KR100321021B1 - Nitric and silicide compound based conversion coating composition for printed circuit boards - Google Patents

Abstract

The present invention is a coating film composition based on nitrogen and silicon compounds used in the surface treatment of a printed circuit board (PCB), and more specifically in the blackening process of the inner layer of the printed circuit board manufacturing process (Conversion Coating) Composition, according to the present invention,

(1) sulfuric acid;

(2) organic acids;

(3) hydrogen peroxide;

(4) nitrogen compounds;

(5) silicon compounds; And

(6) Provided is a chemical conversion film composition for a printed circuit board comprising at least one component of a film forming aid, an etching rate control agent, a reaction accelerator, and a stabilizer.

By using the chemical conversion coating composition for a printed circuit board according to the present invention, it is possible to perform blackening at a low temperature by a shortening process in a short time as compared with the conventional blackening treatment, and also with the conversion coating composition according to the present invention. The printed circuit board has excellent acid resistance and adhesive strength. In addition, by eliminating the reduction treatment process, the use of expensive reducing treatment chemicals conventionally used is eliminated, and the amount of wastewater generated is reduced by 50% or more, which is more economical.

Description

Chemical coating composition for printed circuit board based on nitrogen and silicon compound {NITRIC AND SILICIDE COMPOUND BASED CONVERSION COATING COMPOSITION FOR PRINTED CIRCUIT BOARDS}

The present invention relates to a chemical conversion coating composition used for the surface treatment of a printed circuit board (PCB), and more specifically to the nitrogen and silicon compounds used in the blackening process of the inner layer of the printed circuit board manufacturing process It relates to a conversion coating composition mainly.

In the manufacturing process of multi-layer printed circuit board (MLB), the blackening process of inner layer circuit is adopted. The blackening process protects the inner layer circuit from the surrounding environment in the manufacture of multi-layered board and maximizes the adhesive strength in the lamination process combining each inner layer and outer layer. This is an indispensable process for the purpose of doing so.

Until now, in the PCB industry, to oxidize the multilayer printed circuit board (MLB) inner layer (Black Oxide), using an oxidizing agent such as sodium chlorite under an alkaline atmosphere of caustic soda or caustic alkali (NaOH, KOH) (70 ~ A method of oxidizing an inner layer circuit made of copper to black at 80 ° C.) has been used.

The blackening film produced by the conventional blackening process is a second copper oxide (CuO) layer in which copper (Cu) is oxidized. During the etching process (Soft-etching, H ₂ SO ₄ / H ₂ O ₂ ), acid copper plating bath (CuSO ₄ / H ₂ SO ₄ ) and its pretreatment process, the blackening film around the drilled hole is eroded by acid There is a problem called pinking occurs. In order to solve this problem, conventionally, a process of reducing a CuO (Cupric Oxide) layer to a Cu ₂ O (Cuprous Oxide) layer having excellent acid resistance is adopted. Etching process and the problem of dissolving in inorganic acids such as sulfuric acid (H ₂ SO ₄ ), hydrochloric acid (HCl), nitric acid (HNO ₃ ), etc. were not solved, and Cu ₂ O (Cuprous Oxide) layer at higher temperature It has caused the problem of re-assignment to).

Reducing agents used in the reduction process include DMAB (Dimethyl Amine Borane), MPB (Morpholine Borane), HCHO (Formalin), NaBH ₄ (Sodium Borohydride), and KBH ₄ (Potassium Borohydride). It is an expensive drug and accounts for most of the cost of the blackening process.

In addition, there are some blackening treatment processes currently under acidic crisis, but they are very sensitive to chlorine ion concentration in baths, which makes them difficult to manage. The most important adhesive strength (Peel or Bonding Strength) is less than 1.0 kg / ㎠ It is weak in terms of reliability.

Accordingly, an object of the present invention is to solve the problems of the conventional alkali blackening process and the recent acid blackening process, and it is possible to form a black-brown oxide film having excellent acid resistance and adhesive strength mainly based on organic and inorganic nitrogen compounds and silicon compounds. The present invention provides a conversion coating composition used for copper and copper alloy.

It is another object of the present invention to provide a chemical conversion coating composition which forms a blackish brown film on a printed circuit board without the pretreatment and posttreatment processes required for the conventional blackening process.

It is still another object of the present invention to provide a chemical conversion coating composition that exhibits strong adhesion when forming a multilayer printed circuit board.

According to the present invention

(1) sulfuric acid;

(2) organic acids;

(3) hydrogen peroxide;

(4) nitrogen compounds;

(5) silicon compounds; And

(6) Provided is a chemical conversion film composition for a printed circuit board comprising at least one component of a film forming aid, an etching rate control agent, a reaction accelerator, and a stabilizer.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The chemical conversion coating composition according to the present invention is a composition based on an acid, nitrogen and silicon compound used for surface treatment and improved adhesion of a printed circuit board. In particular, the blackening process of an inner layer circuit in a multilayer printed circuit board (MLB) manufacturing process. It can be used to exhibit excellent adhesive strength and acid resistance, and can significantly shorten the blackening treatment process conventionally used.

The chemical conversion coating composition for a printed circuit board according to the present invention (hereinafter, referred to simply as a 'coating composition') is a composition containing sulfuric acid, hydrogen peroxide, nitrogen, and silicon compounds as main components. In the case of treatment, a black copper oxide (CuO) film having weak acid resistance is formed, but when the printed circuit board is treated with the coating composition according to the present invention, a black brown organic coating film having excellent acid resistance and adhesive strength is formed.

In the process of applying the coating composition of the present invention to the copper circuit, sulfuric acid and hydrogen peroxide in the composition act to etch copper while maintaining the acidity of the composition, and nitrogen and silicon compounds are colored on the surface of metal copper by using such etching. As a result, a black brown film is formed.

At this time, inorganic and organic acids including sulfuric acid and hydrogen peroxide have a secondary function of increasing the cohesion of the resulting coating film, increasing the adhesion and assisting the color of the coating film.

Sulfuric acid in the coating composition for a printed circuit board according to the present invention is used at 0.1-30 v%, preferably 1.0-15 v%, based on 98% sulfuric acid. If the amount of sulfuric acid is less than 0.1 v%, it is difficult to form a film. If the amount of sulfuric acid is 30 v% or more, the structure of the film is not formed densely.

The organic acid uses 0.01-10 wt%, preferably 0.01-5 wt%, more preferably 0.05-2.5 wt% with respect to the total weight of the composition. If it is less than 0.01wt%, its effect is insignificant, and if it is more than 10wt%, the cohesion of the coating film is rather weakened.

As the organic acid, an organic compound containing at least one -COOH group such as acetic acid, propionic acid, glycolic acid, citric acid, tartaric acid, maleic acid, malonic acid, succinic acid, phthalic acid, benzoic acid, acrylic acid is used, and anhydrides of organic acids may also be used.

When hydrogen peroxide is 35% hydrogen peroxide, 0.1-15v%, preferably 1.0-10v%, relative to the total volume of the coating composition is used. If the amount of hydrogen peroxide is less than 0.1 v%, it is difficult to form a film. If the amount of hydrogen peroxide is more than 15 v%, the etching ability of copper (Cu) is excessively activated, resulting in an uneven film and a risk of re-dissolution.

The nitrogen compound is used in the range of 0.1-30 wt%, preferably 0.1-20 wt%, more preferably 0.5-15 wt%, based on the total weight of the coating composition. If less than 0.1 wt% coating layer is formed too thin, if more than 30 wt% the coating layer is thickened to reduce the adhesion.

Nitrogen compounds used in the present invention include urea and thio-urea derivatives as organic compounds, hetero-cyclic compounds containing nitrogen, in particular imidazole, triazole, thiazole and derivatives thereof, or = NH, -N =,- Compounds containing active nitrogen such as NH-, -NOH-, -N = N-, = NSN = and the like can be used.

The silicon compound is used in the range of 0.01-10 wt%, preferably 0.1-5.0 wt%, based on the total weight of the coating composition. If it is less than 0.01 wt%, the bonding strength of the coating layer is weak, and if it is 10 wt% or more, the degree of curing of the coating layer is excessively increased to lower the adhesion.

Inorganic silicon compounds such as sodium silicate (Sodium Silicate: Na ₂ SiO ₃ , Na ₆ Si ₂ O ₇ , Na ₂ Si ₃ O ₇ ), silicic acid (H ₂ SiO ₃ ), and the like are used in the present invention. And organosilanes and derivatives thereof comprising structures such as silanol (R ₃ SiOH, R ₂ Si (OH) ₂ , RSi (OH) ₃ ) and -Rx-Si-, -Rx-Si-O- and the like. Rx may use a compound in the range of C ₁ -C ₁₂ as alkyl or other hydrocarbon group.

The coating composition according to the present invention contains at least one of the following additives in order to increase the reactivity and reliability in addition to the above compounds.

As an additive, an auxiliary agent for obtaining a uniform colored film (hereinafter, simply referred to as an 'film forming aid') and an auxiliary agent added to control the etching rate of copper which is a driving force for the coating reaction (hereinafter, referred to as an 'etching rate adjusting agent') And accelerators (hereinafter referred to only as reaction promoters) and stabilizers to aid in reaction promotion and film formation.

As an encapsulation aid, hydroquinone, resorcinol, pyrocatehol, pyrogalol and derivatives thereof, and inorganic and organic sulfur compounds may be used. Inorganic sulfur compounds include ammonium salts of sulfur compounds (such as (NH ₄ ) ₂ S) or alkali metal salts (Na ₂ S, K ₂ S) and sulfo sulfonates as organic sulfur compounds, and thiocyanate as thio compounds. Sulfur, such as salts, thiourea and derivatives thereof, thiophosphoric acid and salts thereof, thioglycolic acid and salts thereof, thiosulfate and sulfonate compounds and mercapto compounds, All kinds of organic compounds can be used.

On the other hand, -S- or -SS-, -SSS-, RS-, R-SH, R = S, RS- (wherein R is carbon, hydrocarbon, or nitrogen and radicals or compounds containing them) and the like. Sulfur compounds containing the same active sulfur are more preferred, and it is more preferable to contain nitrogen in the sulfur compounds.

The above film forming auxiliary agent is used in an amount of 0.1-20 wt%, preferably 0.1-15 wt%, more preferably 0.5-10 wt%, based on the weight of the coating composition. If it is used at less than 0.1 wt%, its effect is insignificant, and if it is more than 20 wt%, it prevents the film forming reaction or lowers the bond strength of the film.

Etch rate regulators include N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 2-pyrrolidone, dimethylformamide, dimethyl acetamide, tetrahydrofuran, acetonitrile, dioxane, Polar solvents selected from the group consisting of alkyl lactates, alkyl glycolates, alkyl phosphates, ketones, alcohols and the like are used alone or in combination.

The etching rate control agent is used in the range of 0.1-30 wt%, preferably 0.1-20 wt%, more preferably 0.5-10 wt% based on the weight of the coating composition. When used below 0.1 wt%, the etching rate is not affected. When used above 30 wt%, the solubility of copper etched is significantly reduced.

Reaction accelerators include: persulfates such as ammonium, sodium, potassium peroxulate, monosulfates such as sodium, potassium peroxy monosulfate; Chlorides including chlorate and hydrochloric acid such as NaClO ₃ , KClO ₃ , NH ₄ Cl, FeCl ₃ , CuCl ₂ ; Nitrates or nitrates such as sodium nitrate, potassium nitrate, ammonium nitrate; Phosphoric acid or phosphate salts; Trivalent iron salts such as iron nitrate, iron sulfate and iron citrate; One or more compounds selected from the group consisting of are used in the range of 0.1-20 wt%, preferably 0.1-15 wt%, more preferably 0.5-10 wt%, based on the weight of the coating composition. When it is used below 0.1 wt%, reaction promoting effect is insignificant. When it is used above 20 wt%, the film color is blurred overall and it is difficult to obtain uniform color.

Stabilizers include chelating agents such as Nitrilo Triacetic Acid (NTA) and its metal salts, EDTA and its metal salts, DPTA and its metal salts, such as 0.1-20 g / l, preferably 1-5 g / l, based on the volume of the coating composition. Use in quantity.

If it is used below 0.1 g / l, the effect of protecting hydrogen peroxide is insignificant. If it is used above 20 g / l, the copper etching rate is significantly reduced.

The coating composition of the present invention is a substrate after washing and washing the inner layer substrate without the need to go through the soft-etching, acid treatment, reduction process that has been performed in the conventional blackening process of the multilayered printed circuit board (MLB) substrate When applied to, a black-brown film is formed in the copper circuit to impart acid resistance and lamination.

In addition, the coating composition of the present invention is applied to the surface treatment of the substrate, laser drill, roll coater, dry film adhesion, printed circuit ink or thermosetting ink to increase the adhesion.

Hereinafter, embodiments of the present invention will be described in detail.

The following examples were performed under general process conditions, and the concentration of each composition according to the change in the working conditions can be variously changed without particular limitation in a predetermined range, and the present invention is not limited to the following examples.

Example

In each of the following examples, 30 ml / l hydrogen peroxide and 5 ml / l sulfuric acid were degreased in HD 250 (alkaline degreasing agent) for 3 minutes at 50 ° C., followed by washing with water to protect the conversion coating composition and activating the copper surface. Pre-dip at 25 ° C. for 1 minute in a pre-preparation composition consisting of a mixture of 1 g / l phosphoric acid, 0.1 g / l acetic acid and 25 g / l 2-mercapto pyridine, followed by copper foil and laminate. To the core specimen (20 × 30 cm) was applied to each composition of the following Table 1-1 to Table 3-1 was subjected to the chemical coating treatment and the results are shown in Table 1-2 to 3-2.

After the treatment, the copper foil and the laminate cores were washed with water and dried at 100 ° C. for 30 minutes, and then laminated under the following conditions.

<Lamination Conditions>

2 pieces of prepreg 1080 (140 degrees Celsius Tg multifunctional epoxy resin)

Pressure 30kg / ㎠

Molding temperature 185 ℃

170 minutes

Meanwhile, after coating the copper foil and the laminated core specimens with the chemical conversion coating composition, the external circuit, the adhesive strength and the thermal shock of the printed circuit board were measured.

The appearance of the printed circuit board was visually observed.

The adhesive strength is formed by laminating a coated copper foil with one inner layer (CCL disc) and two upper and lower prepregs (1080), attaching a 1cm wide tape to the molding, and removing the copper foil. After cutting to prepare a specimen of 3cm length, after removing the tape and copper foil was measured by measuring the tensile strength of the specimen.

In addition, a thermal shock test was performed on the laminated core after lamination, and the thermal shock test was carried out for 20 seconds (1 second) for the specimens laminated in the 260 ° C and 288 ° C baths in which lead (Pb) was dissolved and the finished circuit board. Cycle, 260 ° C.), 10 seconds (1 cycle 288 ° C.) was deposited and suspended, followed by micro-section to observe whether the laminate was lifted or damaged with a metal microscope.

Example 1

After preparing the chemical conversion composition of Table 1a, the copper foil and laminate core specimens subjected to alkali degreasing and preliminary deposition treatment as described above were changed to the composition solution while changing the temperature of the chemical composition composition to 30 ° C, 35 ° C and 40 ° C for 3 minutes. It was immersed and subjected to chemical treatment. At this time, the composition liquid was stirred at a speed of about 0.1 m / sec.

Chemical Coating Composition ingredient Composition Sulfuric acid (98%) nitric acid (60%) propionic acid hydrogen peroxide (35%) 2-imidazolidinone silicic acid (Silicic Acid) pyrocateol N-methyl-2-pyrrolidone DPTA-5Na 50 ml / l5 g / l10 g / l45 ml / l60 g / l20 g / l10 g / l40 ml / l2 g / l

Processing result Item 30 ℃ 35 ℃ 40 ℃ Exterior Dark brown maroon maroon Adhesive strength 1.1 kg / cm ² 1.3 kg / cm ² 1.4 kg / cm ² Thermal shock Laminate lifting none none none Laminate damage none none none

As can be seen from the results of Table 1b, a brown oxide film having sufficient strength was formed by coating with the chemical conversion film composition according to the present invention, and there was no laminate lifting and damage.

Example 2

After preparing the chemical composition composition of Table 2a, the copper foil and the laminate core specimens subjected to the alkali degreasing and preliminary deposition as described in the Examples were coated while changing the coating treatment time to 2 minutes, 3 minutes, and 4 minutes. The results are shown in Table 2b below. At this time, the temperature of the coating liquid was fixed at 35 ° C., and the composition liquid was stirred at a speed of about 0.1 m / sec.

Chemical Coating Composition ingredient Composition Sulfuric acid (98%) Phosphoric acid (70%) Citric acid Hydrogen peroxide (35%) 1 H benzotriazole sodium silicate pyrogallol 2-pyrrolidone 50 ml / l4 g / l8 g / l40 ml / l50 g / l5 g / l15 g / l50 ml / l

Processing result Item 2 mins 3 mins 4 mins Exterior maroon maroon maroon Adhesive strength 1.1 kg / cm ² 1.3 kg / cm ² 1.4 kg / cm ² Thermal shock Laminate lifting none none none Laminate damage none none none

As can be seen from the results of Table 2b, a black-brown oxide film having sufficient strength was formed by chemical conversion coating with the chemical conversion composition according to the present invention, and there was no lamination lifting and lamination pores.

Example 3

After preparing the chemical composition composition of Table 3a, the pretreated copper foil and laminate core specimens were coated as described in the Examples, and the stirring conditions of the composition were changed to stagnation, 0.1 m / s and 0.2 m / s. The specimens were treated as they were, and the results are shown in Table 3b. At this time, the temperature of the coating liquid was fixed at 35 ℃ and the specimen was deposited for 3 minutes.

Chemical film composition ingredient Composition Sulfuric acid (98%) phosphoric acid (70%) acetic acid hydrogen peroxide (35%) 2-mercapto pyridine sodium silicate nitrile triacetate sodium salt dimethyl formamide 45 ml / l5 g / l1 g / l40 ml / l120 g / l5 g / l1.0 g / l30 ml / l

Processing result Item Identity Stirring (0.1m / s) Stirring (0.2m / s) Exterior maroon maroon maroon Adhesive strength 1.3 kg / cm ² 1.3 kg / cm ² 1.2 kg / cm ² Thermal shock Laminate lifting none none none Laminate damage none none none

As can be seen from the results of Table 3b, a brown oxide film of sufficient strength was formed by conversion coating with the conversion coating composition according to the present invention, and there was no lamination lift and laminate damage.

Example 4

For each of the following items, an environmental test was conducted on a printed circuit board subjected to chemical conversion using the chemical conversion composition according to the present invention.

In this example, 5% 250 ™ was used to wash for 3 to 5 minutes at 50 ° C, preliminary immersion at 40 to 50 ° C for 1 minute, and chemical conversion treatment at 40 ° C for 3 minutes. In addition, the process was performed as described in the said Example, and the prepositioned composition used the composition of Example 3 for the chemical conversion film composition for the Example, respectively.

In accordance with the JIS test standards, thermal stress-solder, air to air thermal cycle, liquid to liquid thermal shock, and high temp. And humidity test were performed. , And exhibited good characteristics of passing the physical properties required by the JIS test standard.

By using the chemical conversion coating composition for a printed circuit board according to the present invention, it is possible to perform blackening at a low temperature by a shortening process in a short time compared to the conventional blackening treatment, and also to the conversion coating composition according to the present invention. Treated printed circuit boards exhibit excellent acid resistance and adhesion strength. Furthermore, the elimination of the reduction treatment eliminates the use of expensive reduction treatment chemicals, which are conventionally used, and is more economical because the amount of wastewater generated is reduced by 50% or more.

Claims (18)

(1) sulfuric acid; (2) organic acids; (3) hydrogen peroxide; (4) nitrogen compounds; (5) silicon compounds; And (6) Conversion Coating Composition for Printed Circuit Boards consisting of at least one of film forming aids, etching rate control agents, reaction promoters and stabilizers According to claim 1, wherein the sulfuric acid is 0.1-30 v% based on the volume of the chemical conversion composition, the organic acid is 0.01-10 wt% based on the weight of the chemical conversion composition, the hydrogen peroxide is based on the volume of the chemical conversion composition 0.1-15 v%, wherein the nitrogen compound is 0.1-30 wt% based on the weight of the chemical composition, and the silicon compound is 0.01-10 wt% based on the weight of the chemical composition. Composition The method of claim 2, wherein the sulfuric acid is 1.0-15 v% based on the volume of the chemical conversion composition, the organic acid is 0.01-5.0 wt% based on the weight of the chemical conversion composition, the hydrogen peroxide is based on the volume of the chemical conversion composition 1.0-10 v%, wherein the nitrogen compound is 0.1-20 wt% based on the weight of the chemical composition, and the silicon compound is 0.1-5.0 wt% based on the weight of the chemical composition. Composition The composition of claim 3, wherein the organic acid is 0.05-2.5 wt% and the nitrogen compound is 0.5-15 wt% based on the weight of the chemical composition. The chemical film composition according to any one of claims 1 to 4, wherein the film forming aid is used at 0.1-20 wt% based on the weight of the chemical film composition. The chemical film composition of claim 5, wherein the film forming aid is used in an amount of 0.1-15 wt% based on the weight of the chemical film composition. The chemical film composition according to any one of claims 1 to 4, wherein the etching rate control agent is used at 0.1-30 wt% based on the weight of the chemical film composition. The chemical film composition of claim 7, wherein the etching rate control agent is used in an amount of 0.1-20 wt% based on the weight of the chemical film composition. The chemical film composition according to any one of claims 1 to 4, wherein the reaction accelerator is used in an amount of 0.1-20 wt% based on the weight of the chemical film composition. 10. The chemical composition of claim 9, wherein the reaction accelerator is used in an amount of 0.1-15 wt% based on the weight of the chemical composition. The chemical composition according to any one of claims 1 to 4, wherein the stabilizer is used at 0.1-20 g / l based on the volume of the chemical composition. The organic compound according to any one of claims 1 to 4, wherein the organic acid comprises at least one -COOH group such as acetic acid, propionic acid, glycolic acid, citric acid, tartaric acid, maleic acid, malonic acid, succinic acid, phthalic acid, benzoic acid, acrylic acid, and the like. Chemical coating composition, characterized in that selected from the group consisting of anhydride The compound according to any one of claims 1 to 4, wherein the nitrogen compound is selected from organic nitrogen compounds such as urea and thio-urea and derivatives thereof; Heterocyclic compounds containing nitrogen such as imidazole, triazole, thiazole and derivatives thereof; And a compound containing active nitrogen, such as = NH, -N =, -NH-, -NOH-, -N = N-, = N-S-N =, and the like. The silicon compound according to any one of claims 1 to 4, wherein the silicon compound is an inorganic silicon compound such as sodium silicate, silicic acid (H ₂ SiO ₃ ), silanol and -Rx-Si-, -Rx-Si-O. (Wherein R is an alkyl or hydrocarbon group a substituent of C _{1 to} C ₁₂ ), and the like. The chemical film composition of claim 1, wherein the composition is selected from the group consisting of organosilanes and derivatives thereof. The method of claim 5, wherein the encapsulation aid is hydroquinone (Hydro Quinone), Resorcinol (Resorcinol), Pyrocatehol (Pyrocatehol), Pyrogalol and derivatives thereof; Inorganic sulfur compounds such as ammonium salts and alkali metal salts of sulfur compounds; Sulfo Sulfonate, Thiocyanate salts, Thiourea and its derivatives, Thiophosphoric acid and its salts, Thioglycolic acid and its salts, Thiosulfate and Sulfonate A compound comprising a thio compound such as a compound) and an organic sulfur compound such as a mercapto compound. The method of claim 7, wherein the etch rate regulator N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 2-pyrrolidone, dimethylformamide, dimethyl acetamide, tetrahydrofuran Chemical composition, characterized in that it is selected from the group consisting of a polar solvent such as acetonitrile, dioxane, alkyl lactate, alkyl glycolate, alkyl phosphate, ketone and alcohol 10. The method of claim 9, wherein the reaction accelerator comprises: persulfates such as ammonium, sodium, potassium peroxulate, monosulfates such as sodium, potassium peroxy monosulfate; Chlorides including chlorate and hydrochloric acid such as NaClO ₃ , KClO ₃ , NH ₄ Cl, FeCl ₃ , CuCl ₂ ; Nitrates or nitrates such as sodium nitrate, potassium nitrate, ammonium nitrate; Phosphoric acid or phosphate salts; Chemical conversion coating composition, characterized in that it is selected from the group consisting of trivalent iron salts such as iron nitrate, iron sulfate, iron citrate 12. The chemical composition according to claim 11, wherein the stabilizer is selected from the group consisting of chelating agents such as Nitrilo Triacetic Acid (NTA) and its metal salts, EDTA and its metal salts, DPTA and its metal salts, and the like.