JPS601937B2 - Oxidation-resistant lead-tin solder master alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new master alloy for use in lead-tin solder alloys.

More particularly, the present invention relates to a master alloy used to form a lead-tin solder alloy that is oxidation resistant in the molten state or in a heat chamber exposed to temperatures slightly below the melting point. Solder used as a plating material or a brazing material undergoes air oxidation in a molten state, producing an oxide film on the surface of the molten solder.

Therefore, when soldering and solder plating are performed using a molten solder tank, the presence of oxides on the surface of the molten solder will cause poor soldering and plating, so it is necessary to scrape off the oxides on the surface or remove the molten solder. It must be circulated and overflowed so that new surfaces are always brought to the surface. This is an important problem, especially when soldering printed wiring boards. Also, wiring for electronic equipment,
The temperature of the solder bath used for wiring, assembly, etc. is usually 200℃.
Mostly in the range ~300oo, but sometimes 400-5000
There is also a heat sink used in the range of 0, and the longer the solder layer is exposed to high temperatures, the more oxides on the surface will contaminate the bath and the more the solder will be wasted. .

However, the inventors of the present invention have attempted to solve the above-mentioned problems.As a result of extensive research, we have found that it is difficult to form an oxide film on the surface of the molten solder, or that aluminum is added to the tin solder in order to prevent the formation of an oxide film on the surface of the molten solder. We have discovered a master alloy that can be used in the added oxidation-resistant lead-tin solder alloy, and have completed the present invention.

That is, the present inventors first applied aluminum 0.005
~0. It was confirmed that a composition consisting of 0.2 to 9% by weight of tin, 0.2 to 9% by weight of tin, and the balance lead is effective as a substantially oxidation-resistant lead-tin alloy. They have discovered a master alloy that can be suitably used in the production of alloys.

By the way, there is a method in which a uniform molten solder alloy containing 0.005 to 0.2% by weight of aluminum is poured into lead-tin solder and the aluminum is directly melted into the molten solder, depending on the temperature of the molten metal. substantially the melting point of aluminum (66
Since lead, tin, aluminum, etc. are consumed by atmospheric oxidation since the solder is processed at a temperature higher than 0 qo), it is difficult to pass through the molten lead-tin-aluminum solder that has the target composition and is healthy.

Therefore, a mother alloy of aluminum-tin or aluminum-lead-tin solder containing one to several hundred times as much aluminum as the amount of aluminum that will be ultimately used is prepared in advance, and then it is soldered to a base alloy that does not contain substantially aluminum. By adding it to a solder bath and diluting it, a lead-tin solder alloy with good oxidation resistance can be easily spread.

On the other hand, aluminum-lead alloys have a drawback in that the solubility of aluminum in lead is extremely low in the liquid phase state. For example, even in 90000, the amount of dissolved aluminum relative to lead is less than 0.5% by weight, and if more aluminum is included, it will separate into two phases, aluminum and lead, resulting in a large amount of segregation, making it unsuitable for use as a master alloy. Undesirable. The present invention overcomes these drawbacks,
Using a specific aluminum-tin or aluminum-lead-tin solder alloy master alloy that uniformly contains aluminum at a high concentration in the tin or lead-tin solder alloy and reduces segregation, aluminum can be soldered at a certain dilution ratio. It can be easily and stably used as a lead-tin solder alloy having oxidation resistance by dissolving it in a lead-tin solder bath that does not contain lead-tin. Next, the present invention will be explained in detail with reference to Examples.

Example 1 After adding flux to the surface of aluminum to prevent oxidation and heating and melting it to 800 qo, tin or lead-tin solder was added and melted to have the prescribed composition shown in Table 1.
After praying well, the mixture was held at 80,000 for 5 minutes and cast into a 60 OO plate graphite mold.

Appropriate amounts of these master alloys were sampled and the solidus and liquidus lines of each master alloy were measured using a differential thermal analyzer. Table 1 shows the results of evaluating the solubility (dissolution state) of each mother alloy by adding each mother alloy so that the aluminum concentration in the medium was 0.1%.

In Table 1, the state of penetration was evaluated as follows.

◎: Completely melts within 4 minutes ○: Completely melts within 15 minutes ×: Difficult to melt even after 15 minutes The lead-tin solder used is JIS standard 9$, 6T, 4, and 5A. It is.

Table 1 As can be seen from Table 1, the melting state is poor in those with a liquidus temperature slightly lower than 600 oo and in those with a liquidus temperature exceeding 600° C., but otherwise good.

Therefore, to summarize these, the composition range of the alloy surrounded by points A, B, C, D, E, F, and G on the triangular graph as shown in Fig. 1 is the effective composition range of the master alloy of the present invention. be. That is, the master alloy of the present invention is a ternary alloy of lead-tin-aluminum, and as shown in FIG.
9.8%, AIO. 2%), point C (Pb94.8%, S
n5%, AIO. 2%), one point D (Pb94.5%, S
n5%, MO. 5%), point E (Pb57%, Sn38%
, AI5%), point F (Pb36%, Sn54%, AIl
O%) and point G (Pb4%, Sn76%, AI20%
) is a master alloy for oxidation-resistant lead-tin solder with a composition within the range enclosed by.

To explain these in more detail, point A (Sn 70%, peak 30%), point B (Sn 99.8%, A
IO. 2%), when the amount of aluminum increases from point A, the liquidus temperature increases, and the melting of the parent alloy becomes weaker when added to lead-tin solder that does not contain aluminum. It becomes difficult to adjust the tin solder bath composition.

Furthermore, when the aluminum content decreases from point B, even if the penetration of the mother alloy is good, the oxidation-resistant lead-tin solder alloy contains up to 0.2% aluminum, so it loses its meaning as a mother alloy. . Point B, point C (Pb94
．． 8%, Sn5%, AIO. If the amount of aluminum is less than the line connected by 2%), as mentioned above,
The meaning of the mother alloy becomes meaningless.

Point C, point D (Pb94.5%, Sn5%, AIO.5%
) When the amount of lead is greater than the wires connected by the wires, primary crystals of aluminum will crystallize in the form of particles in the mother alloy.
Aluminum floats on the bath surface and inhibits the soldering function of oxidation-resistant lead-tin solder alloys. Point D, point E (Pb57%, S
n38%, AI5%), point F (Pb36%, Sn54%
, AIIO%), point G (Pb4%, Sn76%, AI2
0%), when the amount of aluminum is larger than the line connecting points A sequentially, the temperature of the liquidus line becomes higher, and the melting of the parent alloy added to the lead-tin solder, which does not contain aluminum, increases. I become angry. This is the result of the aluminum crystallized in the mother alloy growing large in the form of particles, and as the amount of aluminum increases further, aluminum and lead-tin solder separate into two phases, with aluminum on the upper side and aluminum on the lower side in the mother alloy. Aluminum-lead-tin solder is formed on the surface, making it impossible to obtain a uniform and sound mother alloy. Next, we will show the results of observations of typical compositions using an optical microscope and a scanning electron microscope.

That is, FIG. 2 is an optical micrograph of the three-spot b-5 and n-5AI alloy of the present invention, where the white part is aluminum and the black part is the matrix lead-tin alloy. It can be seen from Figure 2 that aluminum is finely and uniformly dispersed. FIG. 2a is a secondary electron beam image taken by a scanning electron microscope of an alloy with the same composition, where the black leaf pattern is aluminum and the white part is gold when the matrix is lead-rich. Second
From figure a, it is clearer that the aluminum is finely and uniformly dispersed. In Figure 4, 3 is b-4$n-20AI
The alloy shown in Figure 3 is 94.1Pb-4. These are optical micrographs of the $n-IAI alloy, where the white part is aluminum and the black part is the matrix lead-tin alloy. Fourth
It can be seen from the figure that the primary crystals of aluminum have grown and become coarse, and from Figure 3 it can be seen that the aluminum and lead-tin solder alloy have separated into two phases. When the master alloys for aluminum-lead tin solder shown in Figures 3 and 4 are added to lead-tin solder that does not contain aluminum, the melting is slow and aluminum is liberated on the surface, making it difficult to adjust the case composition. This indicates that it is difficult and inhibits the soldering function.
Example 2 39. of the present invention obtained in Example 1. Spot b-59. Quasi-n-
An oxidation-resistant lead-tin solder master alloy, which is an IAI alloy, is added to a lead-tin solder bath that does not contain aluminum, and the composition is finally adjusted to the composition shown in Table 2. An oxidation-resistant lead-tin solder alloy to which the oxidation-resistant lead-tin solder master alloy according to the invention was added was held at 450°C, and the formation time of a surface oxide film in a stationary state was investigated.

The results are shown in Table 2. The amount of aluminum is 0. From Table 2, the amount of aluminum is 0. When it exceeds 0.05%, it shows the effect of preventing the formation of an oxide film, but when it exceeds 0.2%, although the oxidation prevention effect is seen, the solder surface is not mirror-like, has fine suspended particles scattered, and melts. Example 3: 8$n-20AI master alloy was heated to a bath temperature of 280°C and 310°C.
The aluminum concentration was adjusted in the range of 0.05 to 0.15% in a tin bath containing no aluminum, and the formation of an oxide film was investigated.

Also, only a tin bath that does not contain aluminum (blank test)
The formation of oxide film was also investigated. These results are almost the same as the values shown in Table 2. From this result, when aluminum is contained in an amount of 0.1 to 0.2%, no oxide film is formed even if heated for 2 hours. Aluminum concentration is 0.
If it exceeds 2%, the effect of preventing oxidation can be seen, but the surface is not mirror-like and has fine floating particles scattered, which is not preferable in terms of tin adhesion or tin plating. From the above results, by adding the oxidation-resistant lead-tin solder master alloy of the present invention to lead-tin solder that does not substantially contain aluminum, a uniform oxidation-resistant lead-tin solder master alloy can be easily produced. It can be seen that both productivity and workability have been significantly improved, and the industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a triangular graph showing the effective composition range of the lead-tin-aluminum ternary alloy of the present invention, and FIGS. 2 and 2a are optical micrographs and scans, respectively, of the master alloy having the composition of the present invention. Figures 3 and 4 are optical micrographs of alloys other than the compositions of the present invention. Figure 2 Figure 2a Figure 3 Figure 4

Claims (1)

[Claims] 1 In a lead-tin-aluminum ternary alloy, point A (Sn70%, Al30%) and point B (Sn
99.8%, Al0.2%), point C (Pb94.8%,
Sn5%, Al0.2%), point D (Pb94.5%, S
n5%, Al0.5%), point E (Pb57%, Sn38
%, Al5%), point F (Pb36%, Sn54%, Al
10%) and point G (Pb4%, Sn76%, Al20
A mother alloy for oxidation-resistant lead-tin solder, characterized by having a composition within the range enclosed by %).