JP3418773B2 - Bismuth / tin two-layer plating film for soldering base - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bismuth / tin two-layer plating film useful as a base plating film for soldering.

[0002]

2. Description of the Related Art Conventionally, a Sn--Pb alloy film has been widely used as a base film for soldering electronic components. However, in recent years, environmental pollution due to Pb has become a problem, and there is a high possibility that the use of lead will be restricted in the future. Therefore, development of a low melting point alloy film that can be used as a substitute for the Sn-Pb alloy is desired. Or, Bi-Sn, Sn
The use of various alloys such as -In, Sn-Sb, Sn-Ag, and Sn-Zn has been studied.

Further, with the development of the electronic industry, a lower solder joint temperature is required in the semiconductor-related industry due to trends such as miniaturization of parts and consideration of introduction of a plastic substrate. Has a eutectic point of 1
The temperature is 83 ° C., and soldering below this temperature is difficult. Among the alloys not containing Pb, the eutectic point of Bi—Sn alloy is 139 ° C., and the eutectic point of Sn—Pb is 40.
Since the temperature is low at about 0 ° C. and Bi is cheaper than other metal elements such as In and Ag, expectations for Bi—Sn alloy as a low-temperature bonding film are increasing.

Heretofore, as a Bi-Sn alloy plating bath, a sulfuric acid bath, an organic sulfonic acid bath (JP-A-63-14887) and the like have been reported. However, when a known sulfuric acid bath, organic sulfonic acid bath or the like is used, the Bi content tends to be low at a low current density, and the Bi-Sn alloy coating and the anode electrodeposited in the plating bath have a B content of B.
There is a problem that substitution precipitation of i occurs. Also, Bi
According to the equilibrium diagram of the -Sn system, Bi-Sn alloy is Bi
Is less than 57% by weight, the melting point of the coating tends to increase as the Bi content decreases, and the current density decreases in the through-hole portion of the printed wiring board. Therefore, the Bi content decreases and the solder wettability decreases. there is a possibility.

Further, in the known Bi-Sn alloy plating bath, in order to deposit Bi and Sn as alloys, which have greatly different deposition potentials, methanesulfonic acid, gluconic acid or the like is added as a complexing agent, and the deposition potential of Bi is increased. Is allowed to co-deposit with Sn by shifting to a base direction (Japanese Patent Laid-Open No. 2-8
No. 8789), the deposition potential in the alloy plating bath shifts to the base direction by the addition of the complexing agent, and as a result, the current efficiency is expected to decrease.

Furthermore, in order to obtain a good gloss appearance, Bi-Sn alloy plating baths usually use a nonionic interfacial lubricant (such as polyoxyethylene nonylphenyl ether) as a smoothing agent and Sn as a brightening agent. Alternatively, known brighteners for Sn-Pb have been added, but when these additives are blended, a further decrease in current efficiency and a large decrease in Bi content in the film are observed.

Further, in the alloy plating bath, when the metal concentration fluctuates, the composition of the electrodeposited film is likely to fluctuate with it, and in order to stably form a film having a certain performance, bath management is very important. It is complicated.

In addition to the above, a major drawback of the Bi--Sn alloy bath is that in the known sulfuric acid bath and organic sulfonic acid bath,
In both cases, since Bi is a noble metal with respect to Sn, the Bi ions in the bath are likely to cause a substitution reaction, and when the object to be treated is immersed in the bath or pulled out from the bath, no electric current is applied. Bi may be substitutionally deposited on the object to be processed or the surface of the formed Bi-Sn alloy film. In this way, when Bi is deposited by substitution on the object to be treated, good adhesion cannot be obtained even if a Bi-Sn alloy film is formed on it, and Bi is deposited on the obtained Bi-Sn alloy film. However, since the Bi-oxide is contained in a large amount in the deposited film, the wettability of the film and the bonding strength of the film are adversely affected. Further, when Sn or Bi-Sn alloy is used as the anode in the Bi-Sn alloy plating bath, substitutional precipitation of Bi occurs even when the anode is not energized, which causes Bi and Sn metal in the plating bath. The concentration varies, and the composition of the Bi—Sn alloy film obtained by electrodeposition also varies.

As described above, the Bi-Sn alloy plating film has a low melting point, is relatively inexpensive, and is promising as an alternative solder bonding film because it does not contain lead, but it has good workability during plating. It is very bad and has various problems such that very complicated bath management is required to form a good plating film.

[0010]

The main object of the present invention is to provide a good solder joint strength, solder wettability, etc., which is useful as an undercoat for solder joining, and contains harmful components. It is an object of the present invention to provide a soldering base plating film that can be formed by a simple operation.

[0011]

The inventor of the present invention has conducted extensive studies to achieve the above-mentioned object. as a result,
A two-layer plating film formed by sequentially forming a bismuth plating film and a tin plating film melts and easily alloys when heated by soldering, and becomes a film excellent in solder joint strength, solder wettability, etc., Moreover, they have found that this two-layer plating film can be formed very easily without the need for complicated bath management, and have completed the present invention.

That is, the present invention relates to a bismuth / tin two-layer plating film for a soldering base, which is formed by sequentially forming a bismuth plating film and a tin plating film.

The soldering base plating film of the present invention is formed by sequentially forming a bismuth plating film and a tin plating film. As described above, according to the present invention, the bismuth plating film is used as the base, and the tin plating film is formed on the bismuth plating film.
By plating with Sn having a low deposition potential, it is possible to prevent substitutional precipitation of Bi in the deposit. Also, since the plating bath used is a single metal plating bath,
It is not necessary to use an alloy as the anode, and substitutional precipitation on the anode can be prevented. Furthermore, unlike the case of using an alloy plating bath, it is not necessary to control the metal concentration ratio in the plating bath,
A plating film having an arbitrary alloy composition can be formed at the time of soldering only by controlling the film thickness ratio of the plating film, and a plating film having a stable composition can be easily obtained.

In the two-layer plating film of the present invention, it is considered that the two-layer plating film is melted and alloyed during soldering. Therefore, a plating film having an arbitrary film thickness ratio may be formed according to the desired alloy composition. In particular, considering the solder joint strength, solder wettability, etc., which are the required performances of the base plating film for soldering, the bismuth plating film: tin plating film (film thickness ratio) = about 2: 8 to 8: 2 is preferable, It is more preferably about 4: 6 to 6: 4.

Further, the thickness of the plating film is not particularly limited and may be within a range capable of functioning as a base plating film for soldering. Usually, the total thickness of the two plating films is 2 to 20 μm is preferable, and 5 to 10
More preferably, it is about μm.

In the present invention, as the plating bath used for forming the bismuth plating film and the tin plating film,
There is no particular limitation, and conventionally known bismuth plating baths and tin plating baths can be used.

As the bismuth plating bath, specifically,
Known plating baths such as so-called bismuth methanesulfonate plating bath and bismuth sulfate plating bath can be used. An example of the basic bath composition and plating conditions of these plating baths is as follows.

* Methanesulfonic acid bismuth plating bath 70% methanesulfonic acid 50 to 500 ml / l bismuth oxide 5 to 100 g / l cathode current density 0.2 to 5 A / dm ² bath temperature 15 to 40 ° C * bismuth sulfate plating bath 98 % Sulfuric acid 50 to 200 ml / l Bismuth nitrate 5 to 100 g / l Cathode current density 0.2 to 5 A / dm ² Bath temperature 15 to 40 ° C. These methanesulfonic acid bismuth plating baths, bismuth sulfate plating baths and the like are usually used. As a smoothing agent, α or β
5 to 50 g of nonionic surfactants such as naphthol ethoxylate, α- or β-naphthol propoxy ethoxylate, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polynuclear phenol ethoxylate, and polyoxyethylene dodecyl phenyl ether / L is added. Further, the bismuth plating film is used as a base of the tin plating film, and it is not necessary to add a brightening agent component in particular, but a known brightening agent can be added if necessary. However, if the amount of the brightening agent added is too large, the deposition rate may decrease, so it is preferable to reduce the amount of addition as much as possible, usually 0.01 to 20 g /
It can be about 1. Examples of such brighteners include aliphatic aldehydes such as formalin and acetaldehyde, aromatic aldehydes such as benzaldehyde and o-chlorobenzaldehyde, triazoles, triazines, condensed ring compounds of triazoles or triazines, acetaldehyde and o-toluidine. Examples thereof include reaction products. In the present invention, particularly as a bismuth plating bath, as a smoothing agent, α or β-naphthol ethoxylate,
It is preferable to use a bismuth methanesulfonate plating bath or a bismuth sulfate plating bath containing α- or β-naphthol propoxyethoxylate.

As the tin plating bath, known plating baths such as so-called tin methanesulfonate plating bath and tin sulfate plating bath can be used. An example of the basic bath composition and plating conditions of these plating baths is as follows.

* Tin methanesulfonate plating bath Tin methanesulfonate 50-500 ml / l 70% Methanesulfonic acid 50-200 ml / l Cathode current density 0.2-5 A / dm ² Bath temperature 15-40 ° C * Tin sulfate plating bath of 98% sulfuric acid 50~200ml / l tin sulfate 5 to 100 g / l cathode current density 0.2~5A / dm ^{2 2} bath temperature 15 to 40 ° C. these methanesulfonic acid tin plating bath, the tin sulfate plating bath, etc. , Usually as a film smoothing agent, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polynuclear phenol ethoxylate,
A nonionic surfactant such as α or β-naphthol ethoxylate and α or β-naphthol propoxyethoxylate is added in an amount of about 5 to 50 g / l. Further, when considering only the function as a base film for soldering, it can be used without adding a brightener component, but if necessary, a known brightener for tin plating may be added. . The amount of the brightener added is not particularly limited and is usually 0.01 to
The amount can be set to about 20 g / l, but if the amount of the brightener added is too large, the organic substance storage amount of the plating film may increase and the wettability of the solder may decrease. Is preferably 0.01 to 1
It is preferably about g / l. Examples of brightening agents that can be used include aliphatic aldehydes such as formalin and acetaldehyde, benzaldehyde, aromatic aldehydes such as o-chlorobenzaldehyde, triazoles, triazines, triazoles or condensed ring compounds of triazines,
Examples thereof include reaction products of acetaldehyde and o-toluidine.

As described above, the bismuth plating bath is a plating bath containing only a small amount of an additive without containing a brightening agent, and the tin plating bath contains an additive component and a small amount of a brightening agent. The two-layer plating film formed by using the plating bath becomes a solder bonding film having a good gloss appearance with a small amount of stored organic matter as a whole film, and the formed two-layer plating film does not generate gas during reflow treatment. It is a good underplating film for soldering, which is generated in a small amount and suppresses appearance defects such as spots.

The method for forming a plating film using the various plating baths described above may be the same as the ordinary plating method. After performing degreasing treatment, activation treatment and the like in accordance with a conventional method, the plating treatment is performed. You can do it.

In the present invention, the object to be plated for forming the two-layer plating film is not particularly limited, and various conductive materials that require soldering can be used as the object to be plated. When the wiring board is used as the object to be processed, the two-layer plating film of the present invention is formed on the conductor circuit made of copper metal to be soldered.

The bismuth / tin two-layer plating film of the present invention is used as a base plating film for soldering. After forming the two-layer plating film, various components are soldered in accordance with a conventional method. Be done. In the usual solder joining method, joining by solder is performed at a relatively high temperature of about 220 to 260 ° C., but the Bi—Sn alloy is a eutectic alloy-based metal like the Sn—Pb alloy,
The melting point at the eutectic point is 139 ° C., which is 1 of Sn-Pb alloy.
40 ° C or more lower than 83 ° C, and Bi-Sn alloy is S
It is an alloy system having a smaller solid solution region than that of the n-Pb alloy, and Bi and Sn are hardly dissolved in the alloy plating film. Therefore, in the two-layer plating film of bismuth and tin of the present invention, when solder bonding is performed, the film is held at a temperature considerably higher than the melting point for a short time and melted, and accordingly Bi and Sn are filmed. It is considered that a eutectic structure dispersed therein is formed. In this way, the two-layer plating film of the present invention is easily alloyed during soldering, and the Bi-Sn alloy film formed is excellent in solder joint strength, solder wettability, etc. It is suitable as a base plating film for use.

[0025]

The two-layer plating film of the present invention is highly safe and does not contain Pb, which is a harmful component, and melts when heated by soldering to easily alloy, The formed Bi—Sn alloy film has a low melting point and is highly useful as a film for low temperature bonding.

The bismuth / tin two-layer plating film of the present invention is formed by using a bismuth plating bath and a tin plating bath each containing bismuth and tin alone as metal components. By simply controlling the film thickness ratio, a plating film having an arbitrary alloy composition can be formed during soldering, and a soldering base film having a stable composition can be easily obtained. Therefore, when the layer plating film of the present invention is formed, bath management is not as complicated as when an alloy plating film is formed using an alloy plating bath. In addition, there is no substitutional precipitation of Bi on the precipitate or the anode, and the plating operation is simple.

[0027]

【Example】

Example 1 Bi plating baths and Sn plating baths having the following compositions were prepared.

* Methanesulfonic acid Bi plating bath 70% methanesulfonic acid 200 ml / l bismuth oxide 22.3 g / l β-naphthol ethoxylate (EO13 mol adduct) (trademark: BN-13, manufactured by Aoki Yushi) 10.0 g / L * Methanesulfonic acid Sn plating bath Tin methanesulfonate 70 ml / l 70% Methanesulfonic acid 100 ml / l β-naphthol ethoxylate (EO13 mol adduct) (trademark: BN-13, manufactured by Aoki Yushi) 10 g / l gloss Agent solution (Trademark: Toptina MS No. 2, manufactured by Okuno Chemical Industries Co., Ltd.) 10 ml / l Using the above Bi plating bath and Sn plating bath, using a copper clad laminate as the object to be degreased (Okuno Pharmaceutical Co., Ltd., OPC-380 Condy Clean M), soft etching (Okuno Pharmaceutical Co., Ltd.) , OPC-40
0) and desmutting (10% H ₂ SO ₄ ) respectively, and then the plating time of Bi plating and Sn plating is changed to sequentially form Bi plating film and Sn plating film having different plating film thickness ratios. Formed. The plating conditions of Bi plating and Sn plating are the same, and are as follows. In each case, the total film thickness of the Bi plating film and the Sn plating film was 10 μm.

(Plating conditions) Cathode current density 2 A / dm ² bath temperature 25 ° C. agitation cathode rocker anode Bi or Sn (99.99% or more) The plating time and film thickness ratio for Bi plating and Sn plating The results are shown in Table 1 below.

[0030]

[Table 1]

Each of the obtained plating films had a good gloss appearance. The solder characteristics of these plating films were evaluated by the meniscograph method using a solder checker. The measurement conditions of the meniscograph are as follows.

(Meniscograph measurement conditions) Solder bath 60:40 Eutectic solder bath Temperature 230 ° C. Immersion depth 2 mm Immersion time 10 seconds Immersion speed 8 mm / sec Flux WW Rosin type Bi plating film thickness and zero cross obtained by the above measurement The time relationship is shown in FIG. As is clear from this result, the zero cross time is 2.5 with the plating film of Bi alone.
Second, the plating film of Sn alone was 1.75 seconds, but when the Bi film and the Sn film were formed at a film thickness ratio of 2: 8 to 8: 2, 1.0 to 1.2 seconds. To a degree,
It has good solderability.

FIG. 2 shows the relationship between the Bi plating film thickness and the maximum wetting force. From these results, it was confirmed that the solder wettability was improved when the Bi film and the Sn film were sequentially formed.

Next, a solder joint strength test was conducted on the Bi / Sn two-layer plating film. As a test method,
Form a plating film on the copper clad laminate under the same conditions as above,
After using the eutectic solder paste to bond the tensile test pins of the copper material, the tensile strength of the test pins was measured using a tensile tester. S for reflow processing
Bonding was performed using a MT-batch oven at a substrate temperature of 205 ° C.

The results of the solder joint strength test are shown in FIG.
The bonding strength of the Sn-only plating film was 1.6 kg, and the bonding strength of the Bi-only plating film was 1.2 kg, whereas when the Bi plating film was formed as the base of the Sn plating film, Bi plating film is 2 to 6 μm
Showed a high joint strength of about 3.8 to 4.4 kg.
From this result, the film thickness ratio of Bi film and Sn film is 2: 8.
It can be seen that in the case of ˜6: 4, a film having good solder joint strength is formed.

Example 2 A Bi plating bath and a Sn plating bath having the following compositions were prepared, a solder joint strength test sample was prepared under the same plating conditions as in Example 1, and a solder joint strength test was conducted.

* Sulfuric acid Bi plating bath 98% Sulfuric acid 100 ml / l Bismuth nitrate 11.6 g / l β-naphthol ethoxylate (EO25 mol adduct) (Trademark: BN-25, Aoki Yushi) 5.0 g / l * Sulfuric acid Sn plating bath 98% Sulfuric acid 100 ml / l Tin sulfate 30 g / l β-naphthol ethoxylate (EO25 mol adduct) (trademark: BN-25, Aoki Yushi) 5.0 g / l Brightener solution (trademark: top Tina MS No. 2, manufactured by Okuno Chemical Industries Co., Ltd. 10 ml / l The test results are shown in FIG. As is clear from this result,
The two-layer plating film in which the Bi film and the Sn film are sequentially formed is
The solder bonding strength was higher than those of the Sn-only plating film and the Bi-only plating film.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between Bi film thickness and zero cross time in Example 1.

2 is a graph showing the relationship between Bi film thickness and maximum wetting force in Example 1. FIG.

FIG. 3 is a graph showing the relationship between Bi film thickness and bonding strength in Example 1.

FIG. 4 is a graph showing the relationship between Bi film thickness and bonding strength in Example 2.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-169589 (JP, A) JP-A-48-78042 (JP, A) JP-A-47-38539 (JP, A) JP-A-2- 4984 (JP, A) JP-A 1-116096 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C25D 5/10 C25D 3/30 C25D 3/54

Claims (2)

(57) [Claims] 1. A bismuth / tin two-layer plating film for a soldering base, which is formed by sequentially forming a bismuth plating film and a tin plating film. 2. The bismuth / tin 2 for soldering base according to claim 1, wherein the film thickness ratio of the bismuth plating film and the tin plating film is the former: the latter = 2: 8 to 8: 2. Layer plating film.