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
  • C23C18/405—Formaldehyde

Definitions

• Electroless copper plating solutions which employ alkaline formaldehyde as the reducing agent for cupric ions are autocatalytic and therefore frequently are unstable, i.e., they have a tendency to plate-out prematurely. Many methods have been proposed to minimize the autodecomposition of electroless copper baths.
• cuprous ion is extremely active in promoting the autodecomposition of electroless copper plating solutions.
• This practice converts the cuprous ion to cupric ion and is commonly used in the art.
• This method when used as the sole means of bath stabilization, has two major drawbacks. Firstly, the deposits which result are usually dark and nonmetallic in appearance, probably due to an outer layer of cupric oxide; and, secondly, a large amount of formaldehyde is volatilized by the oxygen passing through the solution, making control of the chemical balance more difficult.
• the conventional electroless copper solution can be stabilized over a wide range of temperatures for extremely long periods with no sacrifice in the quality or color of the metal deposit or the rate of deposit.
• the electroless copper baths of the invention are used continuously, with replenishing of the constituents lost by chemical reaction or drag-out, at high efficiency.
• the baths as stabilized by this invention will tolerate repeated heating and cooling procedures and will generally operate efficiently at ambient temperatures.
• the resulting copper films are bright pink and composed of pure copper metal. They are completely devoid of dark and grainy areas of copper oxides commonly seen in previously known films.
• R and R' are the same or different and are a lower alkyl group having from 1 to 12 carbon atoms, preferably from 1 to 4 carbon atoms or an aryl group, such as a phenyl or a naphthyl group, or a substituted alkyl or aryl group.
• X, Y and Z may be oxygen and sulfur, most preferably X and Y are oxygen.
• R may represent a wide variety of chemical groups. The main criteria in selecting R is that it, together with the Z, form an acidic group which will slowly hydrolyze in the alkaline plating bath so as to form an R (X)R(Y)P(S z) moiety.
• R may be hydrogen, a substituted alkyl or aryl group wherein the substitution is a halogen, e.g., chloride, bromide or iodide; a hydroxyl; an amino or lower alkyl or alkanol amino; nitro; carbalkoxy; alkylthio; alkoxy; or aroxy group.
• the alkyl groups may have 1 to 12 carbon atoms, preferably, from I to 4.
• the aryl group may be phenyl or naphthyl.
• Such groups as: a para-nitrophenyl group, an ethylthioethyl group, a N-methylcarbamoylmethyl group, a trichloroethyl group, a l,2-di(ethoxycarbonyl) ethylthio group. In no event, however, shall more than one of the three R groups be hydrogen.
• Representative compounds include: diethyl pnitrophenyl thionophosphate (Parathion); dimethyl S-2-ethylthioethyl thiolophosphate; monomethylamide of O,O-dimethyldithiophosphoryl acetic acid; diethyl ester of 0,0-dimethyldithiophosphoryl succinic acid (Malathion); and diethyl 2-isopropyl-4-methylpyrimid- 6-yl thionophosphate.
• Parathion diethyl pnitrophenyl thionophosphate
• dimethyl S-2-ethylthioethyl thiolophosphate monomethylamide of O,O-dimethyldithiophosphoryl acetic acid
• diethyl ester of 0,0-dimethyldithiophosphoryl succinic acid diethyl 2-isopropyl-4-methylpyrimid- 6-yl thionophosphate.
• the X may be the bivalent oxygen, carbonyl, sulfur, sulfonyl, sulfoxide or imino or a trivalent nitrogen; n is an integer from I to 3.
• R" may be an alkyl group having from I to 12 carbon atoms, preferably from 1 to 6; a phenyl or naphthyl group.
• R" may represent two or more of the aforesaid groups, or may form a ring with carbon alone or carbon and oxygen jointly with the nitrogen group.
• the X in the above formula is a nitrogen group and the R" and the N together represent a phthalimide or a propargyloxy phthalimide.
• Examples of other compoundswhich may be employed include: N- propargylmaleimide; N-propargylsuccinimide; N-alkyl- N-propurgylamides; N,N-dialkyl-N-propargylamines; aryl and alkyl propargyl ethers; aryl and alkyl propargyl thioethers; aryl and alkyl .propargyl ketones; and aryl and alkyl propargyl sulfones.
• the amount of propargyl-type compound which may be used is preferably expressed in terms of the cupric salt in a liter of the electroless copper plating bath. Generally from 0.0001 to 0.001 moles are-employed, preferably from 0.0002 to 0.0004.
• the electroless copper plating solutions of the present invention are alkaline aqueous solutions containing a source of cupric ions, at least one complexing agent for cupric ions, and an active reducing agent.
• the alkalinity can typically be provided by sodium or potassium hydroxides, carbonates, or phosphates, although not limited to these bases.
• the preferred alkali is a mixture of an alkali metal hydroxide and carbonate. .This mixture is economical and allows a facile control of pH.
• the sodium salts are generally preferred due to their low cost.
• SuitaBlsources drastic ion are water-samsiaza per salts such as cupric sulfate, cupric nitrate, cupric' s
• Menb'le reducing agents are formaldehydeand formaldehyde sources including aqueous formaldehyde, paraformaldehyde, and derivatives thereof.
• aqueous formaldehyde is the preferred reducing agent due to its low cost, availability, and convenience of use.
• the complexing agent should be 1 to 4 times the moles of copper present, and preferably approximately 2 to 2.5 times to the cupric salt present.
• the electroless copper plating solutions of the invention are stable for an extended perind of time at ambient temperatures. Furthermore, the electroless copper plating solutions of the invention are stable for an extended perind of time at ambient temperatures. Furthermore, the electroless copper plating solutions of the invention are stable for an extended perind of time at ambient temperatures. Furthermore, the electroless copper plating solutions of the invention are stable for an extended perind of time at ambient temperatures. Furthermore, the electroless copper plating solutions of the invention are stable for an extended perind of time at ambient temperatures. Furthermore,
• the electroless plating solutions of this invention are preferably maintained at a specific gravity of 1.04 1.05 and a temperature of F. Under these conditi orisf a deposition rate of approximately one millionth of an inch-per minute can be achieved. At elevated temperature, deposition rates are increased.
• the electroless copper plating solution is held in plastic or plastic-lined metal tanks at 70-- l0OF., preferably with mechanical agitation.
• the pieces to be plated are cleaned and sensitized, if necessary, by methods wellknown to those skilled in the art. Immersion of the object to be plated for 1030 minutes is generally sufficient to produce the desired plating thickness. Subsequent deposition of ad-' ditional metal plate by electrolytic means is then easily accomplished, if desired.
• the surface to be plated must be free of grease and other contaminating material.
• the surface areas to receive the deposit should first be treated, as in conventional processes, with conventional sensitizing and seeding solutions, such as stannous chloride (SnC1 followed by treatment with a dilute solution of palladium chloride (PdCI
• stannous chloride SnC1
• PdCI palladium chloride
• a metal surface such as stainless steel
• acid such as hydrochloric or phosphoric acid to free the surface of any oxide.
• the electroless deposit is to be made on a plastic or ceramic base which is impregnated with cuprous oxide (Cu,O), the cleaned base is immersed in the electroless plating bath and allowed to remain until the deposit is sufficiently thick.
• EXAMPLE I seven electroless copper plating solutions are'prepared. Formulation of the solutions is as follows: To approximately one-half liter of water is added, in the order shown in the table, the several compounds named.'Prior to addition, the stabilizers are solvated with a cosolvent, such as a glycol ether, as weill be-readily understood by one skilled in the art. After all of the components are added, water sufficient to make one liter is added. Each of the solutions contains 9.25 grams of CuSO '5 H 0; 16 grams of NaOH; 5 grams of Na CO and 30 grams of 37% formaldehyde.
• a cosolvent such as a glycol ether
• Accelerated stability tests are carried out by sealing each of the above solutions in glass vials and storing at 130F; for up to 12 days.
• the following table describes the percent loss of cupric ion at various periods of time 6 EXAMPLE It In order to show the use of other stabilizers within the scope of the invention, additional solutions are pre during storage. 5 pared. These solutions are essentially the same as Solu- TABLE B Time at 130F. Percent Loss of Cupric lon Solution Number 1 2 3 4 5 6 Control* 1 hr.
• nd nd nd tr nd nd 20 2 hrs nd nd l l0 nd nd 50 3 hrs nd nd tr tr 75 4 hrs nd nd 50 20 1O hrs nd tr 10 100 6 hrs tr 30 l5 72 hrs. l5 100 100 12 days 50 50 50 40.
• the above table shows the markedly improved stability of the solutions of the invention as compared to the control.
• each of the seven solutions are used to plate epoxy plastic panels. The panels are scrubbed and sensitized according to procedures well-known in the art. The sensitized panels are then immersed into beakers containing each of the above solutions at 75F. and pH 13.3 for ten minutes.
• the following table shows the electroless copper plating thickness observed for each of the solutions:
• the plated material contained a copper plating approximately 10 millionths of an inch thick. This is equivalent to a plating rate of one millionth of an inch per minute.
• the copper plate is of excellent quality, pink in color, and free from impurities. A particularly good'quality plate is obtained where the secondary stabilizer is added.
• Example 1 tion N6. 5 described in Example l, except that the stabilizers are 0.005 grams of various dialkyl mercaptothionophosphates and are used in place of the Malathion. Using the same tests as shown in Example I the following stability and plating rates are obtained:
• the copper plate is of excellent quality, pink in color, and free from impurities.
• the stabilized electroless copper plating solutions described in the above examples are stable for extended periods of time at ambient temperatures and at elevated temperatures up to F. when compared to control solutions without the stabilizers of this invention. Electroless plating solutions containing the stabilizers of this invention can, in some cases, be brought to the boil without deleterious effects.
• an alkaline electroless copper plating bath having a pH in the range 10.5 to 14, and comprising water, a water soluble copper salt, a complexing agent for cupric ion, and formaldehyde, the improvement of maintaining in the bath from 0.0001 to 0.001 mole, per mole of cupric ion, of a primary stabilizer having the following general formula:
• R and R' are the same or different, and are an alkyl group having from 1 to 12 carbon atoms, a phenyl or naphthyl group;
• X, Y and Z are oxygen or sulfur; and
• R is hydrogen, a substituted alkyl or a substituted aryl group, wherein the substitution may be halo, a hydroxyl, an amino or lower alkylor alkanol-amino, a nitro, a carbalkoxy, alkylthio, alkoxy, or aryloxy group; wherein the alkyl groups have from.1 to 12 carbon atoms and the aryl groups are phenyl or naphthyl.
• R"X(CH ),,C E CH wherein R" is an alkyl group having 1 to 12 carbon atoms, a phenyl or naphthyl group, or a substituted phenyl or naphthyl group; X is a thio, a sulfonyl, a sulfoxide, oxy, carbonyl orimino group; n is l, 2 or 3; or R"X is an imide or a heterocyclic ring composed of nitrogen and carbon with or without oxygen group, is also maintained in the bath.
• dialkyl group is dimethyl, diethyl or di-npropyl.
• n is l and RX' is a phthalimide group.
• R and R" are the same or different, and are an alkyl group having from 1 to 12 carbon atoms, a phenyl or a naphthyl group;
• X, Y and Z are oxygen or sulfur;
• R is hydrogen, a substituted alkyl or a substituted aryl group, wherein the substitution may be halo, a hydroxyl, an amino or lower alkylor alkanolamino, a nitro, a carbalkoxy, alkylthio, alkoxy, or aryloxy group; wherein the alkyl groups have from 1 to 12 carbon atoms and the aryl groups are phenyl or naphthyl.
• R" is an alkyl group having l to 12 carbon atoms, a phenyl ora naphthyl group, or a substituted phenyl or naphthyl group;
• X is a thio, a sulfonyl, a sulfoxide, oxy, carbonyl or imino group, n is 1, 2 or 3; or
• R"R' is an imide or a heterocyclic ring composed of nitrogen and carbon with or without oxygen group, is also maintained in the bath.

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Citations (3)

• 0
  • BE BE794048D patent/BE794048A/xx not_active IP Right Cessation
• 1972
  • 1972-01-17 US US00218459A patent/US3790392A/en not_active Expired - Lifetime
• 1973
  • 1973-01-05 AU AU50768/73A patent/AU464729B2/en not_active Expired
  • 1973-01-08 DE DE2300748A patent/DE2300748C3/de not_active Expired
  • 1973-01-08 AT AT13573A patent/AT320372B/de not_active IP Right Cessation
  • 1973-01-11 NO NO123/73A patent/NO135188C/no unknown
  • 1973-01-12 SE SE7300440A patent/SE387664B/sv unknown
  • 1973-01-15 FR FR7301315A patent/FR2168364B1/fr not_active Expired
  • 1973-01-15 GB GB207373A patent/GB1414896A/en not_active Expired
  • 1973-01-15 CH CH52373A patent/CH599981A5/xx not_active IP Right Cessation
  • 1973-01-15 LU LU66834A patent/LU66834A1/xx unknown
  • 1973-01-16 ZA ZA730328A patent/ZA73328B/xx unknown
  • 1973-01-16 FI FI117/73A patent/FI54500C/fi active
  • 1973-01-16 NL NLAANVRAGE7300599,A patent/NL177330C/xx not_active IP Right Cessation
  • 1973-01-16 DK DK23573A patent/DK143948C/da not_active IP Right Cessation
  • 1973-01-16 DD DD168260A patent/DD107490A5/xx unknown
  • 1973-01-16 ES ES410652A patent/ES410652A1/es not_active Expired
  • 1973-01-16 IT IT67057/73A patent/IT980460B/it active
  • 1973-01-17 IL IL41331A patent/IL41331A/xx unknown
  • 1973-01-17 PL PL1973160307A patent/PL94000B1/pl unknown
  • 1973-01-17 JP JP774073A patent/JPS5519983B2/ja not_active Expired
  • 1973-01-17 RO RO7373524A patent/RO69172A/ro unknown
• 1976
  • 1976-10-14 HK HK650/76*UA patent/HK65076A/xx unknown

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