JPH03287780A - Electroless copper plating bath - Google Patents

Abstract

PURPOSE:To obtain the electroless copper plating bath capable of forming a flexible film excellent in adhesion even on a material low in alkali resistance by forming the bath from a copper compd. supplying a copper coplex ion, a reducing agent consisting of hydrazine and a copper ion complexing agent consisting of a chelating amine. CONSTITUTION:This electroless copper plating bath is formed from a copper compd. supplying a copper complex ion such as CuSO4.5H2O, a reducing agent consisting of hydrazine and a copper ion complexing agent consisting of a chelating amine. Since the bath has the above-mentioned characteristics and an expensive substance such as dimethylamine borane need not be used, electroless plating is carried out at a low cost in the pH region close to the neutral. Besides, ethylenediamine, etc., are exemplified as the chelating amine, and the requisite concn. is controlled to 2-25 times the number of mols of Cu<2+> complex ion.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electroless copper plating bath, and more specifically,
The present invention relates to an electroless copper plating bath that is capable of plating in a pH range near the neutral point of weak acid to weak alkalinity.

[Prior art and its problems]

Traditionally, EDTA has been used as a complexing agent in electroless copper plating baths.
(ethylenediaminetetraacetic acid) as a reducing agent, HCH
Alkaline bath (pH 12) using ○ (formaldehyde)
, around 5) is commonly used. However, because this conventional bath is a highly alkaline bath, it is difficult to directly plate metal materials with low alkali resistance such as Aβ and Zn, and resin materials with low alkali resistance such as polyimide and positive photoresists. It was said that

As a method to solve these drawbacks of highly alkaline baths, we developed an ``electroless copper plating bath'' that enables electroless plating of alkali-sensitive substrates by using aminephorane-based compounds such as dimethylamineporane (DMAB) as a reducing agent. ” (
Japanese Unexamined Patent Publication No. 1-242781) has been proposed. However, this bath is extremely unstable because it uses an amineporan compound with a large reducing power, and unless EDTA and alkanolamine are used as complexing agents in a delicate mixing ratio, the plating bath will decompose. The problem is that it is difficult to put it into practical use because it is easy to use, and the amine borane reducing agent used in the bath is extremely expensive.

Furthermore, since the film obtained by plating in this bath contains boron (B), it has problems such as being hard, brittle, and having high electrical resistance.

In addition, as another method to solve the drawbacks of the alkaline bath, by using hypophosphite as a reducing agent and birophosphoric acid as a complexing agent, it can be done at low cost without using formaldehyde, which has strong odor and toxicity. Performing electroless copper plating
``Electroless copper plating method'' (Japanese Unexamined Patent Publication No. 1-180986) has been proposed. However, the film obtained by plating using this plating bath has phosphorus (P) eutectoid, which has the same problems as the above method using a B-based reducing agent, and the plating speed is low. The problem was that it was extremely small.

Therefore, the inventors of the present invention sought to solve the problems of the prior art as described above (through intensive research and repeated various systematic experiments, they came up with the present invention).

[Purpose of the invention]

An object of the present invention is to provide an electroless copper plating bath that can form a flexible film with excellent adhesion even on materials with low alkali resistance.

The present inventors have focused on the following regarding the problems of the prior art described above. That is, first, problems encountered when the conventional technique was applied to electroless copper plating of a material with low alkali resistance were investigated.

In this case, first of all, the type of reducing agent is inappropriate.

That is, although aldehydes such as formaldehyde are disclosed as reducing agents in the prior art, these aldehydes are reducing agents that can exhibit sufficient reducing power only in highly alkaline conditions, and when applied to materials with low alkali resistance. It is unsuitable for use because it corrodes or deteriorates the material.

Further, a plating bath using a substance other than Cu as another reducing agent, for example, borane such as dimethylamine borane which eutectoids B, and hypophosphite which eutectoids P, is disclosed. The Cu film produced by this reducing agent is hard and brittle, so it is not suitable.

Second, the type of complexing agent is inappropriate. That is, EDTA (ethylenediaminetetraacetic acid) disclosed in the prior art highly alkaline bath has too large a complexing power in the neutral region, so it reduces Cu-complex ions in the 1) H region near the neutral point. It is difficult to do so.

Third, the pH of the plating bath is inappropriate. That is, when a material with low alkali resistance is plated using a conventional highly alkaline bath, a Cu film with good adhesion cannot be obtained due to corrosion, alteration, and deterioration of the treated material.

Therefore, as an electroless copper plating bath that overcomes these problems of the conventional technology, (a) the use of a reducing agent that exhibits reducing power in the pH range near the neutral point and that does not eutectoid substances other than Cu; b) A complexing agent that can stably dissolve Cu as a Cu-complex ion in the pH range near the neutral point, and that can stably precipitate Cu in the presence of a reducing agent that satisfies the condition (a) above. ((JThe pH is such that it can ensure high adhesion to the Cu film on materials with low alkali resistance,
We focused our attention on creating an electroless copper plating bath that satisfies the three-stripe property.

The present inventors used hydrazines as the reducing agent and chelating amines as the complexing agent to achieve a pH of 6 to 1.
By constructing an electroless copper plating bath of 0.0, we have achieved an electroless copper plating bath that is not only stable but also capable of forming a flexible copper film with excellent adhesion even on materials with low alkali resistance. Ta.

[Description of the first invention] Structure of the first invention The electroless copper plating bath of the first invention is an electroless copper plating bath comprising a copper compound supplying copper-complex ions, a reducing agent, and a copper ion complex forming agent. The bath consists of hydrazines as a reducing agent and a chelating amine as a copper ion complex forming agent, and the pH of the bath is 6 or more and 10 or less.

Functions and Effects of the First Invention The electroless copper plating bath of the first invention can form a flexible film with excellent adhesion even on materials with low alkali resistance.

Although the mechanism by which the electroless copper plating bath of the first invention exhibits the above-mentioned effects is not yet clear, it is thought to be as follows.

That is, the electroless copper plating bath of the first invention employs hydrazines as the reducing agent. The reducing action of hydrazines becomes greater as the pH becomes higher (alkaline). However, the decomposition reaction of the plating bath also increases accordingly. The present inventors have conducted intensive research on these hydrazines and conducted systematic experiments. As a result, the appropriate pH range of the plating bath when hydrazines are used as a reducing agent is pH 6.
It was found that the pH was in the range of ~10. On the other hand, the plating bath becomes acidic as the reaction progresses, and the chelating amine contained as a complexing agent is used not only as a complexing agent for copper ions, but also in an appropriate pH range for acidification. It is thought that by acting as a buffer to inhibit hydrazines, the hydrazines act as reducing agents (the pH can be maintained at the set pH of 6 to 10, and that the reducing power of hydrazines was fully demonstrated. In other words, The oxidizing amine forms a stable CU- complex ion with Cu2+ in the pH range near the neutral point, and also has a stable p) between pH 6 and pH 10.
(This is thought to be because Cu ions are stably precipitated in the pH range near the neutral point due to the sufficient reducing action of hydrazines. Therefore, when plating materials with low alkali resistance, It is thought that the Cu film can be applied before the material undergoes corrosion and chemical alteration, and that adhesion can be ensured.

In addition, since hydrazines do not contain elements that inhibit the performance of copper coatings such as P and B in their molecules, there is no possibility that these performance-inhibiting elements will co-deposit into the precipitated Cu coating, and furthermore, the precipitated Cu coating is flexible. It is possible to demonstrate one's nature.

Therefore, it seems possible to form a flexible film with excellent adhesion even with materials having low alkali resistance.

[Description of the second invention] Below, as the second invention, an invention that further embodies the first invention will be described.

In the second invention, the copper compound is a copper ion supplying substance as a main material for forming a plating film, and Cu"
-It is a substance that supplies complex ions.

Specifically, copper sulfate (Cu SO4, Cu SO4
5H20)'P, cupric chloride (CuCA2, CuCf2
-2H20), copper nitrate (CuNO2, (: u
N O2・3H20), copper hydroxide (Cu(OH)2
) can be used. Among these, copper sulfate (CuSO4) is the substance.
This is preferable because it does not contain chlorine ions, which are highly corrosive halogen ions.

The copper ion concentration of the copper compound is preferably about 0.02 to 0.4 mol. If it is less than 0.02 mol, the plating rate will be slow, and if it exceeds 0.4 mol, the plating bath will become unstable, which is not preferable. In addition, the copper ion concentration is 0.04 to 0.1
When the amount is molar, it is more preferable because the plating rate can be increased and the plating bath can be kept more stable.

Next, hydrazines include hydrazine (N, H,) alone, hydrazine hydrate ((N2H, .N20), hydrazine hydrochloride (N2H-.28 Cl), and hydrazine sulfate (N2H, .H2S O4). Also, hydrazine monosubstituted products such as methylhydrazine and phenylhydrazine, and salts thereof can be used. Among these, when hydrazine monosubstituted products such as methylhydrazine are used as a reducing agent, plating It is advantageous because the speed can be increased, and it is preferable to use hydrazine hydrate or hydrazine sulfate because it is economical.

In the following explanation, hydrazine will be explained as a representative of the hydrazines.

The oxidation reaction of hydrazine is N2H, +40H-= N2 +4820+4 eE
As shown by o = 0.31 0.06pH, 4 electrons are released per mol. Therefore, the required concentration of hydrazine in the plating bath is the chemical equivalent of reducing C
It is preferable that it be close to 1/2 of the u'+ complex ion. It should be noted that if the hydrazine concentration is less than 1/1 of the Cu2+ complex ion concentration, the plating rate will decrease, which is not preferable, and if it exceeds twice the Cu2'' complex ion concentration, the plating bath will become unstable, which is not preferable.

Next, the chelating amine is at least one of polyamines having at least two nitrogens (N), such as ethylenediamine, diethylenetriamine, triethylenetetramine, triaminotriethylamine, tetraethylenepentamine, and pentaethylenepentamine. It is.

Furthermore, N-methyldiamine having a substituent on these, N
- It is preferable to use at least one kind of these derivatives such as ethylethylenediamine because the plating rate is improved. Note that among these, ethylenediamine is inexpensive and is economically the most preferable.

The required concentration of these chelating amines is preferably 2 to 25 times the number of moles of Cu2+-complex ion, although it depends on the type of amine. If the concentration of the chelating amine is less than twice the number of moles of the Cu complex ion, the plating bath will become extremely unstable; if it exceeds 25 times, the plating bath will become too stable and the plating rate will be too high. is undesirable because the concentration decreases from 8 to 8 moles of Cu''-complex ion.
It is more preferable if it is 16 times.

Moreover, the pH of the bath is 6-10. This has a pH of 6
If the pH is less than 10, the reducing power of hydrazine decreases, which is not preferable, and if the pH exceeds 10, the bath becomes unstable, which is not preferable. Note that this pH condition of 6 to 10 is advantageous from the viewpoint of minimizing the corrosiveness of Kl and Zn-based alloys and preventing alteration and deterioration of organic materials with low alkali resistance. In addition, especially when the pH of the bath is set to 8 to 9, the reducing power of hydrazine can be sufficiently achieved and the stability of the bath can be made good.
Particularly preferred.

The pH can be adjusted by changing the concentration and amount of the chelating amine, since the chelating amine exhibits a buffering effect in the pH range of 6 to 10.
j', H2S O4, CH, COOH and other acids and Na
The pH can be adjusted using an alkali such as 0HSKOH. Note that when adjusting the pH using ammonia (NH) or an organic acid, the NH or organic acid may act as a complexing agent, changing the complexation properties and changing the plating rate. be. Furthermore, organic acids and organic acid salts are
An appropriate amount may be added as an H buffer.

The electroless copper plating bath of the second invention comprises three types of substances as essential elements: a Cu compound for supplying the Cu''-complex ions, a chelating amine, and hydrazines.Furthermore, To increase plating speed,
Appropriate amounts of alkanolamines such as triethanolamine and Quadol, nitrogen-containing compounds such as imidazole, and ammonium salts such as ammonia and (NH4)2S04 may be added.

Furthermore, surfactants (polyethylene glycol, alkylamine nonionic surfactants, sodium lauryl sulfate, etc.) and nitrogen-containing cyclic compounds (α.

It is preferable to add a small amount of α-bivirdyl, 1,10-phenanthroline, quinoline, etc. to reduce plating defects and improve the mechanical properties of the plated film.

The temperature of the plating bath is preferably as high as possible, at 70° C. or higher, from the viewpoint of improving the plating speed.

According to the second invention, the electroless copper plating bath can be made weakly acidic to weakly alkaline with a pH of 6 to 10.
It is possible to form a plating film with excellent adhesion to n-based materials and resin materials with low alkali resistance. Furthermore, the plated film is extremely flexible, with very few cracks occurring even when the plated material is bent.

In addition, when the plating bath is used for treatment, a Cu film can be obtained which is highly flexible, has low resistivity, and is excellent in electrical conductivity since no B or P is eutectoid in the film.

In addition, this plating bath has almost no odor, which is a problem with conventional alkaline baths containing formalin, and has a pH in the neutral pH range, so it is not toxic even if it accidentally comes into contact with the human body. Low and safe.

Furthermore, since this plating bath does not require the use of an expensive substance such as dimethylamine borane as a reducing agent, electroless copper plating can be performed at low cost in a pH range near the neutral point.

Furthermore, unlike the disposable two-component spray type plating method, a continuous dipping bath can be used, which is economical and the process can be simplified. Furthermore, the bath of the present invention has the advantage that plating can be stably and continuously carried out by the immersion method, which is carried out in one bath and open to the atmosphere.

Furthermore, it is economical because the solution concentration can be lowered compared to a two-component type bath that utilizes the disproportionation reaction of Cu'' ions.In other words, in the present invention, Cu''! Since the direct reduction reaction from ion is used, there is no need to perform plating with extremely high Cu'' ion concentration, making it economical.

〔Example〕

The present invention will be explained in detail below.

Example 1 An electroless copper plating bath according to this example was prepared using Cu5Oa・5H20, N2H4-H2SO, and a complexing agent under the conditions shown in Table 1 and the bath temperature was 95°C (sample numbers 1 to 1).
11).

Next, a performance evaluation test of this plating bath was conducted.

First, a glass epoxy substrate with a size of 30 mm x 20 mm and a thickness of 2 mm was chemically etched using a conventional method, and then a commercially available Pd-3n colloidal catalyst (Silapray, manufactured by Far East Co., Ltd.) was adsorbed, and then the glass and epoxy substrate were etched. The material to be tested was prepared by activating it in a conventional manner.

Next, this material to be tested was immersed in the plating bath and subjected to plating treatment under the treatment conditions shown in Table 1. The plating baths of sample numbers 1 to 11 all showed stable plating. I was able to do it. When the test materials were taken out from the plating bath after a predetermined period of time had elapsed, uniform and smooth Cu plating films were formed on the substrates of all of the test materials. Further, when this plating film was subjected to an X-ray diffraction test to identify the substance, no diffraction lines other than Cu such as Cu2O were observed, confirming that it was a pure Cu film.

For comparison, a comparative plating solution was prepared in the same manner as in Example 1, except that the complexing agent shown in Table 2 was used. The material to be tested was subjected to a plating treatment, and a performance evaluation test was conducted on the material. As a result, in sample numbers 01 to C3, the plating baths were extremely unstable and rapidly decomposed at room temperature immediately after bath preparation, resulting in Cu2O
A large amount of precipitate was formed, and plating could not be carried out. Furthermore, in sample No. C4 in which EDTA, which is used in the conventional highly alkaline formaldehyde bath, was used as a complexing agent, the plating rate was extremely slow, and no plating was formed at all. Furthermore, in comparison plating baths whose pH was outside the range of the present invention, the plating rate was very low in sample number C5, and the plating rate in sample number C6 became unstable, causing Cu to precipitate here and there in the solution and decompose. have done.

As is clear from the above, the plating bath of this example uses inexpensive hydrazine as a reducing agent without using expensive amine borane, thereby producing a high-quality, flexible Cu plating film with excellent adhesion. You can see that you are getting it.

Example 2 An electroless copper plating bath according to this example was prepared by mixing CuSOa・5H20, N2H4, and the complexing agent shown in Table 2 in the composition ratio shown in Table 2, and having a pH of 9 and a bath temperature of 95°C. were prepared (sample numbers 12 to 25).

Next, a performance evaluation test of this plating bath was conducted.

First, a copper plate having a size of 30×20 mm and a thickness of 0.3+nn+ was prepared as a material to be tested.

Next, this test material was immersed in the plating bath and subjected to plating treatment under the treatment conditions shown in Table 2. When the test material was removed from the plating bath after the predetermined time had elapsed,
In all of the materials to be tested, a uniform and smooth Cu plating film was formed on the substrate. In addition, when we conducted an X-ray diffraction test to identify the substances in this plating film, we found that carbon dioxide such as Cu2O
No diffraction lines other than u were observed, confirming that it was a pure Cu film. Furthermore, the flexibility of the obtained copper film was increased by 9
When visually inspected in the 0° bending test, no large rack was observed.

In addition, in sample number 20, the plating bath was decomposed and plating could not be performed. This depends on the concentration of the complexing agent or Cu
This is thought to be because the number of moles is less than twice the number of moles of the 2+ complex ion. Furthermore, in sample number 21, the plating speed was significantly reduced. This is thought to be because the concentration of the complexing agent exceeded 25 times the number of moles of Cu'' complex ions, making the bath too stable. Furthermore, in sample No. 22, the plating rate decreased significantly. Concentration or 1/10 of copper complex ion
This is thought to be because it is less than In addition, in sample number 23, the plating bath became somewhat unstable. This is considered to be because the concentration of hydrazine exceeded twice that of copper complex ions.

Further, in sample number 24, the plating speed was slightly low, and in sample number 25, the plating bath became slightly unstable.

From the above, in this example, the concentration of copper complex ions is 0.02
~0.4 mol, it is found that it is preferable that the concentration of the chelating amine is 2 to 25 times that of the copper complex ion, and that the concentration of hydrazines is 1/10 to 2 times that of the copper complex ion. .

Example 3 0.04 mol of copper compounds shown in Table 3, 0.04 mol of hydrazines.
Electroless copper plating baths according to this example having a bath temperature of 95° C. were prepared by mixing 0.4 mole and chelating amine in the composition ratio shown in the same table (sample numbers 26 to 33).

Next, a performance evaluation test of this plating bath was conducted.

First, the material to be tested was prepared in the same manner as in Example 2, and then
The material to be tested was immersed in the above-mentioned plating solution and subjected to plating treatment under the same treatment conditions.

After the predetermined period of time had elapsed, the test materials were removed from the plating bath.
A u plating film was formed.

Further, when this plating film was subjected to an X-ray diffraction test to identify the substance, no diffraction lines other than Cu such as Cu2O were observed, confirming that it was a pure Cu film. Furthermore, when the flexibility of the obtained copper film was visually examined by a 90° bending test, no cracks were observed.

As is clear from Table 4, in this example, the reducing agents used were hydrazine hydrate (N2H4・N20), hydrazine hydrochloride (N2H4・28CI, hydrazine sulfate (N2H4・N20),
It can be seen that a Cu-plated film of good quality and excellent flexibility with excellent adhesion was similarly obtained no matter which hydrazine was used, such as H2S04) or methylhydrazine sulfate.

It is also found that the plating rate can be improved by adding appropriate amounts of (NH,)2SO, imidazole, quadol, or triethanolamine to the chelating amine (ethylenediamine) as the main complexing agent.

In addition, as a copper compound, Cu CI! ! , (: u
It can be seen that even when S O4, Cu N O3, etc. are used, a Cu plating film with excellent adhesion, high quality, and excellent flexibility can be obtained.

Example 4 0.12 mol of CuSO4.5H20 and N2H, .H2
Mix 0.04 mol of SO4, 0.06 mol of guadol, and 0.96 mol of ethylenediamine, and adjust the pH to 9.
An electroless copper plating bath according to this example having a bath temperature of 90°C was prepared.

Next, a performance evaluation test of this plating bath was conducted.

First, a pure AA plate (AIloo) having a size of 50 x 50 mm and a thickness of 1 mm was prepared, a plated surface with a 2 x 2 mm opening was formed, and the rest was covered with masking resin to be used as a test material.

Next, this material to be tested was subjected to N1-P electroless plating at 0.
After forming a 5 μm thick film, it was immersed in the plating bath and plated for 1 hour. Next, a thin layer of N1-P plating was applied to the obtained plated surface to prevent solder corrosion, and then soldering was performed via a Sn-plated Cu wire, and the adhesion strength was measured using a peeling tester. As a result, 8 kg
A value of /2 mm or more was obtained, and the broken point was the solder part.

For comparison, 0.0% formaldehyde was used as the reducing agent.
08 mol, 0.08 mol of EDTA as a complexing agent, Cu
”-CuSOa・5H70 as ion-supplying compound
A comparative alkaline electroless copper plating bath (pH 12.6, bath temperature 60"C) was prepared using 0.04 mol of Ni.Next, a performance evaluation test was attempted in the same manner as above.
AI through the pinhole in the membrane! is severely corroded, causing blisters and defects in the plating film, and almost no adhesion.
It was not possible to subject it to an adhesion strength test.

Claims (1)

[Claims] (1) In an electroless copper plating bath consisting of a copper compound that supplies copper-complex ions, a reducing agent, and a copper ion complex forming agent,
An electroless copper plating bath comprising hydrazines as a reducing agent and a chelating amine as a copper ion complex forming agent, and having a pH of 6 or more and 10 or less.