TWI646203B - Solder alloy - Google Patents

Abstract

A novel solder alloy is provided which contains Sn, Bi and Zn, and has a Bi content of 42 to 62% by mass, a Zn content of 0.2 to 3.6 mass%, and a remainder of Sn and an unavoidable impurity, which can be used in a low temperature region.

Description

Solder alloy

This invention relates to a solder alloy.

For environmental considerations, solder alloys that do not contain lead are recommended. The solder alloy varies depending on its composition and the temperature region suitable for use as a solder.

In the past, lead-based solder Sn-37Pb has a melting point of 183 ° C, and has good solder properties and workability. However, since lead is contained, lead-free is promoted in terms of environmental problems, and Sn-3.0Ag is developed as a lead-free solder. 0.5Cu was put into practical use (Patent Document 1).

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent No. 3027441

The above Sn-Ag-Cu has a higher melting point of 217 °C. Therefore, as a further low-melting-point lead-free solder, a Sn-Ag-Bi-In having a melting point of 200 ° C and lower than Sn-Ag-Cu has been developed, but is still higher than the melting temperature of Sn-Pb, thereby seeking a kind of Lower melting point solder. Again, as A known binary solder alloy is also known as Bi-42Sn (melting point 135 ° C). However, this solder has a low modulus of elasticity and poor fatigue characteristics. In addition, the composition of the solder is represented by mass% unless otherwise specified, and the Bi-42Sn is a composition of Sn: 42% by mass and the remaining portion Bi.

Accordingly, it is an object of the present invention to provide a novel solder alloy that can be used in low temperature regions without the addition and without lead.

As a result of intensive studies, the inventors have found that the above object can be attained by the following Bi-Sn-Zn-based solder alloy, and the present invention has been completed.

Therefore, the present invention contains the following (1) or less.

(1)

A solder alloy containing Sn, Bi and Zn, Bi is 42-62 mass%, Zn is 0.2-3.6 mass%, and the remainder is Sn and unavoidable impurities.

(2)

The solder alloy according to (1), wherein Sn is 36 to 56% by mass.

(3)

The solder alloy according to any one of (1) to (2), wherein Bi is 47 to 57% by mass.

(4)

The solder alloy according to any one of (1) to (3) wherein Zn is 0.6 to 2.0% by mass.

(5)

The solder alloy according to any one of (1) to (4), wherein the solidus temperature is 135 ° C or lower.

(6)

The solder alloy according to any one of (1) to (5), wherein the liquidus temperature is 160 ° C or lower.

(7)

The solder alloy according to any one of (1) to (6), wherein the value of the following formula: [liquidus temperature] - [solidus temperature] is 25 ° C or lower.

(8)

The solder alloy according to any one of (1) to (7), which has an elastic modulus of 450 MPa or more.

(9)

An internal joint welded joint of an electronic component obtained by welding the solder alloy according to any one of (1) to (8).

(10)

A solder joint of a power transistor, which is obtained by welding a solder alloy according to any one of (1) to (8).

(11)

A printed circuit board comprising the solder alloy according to any one of (1) to (8).

(12)

An electronic component comprising the solder alloy according to any one of (1) to (8).

(13)

A power transistor having the solder alloy according to any one of (1) to (8).

(14)

An electronic device comprising the solder joint according to any one of (9) to (10), or the printed circuit board according to (11), the electronic component described in (12), or the power transistor described in (13).

(15)

A power device comprising the solder joint according to any one of (9) to (10).

(16)

A member comprising the solder alloy according to any one of (1) to (8) as a material.

(17)

The solder alloy according to any one of (1) to (8), wherein the bonding strength is 10 MPa or more.

According to the present invention, it is possible to obtain a solder alloy which does not contain and does not contain lead and which has excellent characteristics in a temperature region of a low temperature of 160 ° C or lower. Since the solder alloy of the present invention is not added and does not contain lead, it is also advantageous from the viewpoint of environmental limitations in the future, and since expensive Ag or the like is not used, it is advantageous in terms of material price.

Hereinafter, the present invention will be described in detail by way of examples. The invention is not limited to the specific embodiments set forth below.

[solder alloy]

The solder alloy of the present invention contains Sn, Bi and Zn, Bi is 42 to 62% by mass, Zn is 0.2 to 3.6% by mass, and the remainder is Sn and unavoidable impurities.

The solder alloy of the present invention is a so-called lead-free solder alloy. Lead-free solder alloys are also known as Pb-free, but can be used at levels that are sufficiently low in environmental load, and lead is inevitable. Impurities. The solder alloy of the present invention has excellent characteristics in a temperature region (for example, a temperature region of 160 ° C or lower) using conventional Pb-free solder. That is, the solidus temperature and the liquidus temperature are at a low temperature, and the properties required for solder such as wettability and strength are excellent.

[Sn]

Sn (tin) is contained as a main constituent element of the solder alloy of the present invention. In a preferred embodiment, the content of Sn relative to the solder alloy can be, for example, 36 to 58% by mass, 36 to 56% by mass, 41 to 51% by mass, and 43 to 49% by mass.

[Bi]

The content of Bi with respect to the solder alloy can be, for example, 42 to 62% by mass, 42 to 61% by mass, 47 to 57% by mass, and 49 to 55% by mass.

[Zn]

The content of Zn relative to the solder alloy can be, for example, 0.2 to 3.6 mass%, 0.6 to 2.0 mass%, and 0.6 to 1.8 mass%.

[solidus temperature]

The solidus temperature can be, for example, 135° C. or lower, 134° C. or lower, or 133° C. or lower, and can be, for example, 120° C. or higher, 131° C. or higher, or 133° C. or higher.

[liquidus temperature]

The liquidus temperature can be, for example, 159 ° C or lower and 136 ° C or lower, and can be, for example, 120 ° C or higher, 131 ° C or higher, 136 ° C or higher, or 138 ° C or higher.

[liquidus temperature and solidus temperature]

In a preferred embodiment, the following formula: [liquidus temperature] - [solidus temperature] (solid phase liquid temperature difference: PR) can be set to 25 ° C or less, 20 ° C or less, 10 ° C. the following. PR can be set, for example 3 ° C or more. Since the solder alloy of the present invention has a small PR, it can achieve excellent dimensional accuracy when used for soldering.

In the welding, if the PR is large, the solder hardly hardens and the dimensional accuracy is deteriorated. In particular, for a solder ball or the like which has a certain size and is liable to cause soldering failure depending on the shape, the influence due to the size of the PR is large. For example, in the case of a solder ball formed of a large solder alloy of PR, even if it is hard, it is only the outer side, and the inside is in a state in which a liquid is mixed, and the shape is deformed by the pressure at the time of the next. When a single wafer is bonded by a plurality of solder balls, solder balls having different shapes (heights) are used, and the wafer cannot be smoothly bonded, and soldering failure (for example, tombstoning or lift-off) is likely to occur. When the PR is small, it is solidified immediately, so that the voids are small, and the time for mixing the liquid phase solid phase during welding is short, so that soldering defects are less likely to occur.

[better composition]

In a preferred embodiment, the composition of the solder alloy can be set, for example, as follows.

Sn: Bi: Zn = 45.4 to 47.4% by mass: 51.4 to 52.4% by mass: 1.0 to 1.4% by mass

Sn: Bi: Zn = 46.37 mass%: 52.40 mass%: 1.23 mass%

[joint strength]

The bonding strength of the solder alloy can be measured by the means described in the examples. In a preferred embodiment, the joint strength can be, for example, 10 MPa or more or 15 MPa or more.

[Elastic Modulus]

The solder alloy has a higher modulus of elasticity than Bi-42Sn which is an alloy known from the prior art, and is excellent in fatigue characteristics. In a preferred embodiment, the solder alloy may have an elastic modulus of 450 MPa or more. The upper limit of the elastic modulus of the solder alloy is not particularly limited, and may be, for example, 600 MPa or less and 550 MPa or less.

The elastic modulus is also called the alias spring constant, which is the characteristic value of the stress region (also called the elastic region) where plastic deformation does not occur. If it is a stress in the elastic region, the metal ruthenium appears to be deformed (for example, elongated), but if the stress is released, the original shape is restored to its original shape (the original length). In general, the fatigue test is carried out under low stress, so the elastic modulus becomes an important characteristic factor. In the so-called low fatigue region where the elastic modulus becomes a certain stress range, the material with large elastic modulus reaches the long life of the fracture, and the relationship between the life and the elastic modulus is expressed by the formula of Basquin's law.

Bi-Sn solder is an alloy of eutectic structure. When Zn is added to the alloy composition, Zn does not form an intermetallic compound with Bi and Sn, and Zn is separately precipitated in the BiSn liquid phase. If the cooling rate is fast, it becomes spherical, and if it is slow, it becomes dendrite crystal. The inventors believe that by this mechanism, it is hardened in the present invention, and the elastic modulus is improved.

[Shape of solder alloy]

The shape of the solder alloy of the present invention can be suitably used as a shape desired for solder. As described in the examples, the member may be formed into a sheet shape, and further, for example, it may be formed into a member having a shape such as a thread, a powder, a ball, a plate, or a rod. The shape of the solder alloy is particularly preferably formed into the shape of a powder, the shape of a solder ball (spherical shape), or a sheet shape. The solder ball means, for example, a ball having a diameter of 50 μm to 500 μm. The solder powder refers to, for example, a powder having a particle diameter of 50 μm or less. Solder powder can be used for solder paste.

[Examples]

Hereinafter, the present invention will be described in detail by way of examples. The invention is not limited to the examples exemplified below.

[example 1]

[Example 1]

A specific amount of Sn, Bi, and Zn was weighed, and the ingot was melted by vacuum melting. The components of the ingot were determined by fluorescent X-rays and are described in the table. It was processed into a sheet having a thickness of 0.2 mm. Furthermore, the components of the ingot can also be analyzed using an ICP emission spectrometer.

The measurement of the solidus temperature and the liquidus temperature of the solder alloy was carried out by a method by Differential Scanning Calorimetry (DSC) in accordance with JIS Z3198-1:2014.

Each 2 mm SiC wafer was prepared, and a Ni layer (thickness: 1 μm) and an Au layer (thickness: 0.05 μm) were sequentially formed on one surface by sputtering. A Ni layer (thickness: 1 μm) was formed on the underlayer by electroplating, and an Au layer (thickness: 0.05 μm) was formed on the lead frame of the outermost layer, and a Sn-Bi-Zn piece having a thickness of 0.2 mm cut every 2 mm was placed. The SiC wafer was placed on the sputtering surface opposite to the above-mentioned sheet, and heated to 150 ° C in a formic acid (partial pressure 40 mmHg) environment to bond the lead frame to the SiC wafer. The joint strength was measured.

Bonding strength was measured in accordance with MIL STD-883G. The tool mounted on the load sensor is lowered to the surface of the substrate, the device detects the surface of the substrate and stops falling, the tool rises from the surface of the substrate to the set height, and the load is measured by the tool pressing the joint.

<Measurement conditions>

Body: dage series 4000 manufactured by dage

Method: Wafer Shear Strength Test

Test speed: 100μm/s

Test height: 20.0μm

Tool movement amount: 4mm (test piece 2mm)

Further, the elastic modulus is measured by a nanoindentation according to ISO 14577-1.

<Measurement conditions>

Device: Ultra-indentation hardness tester ENT-2100 Manufactured by Elionix

Indenter: Berkovich indenter

Load: 100mN

[Examples 2 to 5]

In the same procedure as in Example 1, a specific amount of Sn, Bi, and Zn was weighed, and the ingot was melted by vacuum melting, and each component of the ingot was obtained by fluorescent X-ray, and processed into a thickness of 0.2 mm. In the form of a sheet, DSC measurement was performed to determine the solidus temperature and the liquidus temperature, and the joint strength and the modulus of elasticity were measured. The summary is shown in Table 1.

[Example 2]

[Comparative Examples 1 to 5]

In the same procedure as in Example 1, a specific amount of Sn, Bi, and Zn was weighed, and the ingot was melted by vacuum melting, and each component of the ingot was obtained by fluorescent X-ray, and processed into a thickness of 0.2 mm. In the form of a sheet, DSC measurement was performed to determine the solidus temperature and the liquidus temperature, and the joint strength and the modulus of elasticity were measured. The summary is shown in Table 1.

[Example 3]

[Reference Example 1~2]

In the same procedure as in Example 1, a specific amount of Sn, Bi, Ag, and In was weighed, and the ingot was melted by vacuum melting, and the components of the ingot were obtained by fluorescent X-ray to be processed to a thickness of 0.2. The sheet shape of mm was measured by DSC to determine the solidus temperature and the liquidus temperature, and the joint strength and the modulus of elasticity were measured. The summary is shown in Table 1.

[result]

The above results are summarized in Table 1 below.

When the examples 1 to 5 were compared with the comparative examples 1 to 3, the elastic modulus of the comparative examples 1 to 3 was only about half of the value of the example, which was remarkably inferior. Further, the elastic modulus of Comparative Examples 4 and 5 was the same as those of Examples 1 to 5, but the joint strength was 10 MPa or less, which was a result of poor joint strength.

[Industrial availability]

The present invention provides a solder alloy having excellent characteristics in a low temperature temperature region. The present invention is an industrially useful invention.

Claims (14)

A solder alloy containing Sn, Bi and Zn, Bi is 42-62 mass%, Zn is 0.2-3.6 mass%, the remainder is Sn and unavoidable impurities, solidus temperature is 120-135 ° C, liquidus The temperature is 120~159°C, and the following formula: [liquidus temperature]-[solidus temperature] has a value of 1~25°C. For example, in the solder alloy of claim 1, wherein Sn is 36 to 56% by mass. The solder alloy according to any one of claims 1 to 2, wherein Bi is 47 to 57% by mass. The solder alloy according to any one of claims 1 to 2, wherein Zn is 0.6 to 2.0% by mass. The solder alloy according to any one of claims 1 to 2, which has a modulus of elasticity of 450 MPa or more. The solder alloy according to any one of claims 1 to 2, which has a bonding strength of 10 MPa or more. An internal joint welded joint of an electronic component obtained by welding a solder alloy according to any one of claims 1 to 5. A solder joint of a power transistor is soldered to a solder alloy according to any one of claims 1 to 5. A printed circuit board having the solder alloy of any one of claims 1 to 5. An electronic component having the solder alloy of any one of claims 1 to 5. A power transistor having the solder alloy of any one of claims 1 to 5. An electronic machine having a solder joint of claim 7 or 8 or a printed circuit board of claim 9 or an electronic component of claim 10 or a power supply of claim 11 Crystal. A power device having a solder joint of claim 7 or 8. A member using the solder alloy of any one of claims 1 to 5 as a material.