KR20090034370A - Whisker preventive agent for tin or tin alloy plating, and method of whisker prevention making use of the same - Google Patents

Abstract

Simple means for unfailing prevention of whisker occurrence even when leaving is made at room temperature for 5000 hr after tin or tin alloy plating. There is provided a whisker preventive agent for tin or tin alloy plating, comprising (A) sulfuric acid, an alkanesulfonic acid, an alkanolsulfonic acid and derivative thereof, (B) a peroxide and (C) ions of a metal noble in potential to copper. Further, there is provided a method of whisker prevention for tin or tin alloy plating, characterized in that after immersion of a material to be plated in the above whisker preventive agent for tin or tin alloy plating, tin or tin alloy plating is carried out.

Description

WHISKER PREVENTIVE AGENT FOR TIN OR TIN ALLOY PLATING, AND METHOD OF WHISKER PREVENTION MAKING USE OF THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a whisker preventing agent of tin or tin alloy plating capable of effectively preventing a whisker generated in a plating film after tin or tin alloy plating, and a whisker preventing method using the same.

Tin plating and tin alloy plating (hereinafter referred to as "tin-based plating") are widely used in electronic component materials because of their flexibility and other properties, but needle-like crystals called whiskers are generated in the tin-based coating film. There was a problem causing problems such as short circuits. As a method for preventing such a whisker, it is effective to perform reflow after plating, which is often performed, but there is a problem that the work efficiency is lowered, and because the film characteristics change, it may not be used. There was a problem.

In view of the above problems, it is considered that pretreatment of the material to be plated before tin-based plating is more effective than post-treatment that performs whisker-preventing treatment after tin-based plating, and there are already many pre-treatment methods for preventing whiskers. Is disclosed. As such a pretreatment method, (1) a method of removing surface smoothness by oxidizing agent or electrolytic action (patent documents 1 to 3) and (2) a different type of thin as a base of a tin-based coating film It is divided roughly into two types of methods (patent documents 4-6) of forming a metal layer.

However, in the method (1), since the surface to be plated varies depending on the material, there is a problem that an etching amount of 2 µm or more is required to produce a sufficient effect on any material. Particularly, since the electronic parts are becoming finer and denser, and the etching amount is large, there is a problem in the dimensional accuracy. Therefore, the etching amount is preferably 1.5 mu m or less, preferably 1 mu m or less, but the method (1) satisfies this. It is difficult.

On the other hand, as a method of forming the base metal layer of the method (2), dry methods such as sputtering, substitution plating, and electroplating have been mentioned. Among these, the dry method causes problems of cost and work efficiency. The stability and safety of the bath, and furthermore, electroplating had a problem to be solved, such as an influence on the characteristics of the electronic component.

Moreover, a common problem of the methods (1) and (2) is that it is uncertain whether the whisker prevention effect is sufficient. In other words, there are various methods of investigating the occurrence of whiskers, but for electronic components, especially lead frames, the method of leaving room at room temperature after plating is the most appropriate method. Many of the device makers have decided that the criteria for whiskers are "nothing more than 50 µm after being left at room temperature for 5000 hours", but in the above document, only the observation results of 1000 to 2000 hours long and 200 hours short are described. However, if whiskers do not occur for up to 2000 hours, it cannot be said that whiskers do not occur for up to 5000 hours, and it is insufficient as a method for evaluating the effect of whiskers if not tested for up to 5000 hours.

Patent Document 1: Japanese Patent Publication No. 2004-285417

Patent Document 2: Japanese Patent Publication No. 2004-263291

Patent Document 3: Japanese Patent Laid-Open No. 5-148658

Patent Document 4: Japanese Patent Publication No. 2004-91824

Patent Document 5: Japanese Patent Publication No. 2003-332391

Patent Document 6: Japanese Patent Publication No. 2003-129278

Therefore, even after leaving tin-based plating for 5000 hours at room temperature, it has been desired to provide a simple means for preventing the occurrence of whiskers, which is a problem, and the provision of such means is a problem of the present invention.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining prevention of whiskers, it discovered that by adding the metal ion which has a noble metal electric potential to a general etching agent composition, an etching amount can effectively prevent the generation of a whisker, and this invention Completed.

That is, the present invention provides the following components (A) to (C)

(A) sulfuric acid, alkanesulfonic acid, alkanolsulfonic acid and derivatives thereof

(B) peroxide

(c) metal ions with higher potential than copper

It is a whisker prevention agent for tin type plating containing these.

In addition, the present invention is a method for preventing whiskers of tin plating, wherein the plating material is immersed in the tin-based whisker inhibitor, and then tin plating is performed.

In the anti-whisker agent for tin plating of the present invention (hereinafter referred to as "whisker inhibitor"), examples of sulfuric acid, alkanesulfonic acid and alkanolsulfonic acid and derivatives thereof used as component (A) include sulfuric acid, methanesulfonic acid, methanol sulfonic acid, Propanesulfonic acid, hydroxymethanesulfonic acid, hydroxyethanesulfonic acid, hydroxypropanesulfonic acid and the like. Among these, sulfuric acid and methanesulfonic acid are preferable, and sulfuric acid is especially preferable. Moreover, 10-300 g / L is preferable as a density | concentration at the time of use, and, as for the quantity of the component (A) in the whisker inhibitor of this invention, 20-20 Og / L is especially preferable. Moreover, when content is less than 10 g / L, sufficient whisker prevention effect will not be acquired, and even if it is more than 300 g / L, an effect will not change.

Moreover, as an example of a peroxide used as a component (B) of this invention, a peroxo-sulfuric acid compound, such as hydrogen peroxide and peroxosulfate, sodium peroxosulfate, potassium peroxosulfate, and ammonium peroxosulfate, is mentioned. Among these, hydrogen peroxide is preferable. Moreover, 2-100 g / L is preferable as a density | concentration at the time of use, and, as for the quantity of the component (B) in the whisker inhibitor of this invention, 5-50 g / L is especially preferable. If the content is less than 2 g / L, sufficient whisker prevention effect cannot be obtained. If the content is more than 100 g / L, for example, when the material to be plated is copper, etching proceeds too much, which is not preferable.

Moreover, silver ions, palladium ions, gold ions etc. are mentioned as an example of the metal ion whose potential is higher than copper used as a component (C) of this invention. Among these, silver ions and palladium ions are preferable, and silver ions are particularly preferable. In order to contain these metal ions in the whisker inhibitor of the present invention, for example, silver compounds such as silver nitrate, silver methanesulfonic acid, silver sulfate, silver oxide, palladium compounds such as palladium chloride, palladium hydroxide, palladium sulfate and palladium nitrate, Metal salts, such as gold compounds, such as gold oxide, may be used. Among these, a silver compound is preferable, and sulfuric acid especially silver nitrate is preferable. Moreover, 0.1 mg / L-20 mg / L are preferable as a metal ion concentration at the time of use, and, as for the quantity of the component (C) in the whisker inhibitor of this invention, 0.2-5 mg / L is more preferable especially. Moreover, when content is less than O.lmg / L, sufficient whisker prevention effect will not be acquired, and even if it is more than 20 mg / L, an effect will not change.

The whisker-preventing agent of the present invention obtains a sufficient whisker-preventing effect even when the above three components are dissolved in water or the like. Again, tetrazole or derivatives thereof may be used as the component (D). Such tetrazole and derivatives thereof can be used without particular limitation as long as they are water-soluble, but specific examples thereof include tetrazole, 5-aminotetrazole, 5-methyltetrazole, 1-methyl-5-ethyltetrazole, and 1-methyl-5. -Amino tetrazole, 1-ethyl-5-amino tetrazole, etc. are mentioned. Among these, 5-amino tetrazole is preferable. In addition, the amount of component (D) in the whisker inhibitor of the present invention is preferably from 0.1 to 10 g / L, particularly preferably from 0.1 to 8 g / L, as the amount in the whisker inhibitor at the time of its use.

The whisker inhibitor of the present invention is prepared by combining the component (C) or the component (D) with a suitable carrier in the component (A), but furthermore, if necessary, within the scope not impairing the effects of the present invention, As a humectant, you may contain additives, such as a water-soluble alcohol and diols, as a nonionic surfactant, anionic surfactant, or a stabilizer of a peroxide.

In order to prevent whisker generation in the tin-based coating film by using the whisker inhibitor of the present invention described above, after degreasing the plated material according to a conventional method, it is dissolved in a suitable solvent, for example, water, if necessary. Alternatively, it may be immersed in a diluted whisker inhibitor, and then tin-plated. As specific immersion conditions, Preferably it is 10-50 degreeC, More preferably, you may be liquid temperature of 20-40 degreeC, Preferably you may immerse for 10 second-2 minutes, More preferably, 20 second-1 minute.

According to the method of the present invention, the plated material which can prevent the occurrence of whiskers in the tin-plated film is not particularly limited as long as it is a copper material that can be used for a printed wiring board or a lead frame. Copper plating films formed by plating or electroless plating, and alloys containing at least one of iron, nickel, tin, zinc, phosphorus, chromium, silicon and the like as main materials are included. Moreover, tin plating may use the thing of any well-known composition. In addition, it means that tin alloy plating in tin-based plating in this specification and 0.01% or more of copper, silver, bismuth, zinc, nickel, lead etc. are contained in a plating film as alloy components other than tin. do.

[Action]

Although the mechanism of whisker prevention by the whisker-proofing agent of this invention is not clear yet, many guesses are as follows at present.

That is, it is known that "formation of base layer by dissimilar metal" and "removal of deteriorated layer of material surface" are effective as the pre-treatment of whisker prevention in the prior art. As a synergistic effect thereof, it is estimated that an effect superior to the conventional one is obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples and Test Examples, but the present invention is not limited by these Examples.

Example 1

According to the following composition, the whisker inhibitor for tin plating was prepared.

(Whisker prevention composition)

Sulfuric acid 1OOg / L

Hydrogen peroxide 10g / L

Silver ions (as silver sulfate) 3 mg / L

Example 2

According to the following composition, the whisker inhibitor for tin plating was prepared.

(Whisker prevention composition)

Sulfuric acid 100g / L

Hydrogen peroxide 10g / L

1 mg / L palladium ion (as palladium nitrate)

Example 3

According to the following composition, the whisker inhibitor for tin plating was prepared.

(Whisker prevention composition)

Sulfuric acid 50g / L

Hydrogen Peroxide 15g / L

Silver ions (as silver nitrate) 2 mg / L

5-aminotetrazole O.5 g / L

Example 4

According to the following composition, the whisker inhibitor for tin plating was prepared.

(Whisker prevention composition)

Methanesulfonic acid 200g / L

Hydrogen Peroxide 15g / L

2 mg / L palladium ion (as palladium nitrate)

Tetrazole O.lg / L

Test Example 1

With respect to the whisker inhibitor obtained in Examples 1 to 4, the etching amount during immersion and the whisker-preventing effect after tin plating were applied to the following evaluation method using EFTEC64T material (Furukawa Electric Co., Ltd.), a copper alloy for lead frames. Investigated accordingly. The process to tin plating and the tin plating liquid to be used are as follows. As a comparison, the following comparative etchant was used instead of the whisker inhibitor (Comparative Example 1), the immersion time in the comparative etchant was increased from 30 seconds to 60 seconds (Comparative Example 2), and the whisker prevention treatment was not performed. (Comparative Example 3) was used.

(Tin plating solution composition)

Tin 60g / L

Methanesulfonic Acid 140g / L

Additive UT-55 * 40mL / L

* Product made by Ebara Yuji Light Co., Ltd. (Ebara-Udylite Co., Ltd.)

(Tin plating process)

(1) Cathodic Electrolytic Degreasing (50 ° C, 5A / dm 2, 30 Second Treatment)

(2) Whisker prevention treatment (35 ℃, 30 seconds treatment)

(3) Tin plating (40 degreeC, 10 A / dm <2>)

Plating film thickness: 3 μm (for whisker evaluation)

             10 μm (for solderability evaluation)

(Comparative etchant composition)

Sulfuric acid 100g / L

Hydrogen Peroxide 20g / L

(Assessment Methods)

1. Etching amount

The etching amount was computed by the following formula.

[1]

Etching Amount (μm) = (ΔW × 10000) / (S × d)

ΔW: difference in weight before and after etching (g)

S: surface area of the test piece (cm 2)

d: copper density (8.9 g / cm 3)

2. Whisker Condition

After tin plating, it was left to room temperature and observed with a stereomicroscope every 1000 hours until the leaving time 5000 hours, and the whisker generation state was evaluated according to the following evaluation criteria.

Evaluation Criteria Evaluation Content

     ◎: no whiskers at all

(Circle): Whistle generate | occur | produces, but all are 10 micrometers or less

(Triangle | delta): Although a whisker has generate | occur | produced, all 30 micrometers or less

     X: 50 micrometers or more of whiskers generate | occur | produce a little

     ××: A large number of whiskers of 50 μm or more were generated

3. Solder ability evaluation

The solderability was evaluated on the following reference | standard by the following solder baths and the soldering method.

Solder bath:

Sn-Ag3% -Cu 0.5%, 245 ° C

Immersion time:

5 sec

Flux:

Rosin flux

Evaluation criteria Evaluation contents

      ◎: within 2 seconds of wet time with solder

      ○: 2 to 3 seconds wet with solder

      △: 3 to 5 seconds of time wet with solder

      ×: time of 5 seconds or more wet with solder

(result)

Etching amount Solderability             Whisker occurrence 1000 hours 2000 hours 3000 hours 4000 hours 5000 hours Example 2 0.5 μm    ◎    ◎    ◎    ◎    ◎    ◎ Example 2 0.5 μm    ◎    ◎    ◎    ◎    ◎    ◎ Example 3 0.7 μm    ◎    ◎    ◎    ◎    ◎    ◎ Example 4 0.6 μm    ◎    ◎    ◎    ◎    ◎    ◎ Comparative Example 1 1.0 μm    ◎    ◎    ○    △    ×    × Comparative Example 2 2.0 μm    ◎    ◎    ◎    ○    △    △ Comparative Example 3    -    ○    △    ×    ×   ××   ××

When the whisker inhibitors of Examples 1 to 4 were used, the whiskers did not occur at all even after 5000 hours of standing, and the solder wettability was good even though the etching amount was 1 µm or less.

On the other hand, in the case of the comparative examples 1 and 2, although the whisker prevention effect was recognized rather than the untreated comparative example 3 in order to remove the surface-processing deterioration layer by the etching of 1-2 micrometers, the effect was considerably low compared with this invention.

The whisker prevention agent for tin plating of this invention can prevent generation | occurrence | production of the whisker which arises in a tin plating layer, for example, hardly etching the to-be-plated material, such as a copper alloy for lead frames.

Therefore, by using this whisker inhibitor as a pretreatment for tin plating on electronic parts, it is possible to effectively prevent the occurrence of whiskers, and in particular, it can be widely used as a whisker prevention method for electronic parts requiring miniaturization and high density. Do.

Claims (6)

Next component (A) to (C) (A) sulfuric acid, alkanesulfonic acid, alkanolsulfonic acid and derivatives thereof (B) peroxide (C) higher metal ions than copper Whisker inhibitor for tin or tin alloy plating containing a. The whisker inhibitor for tin or tin alloy plating according to claim 1, wherein component (C) is silver or palladium. The component according to claim 1 or 2, wherein (D) tetrazole or derivatives thereof Whisker inhibitor for tin or tin alloy plating containing. The whisker inhibitor for tin or tin alloy plating according to any one of claims 1 to 3, which is used for a lead alloy copper alloy. A method for preventing whiskers in tin or tin alloy plating, wherein the material to be plated is immersed in the tin or tin alloy whisker inhibitor according to any one of claims 1 to 4. 6. The method for preventing whiskers of tin or tin alloy plating according to claim 5, wherein the material to be plated is a copper alloy for lead frame.