JPS58502101A - Electroless copper deposition solution - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Electroless copper deposition solution Background of the invention field of invention By using a non-formaldehyde reducing agent of the hypophosphite type, Formaldehyde and boron compounds commonly used in electroless steel plating TCW Substantial benefits are obtained over the more conventional classes of reducing agents, such as. death However, in the past, the use of hyponate-type reducing agents in electroless copper bath solutions was common. Practical industrial considerations for baths with pH values considerably above pH 5.0 It was limited to simple operations. Although the present invention uses a hypophosphite reducing agent, substantially The present invention relates to an improvement in electroless steel plating baths having a lower H operating range.

Description of prior art Prior to the recent introduction of the hypophosphite electroless copper baths mentioned above, many industrial copper High degree of inclusion of formaldehyde as the sole reducing agent in electroless deposition practices An alkaline complexed cupric solution was used.

Due to the volatility of formaldehyde and the well-known uneconomical side reaction, form Aldehyde trends and relative long-term relationships of formaldehyde-containing copper plating solutions chemical instability has prompted the industry to explore non-formaldehyde plating solutions. I came.

U.S. Patent Application No. 909,209 describes electroless plating of copper on a nonconductor. One of the things that makes it possible to put hypophosphite reducing agents into practical use industrially Making the first disclosure. The patent application specification describes hypophosphite type electroless steel plating. Prior art relating to solutions is extensively dealt with, the disclosure of which is incorporated herein by reference. Incorporate it into the book. Essentially, hypophosphite is used to remove nickel in electroless plating operations. Although it was widely recognized industrially that copper can be deposited by electroless plating, In particular, to the best of the inventor's knowledge, the use of hypophosphite agents , there are no industrial methods that have been successfully used. 5.0 to 13 in the patent application specification. , by maintaining a specific complexing agent/pH relationship in copper baths with pH values up to 0. and that copper plating using a hypophosphite reducing agent is practical and that the method is It is disclosed that it has advantages over commercial operations.

However, in the aforementioned U.S. Patent Application No. 909,209, p At the H value, there is virtually no copper precipitate7, or the precipitate is conductive. In most cases, it is either in the form of a powder, or both. It teaches that it has no utility. Reach the above conclusion 4. Another side A bad situation is when you take a bath. aO°~1. ! Temperatures in the SO'F range were controlled. The appearance of precipitates in cases. Operation of the bath at this temperature will result in a deposited copper film. It is desired to minimize the voids in the Conventionally, when the pH value is 5 or less, Most commercially available organic chelates Poor coating conductivity and low solution stability due to ineffectiveness of agents The possibility of overcoming these obstacles was thought to be almost non-existent. Said patent application details In Book 2, numerous examples demonstrate the basis for the conclusion reached earlier. The following are representative examples: Table A Example 9.10.11.12 Table B Example 30, filtration 1, filtration 2.3 Table C Example 51.52.5, 5A Table Example 64.65.66.67 In the prior art, hypophosphite-based low pH (5) T) To the extent that the applicant has knowledge regarding all electroless steel plating baths. Additionally, the bath described above does not contain a cleaning agent. A suitable flll is oxidized second Composition of copper, ammonium sulfate or ammonium chloride, and sodium hypophosphate No. 6,0.16.159, which discloses a product. This bath operation The operating pH is set at 0, and the operating temperature is set at 9°C (20°C). . However, in carrying out the invention according to the teachings of the patent specification, The precipitate is powder-like, has poor adhesion, has low conductivity, and may continue to If an attempt is made to form the deposit to a useful thickness by electroplating techniques, It's completely burnt.

A single document, IBM Technical Disclosure Bulletin (IBM) Technical Disclosure Bulletin), Volume 12 , No. 2, July 1969, U.S. Patent No. 3. OA No. 6,159 Specification Baths exactly similar to those described in 2006 produced deposited films whose conductivity was not very high. We have confirmed that The report describes the use of ``plating'' to create a conductive layer. "Continued in a alkaline electroless copper bath", i.e. conventional formaldehyde Containing baths are recommended.

Another document, U.S. Pat. No. 650,777, describes acidic electrolytic A brief mention is made of the possible use of hypophosphites in plating baths (Chapter 1). (see column 2, lines 15-17), but there is no instruction on how to achieve this. An example of a bath illustrating carrying out some reduction may be None have been given.

Therefore, in short, the patent specifications and technical literature to date mainly focus on low pH values. The difficulty of contemplating the use of hypophosphite as a reducing agent for electroless steel plating The prior art teachings regarding difficulties are explained, and the conclusions presented are based on the main difficulties is a powdery copper film with poor conductivity and a large amount of precipitated insoluble particles. This was to make the above baths impracticable.

Summary of the invention The present invention provides that the hypophosphite reducing agent is effective against divalent copper at a bath pH of about 2.0 to 5. is usefully used as a reducing agent to produce a conductive material on a suitably catalyzed nonconducting substrate. relating to the discovery that copper 7 films can be produced. copper like this The precipitate has good conductivity, giving the precipitate good adhesion to the substrate, and Serves as an excellent substrate for further electrolytic deposition of additional copper or other metals fulfill.

The undesirable results that create difficulties in the prior art teachings are primarily due to Chlorine ions introduced by using cupric chloride as the main copper-containing component of It was discovered that the cause was the presence of on in the bath. Bromine in the bath composition, Other anions such as iodine, fluorine and acetate also base hypophosphite. Conductive copper film in the pH range of 2 to 5 in a copper metallisong solution Similarly, the precipitation of

Of course, if you select an appropriate complexing agent that provides some coordination to copper in this pH range, There is another necessary condition.

Chloride ions and the other ions mentioned above It is currently not known exactly why the song bath interferes with its normal function. these Interfering ions stabilize and react regardless of the cuprous state: Cu++e−+CuO It is theorized that this makes the process even more dynamically difficult.

However, this is just a hypothesis, and the important discovery of the present invention is that these bath solutions Knowing the harmful effects of certain anions in liquids, one skilled in the art can now In electroless copper plating baths operating at pH values below 5.0, i.e. This means that it is possible to select ingredients that allow the use of phosphite reducing agents. be.

Description of preferred embodiments Plating solutions embodying the concepts of the present invention are of the usual major component category, namely Raw materials for steel ions and solvents for them, usually water; complexing agents or mixtures thereof and hypophosphite reducing agents.

The most effective complexing agent currently known for use in the electroless copper baths of this invention is N-hydroxy Ethylethylenediaminetriacetic acid (HEF, DTA), ethylenediamine Tetraacetic acid (EDTA), nitrilotriacetic acid (NT8) and these alkali It is a metal salt. These complexing agents require no dissolved harmful anions. conductive material on a suitably catalyzed non-conductive substrate at a pH of 2 to 6.5. Forms an electroconductive copper film.

The main area for introducing interfering anions into the plating solution is the copper used (cupric ions). ) is the raw material for We use cupric sulfates, nitrates or fluoroborates In contrast, 7~locations such as cupric chloride, bromide, etc. oxides, and acetates are electrically conductive when they are present in significant amounts in solution. We have discovered that it should be avoided because it does not cause the copper film to be deposited.

In order to keep the pH within a suitable range, lowering the pH by adding sulfuric acid and hydroxide Signs such as raising the pH by adding sodium-11um or potassium hydroxide Acid adjustment or alkali adjustment may be employed. However, harmful anio An acid or base, such as hydrochloric acid, is introduced to keep the bath operable. should be avoided.

The concentrations of the various components may have a wide range, and may be within a range that produces suitable conditions. can be optimized. @Understood like EDT8 and HEEDTA The concentration of the amine complexing agent is preferably in molar ratio based on cupric ion. On the other hand, in ■, the A complexing agent has a molar ratio based on the cupric ion. The ratio is preferably 2:1. Of course, if the amount of complexing agent is small, some unleaded copper will remain. Ru. This is because particle precipitation interferes with the desired gloss, smoothness, etc. in the final plating. If it is not sufficient to meet the requirements, it can be tolerated within the limits. of the higher ratio There are no problems on the side. Because an excess of complexing agent does not interfere with the operation of the bath. In fact, slight excesses may occur during the bath refilling operation, such as temporary, localized This is because it may be useful for adjusting high copper concentration conditions.

Sodium hypophosphite is the most easily available hypophosphite raw material. and is therefore a preferred form of the reducing agent of the present invention. However, hypophosphorus Acids are also effective, along with pH adjusters that may be necessary when using these acids. It can be used for.

The optimum level of concentration is sufficient to obtain a suitable copper coating. @understand Although operations using large excesses of reducing agent normally do not interfere with bath operation, There is no profit to be made.

The following examples demonstrate preferred conditions for practicing the invention.

Example 1 Typical processed parts consisting of automobile parts molded from Shibuyo's industrial plating grade ABS. First, clean the surface to remove dirt, oil, etc. In this case, typically Use a caustic cleaning solution. This is followed by using mixed chromium sulfate or Chemical corrosion is carried out using only chromic acid, which is also customary in industry. .

Typical operating conditions, degrees and processing times are as follows: U.S. Pat. to act. This uses a commercially available type of mixed palladium/tin catalyst. Be able to achieve this through the "Process" method. Such catalysts, along with their usage It is disclosed in US Pat. No. 652,518. The catalyst was allowed to act. After cleaning, the workpiece is then treated with a so-called "accelerating bath". 5 solution) Put it in J. Again, for example, U.S. Pat. , 652,518. can do. Such accelerator baths generally consist of acid bath liquids. sodium hydroxide Alkaline promoters such as IJum baths have also been used to advantage.

The workpiece is then further cleaned and then prepared for copper plating. In this example The new copper bath used in this process has the following composition: Cu, SO4・5H20o, o 4 M Hamp-〇T-(HEED TA) 0, 05 MNaH2PO2’H200,64M water PH adjuster (H2SO, /Na0H) Keep pH 6 bath at 155"FC68°C) When the workpiece is immersed in it for 10 minutes, the thickness of the copper plating obtained is 1 It is 1 microinch. At 0 minutes of filtration, the thickness of the precipitate was 24 microinches. Ru. The precipitate has a bright pink color and visual characteristics indicate good electrical conductivity. catalytic The coating on the surface is complete, the deposits are well adhered, and there are no bubbles or roughness. It does not have any characteristics. This electroless plated substrate is cleaned and then, for example, in US Pat. , No. 203,878, No. 257,294, No. 267,010, or No. 6,288,690. Put it in a copper strike bath. Initially about 20 per square foot at about 2 volts Electroplating is carried out at ampere speeds. Generally this condition is maintained for about 1 1/2 minutes or Maintain until the deposit thickness is sufficient to provide greater current carrying capacity. the At a time when the plating rate is, for example, AO amps per square foot, The voltage can be increased to about 4 volts and continued until the total required thickness of copper is achieved. child The workpiece may be required for some specific application, so it may be necessary to Further electroplating of nickel, chromium, and gold using the technique Can be done. Many of the limitations on initial current density are based on the effective The amount of rank contact area is related to part size and physical bale roughness. ten If sufficient contact is utilized, the need to monitor the initial current density becomes almost critical. isn't it.

However, manufacturing experience shows that moderate rank contact is not always found. .

The peel strength test for plated workpieces obtained from the bath according to this example was , exhibits an adhesion value of approximately 8 to 10 bonds per inch for copper deposits on ABS substrates. vinegar. Does polyphenylene oxide have similar hydropeel strength? Repro t-ren etc. Including other thermoplastic substrates as well as thermosets such as phenolics, epoxies, etc. Obtained for chemically resistant substrates.

Example■ Identical in all respects to the bath of the previous example except that a different complexing agent is used. Prepare an electroless copper bath.

In this case, the complexing agent is Hapen (Ha) at the same concentration (0.05M) as in the above example. mpene) Na, (Te, Torasodium EDTA), and the PH is In the case of 11 micro inches in 10 minutes at a bath temperature of 155 cm A colored electroless copper deposit was obtained which increased to 25 microinches in 30 minutes. . The coating of the workpiece is completed on the catalyzed surface and the deposits are free of bubbles and roughness. Moreover, it adheres well to the board without any problems. The precipitate forms the desired total thickness. Forms an excellent base for metal plating on top. in that way ゛In the case of plating, the adhesion test conducted on the BSi plate plated according to this example Tests show peel strengths ranging from 8 to 10 bonds per inch.

Example■ Another ABS workpiece is prepared as described above for electroless plating. child In the case of an electroless copper bath, the complexing agent is now 0.10 M Nido II lotriacetic acid (NT A) Identical again to the bath of Example 1 with one exception. 1 in a solution of pH 3 Bright pink adhesion of 14 microinches in 0 minutes and 27 microinches in 60 minutes of copper precipitates are obtained. Add additional copper, nickel or metal to form the desired thickness. After further plating with ROM etc., 8 to 10 bons per inch for ABS. The adhesion value of the peel strength is shown.

Another ABS processed part was prepared for electroless plating as described in Example 1. make In this case, the electroless copper bath has a copper salt of O, CI 4M, fluoroboric acid. Example 1 again except that it is steel (copper fluoroborate). Same as bath. In the bath liquid of the PH filtration, 14 - 29 microinches of light pink, adherent copper deposit is obtained in 0 minutes. desired thickness Further plating with additional copper, nickel or chromium etc. (1, A peel strength adhesion value of 8 to 10 bonds per inch is shown for p and Bs.

Another ABS processed part is prepared. In this case, the copper salt in the electroless copper bath is 0. 04M boron fluoride 1 [-identical to the bath of Example H with certain exceptions. PH Rono 12 microinches in 10 minutes in bath liquid, 26 microinches in 0 minutes in filtration A light pink, adherent copper deposit is obtained. Additional copper, nickel to achieve desired thickness. After further plating with Kel or chrome, 8 to 1 inch per inch for ABs. For electroless plating as described in Example 1, adhesion value of peel strength of 10 d, Another ABS workpiece is prepared. In this case, the electroless copper bath contains 0 copper salt. ．． The bath is again identical to that of Example 1, except that the bath is copper nitrate at port 41vi. PH3 12 microinches of well-adherent pink copper deposits in 10 minutes in bath solution is obtained. with additional copper, nickel or chromium etc. to achieve the desired thickness. After further plating, it has a peel strength of 8 to 1 o bond per inch to ABS. The closing price is shown.

Example■ Another ABS workpiece was prepared for electroless plating as described in Example 1. make In this case, the electroless copper bath is used except that the copper salt is O.04M chloride steel. The bath is again the same as that of Example 1. Copper film conductive in PH3 solution I couldn't get it.

Example h Another ABS workpiece was prepared for electroless plating as described in Example 1. make The electroless copper bath in this case is that the copper salt is 0.04M copper acetate. The bath is again identical to that of Example 1 with the following exceptions. dark on the workpiece in a solution of PH3. A dark brown film is formed. The coating was not appreciably conductive and subsequently was not useful for electroplating.

Example■ Another ABS workpiece was prepared for electroless plating as described in Example 1. make In this case, the copper salt in the electroless copper bath is 0.04M copper bromide. Again the same as Example 1 except. Conductive copper coating in pH 6 bath solution I couldn't get it.

To illustrate the effect of the actual concentration of key bath components such as copper concentration and reducing agent concentration A summary of the results along this line is shown in Table A. This table varies widely A good pink conductive copper film was still obtained using different copper and reducing agent concentrations. to show that This applies to industrial equipment where various parameters are experienced. That's a plus advantage.

Table A A, 04. 05. 17 6.0 10 9 155 Pink B 1 bite 4. 0 5. 17 ro, 0 ro 0 29 155 c, 04. 05, Rod 3 ．． 0 10 12 155 #D, 04. 05, ro 4 ro, 0 ro 0 2 0 155 E, 04. 05. 51 6.010 9 155 #F , 04. 05. 51 ro, 030 16 155 a, 08. 10 ．． 17 6.010 8 155 ff King, 08. 10, ro 4 ro, oi o i4 155 Pink J, 08. 10 -34 31 mouths 30 22 15 5 K, 08. 10. 51 filter 1 mouth 10 11 155 #L, 08 ．． 10.51, 030211551Tlvi, 12. 15. 17 ro, 010 8 155 #o, 12', 15, ro 4 3.0101 ro 155 Pink p, 12. 15. 34 ro, 0 ro 0 26 155 nq , 12. 15.51 s, olo 13155 nR, 12, 15, 51ro , 030 23 155.

Experiments were conducted to determine the PH parameters for various viable anions.

Generally, the optimum pH seems to be about 6, with a practical range of about 2.0 to 6.5. It is.

The stability of the bath begins to decrease as the pH drops from 6 to 2, with pH around 260-2. In step 5, air agitation ( We have discovered that oxygen stabilization) is necessary. Complexation at pH below 2 It seems that the agent stops coordinating with copper, and in fact, at pH below 2, EDTA becomes a solution. It precipitates. As the pH increases from 6 to 6.5, the deposited copper film begins to darken. Finally, at pH 6.5 or above, the formed film turns brown, and then becomes black. color, making it unsuitable for subsequent electroplating.

The data presented in the previous examples are based on conventional formaldehyde-type electroless A plateable grade ABS substrate used for plating plastics with a copper bath. It is based on usage. Noryl (polyphenyleneoxy) (d) and its molded form of endothermic plastic material such as polypropylene. Tests conducted on other substrates have shown that the bath of the present invention is also fully applicable to them. to show that Also, phenol-formaldehyde type and epoxy type thermosetting Thermosetting substrates are also suitable for this invention, as are other types of thermosetting plastics. Can be plated in a bright bath.

The invention relates to plating on plastics, i.e. plated parts or processed parts. Applications where the workpiece needs to have a metallic finish for decorative or protective purposes. It can be particularly applied to The parts of automobiles, instruments, and old objects must be This is an area where more applications will occur. In such applications, electroless deposition is the first step. A thin deposit of copper is then made by a selective electrodeposition procedure, e.g. copper, nickel. Additional thicknesses of chrome, chrome or other metals can be added more quickly and economically. It is usually most practical to be able to add This invention Phosphite-reduced electrolytic copper baths are particularly suitable for such applications. This method copper plating on a palladium/tin catalyzed plastic substrate. The plating rate is initially fast but slows down as the copper thickness increases. This (yo) The copper deposits formed in the bath must be catalyzed by the palladium/tin to the system. In some cases, conductive copper coach ink may occur due to Useful in situations that require a pinch. Because in the new bath Remove all excess plates on tank walls, ranks, heater coils, etc. plate-out is unique Qτ self-limiting tiJ, thus eliminating extra plate outs, tank cleaning problems and latitude. This is because link maintenance problems are reduced.

Fishing equipment on the surface of the substrate, especially plating fishing equipment on plastic construction items, should not be exposed. The above-mentioned chromium sulfuric acid corrosion or total chromic acid corrosion on plastic surfaces Generally encompasses procedures. However, the copper bath of the present invention may be used, for example, in U.S. Pat. Waterbury, Conn., as disclosed in No. 620,9 Rollo. City Rank MacDermid Inco. Printed layout board using PLADD method of Rporatea It can be used for. In this method, a different A substrate preparation is used. In this example, the workpiece in this case is printed. It was originally made of epoxy resin reinforced with glass fiber. It takes the form of an unfinished laminate consisting of aluminum foil glued to a substrate. Distribution To manufacture wire sheets, this unfinished laminate is placed in a hydrochloric acid bath to remove the aluminum foil. A particularly suitable tree for chemically stripping away and accepting subsequent electroless metal deposition. Leave the surface of the greasy substrate. This preliminary operation is an alternative to the chromium sulfuric acid corrosion process described earlier. It is something to do. The peeled substrate was carefully cleaned (after cleaning) with the paste described in Example 1. The catalyst is worked up following the same procedure as for the radium-tin catalyst. The touch The mediumized wiring board was then laminated using the same copper solution as in the previous example. forceps] to plate. This creates a thin copper deposit over the entire surface of the substrate. . Next, screening is performed to form the desired printed wiring. ing), photopolymerization development (phOtopolymeric development) Apply a mask or anticorrosive agent as in step t). then The first electroless deposit is used as a "busbar" to remove the mask in an electrolytic bath. Re-plating the board (which required thin plating) and removing the mask of the wiring board. Increase the thickness of the metal in the dark areas. The anticorrosive agent or mask is then chemically dissolved in a bath. However, the wiring board is manufactured using the method disclosed in U.S. Pat. No. 466,208. A thin film, previously coated with an anti-corrosion agent, is placed in a suitable copper corrosion solution such as The electroplating bath was made up of an odor that was sufficient to remove the initial copper deposits. Insufficient to remove substantially thicker copper (or other metal) trace formation areas for a period of time. This technology is widely used in the industry (often semiaddicted in C). This is called the Sem1-a(l]l txve) method.

Similarly, the present invention interconnects conductive areas on opposite surfaces of standard copper foil laminates. Reduction e(,・ qbtra・~tive) It is also possible to apply it to the J procedure. The unfinished acid vinegar.

The copper solution of the present invention is used after drilling holes in the wire board and catalyzing the board appropriately. Then, the walls of the through holes are electrolessly plated with copper. If desired, remove wall deposits. Additional thickness can be increased by electrolytic deposition.

Apply anti-corrosion agent to form the prescribed trace pattern, then remove all exposed copper. It corrodes away, leaving traces of wiring patterns and interconnecting holes. The anti-corrosion agent is applied to circuit connectors. For further plating such as gold plating, solder coating etc. It may or may not be removed depending on your needs.

Although we have described in detail the specific disaster modes of non-invention above, these It should be understood that this is primarily for illustrative purposes. As would be obvious to a person skilled in the art For specific conditions and components disclosed herein and consistent with the teachings thereof, Improvement 2 can be made to suit the application.

Border investigation report

Claims (1)

[Claims] 1. It is an electroless copper deposition solution that contains, in addition to water, a soluble raw material of cupric ions, A complex effective to keep the cupric ion in solution at pH levels below 5.0 a catalyzing agent which, when in contact with said solution, catalyzes cupric ions into the substrate to be catalyzed. It is useful for reducing deposited conductive metal films on non-conductive surfaces to copper. In this case, the reducing agent is a soluble raw material of hypophosphite ion. Yes; the solution has a pH of about 2.0 to 6.5, and the complexing agent is removed from the solution. Coordinating with the cupric ion within a range that prevents precipitation of the copper ion. in which the solution, if present, is producing the conductive copper film on the catalyzed surface of the substrate placed in contact with the liquid; A significant concentration that prevents the reduction of cupric ions by the hypophosphite reducing agent to An electroless copper deposition bath liquid characterized in that it does not contain any anions. 2. The bath liquid substantially contains interfering ions of the group consisting of halocenides and acetates. The electroless copper deposition solution according to claim 1, wherein the electroless copper deposition solution does not contain. 3. The complexing agent is selected from the group consisting of HEEDTA, EDTA and NTA. An electroless copper deposition bath solution according to claim 2. 4. The soluble raw materials for the cupric ion are mixed with cupric sulfate, cupric fluoroborate and a selected from the group consisting of cupric nitrate; a electroless according to claim 2 or 3; Copper precipitation solution. 5. The molar ratio of HEEDTA and EDTA to cupric ions is about 1:1, but 7. The electroless electroless material of claim 6, wherein the molar ratio of NTA to cupric ions is about 2:1. Copper precipitation bath solution. 6. Prepare the substrate surface to make it better accept plating. In addition to water, a soluble source of cupric ions and a pH level below 5.0 are added. a complexing agent effective for keeping cupric ions in a dissolved state and in contact with the bath liquid; When the cupric ions are present, the cupric ions are allowed to precipitate on the prepared substrate surface. and a reducing agent effective for reducing copper as an electrically conductive metal film, in which case the above-mentioned The reducing agent is a soluble raw material of hypophosphite ion. to use the complexing agent to complex the cupric ions in water fishing with a pH of 2 to 6.5; and, if present, the previous Depletion of cupric ions by the hypophosphite reducing agent to produce a conductive copper film. maintaining said bath liquid free of significant concentrations of anions that would interfere with reduction; A method for electrolessly depositing copper plating on a substrate surface, including each step. Z　The above-mentioned eyelid liquid is treated with interfering anions of the group consisting of lodenide and vinegar acupuncture salt. A copper film is formed on the surface of the substrate according to claim 6, which is maintained in a state in which it is substantially free of Akane. A method of electroless deposition. 8. The complexing agent is selected from the group consisting of HEgDTA, EDTA and NT8. A method for electrolessly depositing a copper film on a substrate surface according to claim 7. 9 The soluble raw materials for cupric io/ are mixed with cupric sulfate, cupric fluoroborate and On the surface of the substrate according to claim 7 or 8, which is selected from the group consisting of cupric acid. A method of depositing a copper film electrolessly. 10, the molar ratio of HEEDTA and EDTA to cupric ions is approximately 1:1, and 9. The group of claim 8, wherein the molar ratio of NTA to cupric ion is about 2:1. A method of electrolessly depositing a copper film on the surface of a plate.