EP0096034A1 - Electroless copper deposition solutions. - Google Patents
Electroless copper deposition solutions.Info
- Publication number
- EP0096034A1 EP0096034A1 EP82900581A EP82900581A EP0096034A1 EP 0096034 A1 EP0096034 A1 EP 0096034A1 EP 82900581 A EP82900581 A EP 82900581A EP 82900581 A EP82900581 A EP 82900581A EP 0096034 A1 EP0096034 A1 EP 0096034A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- copper
- cupric
- solution
- substrate
- ions
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
- C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
- C23C18/31—Coating with metals
- C23C18/38—Coating with copper
- C23C18/40—Coating with copper using reducing agents
Definitions
- non-formaldehyde reducing agents of of 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 electroless copper plating baths employing hypophosphite reducing agents, but having substantially lower pH operating ranges.
- U.S. Patent Application Ser. No. 909,209 provides one of the first disclosures enabling commercially practical use of hypophosphite reducing agents in electrolessly 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 incorporated herein by reference. Essentially, it was shown 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 hypophosphite agents were employed to electrolessly . plate copper.
- 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 of 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.
- 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; complexing agent or mixtures thereof; and hypophosphite reducing agent.
- the most effective complexing agents now known for the electroless copper baths of. the invention are N-hydroxyethyl ethyiehediamine triacectic acid (HEEDTA), ethyiehediamine tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and alkali metal salts of these.
- .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.
- an acid or base which would introduce one of 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.
- hypophosphite is the most readily available hypophosphite material and is accordingly the preferred 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.
- 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 chromicsulfuric 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.
- the workpiece is catalyzed. This can be accomplished in the "one- 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.
- accelerating solution a so-called "accelerating solution”.
- accelerating baths can be employed, for example the one disclosed in 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
- the workpiece is then ready after further rinsing for copper plating.
- the novel copper bath used in this example has the following composition:
- the electroplating is carried out at about 2 volts at 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 then be increased, as for example to about 4 volts at 40 amperes per square foot, and is continued 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 polyphehylehe oxide, polypropylene, etc., as well as thermosetting substrates such as phenolic, epoxy, etc.
- An electroless copper bath identical in all respects to that of the foregoing example is prepared except that a different complexor is used.
- the complexor is "Hampehe Na 4 " (tetrasodium EDTA) at the same concentration (0.05M) as before and the pH is again 3.
- 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 build up a desired total thickness.
- adhesion tests made on the ABS substrate plated in accordance with this example show peel strengths which range from 8-10 pounds per inch.
- ABS workpiece is prepared for electro less plating in the manner described.
- the electroless copper bath here is again identical to that of the first example except for complexor, which in this case is nitrilotriacetic acid (NTA) at 0.10M.
- NTA nitrilotriacetic acid
- a bright pink adherent copper deposit of 14 microinches is obtained in 10 minutes, and.27 microinche in 30 minutes.
- adhesion values of 8-10 pounds per inch peel strength on ABS is recorded.
- ABS workpiece is prepared for electroless 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.
- the copper salt which in this case is copper fluoborate at 0.04M.
- a bright pink adherent copper deposit of 14 microinches is obtained in 10 minutes, and 29 microinches in 30 minutes.
- adhesion values of 8-10 pounds per inch peelstrength on ABS is recorded.
- ABS. workpiece is prepared for. electroless plating as described 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 0.04M.
- the copper salt which in this case is copper fluoborate at 0.04M.
- a bright pink adherent copper deposit of 12 microinches is obtained in 10 minutes, and 26 microinches in 30 minutes
- adhesion values of 8-10 pounds per inch peel strength on ABS is recorded.
- 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 except for the copper salt which in this case is copper nitrate at 0.04M.
- the copper salt which in this case is copper nitrate at 0.04M.
- a good pink adherent copper deposit' of 12 microinches is obtained in 10 minutes.
- adhesion values 8-10 pounds per inch peel .strength on ABS is recorded.
- ABS workpiece is prepared for electro less plating as described in Example I.
- the electroles copper bath here is again identical to that of Example except for the copper salt which in this case is copper acetate at 0.04M.
- the copper salt which in this case is copper acetate at 0.04M.
- a dark browni black film formed on the workpiece. The film was not . appreciably conductive, and not useful for subsequent electroplating .
- ABS workpiece is prepared for electroless 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 bromide at 0.04M.
- the copper salt in this case is copper bromide at 0.04M.
- the solution pH of 3 no plating of a conductive copper film was obtained.
- 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 for commercial installations where varying parameters are experienced. Experimentation was conducted to determine the parameter of pH for the various workable anions.
- the optimum pH appears to be about 3, with a workable range of about 2.0-3, 5.
- 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.
- the complexors apparently discontinue coordination with the copper, in fact EDTA precipitates out of solution at pH less than 2.
- 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.
- thermoplastics such as "Noryl” (polyphenylene oxide) and polypropylene
- 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; that is, to applications where the plated part or workpiece Is required to. have a metal finish for decorative or protective purposes.
- the preparation of the surface of the substrate generally includes the chromic-sulfuric or all-chromic etch 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. In that system, a different substrate preparation is used, preliminary to electroless deposition of the copper. This is illustrated by the following example.
- 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 fiberglass reinforced epoxy resin substrate.
- this blank laminate is placed in a hydrochloric acid bath to chemically strip off the aluminum foil, leaving, the surface of the resin substrat especially suited for subsequent reception of electroles metal deposition.
- This preliminary, operation replaces the chromic-sulfuric etch step mentioned previously.
- 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 produces a thin copper deposit across the entire surface of the substrate.
- a mask or resist is then applied, as by screening, photopolymeric development, etc., to define a desired printed circuit.
- the masked (thin plated) substrate is then further plated in an electro 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 placed in a suitable copper etchant solution, such as that disclosed in U.S. Patent No. 3,466,208, for a time sufficient t ⁇ 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 electrolytic plating bath.
- This technique is sometimes referred to in the art as a semi-additive plating process.
- the invention is applicable to the "subtractive" procedure for preparation of printed circuitboards having through-holes for interconnecting conductor areas on opposite surfaces of standard, copper, foil clad laminates.
- the through-holes are punched in the blank board and the walls of thethroughholes plated with copper electrolessly, using the copper solution of this invention after proper catalization of the substrate. Additional thickness of the wall deposit can be provided by electrolytic deposition, if desired.
- a resist is applied to produce a prescribed circuit pattern, and any exposed copper foil is then etched away, leaving the circuit pattern and throughhole 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.
Abstract
Des solutions cuivriques convenablement complexées peuvent déposer sans passage d'un courant électrique des films conducteurs de cuivre sur des substrats catalysés non-conducteurs, à des valeurs de pH allant d'environ 2,0 à 3,5 dans le bain de placage, en utilisant un réducteur non-formaldéhyde tel que l'hypophosphite. Pour obtenir de bons résultats, les conditions suivantes sont essentielles: 1) le complexeur choisi doit pouvoir chélater le cuivre à des valeurs de pH entre 2,0 et 3,5 à des températures élevées (140o à 160oF); 2) il faut éviter des concentrations importantes de certains anions dans la solution de placage, tels que les halogénures et les acétates; et 3) il faut prévoir une surface catalytique "active" sur le substrat non-conducteur.Appropriately complexed copper solutions can deposit copper conductive films on electrically nonconductive catalyzed substrates without passing an electric current, at pH values ranging from approximately 2.0 to 3.5 in the plating bath. using a non-formaldehyde reducer such as hypophosphite. To obtain good results, the following conditions are essential: 1) the complexer chosen must be able to chelate the copper at pH values between 2.0 and 3.5 at high temperatures (140o to 160oF); 2) avoid large concentrations of certain anions in the plating solution, such as halides and acetates; and 3) an "active" catalytic surface must be provided on the non-conductive substrate.
Description
Claims
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PCT/US1981/001726 WO1983002287A1 (en) | 1981-12-21 | 1981-12-21 | Electroless copper deposition solutions |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0096034A1 true EP0096034A1 (en) | 1983-12-21 |
EP0096034A4 EP0096034A4 (en) | 1984-05-03 |
EP0096034B1 EP0096034B1 (en) | 1986-09-10 |
Family
ID=22161575
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19820900581 Expired EP0096034B1 (en) | 1981-12-21 | 1981-12-21 | Electroless copper deposition solutions |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0096034B1 (en) |
JP (1) | JPS58502101A (en) |
DE (1) | DE3175316D1 (en) |
WO (1) | WO1983002287A1 (en) |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3515563A (en) * | 1967-12-28 | 1970-06-02 | Photocircuits Corp | Autocatalytic metal plating solutions |
US4279948A (en) * | 1978-05-25 | 1981-07-21 | Macdermid Incorporated | Electroless copper deposition solution using a hypophosphite reducing agent |
US4265943A (en) * | 1978-11-27 | 1981-05-05 | Macdermid Incorporated | Method and composition for continuous electroless copper deposition using a hypophosphite reducing agent in the presence of cobalt or nickel ions |
-
1981
- 1981-12-21 DE DE8282900581T patent/DE3175316D1/en not_active Expired
- 1981-12-21 JP JP82500662A patent/JPS58502101A/en active Pending
- 1981-12-21 WO PCT/US1981/001726 patent/WO1983002287A1/en active IP Right Grant
- 1981-12-21 EP EP19820900581 patent/EP0096034B1/en not_active Expired
Non-Patent Citations (2)
Title |
---|
No relevant documents have been disclosed * |
See also references of WO8302287A1 * |
Also Published As
Publication number | Publication date |
---|---|
EP0096034A4 (en) | 1984-05-03 |
WO1983002287A1 (en) | 1983-07-07 |
EP0096034B1 (en) | 1986-09-10 |
JPS58502101A (en) | 1983-12-08 |
DE3175316D1 (en) | 1986-10-16 |
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