75 mass% Cu, 0.0350-0.0600 mass% Ni, 0.0035-0.0200 mass% Ge, 25-300 mass% ppm As, 0-3,000 mass ppm Sb, 0-10,000 mass ppm Bi, and 0-5,100 mass ppm Pb, and the balance Sn, and satisfies Expression (1): 275≤2As+Sb+Bi+Pb and Expression (2): 0.01≤(2As+Sb)/(Bi+Pb)≤10.00, in Expressions (1) and (2), As, Sb, Bi and Pb each satisfy a content (mass ppm) in the alloy composition.SELECTED DRAWING: None

Description

The present invention relates to solder alloys, solder powders, solder pastes, and solder joints using these.

For various electronic devices, a mounting board in which electronic components are mounted on a printed circuit board is used. In addition to a single-layer board, a mounting board in which a plurality of boards are laminated in order to realize a full range of functions is used. Examples of the conduction between the boards and the mounting of electronic components on the board include a method of connecting by surface mounting and a method of inserting terminals into through holes of the board for mounting. Examples of the mounting process on such a printed circuit board include flow soldering, reflow soldering, and manual soldering.

Among these, for mounting electronic components having a certain size, a method of inserting terminals into through holes for mounting is adopted from the viewpoint of connection strength and the like. Flow soldering is usually used as the mounting process. Flow soldering is a method of soldering by applying the jet surface of a solder bathtub to the connection surface side of a printed circuit board.

Examples of the solder alloy used for such flow soldering include Sn—Cu—Ni solder alloys as described in Patent Document 1. In this solder alloy, Cu is added to Sn to strengthen the solid solution of the solder alloy itself, and Ni is added to form an intermetallic compound such as Cu ₆ Sn ₅ or Cu ₃ Sn in the solder alloy. It is said that the occurrence can be suppressed. Further, it is described in the same document that the high melting point of these intermetallic compounds inhibits the fluidity of the molten metal when the alloy is melted.

By the way, in recent years, electronic devices having a solder joint such as a CPU (Central Processing Unit) are required to be miniaturized and have high performance. Along with this, it is necessary to reduce the size of the electrodes of the printed circuit board and the electronic device. Since the electronic device is connected to the printed circuit board via the electrodes, the solder joint connecting the two becomes smaller as the electrodes become smaller. When connecting such fine electrodes, flow soldering is not an appropriate mounting method.

In order to connect an electronic device and a printed circuit board via such fine electrodes, reflow soldering using a solder paste is generally adopted. Reflow soldering is a method in which a paste is collectively applied to electrodes on a printed circuit board via a metal mask, and the printed circuit board on which an electronic device is mounted is introduced into a reflow furnace and soldered. Here, when the solder paste is purchased, normally, not all of the solder paste is used up in one printing. Therefore, the solder paste must maintain an appropriate viscosity at the time of manufacture so as not to impair the printing performance.

For example, Patent Document 2 includes Sn and one or more selected from the group consisting of Ag, Bi, Sb, Zn, In, and Cu in order to suppress the change of the solder paste with time. , A solder alloy containing a predetermined amount of As is disclosed. The document shows that the viscosity after 2 weeks at 25 ° C. is less than 140% of the initial viscosity. The document also describes that it contains less than 10 ppm of Ni as an unavoidable impurity.

Japanese Unexamined Patent Publication No. 2000-197988 JP-A-2015-98052

The invention described in Patent Document 1 is mainly designed for use in flow soldering, and focuses on the fluidity of molten solder and the tensile strength of the solder alloy. As described above, the object to be joined by flow soldering is a relatively large electronic component, and as described above, it is difficult to be adopted for connecting an electronic device having fine electrodes. Further, in the solder joint joined by the solder alloy, the joining interface must not be broken, but in the solder alloy described in Patent Document 1, only the mechanical properties of the solder alloy itself are paid attention to. The solder alloy described in Patent Document 1 contains Ni in order to suppress the formation of a compound of Sn and Cu, but as described above, Ni is consumed in order to improve the mechanical strength of the solder alloy itself, and the solder is soldered. It is uncertain whether the strength at the joint interface of the joint is sufficiently improved. Further studies are required to join the fine electrodes of recent years without any problem.

Further, as described above, the invention described in Patent Document 2 is a solder alloy which can selectively contain 6 kinds of elements in addition to Sn and As. Further, the same document shows that the meltability is inferior when the As content is high.

Here, the meltability evaluated in Patent Document 2 is considered to correspond to the wettability of the molten solder. The meltability disclosed in the document is evaluated by observing the appearance of the melt with a microscope and the presence or absence of solder powder that cannot be completely melted. This is because if the wettability of the molten solder is high, it is difficult for solder powder that cannot be completely melted to remain.

Generally, it is necessary to use a highly active flux in order to improve the wettability of the molten solder. In the flux described in Patent Document 2, it is considered that a highly active flux may be used in order to suppress the deterioration of wettability due to As. However, when a highly active flux is used, the viscosity of the paste increases because the reaction between the solder alloy and the activator proceeds. Further, in view of the description of Patent Document 2, it is necessary to increase the As content in order to suppress the increase in viscosity. In order for the solder paste described in Patent Document 2 to exhibit a lower viscosity increase rate and excellent wettability, it is necessary to continuously increase the active force of the flux and the As content, which causes a vicious cycle.

Recently, solder paste is required to maintain stable performance for a long period of time regardless of the usage environment and storage environment, and further higher wettability is also required due to the miniaturization of solder joints. When trying to meet recent demands by using the solder paste described in Patent Document 2, a vicious cycle is unavoidable as described above.

Further, in order to join fine electrodes, it is necessary to improve the mechanical properties of the solder joint. Depending on the element, when the content increases, the liquidus temperature rises, the liquidus temperature and the solidus temperature spread, and segregation occurs during solidification to form a non-uniform alloy structure. If the solder alloy has such an alloy structure, mechanical properties such as tensile strength are inferior, and the solder joint is easily broken by external stress. This problem has become remarkable with the recent miniaturization of electrodes.

An object of the present invention is a solder alloy that suppresses changes over time in a solder paste, has excellent wettability, has a small temperature difference between the liquidus temperature and the solidus temperature, has high mechanical properties, and exhibits high bonding strength. It is to provide a solder powder, a solder paste, and a solder joint using these.

When suppressing the change over time of the paste and improving the excellent wettability at the same time, it is necessary to avoid a vicious cycle due to the use of a flux having high activity and an increase in As content. Further, the solder joint needs to have high joint strength. The present inventors paid attention to the alloy composition of the solder alloy, and worked diligently to improve the joint strength of the solder joint and to suppress the change of the paste with time and to achieve both excellent wettability regardless of the type of flux. Study was carried out.

First, the present inventors focused on suppressing the formation of a compound of Sn and Cu in the solder alloy and suppressing the deterioration of the wettability due to the oxidation of the molten solder as in the conventional case, and set the SnCuNi solder alloy to Ge. The basic composition was an alloy in which a small amount of solder was added. In this basic composition, the range of Cu content was limited in order to suppress thermal damage to the electronic device due to the rise in the liquidus temperature and to improve the strength of the solder joint. Further, the range of Ni content is also limited from the viewpoint that the growth suppressing effect of the SnCu compound by Ni is exhibited not only in the solder alloy but also at the bonding interface and a large amount of precipitation of the SnCuNi compound near the bonding interface is suppressed. ..

Furthermore, the present inventors examined a solder powder containing As in a SnCuNiGe solder alloy. Then, focusing on the reason for suppressing the change with time of the solder paste when this solder powder was used, the As content was investigated.

The reason why the viscosity of the solder paste increases with time is considered to be that the solder powder reacts with the flux. Comparing the results of Table 1 Example 4 and Comparative Example 2 of Patent Document 2, the result shows that the viscosity increase rate is lower when the As content exceeds 100 mass ppm. In view of these, when focusing on the effect of suppressing the change with time of the paste (hereinafter, appropriately referred to as "thickening suppressing effect"), it seems that the As content may be further increased. However, when the As content is increased, the thickening suppressing effect is slightly increased with the As content, but the thickening suppressing effect is not obtained according to the increase in the As content. It is considered that this is because the amount of As concentrated on the surface of the solder alloy is limited, and even if the amount of As is contained in a predetermined amount or more, the amount of As inside the solder alloy, which is difficult to exert the thickening suppressing effect, increases. Be done. It was also confirmed that if the As content is too large, the wettability of the solder alloy deteriorates.

Therefore, the present inventors have expanded the range of As content to a range in which the As content is low and the thickening suppressing effect is not exhibited, and then add an element other than As that exhibits the thickening suppressing effect. Realizing that it was necessary to do so, I investigated various elements. As a result, by chance, it was found that Sb, Bi and Pb exert the same effect as As. The reason for this is not clear, but it can be inferred as follows.

Since the thickening suppressing effect is exerted by suppressing the reaction with the flux, an element having a low reactivity with the flux includes an element having a low ionization tendency. Generally, the ionization of an alloy is considered in terms of the ionization tendency as the alloy composition, that is, the standard electrode potential. For example, a SnAg alloy containing Ag, which is noble to Sn, is more difficult to ionize than Sn. Therefore, an alloy containing an element nobler than Sn is difficult to ionize, and it is presumed that the effect of suppressing thickening of the solder paste is high.

Here, in Patent Document 2, in addition to Sn, Ag, and Cu, Bi, Sb, Zn, and In are listed as equivalent elements, but in terms of ionization tendency, In and Zn are base to Sn. Element. That is, Patent Document 2 describes that the thickening suppressing effect can be obtained even if an element lower than Sn is added. Therefore, it is considered that the solder alloy containing the element selected according to the ionization tendency can obtain the same or higher thickening suppressing effect as compared with the solder alloy described in Patent Document 2. Further, as described above, as the As content increases, the wettability deteriorates.

The present inventors have investigated in detail Bi and Pb that exert an effect of suppressing thickening. Since Bi and Pb lower the liquidus temperature of the solder alloy, the wettability of the solder alloy is improved when the heating temperature of the solder alloy is constant. However, since the solidus temperature is significantly lowered depending on the content, ΔT, which is the temperature difference between the liquidus temperature and the solidus temperature, becomes too wide. If ΔT becomes too wide, segregation will occur during solidification, leading to deterioration of mechanical properties such as mechanical strength. It was also found that strict control is necessary because the phenomenon that ΔT spreads remarkably appears when Bi and Pb are added at the same time.

Furthermore, the present inventors re-examined the Bi content and the Pb content in order to improve the wettability of the solder alloy, but as the content of these elements increased, ΔT became wider. Therefore, the present inventors select Sb as an element whose ionization tendency is noble with respect to Sn and improve the wettability of the solder alloy, determine the allowable range of the Sb content, and then determine Sb. The relationship regarding the content of each of As, Bi, Pb, and Sb included was investigated in detail. As a result, by chance, when the contents of all the above-mentioned constituent elements are within a predetermined range and the contents of As, Bi, Pb, and Sb satisfy a predetermined relational expression, SnCu at the bonding interface Findings that the growth of the compound is suppressed, the formation of the SnCuNi compound in the vicinity of the bonding interface is suppressed, and there is no practical problem in all of the excellent thickening suppressing effect, wettability, and narrowing of ΔT. Was obtained, and the present invention was completed.

The present invention obtained from these findings is as follows.
(1) Cu: 0.55 to 0.75% by mass, Ni: 0.0350 to 0.0600% by mass, Ge: 0.0035 to 0.0200% by mass, As: 25 to 300% by mass, and Sb: It has an alloy composition consisting of at least one of 0 to 3000 mass ppm, Bi: 0 to 10000 mass ppm, and Pb: 0 to 5100 mass ppm, and the balance of Sn, and the following equations (1) and (2) are used. A solder alloy characterized by filling.

275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
In the above equations (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

(2) Further, the solder alloy according to (1) above, wherein the alloy composition satisfies the following formula (1a).
275 ≦ 2As + Sb + Bi + Pb ≦ 25200 (1a)
In the above formula (1a), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

(3) Further, the solder alloy according to (1) above, wherein the alloy composition satisfies the following formula (1b).
275 ≦ 2As + Sb + Bi + Pb ≦ 5300 (1b)
In the above formula (1b), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

(4) The solder alloy according to any one of (1) to (3) above, wherein the alloy composition satisfies the following formula (2a).
0.31 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2a)
In the above formula (2a), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

(5) The solder alloy according to any one of (1) to (4) above, wherein the alloy composition further contains Ag: 0 to 4% by mass.
(6) A solder powder having the solder alloy according to any one of (1) to (5) above.

(7) A solder paste having the solder powder according to (6) above.
(8) A solder joint having the solder alloy according to any one of (1) to (5) above.

The present invention will be described in more detail below. In the present specification, "ppm" relating to the solder alloy composition is "mass ppm" unless otherwise specified. “%” Is “mass%” unless otherwise specified.

1. 1. Alloy composition (1) Cu: 0.55 to 0.75%
Cu is used in general solder alloys and is an element that improves the joint strength of solder joints. Further, Cu is a noble element with respect to Sn, and when it coexists with As, it promotes the thickening suppressing effect of As. If Cu is less than 0.55%, the strength of the solder joint will not improve. The lower limit of the Cu content is 0.55% or more, preferably 0.55% or more, and more preferably 0.60% or more. On the other hand, if the Cu content exceeds 0.75%, the melting point of the solder alloy rises, causing thermal damage to electronic components. The upper limit of the Cu content is 0.75% or less, preferably less than 0.75%, and more preferably 0.70% or less.

(2) Ni: 0.0350 to 0.0600%
Ni is an element that suppresses the growth of intermetallic compounds such as Cu ₃ Sn and Cu ₆ Sn _{5 at the} bonding interface. When the Ni content is less than 0.0350%, these intermetallic compounds grow and the mechanical strength of the solder joint deteriorates. The lower limit of the Ni content is 0.0350% or more, preferably 0.0350% or more, and more preferably 0.0400% or more. On the other hand, when the Ni content exceeds 0.0600%, a large amount of SnCuNi compound is precipitated in the vicinity of the bonding interface in the solder alloy, and the mechanical strength of the solder joint deteriorates. The upper limit of the Ni content is 0.0600% or less, preferably less than 0.0600%, and more preferably 0.0550% or less.

(3) Ge: 0.0035-0.0200%
Ge is an element that suppresses the oxidation of the solder alloy, prevents discoloration of the solder alloy and deterioration of wettability, and suppresses the generation of dross derived from Fe. When the Ge content is less than 0.0035%, discoloration of the solder alloy and deterioration of wettability occur. The lower limit of the Ge content is 0.0035% or more, preferably 0.0040% or more, more preferably 0.0050% or more, and further preferably 0.0080% or more. On the other hand, if the Ge content exceeds 0.0200%, a large amount of oxides are deposited on the surface of the solder alloy, resulting in deterioration of wettability, and accordingly, the mechanical strength of the solder joint is deteriorated. The upper limit of the Ge content is 0.0200% or less, preferably less than 0.0200%, more preferably 0.0150% or less, and particularly preferably 0.0120% or less.

(4) As: 25 to 300 ppm
As is an element capable of suppressing a change in the viscosity of the solder paste over time. It is presumed that As has low reactivity with flux and is a noble element for Sn, so that it can exert an effect of suppressing thickening. If As is less than 25 ppm, the thickening suppressing effect cannot be sufficiently exerted. The lower limit of the As content is 25 ppm or more, preferably 25 ppm or more, more preferably 50 ppm or more, and further preferably 100 ppm or more. On the other hand, if the amount of As is too large, the wettability of the solder alloy deteriorates. The upper limit of the As content is 300 ppm or less, preferably less than 300 ppm, more preferably 250 ppm or less, further preferably 200 ppm or less, and particularly preferably 150 ppm or less.

(5) At least one kind Sb having Sb: 0 to 3000 ppm, Bi: 0 to 10000 ppm, and Pb: 0 to 5100 ppm is an element having low reactivity with flux and exhibiting a thickening suppressing effect. When the solder alloy according to the present invention contains Sb, the lower limit of the Sb content is 0% or more, preferably more than 0 ppm, more preferably 25 ppm or more, still more preferably 50 ppm or more, and particularly preferably. Is 100 ppm or more, and most preferably 200 ppm or more. On the other hand, if the Sb content is too large, the wettability deteriorates, so it is necessary to set the content to an appropriate level. The upper limit of the Sb content is 3000 ppm or less, preferably 1150 ppm or less, and more preferably 500 ppm or less.

Like Sb, Bi and Pb are elements that have low reactivity with flux and exhibit an effect of suppressing thickening. Further, Bi and Pb are elements that can suppress deterioration of wettability due to As because the liquidus temperature of the solder alloy is lowered and the viscosity of the molten solder is reduced.

If at least one element of Sb, Bi and Pb is present, deterioration of wettability due to As can be suppressed. When the solder alloy according to the present invention contains Bi, the lower limit of the Bi content is 0% or more, preferably more than 0 ppm, more preferably 25 ppm or more, still more preferably 50 ppm or more, and even more. It is preferably 75 ppm or more, particularly preferably 100 ppm or more, and most preferably 200 ppm or more. When the solder alloy according to the present invention contains Pb, the lower limit of the Pb content is 0% or more, preferably more than 0 ppm, more preferably 25 ppm or more, still more preferably 50 ppm or more, and even more. It is preferably 75 ppm or more, particularly preferably 100 ppm or more, and most preferably 200 ppm or more.

On the other hand, if the content of these elements is too large, the solidus temperature is remarkably lowered, so that ΔT, which is the temperature difference between the liquidus temperature and the solidus temperature, becomes too wide. If ΔT is too wide, the liquid phase Bi and Pb will be concentrated because a high melting point crystal phase having a low content of Bi and Pb is precipitated in the solidification process of the molten solder. After that, when the temperature of the molten solder is further lowered, the low melting point crystal phase having a high concentration of Bi and Pb is segregated. Therefore, the mechanical strength and the like of the solder alloy are deteriorated, and the reliability is deteriorated. In particular, since the crystal phase having a high Bi concentration is hard and brittle, segregation in the solder alloy significantly lowers the reliability.

From such a viewpoint, when the solder alloy according to the present invention contains Bi, the upper limit of the Bi content is 10,000 ppm or less, preferably 1000 ppm or less, more preferably 600 ppm or less, and further preferably 500 ppm or less. Is. When the solder alloy according to the present invention contains Pb, the upper limit of the Pb content is 5100 ppm or less, preferably 5000 ppm or less, more preferably 1000 ppm or less, still more preferably 850 ppm or less, and particularly preferably. It is 500 ppm or less.

(6) Equation (1) The solder alloy according to the present invention must satisfy the following equation (1).
275 ≦ 2As + Sb + Bi + Pb (1)
In the above formula (1), As, Sb, Bi, and Pb each represent the content (ppm) in the alloy composition.

As, Sb, Bi and Pb are all elements that have an effect of suppressing thickening. The total of these needs to be 275 or more. In the formula (1), the As content is doubled because As has a higher effect of suppressing thickening than Sb, Bi and Pb.

If the formula (1) is less than 275, the thickening suppressing effect is not sufficiently exhibited. The lower limit of the equation (1) is 275 or more, preferably 350 or more, and more preferably 1200 or more. On the other hand, the upper limit of (1) is not particularly limited from the viewpoint of the thickening suppressing effect, but is preferably 25200 or less, more preferably 10200 or less, from the viewpoint of setting ΔT in a suitable range. It is more preferably 5300 or less, and particularly preferably 3800 or less.

The following equations (1a) and (1b) are those in which the upper limit and the lower limit are appropriately selected from the above preferred embodiments.
275 ≦ 2As + Sb + Bi + Pb ≦ 25200 (1a)
275 ≦ 2As + Sb + Bi + Pb ≦ 5300 (1b)
In the above formulas (1a) and (1b), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

(7) Equation (2) The solder alloy according to the present invention must satisfy the following equation (2).
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
In the above formula (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

If the contents of As and Sb are large, the wettability of the solder alloy deteriorates. On the other hand, Bi and Pb suppress the deterioration of wettability due to the inclusion of As, but if the content is too large, ΔT increases, so strict control is required. In particular, in an alloy composition containing Bi and Pb at the same time, ΔT tends to increase. In view of these, if the contents of Bi and Pb are increased to excessively improve the wettability, ΔT will spread. On the other hand, if the content of As and Sb is increased to improve the effect of suppressing thickening, the wettability is deteriorated. Therefore, in the present invention, the group is divided into As and Sb groups, Bi and Pb groups, and when the total amount of both groups is within an appropriate predetermined range, the thickening suppressing effect, ΔT narrowing, and wettability Are all satisfied at the same time.

If the equation (2) is less than 0.01, the total content of Bi and Pb is relatively large as compared with the total content of As and Sb, so that ΔT spreads. The lower limit of the equation (2) is 0.01 or more, preferably 0.02 or more, more preferably 0.41 or more, further preferably 0.90 or more, and particularly preferably 1.00 or more. Most preferably, it is 1.40 or more. On the other hand, when the equation (2) exceeds 10.00, the total content of As and Sb becomes relatively larger than the total content of Bi and Pb, so that the wettability deteriorates. The upper limit of (2) is 10.00 or less, preferably 5.33 or less, more preferably 4.50 or less, still more preferably 4.18 or less, and even more preferably 2.67 or less. It is particularly preferably 2.30 or less.

The denominator of Eq. (2) is "Bi + Pb", and Eq. (2) cannot be established unless these are included. That is, the solder alloy according to the present invention always contains at least one of Bi and Pb. The alloy composition containing no Bi and Pb is inferior in wettability as described above.

The following equation (2a) is obtained by appropriately selecting the upper limit and the lower limit from the above preferred embodiments.
0.31 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2a)
In the above formula (2a), Bi and Pb each represent the content (mass ppm) in the alloy composition.

(8) Ag: 0-4%
Ag is an optional element capable of forming Ag ₃ Sn at the crystal interface to improve the reliability of the solder alloy. In addition, Ag is an element whose ionization tendency is noble with respect to Sn, and when it coexists with As, Pb, and Bi, it promotes the effect of suppressing thickening. Furthermore, since Ag is 4% or less, the increase in ΔT is sufficiently suppressed. The Ag content is preferably 0 to 4%, more preferably 0.5 to 3.5%, and even more preferably 1.0 to 3.0%.

(9) Equation 10.83 ≤ Cu / Ni ≤ 18.57 (3)
In the above formula (3), Cu and Ni each represent the content (mass%) of the alloy composition.
In the solder alloy according to the present invention, it is desirable that the content of each constituent element is within the above range and that Cu and Ni satisfy the above formula (3). The solder alloy does not function independently of each constituent element, but can exhibit various effects only when the contents of each constituent element are all within a predetermined range. Since Cu and Ni have a total solid solution relationship in the equilibrium phase diagram, they greatly contribute to the suppression of the growth of the SnCu compound and the suppression of the formation of the SnCuNi compound at the bonding interface. Therefore, in the present invention, in addition to the content of each constituent element being in the above range, the effect of the present invention can be more fully exhibited by further satisfying a predetermined relationship between Cu and Ni.
The formula (3) is preferably 10.83 to 18.57, more preferably 11.0 to 15.0.

(10) Remaining: Sn
The rest of the solder alloy according to the present invention is Sn. In addition to the above-mentioned elements, unavoidable impurities may be contained. Even if it contains unavoidable impurities, it does not affect the above-mentioned effects.

2. 2. Solder powder The solder powder according to the present invention is used for a solder paste described later, and is preferably a spherical powder. The spherical powder improves the fluidity of the solder alloy. The solder powder according to the present invention preferably satisfies a size (particle size distribution) satisfying symbols 1 to 8 in the powder size classification (Table 2) in JIS Z 3284-1: 2014. A size satisfying the symbols 4 to 8 (particle size distribution) is more preferable, and a size satisfying the symbols 5 to 8 (particle size distribution) is more preferable. When the particle size satisfies this condition, the surface area of the powder is not too large and the increase in viscosity is suppressed, and the aggregation of the fine powder is suppressed and the increase in viscosity may be suppressed. Therefore, it is possible to solder to finer parts.

The sphericity of the solder powder is preferably 0.90 or more, more preferably 0.95 or more, and most preferably 0.99 or more. In the present invention, the sphericity of the spherical powder is measured using a CNC image measuring system (Ultra Quick Vision ULTRA QV350-PRO measuring device manufactured by Mitutoyo Co., Ltd.) using the minimum region center method (MZC method). In the present invention, the sphericity represents the deviation from the sphere, for example, the arithmetic mean value calculated when the diameter of each of 500 balls is divided by the major axis, and the value is 1.00, which is the upper limit. The closer it is, the closer it is to a true sphere.

3. 3. Solder paste The solder paste according to the present invention contains the above-mentioned solder powder and flux.

(1) Flux components Flux used in solder paste is organic acid, amine, amine hydrohalide, organic halogen compound, thixo agent, rosin, solvent, surfactant, base agent, polymer compound, silane. It is composed of either a coupling agent or a colorant, or a combination of two or more.

Organic acids include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimer acid, propionic acid, 2,2-bishydroxymethylpropionic acid, tartaric acid, malic acid, glycolic acid, Examples thereof include diglycolic acid, thioglycolic acid, dithioglycolic acid, stearic acid, 12-hydroxystearic acid, palmitic acid, oleic acid and the like.

Examples of amines include ethylamine, triethylamine, ethylenediamine, triethylenetetramine, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole and 2-phenyl. Imidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1- Cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecyl imidazolium trimerite, 1-cyanoethyl-2-phenylimidazolium trimerite, 2,4 -Diamino-6- [2'-methylimidazolyl- (1')]-ethyl-s-triazine, 2,4-diamino-6- [2'-undecylimidazolyl- (1')]-ethyl-s- Triazine, 2,4-diamino-6- [2'-ethyl-4'-methylimidazolyl- (1')]-ethyl-s-triazine, 2,4-diamino-6- [2'-methylimidazolyl- (1') 1')]-Ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo [1,2-a] benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, 2-phenylimidazoline, 2,4-diamino- 6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, epoxy-imidazole adduct, 2-methyl Benzoimidazole, 2-octylbenzoimidazole, 2-pentylbenzoimidazole, 2- (1-ethylpentyl) benzoimidazole, 2-nonylbenzoimidazole, 2- (4-thiazolyl) benzoimidazole, 2- (2') -Hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobe Nzotriazole, 2- (2'-hydroxy-3', 5'-di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-5'-tert-octylphenyl) benzotriazole, 2,2 ′ -Methylenebis [6- (2H-benzotriazole-2-yl) -4-tert-octylphenol], 6- (2-benzotriazolyl) -4-tert-octyl-6 ′-tert-butyl-4 ′ -Methyl-2,2'-methylenebisphenol, 1,2,3-benzotriazole, 1- [N, N-bis (2-ethylhexyl) aminomethyl] benzotriazole, carboxybenzotriazole, 1- [N, N- Bis (2-ethylhexyl) aminomethyl] methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazole-1-yl) methyl] imino] bisethanol, 1- (1', 2'-dicarboxy Ethyl) benzotriazole, 1- (2,3-dicarboxypropyl) benzotriazole, 1-[(2-ethylhexylamino) methyl] benzotriazole, 2,6-bis [(1H-benzotriazole-1-yl) methyl) ] -4-Methylphenol, 5-methylbenzotriazole, 5-phenyltetrazole and the like can be mentioned.

Amine halides are compounds obtained by reacting amines with hydrogen halides, and examples of amines include ethylamine, ethylenediamine, triethylamine, diphenylguanidine, ditrilguanidine, methylimidazole, 2-ethyl-4-methylimidazole and the like. Examples of hydrogen halides include hydrides of chlorine, bromine, and iodine.

Examples of the organic halogen compound include trans-2,3-dibromo-2-butane-1,4-diol, triallyl isocyanurate hexabromide, 1-bromo-2-butanol, 1-bromo-2-propanol and 3-bromo. -1-propanol, 3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3- Examples thereof include dibromo-1,4-butanediol and 2,3-dibromo-2-butene-1,4-diol.

Examples of the thixotropy include wax-based thixotropy, amide-based thixotropy, and sorbitol-based thixotropy. Examples of the wax-based thixotropy include castor oil and the like. Examples of the amide-based thixo agent include monoamide-based thixo agent, bisamide-based thixo agent, and polyamide-based thixo agent. , Saturated fatty acid amide, oleic acid amide, erucic acid amide, unsaturated fatty acid amide, p-toluenemethane amide, aromatic amide, methylene bisstearic acid amide, ethylene bislauric acid amide, ethylene bishydroxystearic acid amide, saturated fatty acid bis amide , Methylenebisoleic acid amide, unsaturated fatty acid bisamide, m-xylylene bisstearic acid amide, aromatic bisamide, saturated fatty acid polyamide, unsaturated fatty acid polyamide, aromatic polyamide, substituted amide, methylolstearate amide, methylolamide, fatty acid Examples include ester amide. Examples of the sorbitol-based thixotropy include dibenzylidene-D-sorbitol and bis (4-methylbenzylidene) -D-sorbitol.

Examples of the base agent include nonionic surfactants, weak cationic surfactants, rosins and the like.

Examples of the nonionic surfactant include polyethylene glycol, polyethylene glycol-polypropylene glycol copolymer, aliphatic alcohol polyoxyethylene adduct, aromatic alcohol polyoxyethylene adduct, polyhydric alcohol polyoxyethylene adduct and the like. ..

As weak cationic surfactants, terminal diamine polyethylene glycol, terminal diamine polyethylene glycol-polypropylene glycol copolymer, aliphatic amine polyoxyethylene adduct, aromatic amine polyoxyethylene adduct, polyvalent amine polyoxyethylene addition The body is mentioned.

Examples of the rosin include raw material rosins such as gum rosin, wood rosin and tall oil rosin, and derivatives obtained from the raw material rosin. Examples of the derivative include purified rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin and α, β unsaturated carboxylic acid modified products (acrylicated rosin, maleated rosin, fumarized rosin, etc.), and the polymerized rosin. Examples thereof include purified products, hydrides and disproportionated products of the above, and purified products, hydrides and disproportionated products of the α, β unsaturated carboxylic acid modified products, and two or more kinds can be used. Further, in addition to the rosin-based resin, at least one resin selected from terpene resin, modified terpene resin, terpene phenol resin, modified terpene phenol resin, styrene resin, modified styrene resin, xylene resin, and modified xylene resin is further added. Can include. As the modified terpene resin, an aromatic modified terpene resin, a hydrogenated terpene resin, a hydrogenated aromatic modified terpene resin and the like can be used. As the modified terpene phenol resin, hydrogenated terpene phenol resin or the like can be used. As the modified styrene resin, styrene acrylic resin, styrene maleic anhydride and the like can be used. Examples of the modified xylene resin include a phenol-modified xylene resin, an alkylphenol-modified xylene resin, a phenol-modified resol-type xylene resin, a polyol-modified xylene resin, and a polyoxyethylene-added xylene resin.

Examples of the solvent include water, alcohol solvents, glycol ether solvents, terpineols and the like. As alcohol-based solvents, isopropyl alcohol, 1,2-butanediol, isobornylcyclohexanol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,5 -Dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexine-2,5-diol, 2,3-dimethyl-2,3-butanediol, 1,1,1-tris (hydroxymethyl) Ethan, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,2'-oxybis (methylene) bis (2-ethyl-1,3-propanediol), 2,2-bis (hydroxymethyl) -1,3-propanediol, 1,2,6-trihydroxyhexane, bis [2,2,2-tris (hydroxymethyl) ethyl] ether, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol , 1,4-Cyclohexanedimethanol, erythritol, treitol, guayacol glycerol ether, 3,6-dimethyl-4-octin-3,6-diol, 2,4,7,9-tetramethyl-5-decine-4 , 7-diol and the like. Examples of the glycol ether-based solvent include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, and triethylene glycol monobutyl ether. ..

Examples of the surfactant include polyoxyalkylene acetylene glycols, polyoxyalkylene glyceryl ether, polyoxyalkylene alkyl ether, polyoxyalkylene ester, polyoxyalkylene alkyl amine, polyoxyalkylene alkyl amide and the like.

(2) Flux content The flux content is preferably 5 to 95%, more preferably 5 to 15%, based on the total mass of the solder paste. Within this range, the thickening suppressing effect caused by the solder powder is sufficiently exhibited.

(3) Method for producing solder paste The solder paste according to the present invention is produced by a method common in the art. First, for the production of the solder powder, known methods such as a dropping method in which molten solder material is dropped to obtain particles, a spraying method in which centrifugal spray is applied, and a method in which bulk solder material is crushed can be adopted. In the dropping method and the spraying method, the dropping and spraying are preferably performed in an inert atmosphere or a solvent in order to form particles. Then, each of the above components is heated and mixed to prepare a flux, and the solder powder and, in some cases, zirconium oxide powder can be introduced into the flux, and the mixture can be stirred and mixed for production.

4. Solder joint The solder joint according to the present invention is suitable for connection between an IC chip and its substrate (interposer) in a semiconductor package, or for connection between a semiconductor package and a printed wiring board. Here, the "solder joint" means a connection portion of electrodes.

5. Others The solder alloy according to the present invention may be in the form of a wire in addition to being used as a solder powder as described above.

The method for manufacturing a solder joint according to the present invention may be carried out according to a conventional method.
The joining method using the solder paste according to the present invention may be carried out according to a conventional method using, for example, a reflow method. When flow soldering is performed, the melting temperature of the solder alloy may be approximately 20 ° C. higher than the liquidus temperature. Further, when joining using the solder alloy according to the present invention, it is preferable to consider the cooling rate at the time of solidification from the viewpoint of microstructure miniaturization. For example, the solder joint is cooled at a cooling rate of 2 to 3 ° C./s or higher. Other joining conditions can be appropriately adjusted according to the alloy composition of the solder alloy.

The solder alloy according to the present invention can be produced as a low α-dose alloy by using a low α-dose material as a raw material thereof. When such a low α-dose alloy is used for forming solder bumps around a memory, soft errors can be suppressed.

The present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.
Using the solder alloys shown in Examples and Comparative Examples in Tables 1 to 6, 1. Inhibition of IMC growth with respect to Cu, 2. 2. Suppression of SnCuNi formation in the bump. Suppression of thickening, 4. ΔT, 5. The solder wettability was evaluated.

1. 1. Inhibition of IMC Growth on Cu A Barre-Cu plate coated with a liquid flux was dipped into molten solder having the alloy composition shown in Tables 1 to 6 heated to 280 ° C. to prepare a solder-plated Cu plate. This solder-plated Cu plate was heat-treated for 300 hours on a hot plate heated to 150 ° C. In the cross-sectional SEM photograph of the solder alloy after cooling, the range of 300 μm × 300 μm was performed at any three places, and the maximum crystal grain size of the intermetallic compound was determined.
In this example, the maximum crystal grain size is defined by visually selecting the largest crystal grain among the metal compounds identified from the obtained images so that the interval between the selected crystal grains is maximized. Two parallel tangents were drawn and the distance between them was taken as the maximum grain size.
When the maximum value of the crystal particle size was less than 5 μm, it was evaluated as “◯”, and when the maximum value was 5 μm or more, it was evaluated as “x”.

2. 2. Suppression of SnCuNi formation in bumps Prepare a solder-plated Cu plate in the same manner as in "1." above, and observe any three locations at the interface between the Cu plate and the solder alloy in the same way as in "1." above. Then, the presence or absence of SnCuNi-based compounds was confirmed in the solder alloy. If the formation of SnCuNi-based compound is not observed near the interface of the solder alloy at all points, it is evaluated as "○", and if the formation of SnCuNi-based compound is observed at at least one place, it is evaluated as "x". I evaluated it.

3. 3. Inhibition of thickening Flux adjusted by 42 parts by mass of rosin, 35 parts by mass of glycol-based solvent, 8 parts by mass of solder, 10 parts by mass of organic acid, 2 parts by mass of amine, and 3 parts by mass of halogen, Table 1 A solder paste was prepared by mixing with a solder powder having an alloy composition shown in Table 6 and having a size (particle size distribution) satisfying symbol 4 in the classification of powder size (Table 2) in JIS Z 3284-1: 2014. The mass ratio of the flux to the solder powder is flux: solder powder = 11:89. For each solder paste, the change in viscosity with time was measured. In addition, the liquidus temperature and solidus temperature of the solder powder were measured. Furthermore, the wettability was evaluated using the solder paste immediately after production. The details are as follows.
The viscosity of each solder paste immediately after production was measured using PCU-205 manufactured by Malcolm Co., Ltd. at a rotation speed of 10 rpm, 25 ° C., and in the air for 12 hours. If the viscosity after 12 hours is 1.2 times or less of the viscosity when 30 minutes have passed since the solder paste was prepared, it was evaluated as "○" as having a sufficient effect of suppressing thickening. When it exceeded 1.2 times, it was evaluated as "x".

4. ΔT
For the solder powder before mixing with the flux, DSC measurement was performed using SII Nanotechnology Co., Ltd., model number: EXSTAR DSC7020, sample amount: about 30 mg, temperature rise rate: 15 ° C./min, and solid phase line. Temperature and liquidus temperature were obtained. ΔT was obtained by subtracting the solidus temperature from the obtained liquidus temperature. When ΔT was 15 ° C. or lower, it was evaluated as “◯”, and when it exceeded 15 ° C., it was evaluated as “x”.

5. Solder Wetting Properties Using a solder ball with a diameter of 0.3 mm made of the solder alloy shown in Table 1, the wetting spread test was carried out in the order of "1." and "2." below. The substrate material used was a glass epoxy substrate (FR-4) with a thickness of 1.2 mm.

1. 1. Using the above-mentioned substrate on which a 0.24 mm × 16 mm slit-shaped Cu electrode was formed, a flux WF-6400 manufactured by Senju Metal Industry Co., Ltd. was printed on 0.24 mmφ × 0.1 mm in thickness, and a solder ball was mounted on the substrate. It was held in a temperature range of ° C. or higher for 40 seconds, and reflow was performed under the condition that the peak temperature was 245 ° C.
2. 2. The wet spread area was measured using a stereomicroscope, and a wet spread of 0.75 mm ² or more was judged as “◯”. A wet spread of less than 0.75 mm ² was judged as “x”.

-Comprehensive evaluation "○" was given when all the above tests were "○", and "x" was given when at least one test was "x".
The evaluation results are shown in Tables 1-6.

As shown in Tables 1 to 6, in Examples 1 to 105, in order to satisfy all the requirements of the present invention in any alloy composition, IMC growth inhibition on Cu, SnCuNi formation inhibition in bumps, and thickening inhibition effect. It was found that ΔT was narrowed and excellent wettability was exhibited at the same time. On the other hand, Comparative Examples 1 to 19 did not satisfy at least one of the requirements of the present invention in any of the alloy compositions, and thus at least one of them was found to be inferior.

Claims (8)

Cu: 0.55 to 0.75% by mass, Ni: 0.0350 to 0.0600% by mass, Ge: 0.0035 to 0.0200% by mass, As: 25 to 300% by mass, and Sb: 0 to 3000 It has an alloy composition consisting of at least one of mass ppm, Bi: 0 to 10000 mass ppm, and Pb: 0 to 5100 mass ppm, and the balance of Sn, and satisfies the following equations (1) and (2). Characterized solder alloy.
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
In the above equations (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition. The solder alloy according to claim 1, wherein the alloy composition satisfies the following formula (1a).
275 ≦ 2As + Sb + Bi + Pb ≦ 25200 (1a)
In the above formula (1a), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition. The solder alloy according to claim 1, wherein the alloy composition satisfies the following formula (1b).
275 ≦ 2As + Sb + Bi + Pb ≦ 5300 (1b)
In the above formula (1b), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition. The solder alloy according to any one of claims 1 to 3, wherein the alloy composition satisfies the following formula (2a).
0.31 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2a)
In the above formula (2a), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition. The solder alloy according to any one of claims 1 to 4, wherein the alloy composition contains Ag: 0 to 4% by mass. A solder powder having the solder alloy according to any one of claims 1 to 5. A solder paste having the solder powder according to claim 6. A solder joint having the solder alloy according to any one of claims 1 to 5.