TWI647316B - Solder alloy - Google Patents

Abstract

A novel solder alloy comprising Sn, Bi and Cu is provided, wherein Sn is 0.05 to 1.50% by mass, Cu is 0.03 to 3.2% by mass, and the balance is Bi and unavoidable impurities, and can be used in a high 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 is suitable for use as a temperature region of the solder.

The power device is used as a component for power conversion, and is used in a wide range of fields such as hybrid vehicles and power transmission and distribution. In the past, it has been possible to cope with the device of the Si wafer. However, in the field where high withstand voltage, high current use, and high-speed operation are required, SiC and GaN having a band gap larger than Si have been attracting attention in recent years.

In the conventional power module, the operating temperature is about 170 ° C, but it is said to exceed 200 ° C in the next-generation SiC, GaN, and the like. Along with this, heat resistance and heat dissipation are required for each of the materials used in the module in which the wafers are mounted.

As for the bonding material, Sn-3.0Ag-0.5Cu solder is preferable from the viewpoint of no Pb, but since the operating temperature may exceed 200 ° C in the next-generation module, Sn with a melting point of 220 ° C is used. The heat resistance is further required as compared with the -3.0Ag-0.5Cu solder. Specifically, in terms of the cooling of the heat sink and the allowability of the temperature around the engine, a solder having a melting point of preferably 250 ° C or higher is desired. In addition, the composition of the solder is represented by mass % unless otherwise specified, and the Sn-3.0Ag-0.5Cu-based Ag: 3.0% by mass, Cu: 0.5% by mass, and the remaining Sn group to make. In addition to the limitation of RoHS, Pb solder (Pb-5Sn), which is not good from the viewpoint of environmental restrictions, can cope with the operating temperature of the next-generation module. In the same manner as the Pb solder, Au-based solder (Au-Ge, Au-Si, Au-Sn) is used as the heat-resistant solder (Non-Patent Documents 1 to 3). As an inexpensive solder, a Sn-based solder is known (Patent Documents 1 and 2).

Therefore, in recent years, as a joining material of a next-generation type module, a metal fine powder paste has been attracting attention. Since the metal powder has a small size, the surface energy is high, and sintering starts at a temperature far below the melting point of the metal. Further, unlike the solder, once the sintering is performed, if the temperature is not raised to the vicinity of the melting point of the metal, remelting is not performed. By utilizing such characteristics effectively, development is carried out using Ag fine powder paste (Patent Document 3).

Although Pb-5Sn solder is fully functional as a bonding material for next-generation power modules, it has lead, and it is preferable not to use it from the viewpoint of future environmental limitations. Further, the Au-based solder is preferable as a bonding material in terms of function and environment, but there is a problem of material price. When the Sn-based solder is bonded to the Cu electrode, there is a heat load in the operating environment, and a Kirkendall void is generated due to a difference in diffusion speed between Sn and Cu in the vicinity of the joint interface, so that the joint strength is obtained. Reduce the embarrassment. Further, the Ag fine powder paste can impart sufficient joint strength and heat resistance to the joint layer depending on the conditions, but there is a problem of the material price.

Patent Document 4 discloses a lead-free solder paste in which volume change is suppressed, but the melting point is relatively low, and there is room for improvement in high-temperature characteristics. Further, in the solder alloy of Patent Document 4, since the temperature difference between the solidus temperature and the liquidus temperature is large, it is disadvantageous in terms of dimensional accuracy of welding. Patent Document 5 discloses a solder paste having improved wettability. In the solder paste of Patent Document 5, a plurality of powders having different mixing compositions are formed, and after melting, they are designed as alloys. Therefore, it is necessary to heat more than the melting point of each powder. For example, if Cu powder is used, However, if it is not heated to a melting point of Cu of 1084.6 ° C or more, complete melting cannot be expected, and there is a concern depending on the unevenness of the heating operation at the time of welding.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. Hei 9-271981

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2000-141079

[Patent Document 3] International Publication WO2011/155055

[Patent Document 4] International Publication WO2007/018288

[Patent Document 5] International Publication WO2007/055308

[Non-patent literature]

[Non-Patent Document 1] P. Alexandrov, W. Wright, M. Pan, M. Weiner, L. Jiao and J. H. Zhao, Solid-State Electron., 47 (2003) p.263.

[Non-Patent Document 2] R. W. Johnson and L. Williams, Mater. Sci. Forum 483-485 (2005) p.785.

[Non-Patent Document 3] S. Tanimoto, K. Matsui, Y. Murakami, H. Yamaguchi and H. Okumura, Proceedings of IMAPS HiTEC 2010 (May 11-13, 2010, Albuquerque, New Mexico, USA), p32-39 .

In this way, a solder alloy having excellent characteristics in a high temperature region (for example, a temperature region exceeding 250 ° C) required for a bonding material of a next-generation power module is desired.

Accordingly, it is an object of the present invention to provide a novel solder alloy which can be used in a high temperature region without adding and containing no lead.

As a result of intensive studies, the inventors have found that the above object can be attained by the following Bi-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 Cu, Sn of 0.05 to 1.50% by mass, Cu of 0.03 to 3.2% by mass, and the balance being Bi and unavoidable impurities.

(2)

The solder alloy according to (1), wherein Bi is from 95.3 to 99.92% by mass.

(3)

The solder alloy according to any one of (1) to (2), wherein Sn is 0.05 to 1.0% by mass.

(4)

The solder alloy according to any one of (1) to (3), wherein Cu is 1.0 to 3.2% by mass.

(5)

The solder alloy according to any one of (1) to (4), wherein the solidus temperature is 250 ° C or higher.

(6)

The solder alloy according to any one of (1) to (5), wherein the liquidus temperature is 275 ° C or lower.

(7)

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

(8)

The solder alloy according to any one of (1) to (7) wherein the shape of the solder alloy is a powder, a sphere or a sheet.

(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), or 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 high temperature region (for example, a temperature region exceeding 250 ° C) required for a bonding material of a next-generation power module. Since the solder alloy of the present invention is not added and does not contain lead, it is also advantageous from the viewpoint of future environmental restrictions, and since expensive Ag is not used, it is also 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 Cu, Sn is 0.05 to 1.50% by mass, Cu is 0.03 to 3.2% by mass, and the balance is Bi 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 solders, but can contain lead as an unavoidable impurity at a level that is sufficiently low in environmental load. The solder alloy of the present invention has high temperature due to solidus temperature and liquidus temperature. Therefore, the high temperature region required for the bonding material of the next-generation power module (for example, a temperature region exceeding 250 ° C) also has excellent characteristics.

[Bi]

Bi (铋) is contained as a main constituent element of the solder alloy of the present invention. In a preferred embodiment, the content of Bi with respect to the solder alloy can be, for example, 95.3 to 99.92 mass%, 98.5 to 99.8 mass%, and 99.0 to 99.8 mass%.

[Sn]

The content of Sn with respect to the solder alloy can be, for example, 0.05 to 1.50% by mass, 0.05 to 1.0% by mass, 0.10 to 0.50% by mass, and 0.10 to 0.20% by mass.

[Cu]

The content of Cu with respect to the solder alloy can be, for example, 0.03 to 3.2% by mass and 1.0 to 3.2% by mass.

[solidus temperature]

The solidus temperature can be, for example, 250 ° C or more or 252 ° C or more. In the case of a solder alloy having a low solidus temperature, if it is not a solder paste using an epoxy resin as a reinforcing material, it cannot be used in a high temperature region, but the solidus temperature is high (for example, 250 ° C or higher). In the case of a solder alloy, it is mixed with a flux-free flux, and even if it is a non-epoxy solder paste, it can be used in a high temperature region.

[liquidus temperature]

The liquidus temperature can be, for example, 275 ° C or lower or 272 ° C or lower.

[liquidus temperature and solidus temperature]

In a preferred embodiment, the value of the following formula: [liquidus temperature] - [solidus temperature] (solid phase liquid phase temperature difference: PR) can be set to 25 ° C or less or 22 ° C or less. PR can be set, for example, at 1 ° C or higher. 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: Cu = 0.14 to 0.16 mass%: 99.51 to 99.53 mass%: 0.32 to 0.34 mass%

Sn: Bi: Cu = 0.153% by mass: 99.520% by mass: 0.327% by 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.

[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 of the invention. The invention is not limited by the examples shown below.

(example 1)

(Example 1)

A specific amount of Bi, Cu, and Sn 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 Bi-Sn-Cu 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 in an environment of formic acid (partial pressure 40 mmHg) 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 attached to the load sensor is lowered to the substrate surface, the device detects the substrate surface and stops falling, the tool rises from the detected substrate surface to the set height, and the tool is pressed by the joint to measure the load at the time of the damage.

<Measurement conditions>

Device: 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)

(Examples 2 to 11)

In the same procedure as in the first embodiment, a specific amount of Bi, Cu, and Sn were 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 sheet shape. The differential scanning calorimetry measures the solidus temperature and the liquidus temperature to measure the joint strength. These results are summarized in Table 1.

(Example 2)

(Comparative examples 1 to 5)

In the same procedure as in the first embodiment, a specific amount of Bi, Cu, and Sn were 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 sheet shape. The differential scanning calorimetry measures the solidus temperature and the liquidus temperature to measure the joint strength. These results are summarized in Table 1.

(Example 3)

(Reference example 1)

The alloy of Pb and Sn was vacuum-melted in the same manner as in Example 1 to obtain a sheet having a thickness of 0.2 mm. Using this sheet, the SiC wafer was bonded to the lead frame, and the joint strength was measured.

(Reference example 2)

An alloy of Sn, Ag, and Cu (SAC alloy) was vacuum-melted in the same manner as in Example 1 to obtain a sheet having a thickness of 0.2 mm. Using the sheet, the SiC wafer is bonded to the lead frame, and the joint is measured. strength.

Table 1 shows the bonding strength of the composition of the examples of the present invention, the composition of the comparative example and the reference example, and the bonding strength. As a result, it was found that the lead solder of the reference example 1 was a lead-free solder having substantially the same bonding strength. Further, compared with the SAC alloy of Reference Example 2, the joint strength was also the same. With respect to Examples 1 to 11, the target solid phase liquid phase temperature difference was 25 ° C or less, and the joint strength was also the target value of 10 MPa or more. In Comparative Examples 1 to 3, although the solid phase liquid phase temperature difference satisfies the target value, the joint strength does not satisfy the target value. When the reference examples 1 and 2 and the examples 1 to 11 are observed, it is understood that the solder compositions of the examples 1 to 11 can also be suitably used as a substitute for the current power device. Further, according to the comparison between Example 7 and Example 8, it is understood that even if the amount of Cu is the same, when PR is small, PR tends to be small. Further, according to the tenth and eleventh examples, it is understood that even if the amount of Sn is the same, when the amount of Cu is large, the PR tends to be small. On the other hand, in Comparative Examples 4 and 5, the PR was very large.

[Industrial availability]

The present invention provides a solder alloy which does not contain and does not contain lead and which has excellent characteristics in a high temperature region. The present invention is an industrially useful invention.

Claims (14)

A solder alloy containing Sn, Bi and Cu, Sn of 0.05 to 1.50 mass%, Cu of 0.03 to 3.2 mass%, remainder of Bi and unavoidable impurities, solidus temperature of 250 ° C or more, liquidus The temperature is 275 ° C or less, and the following formula: [liquidus temperature] - [solidus temperature] has a value of 25 ° C or less. For example, in the solder alloy of claim 1, wherein Bi is 95.3 to 99.92% by mass. The solder alloy according to any one of claims 1 to 2, wherein Sn is 0.05 to 1.0% by mass. The solder alloy according to any one of claims 1 to 2, wherein Cu is 1.0 to 3.2% by mass. The solder alloy according to any one of claims 1 to 2, wherein the shape of the solder alloy is a powder, a sphere or a sheet. 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.