ELECTROLESS COPPER DEPOSITION SOLUTIONS

Abstract: Suitably complexed cupric solutions can deposit conductive copper films electrolessly on properly catalyzed non-conductive substrates, at plating bath pH values in the range of about 2.0 to 3.5, using a non-formaldehyde reducer such as hypophosphite. Certain conditions are critical to successful results: (1) ability of the complexer selected to chelate copper at pH values of 2.0 to 3.5 at elevated temperatures (140<o> to 160<o>F); (2) avoidance of certain anions, such as halides and acetates, in significant concentrations in the plating solution; and (3) provision of an "active" catalytic surface on the non-conductive substrate.

Description: ELECTROLESS COPPER DEPOSITION SOLUTIONS BACKGROUND OF THE INVENTION • .Field of the ' Invention The use of non-formaldehyde reducing agents of fp3 the " hypophosphite ' type provide substantial advan- tage over some ' of the more conventional reducing agents, such as formaldehyde and the boro compounds, heretofore used almost exclusively in electroless copper plating. The use of hypophosphite type reducing agents in electro less copper solutions heretofore has, however, been restricted in practical commercial plating operations . to baths of pH values ' generally well in excess of pH 5.0. This invention relates to improvements in electro¬ less copper plating baths employing hypophosphite reducing agents, but having substantially lower pH operating ranges ' . Oescripfion of the ' Prior " Art .The ' predominant commercial practice in electro- • ' less deposition of copper " , prior, to the recent .introduc- . tion of the hypophosphite electroless copper baths mentioned above, " uses ' highly alkaline, complexed cupric solutions containing formaldehyde as the sole reducer. The volatility of formaldehyde, and .its tendency, to undergo the * well-known, wasteful, Cannizzaro side reaction, and the long-term relative instability of formaldehyde-bearing copper plating solutions, have prompted .the art to search for non-formaldehyde plating solutions. v U.S. Patent Application Ser. No. 909,209 provides one of the first disclosures enabling commer- cially practical use " of hypophosphite reducing agents in elec ' trolessly plating copper onto non-conductors. That application deals extensively with what prior art there ' is relating to hypophosphite-type electroless copper plating solutions, and that disclosure is incor- porated herein by reference. Essentially, it was . that while • " hypophosphite has gained industry-wide . acceptance for depositing nickel in electroless plating operations, .there were no ' commercial processes being successfully used to the ' inventors' knowledge in which • 5 hypophosphite agents were employed to electrolessly . plate copper " . .It is disclosed in that application that by maintaining a specified complexer/pH relationship in . the copper bath at pH values ' of 5.0 to 13.0, plating of copper with " hypophosphite reducing agents is practical, 10 and that the " system " has advantages ' for commercial operations. ' • . • --. .It Is taught in Application Ser. No. 909,209, however ' / , that t pH values below 5 copper deposition is virtually absent or is of little usefulness because the 5 deposit 'has poor conductivity, is powdery, or both. Anothe troublesome complication that led to the foregoi conclusion is the appearance of a precipitate when the bath is heated to temperatures " in the range of 140°- to 160°F. Operation of a bath .at this temperature is 0 desired to. minimize voids in the " copper film deposited. .It was previously believed that because of the inef ' fec- . tivehes ' s of most .commercial.organic chelating agents to .strongly coordinate " copper ions in solution .at pH values ' below 5,. there was little chance to overcome the 5 difficulties ' of poor coating conductivity and low " - solution.-stability. In the aforesaid application, numerous examples ' document the " basis for previously reaching, that*conclusion,, the following being .represent¬ ative: " ..* • - 0 Table A Ex. 9, 10, 11, 12 ' Table B Ex. 30, 31, 32, 33 Table C * Ex. 51, 52, 53, 54 Table D Ex. 64, .65, 66, 67 To the ' extent that applicant can find in the 5 prior art any reference tα_hypophosphite-based, low pH (5 or less) electroless copper plating baths, such baths do not contain chelating agents. A case in poin is U.S. Patent No. 3,046,159 disclosing compositions o cupric oxide, ' .ammonium sulfate or chloride, and sodium hypophosphite. ' The operating pH of the T_>ath is given as 3.0; the operating temperature is given as 93°C (200°F) . However it is found in practicing the inventi in accordance with the teaching of the patent that the deposits formed are powdery, have poor adhesion and are poorly conducting, and burn off if .attempt is subsequen made to build them up to useful thicknesses by electro¬ plating techniques ' . In another " reference, IBM .Technical Disclosur Bulletin, .Vol. -12, No'. 2, dated July 1969, .it is confir that a. bath quite simila to the one described in U.S. Patent 3,046,159 produces a deposited film "the conduc¬ tivity of which is not .very high". The bulletin goes on to recommend that in order, to produce a conductive layer " , ."the " plating is continued in an alkaline electro less copper " bath"; i.e. ' a conventional formaldehyde containing bath. " In another " reference, " U.S. Patent No. 3,650,77 fleeting reference is made to possible " use of hypophos¬ phite ' .in acidic, electroless. copper plating baths (see Column 2 , lines ' 15-17) without,, however, teaching how this is accomplished and without giving a single example of a bath to illustrate any reduction to practice. In summary,, therefore, " the foregoing patents and technical literature typically illustrate prior art teaching in respect' to. -.the difficulties of attempting to use hypophosphite " as a reducing agent for electroless copper plating * .at low pH value, " and the conclusion advanced has been that he principal difficulties are poorly conductive powdery copper films and bulk- precipitation of insoluble particles, which make such a bath inoperative ' for practical applications. • SUMMARY. OF THE INVENTION The ' invention here relates to the discovery that hypophosphite reducing agents can be usefully employed as reducing agents for divalent copper .at a bath pH of about "2.0 to 3.5, to produce an electrically conductive " copper " film on a suitably catalyzed non- conductive substrate. " Such copper " deposit has good conductivity,", provides good adherence o the deposit to the substrate, ' and serves as an excellent base for further " electrolytic deposition of additional copper or .other metals. .It has been discovered that the undesirable results causing difficulty in the prior art teachings were " due primarily to presence of chloride ion in the bath, introduced through the use of cupric chloride as the " main copper-bearing constituent of the bath. .Other anions such as bromide, ' iodide, fluoride and acetates - in the b>ath composition will likewise prevent deposition of conductive copper " f lm in the " range of 2 to 5 pH .in hypoph sphite-based' copper metallizing solutions. There " is the " further " xequixement of course that a suitable " complexer be selected which will allow some " coordination of copper " .at this pH range. The eason why chloride and other ions mention above inter ere ' wit proper functioning of hypophosphite base copper metallizing baths " is not properly understoo .at this time. ' -It :is theorized that that hese interferi ions somehow stabilize .th cuprous .state and make the reaction Cu + + e ■ * ■ - Cu° kinet ' ically more difficult. This however is only an assumption' and the "significant finding of the present invention is that, being made " aware " of the deleterious effect of certain anions in these bath solutions, those skilled in the art are now enabled to make component selection which ermits .utilizing hypophosphite reducin agents in electroless.copper plating baths operating at the low pH.values.mentioned; i.e. " below 5.0. • DESCRIPTION OF PREFERRE EMBODIMENTS 5 Plating solutions embodying the invention concept include the usual major categories of component namely, a source of cupric ions and . a solvent .for . these, ' usually water " ; complex ' ing agent or mixtures ■ thereof; and hypophosphite reducing agent. 0 * * The most effective complexing agents now known for. the ' el ' ec ' troles ' s ' copper baths of. the invention are N-hydroxyethyl ".ethyiehediamine triacectic acid - (HEEDTA) , .ethyiehediamine tetraacetic acid (EDTA) , nitrilotriacet ' ic acid (NTA) , and alkali metal salts of - these. " These* complex ' ors will provide an electrically conductive copper film on a properly catalyzed non- conductive ' substrate " in.the pH range of 2 to 3.5, provided detrimental anions are ' not in solution. .The major area of introducing interfering anions into the " plating solution is the source of copper " (cupric ion) used. ' We have found that cupric sulfate, " nitrate " or fluorborate can be used, and in . contrast the cupric. halides " such as chloride, " bromide, etc., also acetate, ' should 'be avoided, as these will not". allow deposition of aΛ electrically conductive " copper " film when ' they ' are significantly present in " solution. • To maintain the " pH in the preferred range, .standard acid or alkaline adjustments can be used, such as by addition of sulfuric acid to- lower pH and sodium . * . or potassium hydroxide to raise pH. However, an acid or base which would introduce one o the detrimental anions, .for example hydrochloric acid, must be avoided to keep " the " bath operative. " Concentrations, of components can have a wide range " and can be optimized within the range to produce . the preferred " conditions. ..The concentration of the amine complexors such as EDTA and HEEDTA in solution is preferably at about one-to-one on a mole " ratio basis with the cupric ion, while the NTA complexor is preferabl on a two-to-one mole ratio with the cupric ion. Lesser amounts of complexor will of course " leave some copper uncomplexed. This can be tolerated within limits, provided precipitation of particles is insufficient to interfere " with ' the " desired degree of luster, smoothness, etc. in the ' finishe plate. " On the higher ratio side, there is no' problem, as excess of complexor does not hinder the " " operation of the bath and in fact a slight excess can be helpful to accommodate for conditions of temporary, locally high copper concentration which may arise ' during bath replenishment operations. Sodium hypophosphite is the most readily available hypophosphite " material and is accordingly the preferre form of this reducing agent. Hypophosphorous acid however " is 'also available and could be used in conjunction with -pH adjusters which might be required when ' using the " acid.. As to concentration, the optimum level " is that which " is sufficient to give an adequate . copper " film. Working with Targe excess of reducer in solution does ' not normally impede bath operation, but . neither does it offer any advantage. .The " following examples illustrate preferred conditions for practicing the invention. . • EXAMPLE 1 A typical workpiece comprising an automotive component molded of .standard commercial plating grade ABS is first cleaned to remove surface grime, oil, etc. An alkaline cleaning solution is typically used here. This is followed by chemical etch using mixed chromic- sulfuric or all chromic acid, also standard in the industry. Typical operating conditions, concentrations and time of treatment are disclosed in U.S.. Patent No. .3,515,649. Following thorough rinsing,, the workpiece is catalyzed. This can be accomplished in the "one- 5 .step" method using a mixed palladium-tin catalyst of commercial type. Such a " catalyst is disclosed in U.S. Patent No. 3,352,518, along with its method of use. Following rinsing, the catalyzed workpiece is next placed in a so-called " "accelerating solution". Again 10 many.types ' of accelerating baths can be employed, for example the one disclosed i the above mentioned patent No. 3,352,518, such accelerating baths generally consist ing of an acid solution. Alkaline accelerators such as sodium hydroxide solution have also been used successful 15 The workpiece is then ready after further rinsing for copper plating. The novel copper bath used in this example has the ' following composition: CuSO 4 * 5H 2 O 0.04M "Hamp-OL" (HEEDTA) 0.05M 20. aH 2 P0 2 -H 2 O 0.34M Water pH adjuster (H 2 SΘ 4 /NaOH) pH 3 The bath is maintained at 155°F. (68°C) and when the work is immersed in it for 10 minutes, the thick 5 ness of copper plate obtained is 11 microinches. In 30 ' minutes ' the thickness of deposit is 24 microinches. The deposit is bright " p ' iήk, a visual characteristic indicatin . good electrical conductivity. Coverage is complete on . the catalyzed surface, " and the deposit is well-adhered 0 and is free of blisters and roughness. This electroless plated substrate ' is rinsed,, then placed in a .standard electrolytic copper " .strike bath similar to any of those described in U.S. Patent Nos. 3,203,878, 3,257,294, 3,267,010 or 3,288,690, for example. Initially, the 5 electroplating is carried out at about 2 volts t a rate of about '20 amperes per square foot. Generally this is maintained for about 1 1/2 minutes, or until . the thickness of deposit is sufficient to provide greater current—carrying ' capability. ' At such time the plating rate " may hen be increased, as for example to about 4 volts .at 40 amperes ' per square foot, and is continue until the " total required thickness of copper is obtained. The workpiece may be further electroplated with nickel ' , chromium, gold, .etc. , as may be required for any given " application, using .standard electroplating . techniques ' . ' Much of the " restriction on initial current density, depends on " the size ' and physical complexity of . parts, along with the amount of rack contact area available per area of workpiece. " If. enough contacts are used,, the need to monitor initial current densities is less critical; however " in production experience, adequate rack contacts cannot always be found. Peel " .strength tests on plated workpieces obtained from baths in accordance with this example show adherence " values of about 8-10 pounds per inch for ..the copper " deposit on ABS substrates. Similar levels '* of peei .strength are obtained for other thermoplastic substrates ' including ' polyphe ylehe oxide, ' polypropylene, tc. , as .well as hermosetting substrates such as phenolic, epoxy,..etc. ' ~ " - " EXAMPLE CI An electroless copper " bath identical in all respects to that of the foregoing example is prepared except that a different complexor is used. In this case,. ' the " complexor is "Hampehe Na." .(tetrasodium EDTA) at the same concentration (0.05M) as before and the pH is again 3. " At a bath temperature of 155°F., a bright pink electroless copper deposit of 11 microinches is obtained in 10 minutes ' , which increases to 25 microinches in 30 minutes. Coverage of the workpiece is complete on the " catalyzed surface, and the deposit is free of " blisters anti roughness and is well adhered to the substrate. " The " deposit forms an excellent base for further metal plating to: buil 'up a desired total . thickness. ' When so plated, adhesion tests made on the ABS substrate plated in accordance with this example show peel strengths which range from 8-10 pounds per inch. 1 ' EXAMPLE -I3M Another " ABS workpiece is prepared for. electro- less plating in the manner described. The electroless copper bath here is again identical to that o the first example except for complexor, which in this case is nitrilotriacetic acid (NTA) at .0.10M. At a solution pH of 3, a bright pink adherent copper deposit of 14 microinches is obtained in 10 minutes, and.27 microinche in 30 minutes ' . After ' being further plated with addition copper " , nickel ' ; chromium o the like,; to build up a desired thickness, adhesion values of 8-10 pounds per inch peel " .strength o ABS is recorded.. - . ' • EXAMPLE ϋV Another ABS workpiece is .prepared for electro¬ less plating as described in Example I. The electroless copper * bath here is again identical to that of Example I except for. the copper " salt,, which in this case is copper " fluoborate " at 0.04M. ' At a solution pH of 3, a bright pink adherent copper deposit of 14 microinches is obtained in 10 minutes, ' and 29 microinches in 30 minutes ' . After " being further plated with additional copper " , nickel, chromium or the like,, to build a desired thickness, adhesion values of 8-10 pounds per inch peel strength on ABS is recorded. — - • EXAMPLE V ' • ' ' : '' , Another " ABS. orkpiece is prepared for. electro¬ less plating as describe in Example I. The electroless copper " bath here is identical to that of Example II except for the ' copper " salt which " in this case is copper fluoborate at O.04M. At a solution pH of 3, a bright pink adherent copper deposit of 12 microinches is obtained " in 10 minutes, and 26 microinches in 30 minutes After " being further " plated with additional copper, - nickel " , hromium or. the like, ' to build a desired thick- - nes ' s, .adhesion -values ' of 8-10 pounds per inch peel .strength on ABS is recorded. ' EXAMPLE VI Another ABS workpiece is prepared for electro- less piating- as described in Example I. The electroless copper bath ' here is again- identical to that of Example I . excep ' t for'the * " copper salt which in this case is copper nitrate at :0.04M: At-.a solution pH of 3, a good pink adherent copper deposit' of 12 microinches is obtained in 10 minutes " . " " After being further " plated with addition copper " , nickel " ', chromium or the " like, to build a desired - thickness, adhesion' alues ' of 8-10 pounds per inch peel .strength " on ABS is recorded. " EXAMPLE vil • Another " ABS workpiece is prepared for electro- - .ies ' s plating as described in Example I. The electroless copper " bath here is again identical to that of Example I excep " t for the copper salt which in this case is copper chloride at ' :0.04M. -At ' a solution pH of 3, no plating - of a conductive copper film was obtained. . . . . • " .EXAMPLE VIII • Another ABS workpiece is prepared for electro less plating as described i Example I. The electroles copper bath here is again identical to that of Example .5 except for. the copper " salt which in this case is copper " acetate at 0.04M. ' At a solution pH of 3, a dark browni black film formed on the workpiece. " * The film was not . . appreciably conductive, " and not useful for subsequent electroplating. " ' ■*' . ." ' 10 - . ' ..- ' • ' ■ • EXAMPLE IX. Another ABS workpiece is prepared for electro¬ less plating as described in Example I. The electroless . copper " bath here is again identical to that of Example I ■ except that the " " copper " salt in this case is copper 15 bromide at 0.04M. At a solution pH of 3, no plating of a conductive " copper " film was obtained. " In order to. illustrate " the effect of varying concentration of he-major bath constituents, such as the copper concentration ' and the reducer concentration, 20. Table " A gives ' a summary of results along these lines. The table " shows that a wide " variation of the copper concentration and reducer concentration can be ^utilized and .still give.good,pink, " .conductive copper films. This is a positive benefit " or commercial installations 5 where varying parameters are experienced. ΈBLE A MOLAR CONCENTRATIONS E__ECTrøLESS DEPOSIT Ex. Cu(BF 4 ) 2 HEEDTA NaH 2 P0 2 -H 2 0 pH A .04 .05 .17 3,0 10 9 155 Pink B ,04 ,05 .17 3,0 30 29 155 II C .04 .05- .34 3,0 10 12 155 11 D ,04 ,05 ,34 3,0 30 20 155 II E .04 .05 .51 3,0 10 9 155 w F .04 .05 ,51 3.0 30 16 155 V G ,08 ,10 .17 3.0 10 8 155 II H .08 .10 .17 3,0 30 17 155 Slight¬ ly fik. Pink I .08 .10 ,34 3,0 10 14 155 ink J ,08 .10 ,34 3.0 30 22 155 π K A 08 .10 ,51 3.0 10 11 155 l« L ,08 ,10 ,51 3.0 30 21 155 It. M .i 2 .15 .17 3,0 10 8 * 155 n N .12 .15 .17 ' 3.0 30 19 155 Slight¬ ly fik. Pink 0 t 12 ,15 .34 3,0 10 13 155 Pink P .12 .15 ,34 3,0 30 26 155 w Q ,12 .15 ,51 3.0 10 13 155 w R .12 .15 .51 3,0 30 23 155 M E- erimentation was conducted to determine . the parameter of.pH for.' the various workable anions. In general""the " optimum pH appears -to be " about 3, with a . workable range of about 2..0-3,5.- 'As the pH is lowered from 3 to. 2 the bath .stability, begins to lessen, and at pH of about 2.0-2.5 we have found that air agitation (oxygen .stabilization) is necessary to prevent bulk precipitation (instability.) of copper from solution. At pH below 2 the complexors apparently discontinue coordination with the " copper " , in fact EDTA precipitates • out of solution at pH less than 2. A§ the pH increases from 3 to: 3.5, the copper film deposited begins to get darker " until at pH more than 3.5,. the films produced are brownish and sometimes black, and are not suitable for subsequent electroplating. • The data presented in the foregoing examples is based on use of .standard platable grade of ABS substrate use in plating of plastics with conventional formaldehyde-type electroless copper baths. Tests made on other " .substrates molded of .standard plating grade thermoplastics, such as "Noryl" (polyphenylene oxide) and polypropylene, " show that the invention baths are applicable 'tα those as well.- • Also"thermosetting substrat of the " phenol-formaldehyde as well as epoxy types can be plated in the invention " baths, as can other types of thermosef plastics. .The invention is especially applicable to. plating on plastics;, hat is,- to applications where the plate part or workpiece Is required to. have " a metal finish for decorative or protective purposes. Automobile, appliance and hardware " parts are fields in which such applications more frequently arise. In such applications it is usually most practical to apply, initially, a thin deposit of copper " by electroless deposition, after which additional thicknesses of copper, nickel, chromium, for example, " or other metal can be . added more rapidly and economically by .standard electrodeposition procedures The hypopho ' sphite-reduced electroless copper baths of . this invention ' are particularly suited for .such applica- . tions.-. In this system * the ' plating rate of copper on paliadium/tih catalyzed plastic substrates ' .is initially - fast but slows as the copper " thickness builds. .It is assume that this Occurs because the copper " deposit . produced in the bath is not as catalytic to the system as is the palladium/tin. • This however is an advantage in situations requiring only a thin conductive copper coating, as .in plating on plastics, since any extraneous plate-out on tank walls, racks, heater coils, " .etc. will be inherently '.self-limiting in the " novel baths, and . therefore reduces the extraneous plate-out loss,, tank clean-out and rack " maintenance problems. The preparation of the surface of the substrate, particularly for plating on plastic applications, generally includes " the chromic-sulfuric or all-chromic tch procedure mentioned above of. bare plastic surfaces. The copper baths ' of the " invention " can be used, however, for printed' circuitboard applications employing, for example, " the ' "PLADD" process of MacDermid.Incorporated, Waterbury, Connecticut,: disclosed " in U.S. Patent No. 3,620,933.- I that system, a different .substrate preparation is used, preliminary to electroless deposi- . tion of the " copper " . This is illustrated by. the xollow- ing. example. " - - ' * . - ' " EXAMPLE X - The workpiece here is to comprise a printed circuitboard which takes the " form initially of a blank laminate consisting of aluminum foil bonded to a fiber¬ glass reinforced ep ' oxy resin substrate. " In preparing the circuitboard, .this blank laminate is placed in a hydrochloric acid bath to chemically .strip off the alu inum foil, leaving, the surface of the resin substrat . especially suited ..for subsequen reception o electroles . etal deposition.* ' . This preliminary, operation replaces . the " chroπtic-sulfuric..etch . ' step * mentioned previously. 5 The . ' stripped ' substrate, ' after careful rinsing, is .then catalyzed " , following the ' same " procedure of palladium- . tin catalysis described' in Example I. .The catalyzed board is then ' copper " plated, using, the same copper solution described in that earlier example. This 10. produces ' a thin copper " deposit across-the entire surface of the substrate'.'' A mask or-,resist is then " applied, as by screening, pho ' topolymer ' ic development, etc.,. to * define a desired printed"circuit.' .The " masked .(thin- plated) substrate " is then further plated in " an electro- 5 lytic bath, using the initial electroless deposit as a "bus" to build up additional metal thickness in .the unmasked regions of .the circuitboard. The resist or mask is next chemically, dissolved and the board is place in a suitable copper ' .et ' chant solution,* such as 0 . that disclosed in U.S. Patent No. 3,466,208, for a time sufficient tσ remove the thin initial copper deposit previously covered by ' the " resist, but insufficient to remove the " ' substantially, thicker circuit-defining regions of copper, (or other, metal)- built up in the 5 electrolytic plating bath. " This technique " is sometimes referred to " in .the " art as a semi-additive plating ** process. In similar manner ' ,, the invention is applicable . to the "subtractive" procedure for preparation of 0 printed circuitboards having through-holes ' for intercon¬ necting conductor areas on opposite surfaces of .standard, copper " , foil clad laminates ' . The " through-holes are ' . punched in the " blank board and the walls of the " through- holes ' plated with " copper " electroles ' sly, using the " . copper " solution of this invention after proper " cataliza- . tion of the " substrate. " Additional thickness of the -1§- wall deposit can be " provided by electrolytic deposition, f desired.*. A resist is applied to produce a prescribed -circuit pattern,* .and an exposed .copper " foil is then .etched away * , leavi g the circuit pattern and through- hole interconnections. .The resist may or may not then be removed, depending on further " plating requirements, such as gold plating of connector, tab areas on the circuit," solder coating,-, .etc. " . Although ' specific embodiments of the present . invention have been ' described above in detail, it is to be understood that these are primarily for purposes of illustration. ' Modifications may be made to the particula conditions and components disclosed, consistent with .. the " teaching herein; as will be apparent to those skilled in the art, 'for adaptation to particular applica- - tions. - "

Claims: CLAIMS : ' 1. An electroless copper deposition .solution comprising, -.in addition to water, a soluble source of cupric ions, a complexing agent effective to maintain said cupric ions in solution at pH levels below- 5.0, and a reducing agent effective to reduce cupric ions to. copper as a deposited conductive metal film on a catalyze non-conductive surface of a substrate when in contact with said solution,' wherein said reducing agent is a soluble source of hypophosphite ions; said solution having a pH of from about .2.0 to. 3.5 and said complexing agent being selected to be effective for coordination with said cupric ions within that range to prevent . - their precipitation'from said solution, wherein said solution is free " of significant concentrations of anions which would ' interfere if. present with .the reduc- tion of the cupric ions by said hypophosphite reducing agent to produce " said conductive copper film on a catalyzed surface of a substrate placed in contact with said solution. - - 2. An electroless copper deposition solution as defined in claim 1, wherein said solution is essen- tially free " of interfering ions of the group consisting of halides and acetates. 3. An electroless copper, deposition solution as defined in claim 2, wherein said complexing agent is .selected from the group consisting of HEEDTA, EDTA and NTA. 4. An electroless copper deposition solution as defined in claims.2 or 3, wherein said soluble source of. cupric ions is selected from the group consist- ing of cupric sulfate, " cupric " fluoroborate and cupric nitrate. " .5. An electroless copper deposition solution as defined in claim 3,. wherein the mole " ratio of HEEDTA * and EDTA to. cupric ion is abou one-to-one, " and .the - mole ratio of NTA to cupric ion is about two-to-one. ' . , 6. A method of electrolessly depositing a copper plating on the surface of a substrate comprising . the ' step ' s of preparing th surface of the substrate to render it more receptive to plating, immersing the substrate in a plating solution comprising, in addition to water ' ,* . a soluble source, of cupric ions, a complex- agent effective to maintain said cupric ions in solution t pH levels below 5.0, and a reducing agent effective to reduce said cupric ions to copper as a deposited metal conductive metal film on the " prepared surface of the substrate hen ' in contact-with the solution, wherein said reducing agent is a soluble ' source " of hypophosphite ions; selecting said complexing agent to be effective at pH levels of 2 to 3.5 for complexing the cupric ions and maintaining- sai ' solution free of significant concentrations of anions ' which would inter ere if present with " the reduction of the cupric ions by said hypophosphite reducing agent to produce said conductive copper film on the " substrate. " 7. * A method of electrolessly depositing a copper " film on the " surface of a substrate as defined in claim 6, wherein said plating solution is maintained substantially free " of interfering anions of the group consisting of halides and " acetates ' . * 8. A method of electrolessly depositing a copper " film on the " surface of a substrate as defined in claim 7, wherein said complexing agent is selected from the group consisting of HEEDTA, EDTA and NTA. 9. A method of. electrolessly depositing a copper film on the ' .surface " , of a substrate as defined in ' claims 7 or ' 8, wherein said .soluble source of cupric ions is .se ec ed from the grou consisting of cupric sulfate, .cupric fluoroborate and cupric nitrate. 10. A method of electrolessly depositing a copper film on the surface of a substrate as defined in ' claim 8, wherein the mole ratio of. HEEDTA and EDTA to cupric ion is about one-to-one, . and the mole ratio of NTA to cupric ion is about two-to-one. "

Inventors: FERRIER DONALD R, GRUNWALD JOHN J, KUKANSKIS PETER E, RHODENIZER HAROLD L, FERRIER, DONALD, R., GRUNWALD, JOHN, J., KUKANSKIS, PETER, E., RHODENIZER, HAROLD, L.
Applicants: MACDERMID INC, MACDERMID INCORPORATED
Application year: 1981
Main classification: C23C3
IPC codes: C23C18, H05K3