WO2022056527A1

WO2022056527A1 - High elongation electroless copper process

Info

Publication number: WO2022056527A1
Application number: PCT/US2021/071391
Authority: WO
Inventors: Roger Bernards
Original assignee: Macdermid Enthone Inc.
Priority date: 2020-09-11
Filing date: 2021-09-08
Publication date: 2022-03-17
Also published as: US20220081776A1; TW202210660A

Abstract

An electroless copper deposition composition, comprising: (a) a source of copper ions; (b) a chelator; (c) a source of alkalinity; (d) a reducing agent; (e) nickel ions; (f) a bipyridine; (g) optionally, an additional stabilizer; and (h) optionally, a water soluble polymer. The electroless copper deposition composition can be used to deposit a ductile copper deposit on a substrate that exhibits high % elongation and high tensile strength.

Description

HIGH ELONGATION ELECTROLESS COPPER PROCESS FIELD OF THE INVENTION [0001] The present invention relates generally to electroless copper plating solutions capable of producing ductile copper deposits and methods for producing ductile copper plating deposits by electroless copper plating. BACKGROUND OF THE INVENTION [0002] Electroless copper plating baths are widely used in metallization industries for depositing copper on various types of substrates. For example, in the manufacture of printed circuit boards, electroless copper baths are used to deposit copper on walls of through-holes and circuit paths as a base for subsequent electrolytic copper plating. Electroless copper plating is also used in the decorative plastics industry to deposit copper on non-conductive surfaces as a base for further plating of copper, nickel, gold, silver and other metals. [0003] Commercial electroless copper baths generally contain water-soluble divalent copper compounds, chelating agents or complexing agents, reducing agents, and various other additives to make the bath more stable, adjust the plating rate and brighten the copper deposit. [0004] In electronics manufacturing, electroless copper plating solutions can be used to deposit copper on printed circuit boards, chip carriers and semiconductor wafers as well as any other circuit carriers and interconnect devices. The copper plating solutions can be used in printed circuit boards and chip carriers, and also for semiconductor wafers, to plate surfaces, trenches, blind micro vias, through hole vias (through holes) and similar structures with copper, and can be used to deposit of copper on surfaces, in trenches, blind-micro-vias, through-hole-vias, and comparable structures in printed circuit boards, chips, carriers, wafers and various other interconnect devices. The term “through hole vias” or “through holes”, as used in the present invention, encompasses all kinds of through hole vias and includes so-called “through silicon vias” in silicon wafers. [0005] Electroless copper deposits plated over the walls of through-holes, vias, interconnects, etc. provides conductivity between surfaces of a board and/or between circuit layers. In additive circuit manufacture, in addition to providing conductivity between surfaces and/or circuit layers, the deposit also serves as the conductor lines. [0006] With increased circuit density, and with more rigorous specifications for circuit boards, the mechanical properties of a deposit become increasingly important, especially deposit ductility. For example, in the manufacture of electronic devices, it is necessary to solder components to a circuit board. The solder increases the temperature of the electroless deposit which causes it to expand and then contract with cooling. The coefficient of expansion of the copper differs from the coefficient of expansion of the surface over which the copper is plated. Therefore, stress is created in the copper which can cause cracking of the deposit, which can result in failure of the circuit board. [0007] Electroless copper is significantly less ductile than other forms of copper (i.e. such electrolytically deposited copper). For example, electroless copper deposits typically possess an elongations of about 0.5 to 3.5 percent while electrolytic copper, as used in the manufacture of through-hole printed circuit boards, typically possesses an elongate in the range of from about 6 to 15 percent. Thus, there remains a need int the art for improved electroless copper plating solutions that can produce a more ductile deposit for use in the manufacture of printed circuit boards and other similar substrates. [0008] In practice, current electroless copper solutions have only been capable of achieving an elongation percentage of about 2-3%, and no electroless copper systems (MID) electroless copper systems currently on the market has been able to offer high elongation. Thus, there remains a need in the art for an improved copper electroless plating bath and plating method that can achieve high % elongation and sufficient tensile strength. [0009] While there are commercial electroless copper baths that contains Ni ions, these baths typically also contain CN derivatives or EDTA, both which causes the Ni ion benefit to be minor, and that also require a high concentration of nickel metal ions (i.e., about 700-1000 ppm or more). [0010] For example, U.S. Pat. No.4,695,505 to Dutkewych, the subject matter of which is herein incorporated by reference in its entirety, describes an electroless copper deposit having an elongation capability of at least 10% by including a minor amount of a source of nickel ions and cyanide and/or ferrocyanide in the plating solution. Dutkewych suggests that with an adequate concentration of cyanide ions, an increase in elongation capability is realized when the nickel content is as low as about 5 ppm. However, Dutkewych requires that the composition contain cyanide ions in order to achieve the desired result which is not desirable from an environmental standpoint. [0011] Thus, there remains a need in the art for an improved electroless copper electroplating solution that can provide a ductile copper deposit exhibiting a % elongation of at least about 10%. In addition, there remain a need in the art for an improved copper electroplating solution that can provide a ductile copper deposit and that has both a cost and environmental benefit. SUMMARY OF THE INVENTION [0012] It is an object of the present invention to provide an improved electroless copper plating solution. [0013] It is another object of the present invention to provide an electroless copper plating solution that is capable of providing a ductile copper deposit on an underlying substrate. [0014] It is still another object of the present invention to provide a ductile copper deposit that exhibits high elongation and high tensile strength. [0015] It is still another object of the present invention to provide an electroless copper plating solution that is at least substantially free of cyanide and/or cyanide derivates and that is also at least substantially free of ethylenediaminetetraacetic acid (EDTA). [0016] It is still another object of the present invention to provide an electroless copper plating solution that is at least substantially free of any amino acids. [0017] It is still another object of the present invention to provide an electroless copper plating solution that includes only a minor amount of nickel in the plating solution. [0018] To that end, in one embodiment, the present invention relates generally to an electroless copper plating solution comprising: [0019] A) a source of copper ions; [0020] B) a chelator; [0021] C) a source of alkalinity; [0022] D) a reducing agent; [0023] E) nickel ions; [0024] F) a bipyridine; [0025] G) optionally, but preferably an additional stabilizer; and [0026] H) optionally, a water soluble polymer. [0027] In addition, the present invention also relates generally to a method of producing a ductile copper deposit on a substrate using the electroless copper plating solution described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0001] The inventors of the present invention have discovered an improved electroless copper electroless plating solution that can produce a ductile deposit on an underlying substrate. In one embodiment, the electroless copper deposit exhibits high elongation and high tensile strength. The electroless copper plating solution described herein is able to produce a deposit exhibiting such high elongation and high tensile strength without the use of undesirable additives. [0002] As used herein, “a,” “an,” and “the” refer to both singular and plural referents unless the context clearly dictates otherwise. [0001] As used herein, the term “about” refers to a measurable value such as a parameter, an amount, a temporal duration, and the like and is meant to include variations of +/-15% or less, preferably variations of +/-10% or less, more preferably variations of +/-5% or less, even more preferably variations of +/-1% or less, and still more preferably variations of +/-0.1% or less of and from the particularly recited value, in so far as such variations are appropriate to perform in the invention described herein. Furthermore, it is also to be understood that the value to which the modifier “about” refers is itself specifically disclosed herein. [0002] As used herein, spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, are used for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. It is further understood that the terms “front” and “back” are not intended to be limiting and are intended to be interchangeable where appropriate. [0003] As used herein, the terms “comprises” and/or “comprising,” specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. [0004] As used herein the term “substantially-free” or “essentially-free” if not otherwise defined herein for a particular element or compound means that a given element or compound is not detectable by ordinary analytical means that are well known to those skilled in the art of metal plating for bath analysis. Such methods typically include atomic absorption spectrometry, titration, UV-Vis analysis, secondary ion mass spectrometry, and other commonly available analytically methods. [0028] All amounts are percent by weight, unless otherwise noted. All numerical ranges are inclusive and combinable in any order except where it is logical that such numerical ranges are constrained to add up to 100%. [0029] The terms “plating” and “deposit” or “deposition” are used interchangeably throughout this specification. The terms “composition” and “bath” are used interchangeably throughout this specification. The term “alkyl”, unless otherwise described in the specification as having substituent groups, means an organic chemical group composed of only carbon and hydrogen and having a general formula: C_nH_2n+1. The term “average” is equivalent to the mean value of a sample. All amounts are percent by weight, unless otherwise noted. All numerical ranges are inclusive and combinable in any order except where it is logical that such numerical ranges are constrained to add up to 100%. [0030] The present invention relates generally to an electroless copper coating composition and a method of using the same to provide a copper deposit exhibiting desired physical properties of high elongation and high tensile strength that are much improved over standard electroless copper coatings currently in the market. The process is applicable in molded interconnect device (MID) applications where it is highly desirable that stray plating does not occur and that there should be good adhesion to the substrate. The electroless copper compositions described herein are also applicable in other processes including, for example, standard circuit board production and interconnect substrate production. [0031] It is desirable that the copper deposit produced has an elongation of greater that about 10%, more preferably greater than about 12%, even more preferably greater than about 14%, and even more preferably, greater than about 15% with a tensile strength of greater than about 30,000 psi, more preferably greater than about 40,000 psi, and even more preferably greater than about 50,000 psi as measured using ASTM E-345. Under these conditions, adhesion to the MID substrate is capable of passing industry standard tape tests according to IPC-TM-650-IPC Test Methods. In addition, electroless copper plating deposits produced by the methods described herein also exhibit minimal, and preferably no stray plating on MID substrates. [0032] In one embodiment, the electroless copper composition comprises: [0033] A) a source of copper ions; [0034] B) a chelator; [0035] C) a source of alkalinity; [0036] D) a reducing agent; [0037] E) nickel ions; [0038] F) a bipyridine; [0039] G) optionally, but preferably an additional stabilizer; and [0040] H) optionally, a water soluble polymer. [0041] The electroless copper composition described herein is an aqueous solution, meaning that the primary solvent of the solution is water. Optionally, additional liquids that are miscible with water, including alcohols and other polar organic liquids may also be added to the composition and would be usable in the compositions described herein. [0042] The source of copper ions may be any suitable copper salt, including copper chloride, copper sulfate, copper nitrate, copper oxide, and combinations of the foregoing. In one preferred embodiment, the source of copper ions is copper sulfate. In another preferred embodiment, the source of copper ions is copper chloride. The concentration of the Cu ion is generally in the range of about 0.1 to about 10 g/L, more preferably about 0.5 to about 4 g/L, and even more preferably, in the range of about 2 to about 4 g/L. [0043] Because simple copper salts are insoluble at a pH above about 4, a chelating system is needed, and various chelators can be in the electroless copper plating baths of the invention. Examples of chelators or chelating agents include tartaric acid and salts thereof, citric acid and salts thereof, malic acid and salts thereof, acetic acids and salts thereof and other similar compounds. In one preferred embodiment, the chelator is a salt of tartaric acid, such as a salt of tartaric acid containing one or both of sodium and potassium. In one preferred embodiment, the tartaric acid salt comprises sodium potassium tartrate. However, while historically ethylenediaminetetraacetic acid (EDTA) has been used as a chelator in electroless copper plating baths of the present invention, it is generally preferred that the electroless copper composition of the present invention be at least substantially free of EDTA, more preferably that the bath does not contain EDTA in any measurable amount. That is, because of the very high affinity of EDTA for any metal ions, even small residual amounts of EDTA can complex with metal ions, making it more difficult to treat the resulting waste stream. [0044] In one embodiment, the molar ratio of the complexing agents, related to the total molar amount of all complexing agents, to copper ions is in the range of 1:1 to 10:1, preferably 1:1 to 8:1, more preferably 1:1 to about 4:1. A molar ratio of 1:1 to 4:1 of complexing agent(s) to copper ions means about 1 to 4 equivalents of complexing agent(s) related to copper. [0045] The source of alkalinity may be any suitable source of alkalinity and is used in an amount sufficient to adjust the solution pH to between about 11.0 and 14.0, more preferably between about 12.0 and about 13.0. In one preferred embodiment, the source of alkalinity is a hydroxide, such as sodium hydroxide or potassium hydroxide. The amount needed to achieve the desired pH may be within the range of about 1 to 15 g/L, more preferably about 5 to about 10g/L. [0046] The reducing agent may be any suitable reducing agent that aids in reducing the copper ions in order to obtain metallic copper for plating. Reducing agents include, but are not limited to, aldehydes, such as, formaldehyde, formaldehyde precursors, formaldehyde derivatives, such as paraformaldehyde, borohydrides, such sodium borohydride, substituted borohydrides, boranes, such as dimethylamine borane (DMAB), saccharides, such as grape sugar (glucose), glucose, sorbitol, cellulose, cane sugar, mannitol and gluconolactone, hypophosphite and salts thereof, such as sodium hypophosphite, hydroquinone, catechol, resorcinol, quinol, pyrogallol, hydroxyquinol, phloroglucinol, guaiacol, gallic acid, glyoxylic acid, 3,4-dihydroxybenzoic acid, phenolsulfonic acid, cresolsulfonic acid, hydroquinonsulfonic acid, catecholsulfonic acid, tiron and salts of all of the foregoing reducing agents. Preferably, the reducing agents are chosen from formaldehyde, formaldehyde derivatives, formaldehyde precursors, borohydrides and hypophosphite and salts thereof, hydroquinone, catechol, resorcinol, and gallic acid. More preferably, the reducing agents are chosen from formaldehyde, formaldehyde derivatives, formaldehyde precursors, and sodium hypophosphite. Most preferably, the reducing agent is formaldehyde. The concentration of the reducing agent in the copper plating bath is preferably within the range of about 1g/L to about 15 g/L, more preferably about 2 g/L to about 10 g/L, and even more preferably about 3 g/L to about 8g/L. [0047] In addition, the electroless copper plating bath of the present invention should contain nickel metal ions in a sufficient amount to aid in increasing e the elongation of the copper deposit to above 10% elongation. Any source of nickel ions can be used in the practice of the invention. However, in one preferred embodiment, the source of nickel ions is nickel sulfate. The nickel ions are preferably present in the electroless copper plating bath of the invention in an amount between about 0.005 g/L to about 2 g/L nickel, more preferably between about 0.01 g/L to about 1.0 g/L, even more preferably between about 0.02 and about 0.04 g/L. [0048] In the preferred embodiment of the present invention even 10-15ppm of Ni ions is of great benefit to the physical properties and rate of the deposit. However, this benefit at low nickel ion concentrations can only be realized if the solution is essentially free of EDTA and cyanide or cyanide derivatives. Lower Ni metal ion concentration has a desirable cost and environmental benefit. [0049] The electroless copper plating baths described herein also include a dipyridyl as a stabilizing agent. In a preferred embodiment, the dipyridyl comprises 2,2’-dipyridyl. The concentration of the dipyridyl is typically within the range of about 0.001 g/L to about 0.05 g/L more preferably about 0.002 to about 0.05 g/L, most preferably about 0.003 to about 0.015 g/L. [0050] In a particularly preferred embodiment, the electroless copper plating bath of the invention includes a combination of nickel metal ions and 2,2’-dipyridyl, the combination of which has been found to produce an electroless copper plating deposit that exhibits the desired ductility (% elongation) and tensile strength described herein. [0051] In addition to the above bath constituents, the electroless copper plating solution may also comprise an additional stabilizing agent to further aid in stabilizing the plating solution against unwanted outplating (i.e., unwanted and/or uncontrolled deposition of copper, for example on the bottom of a reaction vessel or on other surfaces) in the bulk solution. This stabilizing function can be accomplished, for example, by substances that act as catalyst poison (e.g., sulfur or other chalcogenide containing compounds) or by compounds forming copper(I)-complexes, thus inhibiting the formation of copper(I)oxide. [0052] Suitable stabilizers include any stabilizer that is free of CN groups. In one preferred embodiment, the stabilizer is an organic compound containing divalent sulfur. Examples of suitable stabilizing agents include, but are not limited to, dithiobiuret, diethyldithiocarbamate, ammonium (or sodium or potassium) pyrrolidinethiocarbamate, thiomalic acid, and other similar compounds. However, any cyanide-free stabilizing agent or mixtures thereof that are capable of preventing decomposition of the copper electroless plating bath would be known to those skilled in the art and are usable in the compositions described herein. In addition, the stabilizing agent is also beneficially selected so that it does not significantly impact (i.e., decrease) the % elongation of the deposit. The concentration of the additional stabilizer is generally within the range of about 0.000005 g/L to about 0.01 g/L, more preferably about 0.00001 to about 0.0001 g/L, most preferably about 0.00002 g/L to about 0.00008 g/L. [0053] In one preferred embodiment, the electroless copper plating bath also comprises a water- soluble polymer. Suitable water-soluble polymers include those having a molecular weight of at least 300 g/mol. While it is not required that the bath composition contain the polymer, in a preferred embodiment, the bath contains the water-soluble polymer. One preferred polymer that may be used in the bath of the invention is methoxypolyethylene glycol. In a preferred embodiment, the methoxypolyethylene glycol has a molecular weight of at least 750 g/mol. This is preferred because it has a high enough molecular weight to increase % elongation, but if higher molecular weight methoxypolyethyleneglycol is utilized, the plating rate is slower which is less desirable. The concentration of the water-soluble polymer is generally within the range of about 0.01 g/L to about 1 g/L, more preferably about 0.05 to about 0.5 g/L, most preferably about 0.08 to about 0.15 g/L. [0054] Furthermore, it is also noted that polyethylene glycol (i.e., no methoxy) is not desirable because it lowers the elongation of the copper deposit. However, other polymers and surfactants that aid in increasing the elongation (or that do not have a detrimental effect) can also be employed. Other polymers include, for example: [0055] 1) Phosphate ester based surfactants, preferably moderate to low foaming varieties; [0056] 2) Block copolymers of PEG/PPG such as “Pluronic” and “Tetronic” (available from Dow); and [0057] 3) Other polymers identified to increase the elongation of the copper. [0058] In a preferred embodiment, the copper electroless solution should be essentially free of any cyanides, including NaCN, KCN, KFe(CN)₆, and K2Fe(CN)₆. The inventors have found that the presence of cyanide and cyanide derivatives in the bath can lower the elongation of the resulting deposit. [0059] In addition, the electroless copper plating baths described herein also do not require an amino acid in the bath to produce the desired % elongation. That is, to be clear, in one preferred embodiment of the invention, the electroless copper plating bath is free of any amino acid and contrary to certain prior art baths, the present invention does not require the presence of an amino acid to achieve the desired result. [0060] The present invention also relates generally to an electroless copper plating bath consisting essentially of: [0061] A) a source of copper ions; [0062] B) a chelator; [0063] C) a source of alkalinity; [0064] D) a reducing agent; [0065] E) nickel ions; [0066] F) a bipyridine; [0067] G) optionally, but preferably an additional stabilizer; and [0068] H) optionally, a water soluble polymer. [0069] By “consisting essentially of” what is meant is that the bath is free of any additional components that would have a detrimental effect on ductility, including % elongation and tensile strength. [0070] In still another preferred embodiment, the present invention relates generally to an electroless copper plating bath consisting of: [0071] A) a source of copper ions; [0072] B) a chelator; [0073] C) a source of alkalinity; [0074] D) a reducing agent; [0075] E) nickel ions; [0076] F) a bipyridine; [0077] G) optionally, but preferably an additional stabilizer; and [0078] H) optionally, a water soluble polymer. [0079] In still another embodiment, the present invention relates generally to a method of electrolessly depositing copper on a substrate, the method comprising the steps of: [0080] contacting the substrate with an electroless copper plating solution for a period of time to deposit copper on the substrate, the electroless copper plating solution comprising: i) a source of copper ions; ii) a chelator; iii) a source of alkalinity; iv) a reducing agent; v) nickel ions; vi) a bipyridine; vii) optionally, but preferably an additional stabilizer; and [0081] optionally, a water soluble polymer. [0082] Once use of the bath begins, copper, caustic and formaldehyde are consumed in the bath and must be replenished. This is routinely carried out and the bath may be analyzed manually or automatically in order to replenish the bath with a suitable replenishment chemistry. [0083] For example, the substrate may be dipped or immersed in the solution of the invention. In the process a whole surface of a substrate may be plated with copper, or only selected portions. [0084] The copper deposit produced in accordance with the present invention is able to obtain a % elongation of greater than about 10%, more preferably greater than about 12%, even more preferably greater than about 13%, and even greater than about 14%, and even greater than about 15%. [0085] At the same time, the tensile strength of the deposit is greater than about 30,000 psi, more preferably greater than about 40,000 psi, most preferably greater than about 50,000 psi. [0086] While not required, the process has a high plating rate at moderate temperatures, the presence of the Ni ions in the plating bath described herein (with no EDTA or CN or CN derivatives) increases the plating rate above what is obtained in other baths with no Ni ions. The rate advantage is especially apparent when comparing to other electroless copper baths that contain bipyridine. Normally bipyridine causes a lower rate in these types of electroless copper baths and the higher the bipyridine concentration the lower the plating rate. However, in the baths of the present invention, the use of bipyridine in the recited concentration range has virtually no effect on the plating rate. In addition, it was observed that the plating rate is higher than if the Ni ions were removed. So, the use of the Ni ions in the electroless copper plating bath of the instant invention provide two benefits – (1) a higher plating rate, and (2) improved physical properties of the deposit. The ability to obtain a high plating rate at lower temperature allows the bath to be operated at lower temperatures which increases the stability of this and any electroless copper bath. [0087] In one embodiment the solution is agitated during use, as would be known to those skilled in the art. [0088] The process is generally carried out for a sufficient time to yield a deposit of the desired thickness required, which depends on the particular application. [0089] In one embodiment, the substitute is a MID or a PCB. For example, the electroless deposition of copper according to the process of the invention can particularly be used for the through-plating of holes, surfaces, trenches, blind micro vias in printed circuit boards. Double sided or multilayer boards (rigid or flexible) may also be plated by means of the present invention. [0090] The process of the invention can be used to provide an electroless copper deposits with a thickness in the range of 0.05 to 10 μm depending on the substitute. [0091] Substrates used for printed circuit board manufacture are most frequently epoxy resins or epoxy glass composites. But other substances, notably phenolic resins, polytetrafluoroethylene (PTFE), polyimides polyphenyleneoxides, BT (bismaleintriazine)-resins, cyanate esters and polysulphones can be used. In addition, it is also contemplated that the process described herein can be used in a plating on plastics process to electrolessly deposit copper on substrates such as ABS. [0092] In one embodiment, the electroless plating process is carried out at a temperature in the range of about 20 to about 60°C, more preferably about room temperature (i.e., about 25°C) to about 55°C, even more preferably about room temperature to about 45°C. [0093] The plating rate is typically about 3 to 4 µm/hour at a temperature of about 40°C. Temperature and pH level can affect plating rate and can be adjusted if desired to adjust the plating rate. [0094] In a preferred embodiment, it is beneficial and thus desirable to control the plating rate while making the copper deposit at a constant rate. This can be accomplished, for example, by feeding the reaction chemicals with a chemical controller so that the deposition does not fluctuate (i.e., remains substantially constant) while the metal film is being deposited. [0095] The substrate, i.e. the surfaces of the substrate that are to be plated with copper, particularly non-metallic surfaces, may be pretreated to make the substrates more receptive or autocatalytic for copper deposition. In addition, all or only selected portions of a surface may be pretreated. However, a pretreatment is not necessary in every case and depends on the kind of substrate. Within the pretreatment step, it is also possible to sensitize substrates prior to the deposition of electroless copper on them. Which may be achieved by the adsorption of a catalyzing metal (i.e., a noble metal, such as palladium) onto the surface of the substrate. [0096] The pretreatment process depends various factors including the substrate, the desired application, and the desired properties of the copper surface. In one embodiment, the substrate comprises ABS, which has been doped with a copper chromite catalyst. When this doped ABS material is then ablated with a laser, the copper chromite catalyst concentrates on the surface and becomes active. Thus, plating only occurs where the material has been ablated and isolated traces of metal deposit onto the substrate. Therefore, no plating resist is required and a full-build electroless copper deposit directly forms the circuit where it was ablated. [0097] In another kind of pretreatment process a permanganate etching step is employed, which is a multi-stage process, the steps of which are a swelling step, a permanganate etching step and a reduction step. The sweller used in the swelling step is made of a mixture of organic solvents. During this step drill smear and other impurities are removed from the surfaces of the substrate. A high temperature of 60-80° C promotes the infiltration of the sweller which leads to a swelled surface. Therefore, a stronger attack of the subsequently applied permanganate solution is possible during the permanganate etching step. Afterwards the reduction solution of the reduction step removes the manganese dioxides produced during the permanganate step from the surfaces. The reduction solution contains a reducing agent and optionally a conditioner. [0098] The desmear process may be combined with the above described steps. The desmear process may be performed before step a) of the above described pretreatment process or the desmear process may be performed instead of steps a) and b) of the above described pretreatment process. [0099] The present invention will now be described with reference to the following non-limiting examples: [0100] In all of the examples below, the bath constituents are mixed together to form an aqueous electroless copper solution which is then used to deposit electroless copper on an ABS substrate by immersing the ABS substrate into the deposit for 270 minutes to provide an electroless copper deposit of about 13 µm on the substrates. The substrate is one that is first doped with a copper chromite catalyst and laser ablated. Thereafter, % elongation and tensile strength are measured using ASTM E-345 Standard Test Methods of Tension Testing of Metallic Foil IPC-TM-650 IPC Test Method. [0101] In addition a tape test was performed according to industry standards by using 3M® 600 tape, which is applied to the deposited copper film and then peeled off rapidly at 90 degrees. An observation is then made regarding whether the deposited copper film remains adhered to the surface or is removed. If the metallic film remains adhered to the surface, the metallic film is considered to pass the tape test. [0102] The results are summarized in Table 1. Example 1:

Example 2:

Example 3:

Example 4:

Example 5:

Example 6:

Comparative Example 1: [0103] In Comparative Example 1, the electroless copper solution was a standard electroless copper solution of MacDermid MID 100^TM electroless copper (available from MacDermid Enthone, Inc. Waterbury, CT) Comparative Example 2:

Comparative Example 3:

[0104] As set forth below in Table 1, the improved electroless copper plating bath of the present invention is able to produce a ductile copper deposit that exhibits a % elongation that is much higher than the % elongation that is achievable with electroless copper plating solutions of the prior art. Thus, it can be seen that the improved copper plating bath of the instant invention can produce a ductile copper deposit exhibiting a % elongation of greater than about 12.0 %, greater than about 13.0 %, greater than about 14.0 % and even greater than about 15.0 %. This result cannot be achieved with prior art electroless copper plating baths and certainly cannot provide the improved results in the absence of EDTA and CN. Table 1:

[0105] Finally , it should also be understood that the following claims are intended to cover all of the generic and specific features of the invention described herein and all statements of the scope of the invention that as a matter of language might fall there between.

Claims

WHAT IS CLAIMED IS: 1. An electroless copper deposition composition, comprising: a) a source of copper ions; b) a chelator; c) a source of alkalinity; d) a reducing agent; e) nickel ions; f) a bipyridine; g) optionally, an additional stabilizer; and h) optionally, a water soluble polymer.

2. The electroless copper deposition composition according to claim 1, wherein the source of copper ions is selected from the group consisting of copper chloride, copper sulfate, copper nitrate, copper oxide, and combinations of one or more of the foregoing.

3. The electroless copper deposition composition according to claim 1, wherein the chelator is selected from the group consisting of tartaric acid and salts thereof, citric acid and salts thereof, malic acid and salts thereof, acetic acids and salts thereof, and combinations of one or more of the foregoing.

4. The electroless copper deposition composition according to claim 3, wherein the chelator comprises potassium sodium tartrate.

5. The electroless copper deposition composition according to claim 1, wherein the reducing agent comprises formaldehyde.

6. The electroless copper deposition composition according to claim 1, wherein the bipyridine comprises 2,2-dipyridyl.

7. The electroless copper deposition composition according to claim 1, wherein the additional stabilizer is present in the electroless copper deposition composition and is selected from the group consisting of dithiobiuret, diethyldithiocarbamate, ammonium, sodium or potassium pyrrolidinethiocarbamate, thiomalic acid, and combinations of one or more of the foregoing.

8. The electroless copper deposition composition according to claim 7, wherein the additional stabilizer comprises dithiobiuret or thiomalic acid.

9. The electroless copper deposition composition according to claim 1, wherein the concentration of the nickel ions is in the range of about 0.02 to about 0.04 g/L and the concentration of the dipyridyl is in the range of about 0.001 to about 0.05 g/L.

10. The electroless copper deposition composition according to claim 1, wherein the water soluble polymer is present in the composition and comprises a methoxypolyethylene glycol.

11. The electroless copper deposition composition according to claim 1, wherein the composition is at least substantially free of ethylenediaminetetraacetic acid, cyanide, ferrocyanide, or cyanide derivatives.

12. The electroless copper deposition composition according to claim 1, wherein the composition contains no measurable concentration of ethylenediaminetetraacetic acid, cyanide, ferrocyanide or cyanide derivatives.

13. The electroless copper deposition composition according to claim 1, wherein the molar ratio of complexing agents to copper ions is in the range of about 1:1 to about 10:1.

14. An electroless copper plating bath consisting essentially of: a) a source of copper ions; b) a chelator; c) a source of alkalinity; d) a reducing agent; e) nickel ions; f) a bipyridine; g) optionally, but preferably an additional stabilizer; and h) optionally, a water soluble polymer, wherein the electroless copper plating bath is at least substantially free of ethylenediaminetetraacetic acid, cyanide, ferrocyanide or cyanide derivatives.

15. A method of electroless copper deposition, the method comprising the steps of: contacting the substrate with an electroless copper plating solution for a period of time to deposit copper on the substrate, the electroless copper plating solution comprising: a) a source of copper ions; b) a chelator; c) a source of alkalinity; d) a reducing agent; e) nickel ions; f) a bipyridine; g) optionally, but preferably an additional stabilizer; and h) optionally, a water soluble polymer.

16. The method according to claim 15, wherein the substrate comprises acrylonitrile butadiene styrene.

17. The method according to claim 16, wherein the substrate is doped with a copper chromite catalyst and laser ablated, wherein the electroless copper deposits on the laser ablated substrate.

18. The method according to claim 15, wherein the concentration of the nickel ions is in the range of about 0.02 to about 0.04 g/L and the concentration of the dipyridyl is in the range of about 0.001 to about 0.05 g/L.

19. The method according to claim 15, wherein the copper deposit exhibits a % elongation of at least 10%.

20. The method according to claim 15, wherein the copper deposit exhibits a % elongation of at least 12%.

21. The method according to claim 15, wherein the copper deposit exhibits a % elongation of at least 14%.

22. The method according to claim 15, wherein the electroless copper plating solution is at least substantially free of ethylenediaminetetraacetic acid, cyanide, ferrocyanide, or cyanide derivatives.