JP6247819B2 - Aluminum solder and solder joints - Google Patents

Description

  The present invention relates to a solder for aluminum and a solder joint having excellent joint reliability.

Aluminum has a high thermal conductivity compared to other metals and generates less thermal stress. Therefore, aluminum is often used for heat dissipation members such as electronic devices.
In recent years, attention has been paid to lightness and strength of specific gravity, which are characteristics of aluminum, and studies have been made as materials that contribute to weight reduction of motors and the like.

However, when aluminum is used for a heat dissipation member or aluminum for a motor coil or the like, it is common to use solder to join, but there is a problem that sufficient joining strength and reliability cannot be obtained. Yes.

As a solder for aluminum, Patent Document 1 discloses a Sn- (3-40%) Zn- (1-10%) Ag- (0.5-4%) Cu solder alloy, and Patent Document 2 discloses Sn- (0.5 ~ 7%) Mg- (1.5-20%) Zn- (0.5-15%) Ag solder alloys are disclosed respectively.
Patent Document 3 discloses Sn- (10-15%) Zn- (0.1-1.5%) Cu- (0.0001-0.1%) Al- (0.0001-0.03%) Si- (0.0001-0.02%) Ti- ( A 0.0001 to 0.01%) B composition solder alloy, and Patent Document 4 disclose a Sn- (10% or less) Ag- (15% or less) Al composition aluminum alloy direct bonding solder alloy.
In Patent Document 5, as a joining method for joining aluminum materials or between an aluminum material and a dissimilar material, Sn composed of a metal element selected from the group of Cu, Ag, In, Bi, Co, and Ti and the remaining Sn is used. Bonding using a system solder is disclosed.

  However, Patent Documents 1 and 2 have improved corrosion resistance, which is a problem of Sn—Zn solder, but have not been satisfied with respect to corrosion resistance such as salt water. The composition of Patent Document 3 has a problem that the number of elements is large and the management cost increases and the corrosion resistance of the Sn—Zn solder remains. Patent Document 4 is not satisfactory with respect to the corrosion resistance of salt water or the like. Patent Document 5 is attractive in that a flux is not required for joining, but the problem that the process is complicated such as the need to prepare two kinds of joints remains, and the composition is simple. There is a need for a solder joint material that is highly reliable in terms of corrosion resistance, such as salt water.

Japanese Patent Laid-Open No. 50-50250 JP 50-56347 A JP 2006-167800 A JP 2008-142729 A JP 2011-167714 A

An object of the present invention is to provide a solder joint material having a lead-free composition having excellent corrosion resistance such as salt water and having high reliability, and a solder joint using the lead-free solder.

As a result of intensive investigations to achieve the above object, the present inventor has used a solder composed mainly of Sn, Cu, and Ag, so that it can be used for soldering between aluminum materials or between aluminum materials and dissimilar metal materials. The present inventors have found that it has excellent corrosion resistance such as salt water and has excellent bonding strength, and has completed the present invention.

That is, the present invention uses a lead-free solder alloy of 1.5 to 6 % by weight of Cu , 2 to 3 % by weight of Ag , 0.05% by weight of Ni, and the balance of Sn , thereby improving the corrosion resistance of water and the like. The solder joint and the solder joint having an excellent effect on the bonding strength were realized.
Further, by adding Sb to the main component of the present invention, the Cu content can be lowered.

According to the present invention, it is possible to perform solder bonding with excellent corrosion resistance and reliability in joining aluminum materials or between aluminum materials and dissimilar metal materials. It becomes possible.

The schematic diagram of a shear test sample. Enlarged view of the shear test sample. Shear test results. Cross-sectional observation photograph 1 of the shear test sample joint (3a). Cross-sectional observation photograph 2 of the shear test sample joint (3b).

The present invention is described in detail below.
Conventionally, aluminum is known to be a powerful material such as electronic parts, motors, and on-vehicle parts due to its metallic properties. However, in solder joints, problems such as joint strength and electrolytic corrosion (galvanic corrosion) have occurred. Since it was difficult to overcome, it was rarely used in practice.
In particular, in electronic parts and the like, copper and silver compositions are widely used in joints. Therefore, when soldering is performed using an aluminum material, galvanic batteries are formed in the joints and corrosion progresses. Therefore, countermeasures such as inclusion of an element having a small potential difference as in the patent literature have been taken.
In addition, it is also known that electrolytic corrosion progresses at a surprising speed in a harsh environment in contact with salt water such as seawater, and the solder is peeled off in a short time.
Therefore, there has been a demand for highly reliable solder joints that can maintain high joint strength even in harsh environments.

A solder composition composed of Sn, Cu, and Ag is known as a lead-free solder composition, but it is also known that it is not suitable for joining aluminum materials.
Even with lead-free solder compositions based on Sn, Cu, and Ni, as invented by the applicant, sufficient joining reliability can be achieved in harsh environments that contact seawater and other salt water when joining aluminum materials. Sex has not been obtained.

In the present invention, first, focusing on the lead-free solder composition, and considering the combination of elements that can withstand the salt water immersion test, assuming an environment where the salt water contacts, the basic composition is Sn, Cu and Ag. It is characterized by specifying the lead-free solder composition that can withstand the salt water immersion test and the blending amount of the element.

Next, the contents of the present invention will be specifically described.
First, the basic composition of the lead-free solder of the present invention is composed of Sn, Cu, and Ag. If the Cu content is 1.5 % by weight or more, the effect of the present invention is obtained, preferably 3% by weight or more. More preferably, it is 5% by weight or more.
The content of Ag has the effect of the present invention as long as 2 wt% or more, preferably 2-3 wt%.
Sn is the balance in which Cu and Ag are blended, and the effects of the present invention are not impaired even if other inevitable impurities are contained.

And the content of each element which has the effect of this invention at the time of making Sb contain in Sn, Cu, and Ag which are the basic compositions of the lead-free solder of this invention is as follows.
It is preferable that Cu is about 0.7%, Ag is about 3% by weight, and Sb is 1% by weight.

You may mix | blend elements, such as Ni, with the lead-free solder for aluminum joining of this invention in the range which does not impair the effect of this invention.

Moreover, it goes without saying that a solder joint soldered using the lead-free solder for aluminum joining of the present invention has the effects of the present invention.

(Shearing force measurement test)
〔sample〕
No. 1261 manufactured by Nippon Superior Co., Ltd. was prepared as a 25 × 3 × 1 mm aluminum material, a solder alloy having the composition shown in Table 1, and a flux.
[Production of sample]
First, as shown in FIG. 1, after applying about 0.01 g of flux to the end of the aluminum material 1, soldered to the 5 mm of the end of the aluminum material 1 with the solder alloy shown in Table 1 at the soldering temperature. Two were prepared.
Next, the end portions of the soldered aluminum material are overlapped, heated at the soldering temperature shown in Table 1 to join the two aluminum materials, cooled to room temperature, and the test sample shown in FIG. Produced.
〔Preliminary test〕
The sample was completely immersed in a 3% NaCl aqueous solution and allowed to stand at room temperature for 1 week to confirm state changes such as peeling.

The evaluation was made by visually observing that there was no change in the solder joint, and x where change such as peeling was recognized.
The results are shown in Table 1.

Based on the preliminary test results in Table 1, the effects of the present invention will be described in detail.
Samples prepared under the solder alloy composition and soldering conditions shown in Table 2 were left at room temperature for 60 days so that the solder joints were completely immersed in a 3% NaCl aqueous solution, then removed, washed pure and dried. Later, the maximum shear force was measured with a universal testing machine AG-10klS manufactured by Shimadzu Corporation under the condition of a tensile speed of 1 mm / min.

Conventionally, Arusoi45D, which has been used for soldering aluminum materials, was evaluated as a comparison object, and the test results are shown in FIG.
FIG. 3 shows that the lead-free solder of 1.5 wt% or more, Ag of 2 wt% or more, and the balance of Sn according to the present invention, Cu of 0.7 wt%, Ag of 3 wt%, and Sb of 1 It was confirmed that the lead-free solder having a weight percent and the balance of Sn has a maximum shearing force of 100 N or more, can withstand a salt water immersion test, and exhibits high bonding strength.
Moreover, about a joining state by SN100C5 + 3Ag composition, a junction cross-sectional photograph and an element mapping photograph are shown in FIG. 4 (3a location) and FIG. 5 (3b location).

The lead-free solder of the present invention enables corrosion-resistant and reliable solder bonding even between aluminum materials or between aluminum materials and dissimilar metal materials, thus reducing the weight of motors and in-vehicle components. Wide application can be expected.

1: Aluminum test material 2: Solder 3a: Upper part of solder joint 3b: Lower part of solder joint

Claims (2)

  A lead-free solder for joining aluminum materials, characterized in that Cu is 1.5 to 6% by weight, Ag is 2 to 3% by weight, Ni is 0.05% by weight, and the balance is Sn. A lead-free solder for joining aluminum materials according to claim 1, wherein a member containing an aluminum material is joined to at least one of the solder joints.