JP2020011285A - Solder materials, solder paste, and solder joints - Google Patents

Abstract

An object of the present invention is to provide a solder material, a solder paste, and a solder joint which suppress the increase in viscosity over time and have excellent wettability and reliability.
[Solution]
Sn or a Sn-based alloy, containing 40 to 250 ppm by mass of As, 0 to 3000 ppm by mass of Sb, 0 to 10000 ppm by mass of Bi, and 0 to 5100 ppm by mass of Pb (however, the content of Bi and Pb is 0 mass ppm), a solder material having an As-enriched layer.
[Selection diagram] Fig. 1

Description

  The present invention relates to a solder material, a solder paste, and a solder joint.

  Fixing and electrical connection of electronic components in electronic devices, such as mounting of electronic components on a printed circuit board, are generally performed by soldering, which is the most advantageous in terms of cost and reliability.

  Generally, when a solder material contains Sn as a main component, Sn reacts with oxygen in the air during or after production, and a film of Sn oxide is formed on the surface, which may cause yellow discoloration.

  As a method for improving discoloration of a solder material, it is known to add an element such as P, Ge, or Ga to the solder material. These elements have a smaller standard free energy of formation of oxide than Sn and are very easily oxidized. Therefore, when forming a solder material such as a solder powder or a solder ball from a molten solder, elements such as P, Ge, and Ga, not Sn, are oxidized and concentrated on the surface, thereby suppressing the yellow change of the solder surface. it can. However, in general, a solder material is required to have a property of spreading on a metal of an electronic component when melted (wettability). However, when an element such as P, Ge, or Ga is added, the solder material The wettability of the material is reduced. Poor wettability of the solder material causes poor soldering.

Among soldering, in joining and assembling an electronic component to a substrate of an electronic device, soldering using a solder paste is advantageous in terms of cost and reliability and is most commonly performed. The solder paste is a mixture obtained by kneading a solder material (solder powder) and a flux containing components other than the solder material such as a rosin, an activator, a thixotropic agent, and a solvent to form a paste.
The application of the solder paste to the substrate is performed, for example, by screen printing using a metal mask. Therefore, in order to secure the printability of the solder paste, the viscosity of the solder paste needs to be appropriate. However, in general, the solder paste has poor storage stability, and the viscosity of the solder paste may increase with time.

Further, in the solder material forming the solder paste, the difference between the liquidus temperature (T _L) and the solidus temperature _{(T S) (ΔT = T} L -T S) increases, the substrate of the electronic device When solidified after the application, the structure of the solder material tends to be non-uniform, which causes a decrease in future reliability.

Examples of the solder material containing Sb include 2.8 to 4.2% by weight of Ag, 0.4 to 0.6% by weight of Cu, and 50 to 3000 ppm of Sb, with the balance being Sn and unavoidable impurities. A solder alloy powder for bumps having the following composition has been proposed (Patent Document 1).
Examples of the Bi-containing solder material include Ag: 2.8 to 4.2% by weight, Cu: 0.4 to 0.6% by weight, and Bi to 50 to 1000 ppm, with the balance being Sn and inevitable impurities. A solder alloy powder for bumps having the following composition has been proposed (Patent Document 2).
Examples of the solder material containing Pb include 2.8 to 4.2% by weight of Ag, 0.4 to 0.6% by weight of Cu, and 50 to 5000 ppm of Pb, with the balance being Sn and inevitable impurities. A solder alloy powder for bumps having the following composition has been proposed (Patent Document 3).
However, the solder materials described in Patent Literatures 1 to 3 have a problem of suppressing projections generated at the time of bump formation, and do not improve the problem of discoloration or viscosity increase with time when used as a solder paste. .

  As described above, there is a demand for a solder material which suppresses the problems of discoloration and viscosity increase with time when formed into a paste, and which is excellent in wettability and reliability.

JP 2013-237091 A JP 2013-237089 A JP 2013-237088 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a solder material which has a small discoloration and a small increase in viscosity with time when formed into a paste, and is excellent in wettability and reliability.

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the solder material having the As-enriched layer on the surface side has little discoloration and time-dependent change in viscosity when formed into a paste, and contains As. Although a solder material to be used usually has a tendency to have low wettability, it has been found that if the As-enriched layer is formed on the surface, such a decrease in wettability does not occur. The inventors have found that the above-mentioned problems can be solved if used, and have completed the present invention.
That is, specific embodiments of the present invention are as follows.
In the present specification, when "-" is used to represent a numerical range, the range includes the numerical values at both ends. The content of each element can be measured, for example, by analyzing with ICP-AES based on JIS Z3910.

[1] Sn or Sn-based alloy, containing 40 to 250 ppm by mass of As, 0 to 3000 ppm by mass of Sb, 0 to 10000 ppm by mass of Bi, and 0 to 5100 ppm by mass of Pb ((however, Bi and Pb The content does not become 0 mass ppm at the same time), a solder material having an As-concentrated layer.
[2] The solder material according to [1], wherein the contents of As, Sb, Bi, and Pb satisfy the following formulas (1) and (2).
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
However, in the formulas (1) and (2), As, Sb, Bi and Pb represent the contents (mass ppm) in each solder material.
[3] The solder material according to [1] or [2], wherein the form of the solder material is a powder.
[4] A solder paste containing the solder material according to [3] and a flux.
[5] The solder paste according to [4], further comprising a zirconium oxide powder.
[6] The solder paste according to [5], wherein the content of the zirconium oxide powder is 0.05 to 20.0% by mass based on the total mass of the solder paste.
[7] Sn or Sn-based alloy, containing 40 to 250 ppm by mass of As, 0 to 3000 ppm by mass of Sb, 0 to 10000 ppm by mass of Bi, and 0 to 5100 ppm by mass of Pb (provided that Bi and Pb are contained) (The amount does not become 0 mass ppm at the same time), a solder joint having an As-concentrated layer.

  According to the present invention, it is possible to provide a solder material that has little discoloration, good wettability, high reliability such as cycle characteristics, and a small increase in viscosity over time when used as a solder paste.

It is an example of the chart of the XPS analysis of the solder material surface. It is an example of the chart of the XPS analysis of the solder material surface. It is an example of the chart of the XPS analysis of the solder material surface.

Hereinafter, a mode for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described.
However, the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention.

  In the present embodiment, the solder material contains Sn or a Sn-based alloy, 0 to 3000 ppm by mass of Sb, 0 to 10000 ppm by mass of Bi, and 0 to 5100 ppm by mass of Pb. However, the content of Bi and Pb does not become 0 mass ppm at the same time, and the fact that two or more types of Sb, Bi and Pb are contained (the content of two or more types exceeds 0 mass ppm) is required. It is also preferable that all of Sb, Bi and Pb are contained (the content of all three is more than 0 mass ppm).

Here, the purity of Sn is not particularly limited. For example, the purity of Sn is 3N (99.9% or more), 4N (99.99% or more), and 5N (99.999% or more). And a general one can be used.
Examples of the Sn-based alloy include Sn-Ag alloy, Sn-Cu alloy, Sn-Ag-Cu alloy, Sn-Ag-Cu-Ni-Co alloy, Sn-In alloy, and Ag, Cu, In , Ni, Co, Ge, P, Fe, Zn, Al, Ga and the like. The Sn content in the Sn-based alloy is not limited, but can be, for example, more than 40% by mass.
Note that Sn and Sn-based alloys may contain unavoidable impurities.

In the present embodiment, the Sn-based alloy contains 0.005 to 40% by mass of Ag and / or 0.001 to 10% by mass of Cu from the viewpoint of solder wettability, melting point, and other physical properties as a solder material. It is preferable that the balance be Sn.
In this case, from the viewpoint of ΔT, the content of Ag based on the total mass of the solder material is preferably 4% by mass or less. If the Ag content exceeds 3.8% by mass, ΔT tends to increase significantly. The Ag content based on the total mass of the solder material is more preferably 0.1 to 3.8% by mass, and most preferably 0.5 to 3.5% by mass.
Further, from the viewpoint of ΔT, the content of Cu with respect to the total mass of the solder material is preferably 1.0% by mass or less. When the content of Cu exceeds 0.9% by mass, ΔT tends to greatly increase. The content of Cu based on the total mass of the solder material is more preferably 0.05 to 0.9% by mass, and most preferably 0.1 to 0.7% by mass.
The preferred numerical ranges for the Ag and Cu contents are independent of each other, and the Ag and Cu contents can be determined independently of each other.

In the present embodiment, the content of As with respect to the total mass of the solder material is 40 to 250 mass ppm (0.0040 to 0.0250 mass%), preferably 40 to 150 mass ppm, and 50 to 100 mass ppm. More preferred. If the As content is less than 40 ppm by mass, it is extremely difficult to form an As-enriched layer.
As satisfies the condition that the content based on the mass of the entire solder material is 40 to 250 ppm by mass, and if an As-enriched layer is present in the solder material, part or all of the alloy is Sn or a Sn-based alloy. Together with an alloy (such as an intermetallic compound or a solid solution), or may exist separately from the Sn-based alloy, for example, as a simple substance of As or an oxide.

In the present embodiment, the content of Sb is 0 to 3000 mass ppm, the content of Bi is 0 to 10000 mass ppm, and the content of Pb is 0 to 5100 mass ppm with respect to the mass of the entire solder material.
It has been found that when Sb, Bi or Pb is sufficiently present, the increase in viscosity tends to be suppressed. Although the reason is not clear, these elements are noble metals with respect to Sn, and therefore, the Sn—Sb / Bi / Pb alloy is less ionizable than Sn, and as an ion state (salt) to the flux. It is considered that elution hardly occurs. However, the mechanism does not depend on this. Bi and Pb also tend to suppress a decrease in wettability that occurs when the solder material contains As.
On the other hand, if the contents of Sb, Bi, and Pb are too large, the solidus temperature decreases, and the difference between the liquidus temperature (T _L ) and the solidus temperature (T _S ) (ΔT = T _L − T _S ) increases, and in the solidification process of the molten solder, a high melting point crystal phase having a low Bi or Pb content is precipitated first, and then a low melting point crystal phase having a high Bi or Pb concentration is segregated. Therefore, the mechanical strength and the like of the solder material may be deteriorated, and the reliability such as cycle characteristics may be reduced. In particular, since the crystal phase having a high Bi concentration is hard and brittle, the segregation in the solder material may significantly reduce the reliability.

From the above viewpoints, preferred ranges of the contents of Sb, Bi and Pb are as follows.
The lower limit of the Sb content is preferably at least 25 ppm by mass, more preferably at least 50 ppm by mass, further preferably at least 100 ppm by mass, particularly preferably at least 300 ppm by mass. The upper limit of the Sb content is preferably 1150 ppm by mass or less, more preferably 500 ppm by mass or less.
The lower limit of the Bi content is preferably 25 mass ppm or more, more preferably 50 mass ppm or more, further preferably 75 mass ppm or more, particularly preferably 100 mass ppm or more, and most preferably 250 mass ppm or more. It is not less than ppm by mass. The upper limit of the Bi content is preferably 1000 ppm by mass or less, more preferably 600 ppm by mass or less, and further preferably 500 ppm by mass or less.
The lower limit of the Pb content is preferably 25 mass ppm or more, more preferably 50 mass ppm or more, further preferably 75 mass ppm or more, particularly preferably 100 mass ppm or more, and most preferably 250 mass ppm or more. It is not less than ppm by mass. The upper limit of the Pb content is preferably 5,000 ppm by mass or less, more preferably 1,000 ppm by mass or less, further preferably 850 ppm by mass or less, and particularly preferably 500 ppm by mass or less.

  As long as the content of Sb, Bi, and Pb with respect to the mass of the entire solder material satisfies the above-mentioned conditions, even if all of them constitute an alloy (intermetallic compound, solid solution, or the like) together with Sn or a Sn-based alloy. Alternatively, a part thereof may be present separately from the Sn-based alloy.

In the present embodiment, the contents of As, Sb, Bi, and Pb preferably satisfy the following expression (1).
275 ≦ 2As + Sb + Bi + Pb (1)
In the above formula (1), As, Sb, Bi, and Pb represent the contents (mass ppm) in each solder material.
As, Sb, Bi and Pb are elements each exhibiting the effect of suppressing the rise of clay (thickening suppression effect) when made into a paste, so that from the viewpoint of suppression of thickening, the total of these elements is 275 ppm or more. Preferably, there is. In the formula (1), the reason why the As content is doubled is that As has a higher effect of suppressing thickening than Sb, Bi, or Pb.
2As + Sb + Bi + Pb is preferably 350 or more, more preferably 1200 or more. On the other hand, there is no upper limit for 2As + Sb + Bi + Pb, but from the viewpoint of setting ΔT in a suitable range, it is 18600 or less, preferably 10200 or less, more preferably 5300 or less, and particularly preferably 3800 or less.
The following formulas (1a) and (1b) are those in which the upper and lower limits are appropriately selected from the above preferred embodiments.
275 ≦ 2As + Sb + Bi + Pb ≦ 18600 (1a)
275 ≦ 2As + Sb + Bi + Pb ≦ 5300 (1b)
In the formulas (1a) and (1b), As, Sb, Bi, and Pb represent the contents (mass ppm) in each solder material.

In the present embodiment, the contents of As, Sb, Bi, and Pb preferably satisfy the following expression (2).
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
In the above formula (2), As, Sb, Bi, and Pb represent the contents (mass ppm) in each solder material.
Generally, when the content of As and Sb is large, the wettability of the solder material tends to deteriorate. On the other hand, Bi and Pb suppress the deterioration of wettability due to the inclusion of As. However, if the content is too large, ΔT increases, so strict management is required. In particular, in an alloy composition containing both Bi and Pb, ΔT easily spreads, and if the content of Bi and Pb is increased to improve the wettability excessively, ΔT will increase. On the other hand, when the content of As or Sb is increased to improve the effect of suppressing thickening, wettability deteriorates. However, if the group is divided into the group of As and Sb and the group of Bi and Pb, and the total content of both groups satisfies the relationship of equation (2), the content of the group of As and Sb and the group of Bi and Pb The balance between the amounts becomes appropriate, and the effect of suppressing thickening, narrowing of ΔT, and wettability can all be satisfied at the same time.
If (2As + Sb) / (Bi + Pb) is less than 0.01, the total content of Bi and Pb is relatively larger than the total content of As and Pb, and thus ΔT is widened. (2As + Sb) / (Bi + Pb) is preferably 0.01 or more, more preferably 0.02 or more, further preferably 0.41 or more, still more preferably 0.90 or more, and particularly preferably. Is 1.00 or more, and most preferably 1.40 or more. On the other hand, when (2As + Sb) / (Bi + Pb) exceeds 10.00, the total content of As and Sb becomes relatively larger than the total content of Bi and Pb, and the wettability deteriorates. (2As + Sb) / (Bi + Pb) is preferably at most 10.00, more preferably at most 5.33, further preferably at most 4.50, still more preferably at most 2.67, particularly preferably Is 4.18 or less, most preferably 2.30 or less.
Since the denominator of the expression (2) is “Bi + Pb”, when the expression (2) is satisfied, at least one of Bi and Pb is necessarily contained. As described above, a solder material containing neither Bi nor Pb tends to have poor wettability.
The following formula (2a) is one in which the upper and lower limits are appropriately selected from the above preferred embodiments.
0.31 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2a)
In the above formula (2a), As, Sb, Bi, and Pb represent the contents (mass ppm) in each solder material.

  In the present embodiment, the content of As, Sb, Bi and Pb preferably satisfies at least one of the above formulas (1) and (2), and more preferably satisfies both.

In the present embodiment, the solder material has an As-enriched layer on at least a part thereof. Here, the “As-enriched layer” refers to a region where the As concentration is higher than the average As concentration in the solder material (the content of As relative to the mass of the entire solder material). Can confirm the presence.
The As-enriched layer is preferably present on at least a part of the surface side of the solder material, and preferably covers the entire surface.

(Judgment criteria)
Sample of 5.0 mm x 5.0 mm size (If the solder material is not plate-like, solder material (solder powder, solder balls, etc.) spread over the area of 5.0 mm x 5.0 mm without gaps) Is prepared, an arbitrary area of 700 μm × 300 μm is selected therefrom, and XPS analysis using ion sputtering is performed. One area is selected for each sample, and analysis is performed three times, once for each of the three samples. When the magnitude relationship between S1 and S2 described later coincides in all three analyzes (when the As-enriched layer exists on the surface side, S1> S2 in all three analyses) , As concentrated layers are formed.
Here, the definitions of S1, S2 and D1 are as follows.
S1: In the chart of the XPS analysis performed on the sample described above, the integrated value of the detected intensity of As in the region where the depth in terms of SiO ₂ is 0 to 2 × D1 (nm) S2: The XPS analysis performed on the sample described above In the chart, the integrated value of the detected intensity of As in the region where the depth in terms of SiO ₂ is 2 × D1 to 4 × D1 (nm) D1: In the chart of the XPS analysis performed on the above sample, the detected intensity of the O atom is In the portion deeper than the maximum SiO ₂ -converted depth (Do · max (nm)), the first SiO _{2 at which} the detection intensity of O atoms becomes 検 出 of the maximum detection intensity (intensity at Do · max). Conversion depth (nm) (see FIG. 3).
However, the detailed conditions of the XPS analysis in this determination criterion follow the description of “(1) Evaluation of presence or absence of As-enriched layer” described later.
Note that, in this determination criterion, it is assumed that D1 can be defined, that is, the detection intensity of O atoms takes the maximum value in the XPS analysis chart. If D1 cannot be defined (the detection intensity of O atoms is always In such a case, it is determined that the As-enriched layer does not exist.

  It is not clear why the presence of the As-concentrated layer can solve the problems of discoloration, wettability, and increase in viscosity when used as a solder paste. However, the increase in viscosity is due to the activity contained in Sn or Sn oxide and the solder paste (flux). Is considered to be caused by the reaction between various additives such as an agent and the formation of a salt or agglomeration of the solder material. However, if an As-enriched layer is present on the surface of the solder material, the solder alloy It is considered that an As-enriched layer is interposed between the flux and the flux, and the above-described reaction hardly occurs. However, the mechanism does not depend on this.

In the present embodiment, the thickness (in terms of SiO ₂ ) of the As-concentrated layer is not limited, but is preferably 0.5 to 8.0 nm, more preferably 0.5 to 4.0 nm, and 0.5 to 2.0 nm. Is most preferred. Here, the thickness of the As concentrated layer means 2 × D1.
When the thickness of the As-concentrated layer is within the above range, discoloration and an increase in viscosity over time when the solder paste is formed can be sufficiently suppressed without adversely affecting wettability.

  In the solder material of the present embodiment, the content of As and the content of Sb, Bi, and Pb with respect to the mass of the entire solder material are within the above-described ranges. The increase in viscosity over time when the paste is formed is suppressed, and the wettability and reliability are excellent.

There is no limitation on the method of manufacturing the solder material according to the present embodiment, and the solder material can be manufactured by melting and mixing the raw material metals.
There is no limitation on the method of forming the As-enriched layer in the solder material. As an example of a method for forming the As-enriched layer, heating a solder material in an oxidizing atmosphere (air or oxygen atmosphere) can be mentioned. The heating temperature is not limited, but may be, for example, 40 to 200 ° C, or may be 50 to 80 ° C. The heating time is not limited, and may be, for example, several minutes to several days, preferably several minutes to several hours. In order to form a sufficient amount of the As-concentrated layer, the heating time is preferably at least 10 minutes, more preferably at least 20 minutes.

In the present embodiment, the shape of the solder material is not particularly limited, and may be a bar shape such as a bar solder, a wire shape, or a particle shape such as a solder ball or a solder powder. Good.
When the solder material is in the form of particles, the fluidity of the solder material is improved.

  There is no limitation on the manufacturing method of the particulate solder material, and a known method such as a dripping method of dropping a molten solder material to obtain particles, a spraying method of centrifugal spraying, and a method of pulverizing a bulk solder material is used. be able to. In the dropping method or the spraying method, the dropping or spraying is preferably performed in an inert atmosphere or a solvent in order to form particles.

In addition, when the solder material is in the form of particles, if the solder material has a size (particle size distribution) corresponding to the symbols 1 to 8 in the powder size classification (Table 2) in JIS Z 3284-1: 2004, a fine component Soldering is possible. The size of the particulate solder material is more preferably a size corresponding to the symbols 4 to 8, and more preferably a size corresponding to the symbols 5 to 8.
When the solder material is particulate, the sphericity is preferably 0.90 or more, more preferably 0.95 or more, and most preferably 0.99 or more.

  In the present embodiment, the usage form of the solder material is not particularly limited. For example, it may be mixed with an oil or the like to form a cored solder, or when the solder material is in a powder form, mixed with a flux containing a rosin-based resin, an activator, a solvent, etc., and used as a solder paste, Although the solder material can be used as a ball, the solder material of the present embodiment is particularly suitable for use as a solder paste, since the increase in viscosity over time when the solder paste is used is small.

In the present embodiment, the solder paste contains the solder powder and the flux of the present embodiment.
Here, the “flux” refers to the entire components other than the solder powder in the solder paste, and there is no limitation on the mass ratio between the solder powder and the flux (solder powder: flux), which may be appropriately set according to the application. Can be.

  In the present embodiment, the composition of the flux is not limited. For example, a resin component; a solvent; various additives such as an activator, a thixotropic agent, a pH adjuster, an antioxidant, a coloring agent, and an antifoaming agent in an arbitrary ratio. Can be included. There is no limitation on the resin, solvent and various additives, and those generally used in solder paste can be used. Preferred specific examples of the activator include organic acids, amines, and halogens (organic halogen compounds, amine hydrohalides).

In this embodiment, the solder paste may further include a zirconium oxide powder. The content of the zirconium oxide powder based on the total mass of the solder paste is preferably 0.05 to 20.0% by mass, more preferably 0.05 to 10.0% by mass, and most preferably 0.1 to 3% by mass.
When the content of the zirconium oxide powder is within the above range, the activator contained in the flux reacts preferentially with the zirconium oxide powder, and the reaction with Sn or Sn oxide on the surface of the solder powder becomes less likely to occur. The effect of further suppressing the increase in viscosity due to the change is exhibited.

The upper limit of the particle size of the zirconium oxide powder added to the solder paste is not limited, but is preferably 5 μm or less. When the particle size is 5 μm or less, the printability of the paste can be maintained. The lower limit is not particularly limited, but is preferably 0.5 μm or more. The above-mentioned particle diameter is obtained by taking an SEM photograph of the zirconium oxide powder and obtaining the equivalent diameter of the projected circle by image analysis for each particle present in the visual field. The average value of the equivalent diameter is used.
The shape of the zirconium oxide particles is not particularly limited, but a different shape has a large contact area with the flux and has an effect of suppressing thickening. Spherical shape provides good fluidity, and therefore excellent printability as a paste. What is necessary is just to select a shape suitably according to a desired characteristic.

In the present embodiment, the solder paste can be manufactured by kneading the solder material (solder powder) of the present embodiment and a flux by a known method.
The solder paste in the present embodiment can be used, for example, for a circuit board having a fine structure in an electronic device. Specifically, a printing method using a metal mask, an ejection method using a dispenser, or transfer using a transfer pin is used. It can be applied to a soldered portion by a method or the like and reflowed.

In this embodiment, the solder material can be used as a joint (joining portion) for joining two or more various members. The joining member is not limited, and is useful, for example, as a joint for electronic device members.
In the present embodiment, the solder joint includes Sn or a Sn-based alloy, 40 to 250 ppm by mass of As, 0 to 3000 ppm by mass of Sb, 0 to 10000 ppm by mass of Bi, and 0 to 5100 ppm by mass of Pb (provided that , Sb, Bi and Pb do not all become 0 mass ppm at the same time), at least a part of which contains an As-enriched layer. The solder joint of the present embodiment can have the same composition and physical properties as the above-described solder material of the present embodiment, and can be formed using the above-described solder material of the present embodiment.
When the content of As and the content of Sb, Bi and Sb with respect to the mass of the entire solder joint are within the above range, and the solder joint includes an As-enriched layer, the solder joint has no discoloration and excellent reliability. Becomes

  In the present embodiment, the solder joint is, for example, a solder ball made of the solder material of the present embodiment or the solder paste of the present embodiment, placed or applied to the portion to be joined, and heated, such as common in the industry. It can be manufactured by a method.

  Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to the contents described in the examples.

(Evaluation)
For each of the solder powders of Examples and Comparative Examples, (1) evaluation of the presence or absence of an As-concentrated layer, (2) evaluation of suppression of thickening, (3) evaluation of solder wettability, (4) reliability Was evaluated.

(1) Evaluation of presence / absence of As-enriched layer The presence / absence of As-enriched layer was evaluated as follows using depth direction analysis by XPS (X-ray Photoelectron Spectroscopy).
(Analysis conditions)
・ Analyzer: Micro-area X-ray photoelectron spectrometer (AXIS Nova manufactured by Kratos Analytical)
・ Analysis conditions: X-ray source AlKα ray, X-ray gun voltage 15 kV, X-ray gun current value 10 mA, analysis area 700 μm × 300 μm
-Sputtering conditions: ion species Ar ⁺ , acceleration voltage ² kV, sputtering rate 0.5 nm / min (SiO ₂ conversion)
-Samples: Three samples were prepared by spreading a solder material (solder powder in Examples and Comparative Examples) flatly on a stage on which a carbon tape was stuck without gaps. However, the size of the sample was 5.0 mm × 5.0 mm.
(Evaluation procedure)
An arbitrary area of 700 μm × 300 μm is selected from a sample having a size of 5.0 mm × 5.0 mm, and XPS analysis is performed for each atom of Sn, O, and As while performing ion sputtering, and a chart of XPS analysis is performed. I got One area was selected for each sample, and the analysis was performed three times, once for each of the three samples.
An example of a chart obtained by the XPS analysis is shown in FIGS. 1 to 3 show the same sample with the scale of the detection intensity (cps) on the vertical axis changed, and the horizontal axis shows the depth (nm) in terms of SiO ₂ calculated from the sputtering time. In the chart of the XPS analysis, the vertical axis represents the detection intensity (cps), and the horizontal axis represents the sputtering time (min) or the depth in terms of SiO ₂ calculated from the sputtering time using the sputter etching rate of the SiO ₂ standard sample. In FIGS. 1 to 3, the horizontal axis in the chart of the XPS analysis is the depth in terms of SiO ₂ calculated from the sputtering time using the sputter etching rate of the SiO ₂ standard sample. (Nm).
Then, in the chart of the XPS analysis of each sample, the depth in terms of SiO _{2 at} which the detection intensity of O atoms became the maximum was defined as Do · max (nm) (see FIG. 2). Then, in a portion deeper than Do · max, the first depth in terms of SiO ₂ at which the detection intensity of O atoms becomes １ ／ of the maximum detection intensity (intensity at Do · max) is defined as D1 (nm). .
Next, in the chart of the XPS analysis of each sample, the integrated value of the detected intensity of As in the region from the outermost surface to a depth of 2 × D1 (region where the depth in terms of SiO ₂ is 0 to 2 × D1 (nm)) ( S1) and the integrated value of the detected intensity of As in a region from the depth 2 × D1 to a portion further deeper by 2 × D1 (a region where the depth in terms of SiO ₂ is 2 × D1 to 4 × D1 (nm)) ( S2) (see FIG. 3) was obtained and compared.
The evaluation was performed based on the following criteria.
S1> S2 in all three measurements
: As-enriched layer is formed (○)
S1> S2 when the number of measurements is two or less out of all three measurements
: No As-concentrated layer was formed (x)

(2) Evaluation of suppression of thickening Each material having the composition shown in Table 1 below was heated and stirred, and then cooled to prepare a flux. The prepared flux, and the solder powder of each of Examples and Comparative Examples were kneaded so that the mass ratio of the flux to the solder powder (flux: solder powder) was 11:89 to produce a solder paste.

The obtained solder paste was measured using a rotational viscometer (PCU-205, manufactured by Malcom Co., Ltd.) at a rotation speed of 10 rpm according to the method described in “4.2 Viscosity characteristic test” of JIS Z 3284-3. At a temperature of 25 ° C., the viscosity was continuously measured for 12 hours. Then, the initial viscosity (viscosity after 30 minutes of stirring) and the viscosity after 12 hours were compared, and the thickening suppressing effect was evaluated based on the following criteria.
Viscosity after 12 hours ≦ initial viscosity × 1.2: little increase in viscosity over time and good (○)
Viscosity after 12 hours> Initial viscosity × 1.2: Viscosity increase with time is large and poor (×)

(3) Evaluation of solder wettability In the same manner as in “(2) Evaluation of suppression of thickening”, a solder paste was produced using the solder powder of each of the examples and the comparative examples.
The obtained solder paste was printed on a Cu plate using a metal mask having an opening diameter of 6.5 mm, a number of openings of 4 and a mask thickness of 0.2 mm, and in a reflow furnace under a N ₂ atmosphere at a heating rate of 1 ° C. After heating from 25 ° C. to 260 ° C./sec, air cooling was performed to room temperature (25 ° C.) to form four solder bumps. The appearance of the obtained solder bumps was observed using an optical microscope (magnification: 100 times), and evaluated based on the following criteria.
No solder particles that could not be melted were observed in all four solder bumps.
: Good solder wettability (O)
Solder particles that could not be completely melted were observed in one or more of the four solder bumps. : Poor solder wettability (×)

(4) Evaluation of reliability For each of the solder powders of the examples and the comparative examples, using a differential scanning calorimeter (EXSTAR DSC7020, manufactured by SII Nanotechnology Co., Ltd.), the rate of temperature rise: 5 ° C./min (180 ° C.) DSC measurement under the measurement conditions of temperature drop rate: −3 ° C./min (250 ° C. to 150 ° C.), carrier gas: N ₂ , liquidus temperature (T _L ) and solidus temperature (T _S ) was measured. Then, calculate the difference between the liquidus temperature (T _L) and the solidus temperature (T _S) and _{(ΔT = T L -T S)} , were evaluated based on the following criteria.
ΔT within 10 ° C: Excellent reliability (○)
ΔT exceeds 10 ° C .: Poor reliability (×)
If the difference between the liquidus temperature (T _L ) and the solidus temperature (T _S ) of the solder powder is large (ΔT = T _L −T _S ), the solder paste containing the solder powder is applied to the substrate of the electronic device. Later, when solidifying, a structure having a high melting point tends to precipitate on the surface of the solder powder. When a structure having a high melting point is deposited on the surface of the solder powder, a structure having a low melting point is sequentially deposited toward the inside of the solder powder, and the structure of the solder powder is likely to be non-uniform, which lowers reliability such as cycleability. Cause.

(Examples A1 to A18, Comparative Examples A1 to A24)
The contents of Sn, As, Sb, Bi, and Pb are as shown in Table 2 below, and the content of Sn is 100% (Sn, As, Sb, Bi, and Pb is 100%). The powder (average particle diameter: 21 μm, powder size classification of JIS Z3284-1: 2004, Table 4) was obtained by weighing, melting and mixing in an Ar atmosphere. Corresponding to). The obtained powder was heated at 60 ° C. for 30 minutes in the air using a drying device to obtain solder powders of Examples and Comparative Examples. In Comparative Examples A3 to A14, the heat treatment was not performed, and the powder obtained by centrifugal spraying was directly used as a solder powder.
As Sn, a 3N material containing unavoidable impurities was used.

(Examples B1 to B18, Comparative Examples B1 to B24)
The contents of Sn, Cu, As, Sb, Bi and Pb were as shown in Table 3 below, with the content of Cu being 0.7% by mass, and the contents of As, Sb, Bi and Pb as shown in Table 3 below. The powder (average particle size) is weighed, melt-mixed, and centrifugally sprayed in an Ar atmosphere to obtain a powder (average particle diameter) of Sn, Cu, As, Sb, Bi, and Pb so that the total is 100% by mass. 21 μm, corresponding to powder size classification 4). The obtained powder was heated at 60 ° C. for 30 minutes in the air using a drying device to obtain solder powders of Examples and Comparative Examples. In Comparative Examples B3 to B14, the heat treatment was not performed, and the powder obtained by centrifugal spraying was directly used as the solder powder.
As Sn, a 3N material containing unavoidable impurities was used.

(Examples C1 to C18, Comparative Examples C1 to C24)
Sn, Ag, Cu, As, Sb, Bi, and Pb, the content of Cu is 0.5% by mass, the content of Ag is 1.0% by mass, the content of As, Sb, Bi, and Pb is as follows. As shown in Table 4, the sample was weighed and melt-mixed so that Sn became the balance (the balance where the total of Sn, Ag, Cu, As, Sb, Bi and Pb was 100% by mass). A powder (average particle size 21 μm, corresponding to powder size classification 4) was prepared by centrifugal spraying in an Ar atmosphere. The obtained powder was heated at 60 ° C. for 30 minutes in the air using a drying device to obtain solder powders of Examples and Comparative Examples. In Comparative Examples C3 to C14, the heat treatment was not performed, and the powder obtained by centrifugal spraying was directly used as a solder powder.
As Sn, a 3N material containing unavoidable impurities was used.
When the contents of Sn, Ag, Cu, As, Sb, Bi and Pb of the solder powder obtained in Example C1 were analyzed by ICP-AES based on JIS Z 3910, they were consistent with the charged amount. That was confirmed.

(Examples D1 to D18, Comparative Examples D1 to D24)
Sn, Ag, Cu, As, Sb, Bi, and Pb, the content of Cu is 0.5% by mass, the content of Ag is 2.0% by mass, and the content of As, Sb, Bi, and Pb is as follows. As shown in Table 5, the sample was weighed and melt-mixed so that Sn became the balance (the balance where the total of Sn, Ag, Cu, As, Sb, Bi and Pb was 100% by mass). A powder (average particle size 21 μm, corresponding to powder size classification 4) was prepared by centrifugal spraying in an Ar atmosphere. The obtained powder was heated at 60 ° C. for 30 minutes in the air using a drying device to obtain solder powders of Examples and Comparative Examples. In Comparative Examples D3 to D14, the heat treatment was not performed, and the powder obtained by centrifugal spraying was directly used as a solder powder.
As Sn, a 3N material containing unavoidable impurities was used.

(Examples E1 to E18, Comparative Examples E1 to E24)
Sn, Ag, Cu, As, Sb, Bi, and Pb, the Cu content is 0.5% by mass, the Ag content is 3.0% by mass, and the As, Sb, Bi, and Pb contents are as follows. As shown in Table 6, the sample was weighed and melt-mixed so that Sn became the balance (the balance where the total of Sn, Ag, Cu, As, Sb, Bi and Pb was 100% by mass). A powder (average particle size 21 μm, corresponding to powder size classification 4) was prepared by centrifugal spraying in an Ar atmosphere. The obtained powder was heated at 60 ° C. for 30 minutes in the air using a drying device to obtain solder powders of Examples and Comparative Examples. In Comparative Examples E3 to E14, the heat treatment was not performed, and the powder obtained by centrifugal spraying was directly used as a solder powder.
As Sn, a 3N material containing unavoidable impurities was used.

(Examples F1 to F18, Comparative Examples F1 to F24)
Sn, Ag, Cu, As, Sb, Bi, and Pb, the content of Cu is 0.5% by mass, the content of Ag is 3.5% by mass, and the content of As, Sb, Bi, and Pb is as follows. As shown in Table 7, the sample was weighed and melt-mixed so that Sn became the balance (the balance where the total of Sn, Ag, Cu, As, Sb, Bi and Pb was 100% by mass). A powder (average particle size 21 μm, corresponding to powder size classification 4) was prepared by centrifugal spraying in an Ar atmosphere. The obtained powder was heated at 60 ° C. for 30 minutes in the air using a drying device to obtain solder powders of Examples and Comparative Examples. In Comparative Examples F3 to F14, the heat treatment was not performed, and the powder obtained by centrifugal spraying was directly used as the solder powder.
As Sn, a 3N material containing unavoidable impurities was used.

  (1) Evaluation of presence / absence of an As-concentrated layer, (2) Evaluation of suppression of thickening, (3) Evaluation of solder wettability, (4) Evaluation of reliability for each of the solder powders of Examples and Comparative Examples The evaluation results are shown in Tables 2 to 7 below.

  The solder material of the present invention has no discoloration and is excellent in reliability such as solder wettability and cycle characteristics, and can be used for various applications. It can be suitably used as a paste solder material.

In addition, when the solder material is in the form of particles, if the solder material has a size (particle size distribution) corresponding to the symbols 1 to 8 in the powder size classification (Table 2) in JIS Z 3284-1: 2014 , the fine component Soldering is possible. The size of the particulate solder material is more preferably a size corresponding to the symbols 4 to 8, and more preferably a size corresponding to the symbols 5 to 8.
When the solder material is particulate, the sphericity is preferably 0.90 or more, more preferably 0.95 or more, and most preferably 0.99 or more.

(Examples A1 to A18, Comparative Examples A1 to A24)
The contents of Sn, As, Sb, Bi, and Pb are as shown in Table 2 below, and the content of Sn is 100% (Sn, As, Sb, Bi, and Pb is 100%). The powder is weighed so as to obtain a balance of 2% by mass, melt-mixed, and centrifugally sprayed in an Ar atmosphere to obtain a powder (average particle diameter: 21 μm, JIS Z3284-1: powder size classification of 2014 (Table 2) 4). Corresponding to). The obtained powder was heated at 60 ° C. for 30 minutes in the air using a drying device to obtain solder powders of Examples and Comparative Examples. In Comparative Examples A3 to A14, the heat treatment was not performed, and the powder obtained by centrifugal spraying was directly used as a solder powder.
As Sn, a 3N material containing unavoidable impurities was used.

The present invention, viscosity increase over time when the paste is small, and an object thereof is to provide a solder material excellent in wettability and reliability.

Claims (8)

  Sn or a Sn-based alloy, containing 40 to 250 ppm by mass of As, 0 to 3000 ppm by mass of Sb, 0 to 10000 ppm by mass of Bi, and 0 to 5100 ppm by mass of Pb (however, the content of Bi and Pb is 0 mass ppm), a solder material having an As-enriched layer. The solder material according to claim 1, wherein the contents of As, Sb, Bi, and Pb satisfy the following formulas (1) and (2).
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
However, in the formulas (1) and (2), As, Sb, Bi and Pb represent the contents (mass ppm) in each solder material.   The solder material according to claim 1, wherein the Sn or the Sn-based alloy is a Sn-based alloy containing 0.005 to 40% by mass of Ag and / or 0.001 to 10% by mass of Cu.   The solder material according to any one of claims 1 to 3, wherein the form of the solder material is a powder.   A solder paste containing the solder material according to claim 4 and a flux.   The solder paste according to claim 5, further comprising zirconium oxide powder.   The solder paste according to claim 6, wherein the content of the zirconium oxide powder is 0.05 to 20.0% by mass based on the total mass of the solder paste.   Sn or a Sn-based alloy, containing 40 to 250 ppm by mass of As, 0 to 3000 ppm by mass of Sb, 0 to 10000 ppm by mass of Bi, and 0 to 5100 ppm by mass of Pb (however, the content of Bi and Pb is 0 mass ppm), a solder joint having an As-enriched layer.