JPH11333589A - Added alloy for nonlead solder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an added alloy for nonlead solder high in wettability and very high in joinability with a lead wire or the like composing an electronic circuit by adding it to a melting solder vessel. SOLUTION: This alloy is an added alloy for nonlead solder charged and diffused in melting nonlead solder mainly consisting of Sn and contg. 0.1-10 wt.% Ni and the balance Sn. The content of Ni is preferably made to 1-3 wt.%. Further, one or plural components selected out of a group composed of Ge, Ga or P are added respectively by 0.1-5 wt.%. The Ge, Ga or P are preferably made within a range of 0.1-1 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloy for lead-free solder, and is added as an additive to a solder base material.
It relates to an alloy that functions effectively when dissolved in a base material.

[0002]

In the conventional composition of a solder alloy, lead functions very effectively to determine the properties of the solder alloy, but in recent years the toxicity of lead has become a problem, The development of lead-free solder that has been repelled from objects is actively pursued. Most of these lead-free solders contain tin as a main component. That is, tin has low toxicity, gold, silver,
It is indispensable as a main component of a solder alloy for assembling electronic components, because it has high fusion with many metals such as copper, nickel, and zinc, and is highly reactive and well diffuses and wets the metal surface. However, in lead-free solder alloys containing tin as the main component, due to the high reactivity of tin, intermetallic compounds are formed by bonding with added metals and metals such as copper and silver eluted from the base material surface during joining. Will be generated. However, these compounds generally have a melting point higher than the melting point of the solder alloy, which hinders the fluidity of the solder alloy and causes bridges, which are defects in the solder joints, and glazing during soldering. It is a factor to make it. In addition, the compound becomes needle-like crystals during solidification and precipitates in the solder, losing the smoothness of the surface, resulting in a low-gloss, rough-looking solder that not only reduces the commercial value, In a circuit having a high density and dense lines, a microbridge or a needle-like line may be formed, which may cause a short circuit.

Accordingly, the inventors have disclosed a solder alloy containing tin as a main component and a small amount of nickel (0.002 to 1% by weight) as a composition for solving these problems (Japanese Patent Application No. 10-100141). ). Nickel, by adding a relatively small amount, is an alloy of tin and many metals,
For example, it has been confirmed that the alloy with copper used for lead wires and terminals of a printed circuit board has an effect of suppressing needle crystals that are inevitably generated when solidified, and attention has been paid to this fact. Nickel has a very high melting point of 1453 ° C., but if it is in the above amount, it is dissolved in tin and uniformly dispersed. Furthermore, when nickel is included,
Unlike the case not including this, the state of shrinkage cavities caused by volume shrinkage during solidification becomes one large depression and the surface becomes smooth, similar to the characteristics of Sn-Pb eutectic solder. Observed visually. Therefore, by adding a relatively small amount of nickel to tin, it is possible to suppress the generation of a compound in the solder alloy and further suppress the formation of needle-like crystals during solidification of the solder. In addition, it is possible to ensure excellent aging stability and to ensure high reliability and workability without lowering the mechanical strength of the joint.

Since the melting point of nickel is 1453 ° C. as described above, the melting point of the solder alloy tends to be higher even if the amount of nickel added is small. In addition, if nickel has an effect of avoiding the formation of a compound between another alloy and a tin-based alloy, the alloy is not only melted in the solder alloy in advance but also melted. Solder in use can also be improved by separately adding it as an additive to the solder bath. Focusing on this point, the inventor has decided to use nickel, which is suitable as a composition of the solder alloy, as an additive to the molten solder tank.

[0005] It is an object of the present invention to disclose an additive alloy for lead-free solder which can improve the solder by being added to the molten solder bath as described above.

[0006]

According to the present invention, in order to achieve the above-mentioned object, 0.1 to 10% by weight of Ni and S
An n-remainder was used to form an additive alloy for lead-free solder that was introduced and diffused into a molten lead-free solder containing Sn as a main component. Further, as a more preferable Ni content, it is specified in the range of 1 to 3% by weight.

Furthermore, in order to enhance the more effective action of the solder alloy, one or more elements selected from the group consisting of Ge, Ga and P in addition to nickel are each added to 0.1.
An additive alloy for lead-free solder added at 1 to 5% by weight was constituted.
Further, as a more preferable content of these trace metals,
The range is limited to 0.1 to 1% by weight.

[0008] In these means, tin is the same as the main metal of the solder base material, has high wettability, and has very high bondability with a lead wire constituting an electronic circuit. The main reason for using tin in the additive alloy of the present invention is as follows. Nickel has a very high melting point compared to tin, and even if the amount added to the solder is very small, 240
It is difficult to uniformly dissolve and diffuse in a short time in a solder melted at a relatively low temperature of about 250 ° C. Therefore, in the present invention, nickel is preliminarily blended with tin, which is a main component of the lead-free solder being melted in a soldering bath, or by lowering the melting point of the added alloy itself, so that the molten alloy can be rapidly melted. This is to perform uniform diffusion.

From the results of experiments, the nickel content in the lead-free solder is 0.01 to 0.1% by weight. Also, considering that it is necessary to minimize the component change due to the introduction of new tin into the molten solder, the nickel concentration in the added alloy is within the range where the melting point of the added alloy itself does not become too high. Is preferably as high as possible. For this reason, in the present invention, the nickel content is set to 0.1 to 10% by weight. Further, in consideration of the concentration adjustment after being put into the molten solder, a more preferable range is specified as 1 to 3% by weight.
And this added alloy is put into a molten lead-free solder bath,
Adjust the nickel content of the solder itself. For example, an alloy containing 98% by weight of tin and 2% by weight of nickel is melted at 227 ° C.
When the molten solder containing 99.3% by weight of tin and 0.7% by weight of copper was heated to 250 ° C. and put therein, the added alloy was melted smoothly, diffused uniformly in a short time, and Sn—Cu—
A ternary solder of Ni is formed. The reason for melting at a temperature lower than the melting point of the additive alloy is due to the solubility of tin and the homogeneity with the additive, and further, the enormous heat energy of the solder bath. Then, when 1 kg of the additive alloy having the above content is added to 99 kg of the lead-free solder, the nickel content is adjusted to 0.02% by weight. The weight ratio between these lead-free solders and the additive alloys was 0.01 to 0.1, which was indicated as the “nickel content in the lead-free solders”.
It will be adjusted appropriately within the range of weight%. However, this range is not absolute in the present invention, and it goes without saying that the weight ratio in the added alloy is the essence of the present invention.

[0010] Germanium Ge, gallium Ga, and phosphorus P each have the function of preventing the generation of slag floating on the surface of the solder bath.
The effect is exerted at a content of from 0.01 to 0.01% by weight. For example, if the additive alloy is introduced at a ratio of 99: 1 as described above, 0.1 to 1% by weight is sufficient for the distribution in the additive alloy. Adjust in the range of 1 to 5% by weight.

[0011] Considering the solder capacity of a commonly used automatic soldering bath as a basis, in order to obtain an appropriate amount of addition, the shape of the added alloy can be several hundred grams to several kilograms in an ingot shape, It is better to make it stick-shaped. However, in order to accurately input the calculated weight, small pellets, powders, or wires may be used as adjustment aids. In addition, when uniform diffusion is required in a short time, these structures work rather effectively.

[0012]

(Example 1) 2% by weight of Ni prepared in advance (all of the following ratios are also% by weight), and an additive alloy 1 with the balance being Sn
A lump of kg was put into a 99 kg solder bath having a composition of 99.3% Sn and 0.7% Cu and having a melting point of 227 ° C. and a lead-free solder having a melting point of 227 ° C. melted in a 250 ° C. atmosphere. Stir slowly with a spatula. It was confirmed that the lump of the added alloy had already been melted. In this case, the Ni content was 0.02%. Using this solder alloy, when a printed circuit board with a surface mounting IC with a lead interval of 0.65 mm was soldered at 250 ° C. using an RA type flux, no bridging or glaring phenomenon occurred. Was. In addition, the joint is 20
When observed at about twice magnification, the solder surface was smooth and no abnormal crystals were found. Furthermore, it was also confirmed that the surface of the solder alloy when the solder bath was cooled and solidified was smooth, and that no needle-like crystals were formed on the surface.

(Strength Test of Example 1) The strength of the solder alloy after the addition alloy was injected and diffused in Example 1 was inspected by a tensile tester. The test piece was pumped out of the solder bath with a stainless steel scoop, poured into an iron mold, allowed to cool and solidify, taken out, and shaped using a file or the like. Set in a tensile tester, and at room temperature, tensile speed 10mm /
It was measured under the condition of seconds. As a result, the strength was 3.3 kg / mm 2. Incidentally, the same test was conducted on the solder before adding the additive alloy, and the strength was 3.2 kg / mm 2.

Example 2 99.3% of Sn, 0.7 of Cu
% Lead-free solder alloy with a melting point of 227 ° C.
The additive alloy of the present invention containing 10% Ni is charged, and Ni is added.
When the solder alloy adjusted to have a concentration of 1% was inspected in the same manner as in Example 1, the solder alloy surface was very smooth. When a strength test was performed in the same manner as in Example 1, the strength was 3.3 kg / mm 2 as in Example 1.

(Embodiment 3) Ni 2%, Ga
A lump of 1 kg of an alloy containing 0.5% and a balance of Sn was added to Sn99.
A lead-free solder having a composition of 3% and Cu of 0.7% and having a melting point of 227 ° C. was put into a 99 kg solder bath in which an atmosphere of 250 ° C. was melted. After waiting for 2 minutes, the mixture was slowly stirred with a stainless steel spatula. It was confirmed that the lump of the added alloy had already been melted. In this case, the Ni content is 0.02% and the Ga content is 0.005%. Immediately after the addition of the additive alloy, the color of the solder surface of the solder alloy became metallic white, and the generation of slag on the surface, which had occurred up to that time, was drastically reduced. Note that the same effect can be expected even when Ge and P are added.

(Comparative Example) Sn 99.3%, Cu 0.7%
Using a lead-free solder alloy having a melting point of 227 ° C. and a lead pitch of 0.65 mm, a printed circuit board with a surface mounting IC having a composition of
When soldering was performed at 0 ° C., many bridges were generated between the leads. Some of these bridges occurred not only between the leads but also across several leads. Further, when soldering was similarly performed on a printed board with a connector having a lead interval of 2.5 mm pitch, a large number of bridges and icicles also occurred. When the joint was observed at a magnification of about 20 times, an abnormal crystal was observed as a rough surface on the solder. These are Sn
-Needle-like crystals of a Cu metal compound. Also, IC
Very thin needle-like microbridges are found in the bridge between the leads, which have a high melting point and cannot be easily removed even with highly active flux, so it is presumed that improving the soldering quality is difficult. Is done. Needle-like crystals were formed on the surface of the solder alloy when the solder bath was cooled and solidified, and not only irregularities were observed, but also large cracks were generated in some places, and it was observed that there were steps. This is considered to be due to the occurrence of distortion inside the solder.

[0017]

As described above, the present invention does not directly add an additive to the solder alloy base material, but instead forms a separately manufactured bulk or pellet-shaped additive alloy. It mixes very well and diffuses evenly in a short time, so that a calculated solder composition can be achieved in the solder melting bath.

Claims (4)

[Claims] 1. An additive alloy for lead-free solder which contains 0.1 to 10% by weight of Ni and the balance of Sn and is introduced and diffused into a molten lead-free solder containing Sn as a main component. 2. The additive alloy for lead-free solder according to claim 1, wherein the content of Ni is preferably 1 to 3% by weight. 3. The method according to claim 1, wherein one or more members selected from the group consisting of Ge, Ga and P are each 0.1%.
Additive alloy for lead-free solders added by up to 5% by weight. 4. The additive alloy for lead-free solder according to claim 3, wherein Ge, Ga or P is preferably 0.1 to 1% by weight.