JP2910618B2 - Electroless Ni-B plating solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless Ni-B plating solution, and more particularly, to a metal wiring formed on a substrate such as AlN (aluminum nitride) or glass ceramic in a process of manufacturing an IC package or the like. The present invention relates to an electroless Ni-B plating solution useful for, for example, plating a layer with a Ni (nickel) -B (boron) alloy.

[0002]

2. Description of the Related Art In contrast to electroplating in which a current is applied from the outside to reduce and deposit metal ions in a solution on a cathode, metal ions in a solution are reduced and deposited on the surface of a body to be plated without using an external current. The method is called chemical plating. This chemical plating is further roughly classified into immersion plating based on ion substitution and electroless plating using a chemical reducing agent.

In the immersion plating method, for example, a metal object to be plated such as Ni is immersed in a solution containing ions of a noble metal such as Au (gold), and Au is deposited on the object by a so-called substitution reaction. However, once the surface of the object to be plated is covered with Au, the growth of the plating film stops, and there is a problem that it is difficult to form a thick plating film.

On the other hand, the electroless plating method comprises a salt of a metal deposited in a solution, a complexing agent for complexing the metal,
This is a method of immersing an object to be plated in a plating solution at a predetermined temperature mixed with a reducing agent or the like for reducing and depositing a metal simple substance by reducing a metal complex and reducing and depositing the metal on the surface of the object to be plated. .

[0005] This method is widely used industrially because it has the following many excellent features. (1) A power source, electrodes, and the like are unnecessary, and a plating film having a uniform thickness excellent in adhesion, uniformity, and the like can be obtained only by immersing the object to be plated in a plating solution. (2) It is easy to control the thickness and physical properties of the plating film by changing the plating treatment conditions such as the plating solution composition, and it is possible to form a plating film that meets the required characteristics. (3) It is possible to apply a plating process to the object to be plated of any shape with good adherence. (4) It is possible to directly apply a plating process to a non-conductive substance such as plastic, glass, and ceramics.

This electroless plating method includes tin, silver, platinum group,
Au, Co (cobalt), Co-Fe (iron), Co-W
(Tungsten) -P (phosphorus), Ni, Ni-Co, N
i-P, Ni-Co-P, Ni-Fe-P, Ni-W-
Many plating methods using P, Ni-B or the like are known. Among these, electroless Ni-B plating is a method developed in 1957 by DuPont of the United States, and it was practically difficult to use it at first because the plating solution used for the plating was extremely alkaline. After that, the plating solution was repeatedly improved and finally put into practical use.
The basic components of the commercially available electroless Ni-B plating solution are shown in Table 1 below.

[0007]

[Table 1]

FIG. 3 is a cross-sectional view schematically showing a wiring substrate plated with a conventional electroless Ni-B plating solution. In FIG. 3, reference numeral 31 denotes the substrate. A metal wiring layer (or metal pad) 32 made of, for example, W (tungsten) is formed on the substrate 31, and a Ni-B plating film 33 is formed on the surface of the metal wiring layer 32. These substrate 31, metal wiring layer 32, Ni-B plating film 3
3, the wiring board 30 in the middle of the manufacturing process is configured. The Ni-B plating film 33 is formed by immersing the substrate 31 in any one of the electroless Ni-B plating solutions described in Table 1 with the metal wiring layer 32 side facing downward. In the next step, an Au plating process is performed on the surface of the Ni—B plating film 33 to form an Au plating film 34 in many cases.

An object to be plated such as the metal wiring layer 32 is electroless N
When the i-B plating process is performed, the mechanism of the reaction that proceeds in the plating solution to form the Ni-B plating film 33 has not been completely elucidated. However, when an electroless Ni-B plating process is performed using a plating solution containing dimethylaminoborane as a reducing agent, a chemical reaction represented by the following chemical formulas 1 and 2 proceeds in the plating solution. ing.

[0010]

Embedded image 4Ni ²⁺ + 2BH ₄ ⁻ + 6OH ⁻ → 2Ni ₂ B +
6H ₂ O + H ₂

[0011]

Embedded image 4Ni ²⁺ +2 (CH ₃ ) ₂ NHBH ₃ + 3H ₂ O
→ Ni ₂ B + 2Ni + 2 (CH ₃ ) ₂ H ₂ N ⁺ + H ₃ BO
₃ + 6H ⁺ + 1 / 2H _{2 Further} , when an electroless Ni-B plating process is performed using a plating solution containing sodium borohydride as a reducing agent, a chemical reaction represented by the following chemical formula 3 is obtained in the plating solution. Is said to progress.

[0012]

Embedded image 4Ni ²⁺ + 2NaBH ₄ + 6NaOH → 2Ni
The ^{_{2 B + H 2 + 8Na +}} + 6H 2 O Ni-B plating film 33 including the Ni ₂ B film adhesion, heat resistance, excellent in properties such as oxidation resistance and hardness,
It has the property that the wettability with an Au plating solution or the like is extremely good. Therefore, even when the wiring board 30 is affected by various kinds of heat during the manufacturing process of an IC package or the like,
Oxidation of the metal wiring layer 32 is prevented by the Ni-B plating film 33, and quality can be maintained. Further, when Au plating is performed on the Ni-B plating film 33 in the next step, the Au plating film 34 can be formed to be thinner with good adhesion to the metal wiring layer 32, and the cost can be reduced. Become.

[0013]

In the conventional electroless Ni-B plating solution shown in Table 1 above, when the substrate 31 is immersed in the plating solution, the material of the substrate 31 becomes, for example, Al.
_Although there is no problem in the case of ceramics such as ₂ O ₃ (alumina) and metals such as copper and Au, for example, in the case of AlN ceramics and glass ceramics, the vicinity of the substrate surface 31a is easily dissolved and corroded by the plating solution. Wiring board 3
There was a problem that the strength of No. 0 was reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and when immersed in a plating solution, a substrate such as an AlN ceramic or a glass ceramic is prevented from being dissolved or corroded, and the strength of the wiring substrate is reduced. It is an object of the present invention to provide an electroless Ni-B plating solution that can prevent a decrease.

[0015]

The present inventors have conducted various studies on the reduction of corrosion in AlN ceramics and glass ceramic materials, and found that a predetermined amount of ethylenediamine as a complexing agent and a predetermined amount of ethylenediamine as a second complexing agent were used. In an electroless Ni-B plating solution containing a fixed amount of lactic acid,
The inventors have found that the above objects can be almost achieved, and have completed the present invention.

That is, the electroless Ni-B plating solution according to the present invention contains 0.01 mol of nickel chloride (water containing crystallization), nickel sulfate (water containing crystallization), or nickel acetate (water containing crystallization) as a Ni ion source. / Liter or more and 0.05 mol / liter or less, and dimethylaminoborane (hereinafter referred to as DMA) as a reducing agent.
B) is 0.02 mol / L or more and 0.20 mol / L or less, and ethylenediamine (water containing crystallization) is added as a complexing agent in an amount of 0.1 to 0.20 mol / L.
10 mol / l or more and 0.20 mol / l or less, lactic acid as a second complexing agent 0.05 mol / l or more and 0.30 mol / l or less, thiodiglycolic acid as a stabilizer 1 ppm or more and 6 pp
m, Pb ²⁺ ion as an accelerator is 5 ppm or more and 30 pp
m or less.

In the present invention, for example, nickel chloride is described as (nickel-containing water) nickel chloride, which means that nickel chloride may contain water of crystallization or may be anhydrous. doing. This is the same for other compounds. Hereinafter, the compounds to which (water containing crystallization) is added are also referred to by omitting (water containing crystallization).

[0018]

In the above electroless Ni-B plating solution, when the concentration of nickel chloride, nickel sulfate or nickel acetate is 0.01 to 0.05 mol / liter, Ni ions necessary for forming a Ni plating film are formed. Is supplied in an appropriate amount, and the Ni plating film having a normal color can be surely formed. On the other hand, the concentration of the nickel chloride, the nickel sulfate or the nickel acetate is 0.01%.
When the amount is less than mol / liter, the amount of the supplied Ni ions is small, and it is difficult to form a Ni plating film,
In addition, the Ni plating film tends to exhibit a blackish brown color, and when a plating treatment is further performed thereon, the metal (Au or the like) film tends to be adversely affected. On the other hand, when the concentration of the nickel chloride, the nickel sulfate or the nickel acetate exceeds 0.05 mol / liter, powdery or foil-like Ni is easily precipitated in the plating solution, and instead, Ni plating is performed. The deposition rate of the coating will be reduced.

Further, when the concentration of DMAB is 0.02-0.2
In the case of 0 mol / liter, a predetermined reducing power is obtained, and a self-decomposition reaction of the plating solution is prevented.
The DMAB is also a B source in the Ni-B plating film, and the concentration of the DMAB is 0.02 to 0.20 mol.
When the concentration is set to a predetermined value within the range of 1 / liter, the predetermined amount of B within the range of about 0.1 to 7.0% can be surely contained in the Ni-B plating film. On the other hand, when the concentration of the DMAB is less than 0.02 mol / liter, the reducing power is weak, and the Ni-B plating film is hardly formed.
When the concentration of MAB exceeds 0.20 mol / L, the plating solution tends to undergo a self-decomposition reaction, and the deterioration of the plating solution is accelerated.

The concentration of ethylenediamine is 0.10
In the case of ０．２0.20 mol / liter, the complex (1) with Ni and B ions is reliably formed, the generation of free decomposition of free Ni and B ions is suppressed, and the pH is easily adjusted. As a result, the Ni-B plating film can be reliably formed. On the other hand, when the concentration of the ethylenediamine is less than 0.10 mol / liter, the complex (1)
Is insufficient, and self-decomposition of free Ni and B ions tends to occur. On the other hand, when the concentration of the strongly alkaline ethylenediamine exceeds 0.20 mol / l,
A large amount of an adjusting agent is required for the adjustment, and the performance of the plating solution tends to change. As a result, the Ni-B plating film is hardly deposited.

The concentration of lactic acid as an organic acid is 0.0
In the case of 5 to 0.30 mol / liter, the complex (2) of the lactic acid and Ni and B ions is formed concurrently with the complex (1), and the complex (1) is stabilized. At the same time, and all components contained in the plating solution are present as a complex, and the plating solution is a neutral solution.
The dissolution and corrosion of N and glass ceramics can be prevented. On the other hand, when the concentration of the lactic acid is less than 0.05 mol / liter, the stability of the plating solution is insufficient, and self-decomposition tends to occur. On the other hand, the concentration of the lactic acid is 0.30 mol
If it exceeds 1 / liter, the plating solution will be too stable, and the Ni-B plating film will not be easily deposited. In addition, malic acid, malonic acid, tartaric acid,
A plating solution to which an organic acid such as succinic acid is added has a large dissociation constant and a large amount of free carboxy ions (COO ⁻ ), so that the main component of the glass ceramic is easily dissolved and corroded. Not suitable for use.

The concentration of the diglycolic acid is 1 to 6 pp.
In the case of m, while the plating solution is further stabilized,
When the concentration of the diglycolic acid is less than 1 ppm,
As the number of uses increases, the plating solution tends to become unstable gradually. On the other hand, when the concentration of the diglycolic acid is 6 pp
If it exceeds m, the Ni-B plating film tends to exhibit a dark brown color, and the longer the plating time, the more easily the Ni-B plating film is redissolved in the plating solution.

Further, if Pb ²⁺ ion concentration of 5~30ppm, while may accelerate the deposition rate of the Ni-B plating film, when the Pb ²⁺ ion concentration is less than 5ppm, the Ni- It is difficult to increase the deposition rate of the B-based plating film.
On the other hand, when the Pb ²⁺ ion concentration exceeds 30 ppm, the Ni—B-based plating film is not easily deposited.

According to the electroless Ni-B plating solution having the above structure, nickel chloride, nickel sulfate,
Or 0.01 mol / L or more and 0.05 mol of nickel acetate
/ L or less, 0.02 mol / L of DMAB as a reducing agent
Not less than 0.20 mol / l, not more than 0.10 mol / l of ethylenediamine as a complexing agent, not more than 0.20 mol / l, and not more than 0.05 mol / l of lactic acid as a second complexing agent, 0.30 mol
1 liter or less, 1 ppm of thiodiglycolic acid as a stabilizer
6 ppm or less, and Pb ²⁺ ions as a promoter in an amount of 5 ppm or more and 30 ppm or less. Electroless Ni-B is added to a metal wiring layer formed on a glass ceramic substrate or an AlN substrate.
When plating is performed, the glass ceramic substrate and the AlN substrate can be reliably prevented from being melted and corroded and deteriorating in strength, and the metal wiring layer has a film adhesion property.
A Ni-B plating film having excellent properties such as heat resistance, oxidation resistance, and high hardness can be selectively and more quickly formed.

[0025]

EXAMPLES AND COMPARATIVE EXAMPLES Hereinafter, the electroless Ni-
An example of the B plating solution will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an apparatus used when performing an electroless Ni-B plating process on a body to be plated using an electroless Ni-B plating solution according to an example. A substrate made of AlN or glass ceramic is shown. Substrate 21
A metal wiring layer (or metal pad) 22 made of W, for example, is formed on the lower surface of FIG.
The substrate 2 including the substrate 21 and the metal wiring layer 22
0 is configured. On the other hand, a plating tank 11 is provided below the body 20 to be plated, and the plating tank 11 is filled with the electroless Ni-B plating solution 13 according to the embodiment. A heater 12 is provided below the plating tank 11 so that the heater 12 heats the electroless Ni-B plating solution 13 to a predetermined temperature. Plating tank 1
1 is provided with a stirring means (not shown) so that the plating liquid 13 is constantly stirred by the stirring means. These plating tank 11, heater 12, plating solution 1
3. The electroless Ni-B plating apparatus 10 includes stirring means and the like. When the object to be plated 20 is moved in the direction of the arrow in the figure and immersed in the plating solution 12 for a predetermined time, the reaction of the above formulas 1 and 2 proceeds, and the surface of the metal wiring layer 22 is plated with Ni-B. A coating (not shown) is formed.

The substrate 21 is subjected to an electroless Ni-B plating treatment using the electroless Ni-B plating solution 13 according to the embodiment, and the composition of the plating film, the dissolved and corroded state of the substrate 21, The results of an investigation on the breaking strength will be described. As a comparative example, a plating solution having a composition different from the composition of the electroless Ni-B plating solution according to the example,
Alternatively, a case where a commercially available conventional plating solution is used will be described. Experimental conditions and experimental methods are described below.

(1) The composition of the plating solution used in the experiment was
The results are shown in Table 2 below. Although the composition of the commercially available plating solution according to Comparative Examples 2 and 3 is unknown, depending on the color of the plating film,
It is estimated that ethylenediamine and lactic acid are not contained.

[0028]

[Table 2]

(2) The components of the substrate 21 used in the experiment, the average breaking strength and the shape of the substrate 21 before immersion in the plating solution are shown in Table 3 below. The thickness h of the substrate 21 was measured with a micrometer, and the length L and width b were measured with calipers.

[0030]

[Table 3]

(3) The breaking strength test was performed by the following method. To avoid the effects of cracks on the side of the substrate 21,
After this portion is polished in advance with polishing paper, the substrate 21
Is placed on the fulcrums 41 and 42 of the strength test apparatus 40 shown in FIG. Next, the pressing element 43 is pushed down from above the central portion between the fulcrums 41 and 42 (L '= 30 mm), and the load P when the substrate 21 breaks is measured. Based on the average load P 'obtained by repeating this test five times, the average breaking strength F was determined by the following equation (1).

[0032]

F = 3 · P ′ · L ′ / 2 · b · h ² (4) The weight change rate of the substrate 21 is calculated by measuring the weight of the substrate 21 before and after immersion using an electronic balance having four significant figures. It was measured and was determined by the following equation 2 based on the measured value.

[0033]

## EQU2 ## ((substrate weight before immersion−substrate weight after immersion) /
(Weight of substrate before immersion) × 100 (5) Quantitative analysis of eluted components was carried out by a swing-coupled plasma emission spectroscopy (ICP) method. In addition, since Ca and Y were not blended in the glass ceramic, the indication of this component was omitted. Since AlN does not contain Mg, Si, B, and K, the indication of this component is omitted.

First, the electroless Ni-B plating solution 1 according to Examples 1 to 3 in which the pH was adjusted to 7.0 and the temperature was adjusted to about 70 ° C.
3 is immersed in the glass ceramic substrate 21 on which the metal wiring layer 22 of W is formed for about 30 minutes.
The plating film deposited on No. 2 was analyzed. The analysis results are shown in Table 4 below.

[0035]

[Table 4]

As is clear from Table 4, in the electroless Ni-B plating solution 13 according to Examples 1 to 3, B was set to about 0.1 to
A Ni-B plating film containing 7.0% is deposited. It should be noted that substantially the same results were obtained when the substrate 21 was made of AlN.

Next, in the plating solution according to Example 2 in which the pH was adjusted to 7.0 and the temperature to about 70 ° C., or Comparative Example 2 in which the pH was adjusted to 6.8 and the temperature to about 70 ° C. After the substrate 21 was immersed in the plating solution of No. 3 for about 30 minutes, the weight change rate of the substrate 21, the concentration of components eluted into the plating solution, and the average breaking strength of the substrate 21 were measured. The measurement results when the substrate 21 was made of glass ceramic and AlN are shown in Tables 5 and 6 below. The dashed line in the column of elution component concentration indicates that no elution component was detected or ICP
Shows the case where it is below the detection limit in.

[0038]

[Table 5]

[0039]

[Table 6]

As is clear from Tables 5 and 6, Example 2
In the plating solution according to the above, sintering aid components such as Ca and Y do not change much, but in each case, the elution of Al and the like is extremely small, the rate of change in weight is also reduced, and therefore, the deterioration of strength is almost zero. can not see.

Next, using the plating solution of Example 2, the plating treatment time was kept constant for 30 minutes, the pH of the plating solution was changed to 6.5 to 7.5, and the temperature of the plating solution was changed to 60 to 80 ° C. Table 7 below shows the measurement results of the weight change rate of the glass ceramic or AlN on the substrate 21 and the concentration of the eluted component in the plating solution. Further, the pH of the plating solution was adjusted to 6.5 to 7.
5. When the temperature of the plating solution was changed in the range of 60 to 70 ° C. and the plating time was changed in the range of 10 to 40 minutes, the average fracture strength and the presence or absence of corrosion in the glass ceramic or AlN substrate 21 were investigated. The results are shown in Table 8 below. Further, when using the plating solutions according to Comparative Examples 2 and 3, the plating treatment time was kept constant for 30 minutes, the pH of the plating solution was kept constant at 6.8, and the temperature of the plating solution was changed in the range of 60 to 80 ° C., glass ceramic or The results of measuring the weight change rate of the AlN on the substrate 21 and the concentration of the eluted component in the plating solution are shown in Tables 9 and 11, respectively. When the plating solution according to Comparative Examples 2 and 3 was used, the pH of the plating solution was kept constant at 6.8, the temperature of the plating solution was changed to 60 to 70 ° C., and the plating time was changed to a range of 10 to 40 minutes. Table 10 below shows the results of the investigation of the average fracture strength and the presence or absence of corrosion in the ceramics or AlN substrate 21.
The results are shown in Table 12.

[0042]

[Table 7]

[0043]

[Table 8]

[0044]

[Table 9]

[0045]

[Table 10]

[0046]

[Table 11]

[0047]

[Table 12]

As is clear from the results, Comparative Example 2
The plating solution according to Example 3 easily dissolves and corrodes the substrate 21 even when the processing temperature and the processing time are changed. However, the plating solution according to Example 2 causes dissolution and corrosion even when the pH, the processing temperature and the processing time are changed. hard.

As is clear from the above results and description, in the electroless Ni-B plating solution according to the embodiment, the W wiring layer 22 formed on the glass ceramic or AlN substrate 21 is used.
When the substrate 21 is subjected to an electroless Ni-B plating process, it is possible to reliably prevent the substrate 21 from being melted and corroded and from being deteriorated in strength, and to have film adhesion, heat resistance, and oxidation resistance to the W wiring layer 22. It is possible to selectively and more quickly form a Ni-B plating film having excellent properties such as properties and high hardness.

[0050]

As described in detail above, in the electroless Ni-B plating solution according to the present invention, nickel chloride, nickel sulfate, or nickel acetate is used as a Ni ion source at a concentration of 0.02%.
1 mol / L or more and 0.05 mol / L or less, D as a reducing agent
MAB is not less than 0.02 mol / l and not more than 0.20 mol / l,
0.10 mol / l or more and 0.20 mol / l or less of ethylenediamine as a complexing agent and lactic acid of 0.02 mol / l or less as a second complexing agent.
Since it contains 5 mol / l to 0.30 mol / l, thiodiglycolic acid as a stabilizer is 1 ppm to 6 ppm, and Pb ²⁺ ion is 5 ppm to 30 ppm as an accelerator, it can be used on a glass ceramic substrate or AlN substrate. When performing the electroless Ni-B plating process on the metal wiring layer formed in the above, it is possible to reliably prevent the glass ceramic substrate and the AlN substrate from being melted and corroded and being deteriorated in strength, and A Ni-B plating film having excellent properties such as film adhesion, heat resistance, oxidation resistance, and high hardness can be selectively and more quickly formed on a metal wiring layer.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an apparatus for performing an electroless Ni-B plating process on an object to be plated using an electroless Ni-B plating solution according to an example.

FIG. 2 is a cross-sectional view schematically showing an apparatus for measuring the breaking strength of a substrate when performing electroless Ni-B plating using an electroless Ni-B plating solution according to an example. .

FIG. 3 is a cross-sectional view schematically showing a wiring board plated with a conventional electroless Ni-B plating solution.

[Explanation of symbols]

 13 Electroless Ni-B plating solution

Claims (1)

(57) [Claims] 1. A method for reducing nickel chloride (water containing crystallization), nickel sulfate (water containing crystallization), or nickel acetate (water containing crystallization) as a Ni ion source in an amount of 0.01 mol / L or more and 0.05 mol / L or less. Dimethylaminoborane as an agent
2 mol / l or more and 0.20 mol / l or less, ethylenediamine (crystal water) as a complexing agent 0.10 mol / l or more and 0.20 mol / l or less, and lactic acid as a second complexing agent 0.0
An electroless Ni- containing at least 5 mol / liter and not more than 0.30 mol / liter, containing 1 to 6 ppm of thiodiglycolic acid as a stabilizer and 5 to 30 ppm of Pb ²⁺ ions as an accelerator. B plating solution.