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
• • 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
  • C23C18/48—Coating with alloys
  • C23C18/50—Coating with alloys with alloys based on iron, cobalt or nickel

Definitions

• the present invention relates to an electrolyte as well as a method for the electroless deposition of metals, particularly layers of nickel, copper, cobalt, boron or gold, as well as layers of alloys comprising at least one of the aforementioned metals as alloying metal. Furthermore, the present invention relates to the use of ⁇ -amino acids as stabilizer in electrolytes for the electroless deposition.
• electroless plating methods are known from the state of the art for a long time.
• electroless plating also mentioned as chemical plating, the coating of almost every metal and a huge number of non-conductive substrate surfaces is possible.
• the electroless deposited metal layers differing from the galvanically deposited metal layers, i. e. those layers deposited by the use of an external current, in physical as well as mechanical aspects.
• metal alloy layers with non-metal elements like for example cobalt/phosphor, nickel/phosphor or boron carbide layers are deposited by means of electroless deposition methods.
• electroless deposited layers in many cases differ also in their chemical nature from the galvanically deposited layers.
• electroless deposited metal layer is the outline accuracy of the layer thickness of the deposited layer independent from the substrate geometry, which feature makes the electroless methods the first choice in the area of printed circuit boards (PCB) manufacturing, and here especially for the metallization of through hole contacts, vias and trenches.
• PCB printed circuit boards
• electroless methods are also used for the coating of other non-conductive substrates, like for example plastic substrates, to render the surface of such substrates conductive and/or to change the appearance of the substrate in aesthetic respect.
• the material properties of the coated substrate can be improved or amended.
• the corrosion resistance or the hardness of the surface and/or the wear resistance of the substrate can be improved.
• Electroless plating methods are based on an autocatalytic process, in which process the metal ions comprised in the electrolytes are reduced to the elemental metal by a reducing agent which is oxidized during this redox reaction.
• a reducing agent commonly used in the field of electroless deposition of metals on substrate surfaces is sodium hypophosphite. However, also other reducing agents are used in dependency of the metals to be deposited.
• the European patent application EP 1 413 646 A2 discloses, for example, an electrolyte for the electroless deposition of nickel layers having internal compressive stress.
• the electrolyte disclosed in this application comprises a metal salt of the metal to be deposited, a reducing agent, a complexing agent, an accelerator, and a stabilizer.
• the accelerator is used to increase the deposition rate of the metal on the substrate surface.
• the stabilizer is used to avoid the uncontrolled plateout (wild deposition) of the electrolyte, which means the unregulated wild deposition of metal on the substrate surface.
• heavy metals like lead, bismuth, zinc or tin are used as stabilizers.
• ROHS Restriction of the use of certain hazardous substances
• WEEE Wired electrical and electronic equipment
• ELV End of lifetime of vehicles
• an electrolyte for the electroless deposition of a metal layer on a substrate comprising a metal ion source for the metal to be deposited, a reducing agent, a complexing agent, an accelerator, and a stabilizer, characterized in that the electrolyte comprises as stabilizer a ⁇ -amino acid.
• ⁇ -amino acids are capable to replace heavy metal stabilizers, cyanides, selenium compounds as well as sulfur compounds comprising sulfur in an oxidation state between -2 and +5 in electrolytes for the electroless deposition of metal layers, totally.
• the applicant believes that the ⁇ -amino acids due to their indirectly adjacent amino group and carboxyl group are capable to at least temporarily jam the active centers on the substrate surface which are responsible for the uncontrolled deposition. So the wild deposition of the metals can be avoided. Additionally, also the foreign ions comprised in the electrolyte which are responsible for the wild deposition, too, are inactivated by the used ⁇ -amino acid.
• a further benefit of the inventive electrolyte and the inventive use of ⁇ -amino acids is that an effect known as edge weakness can be avoided.
• edge weakness When using electrolytes for the electroless deposition of metal layers which comprise heavy metal ions as stabilizers at high convection of the electrolyte a decreased deposition of metal at the edges of the substrate occurs. This is deemed to be related to an increased assembly of the heavy metal ions used as stabilizers in these areas. This effect deteriorates the outline accuracy of the plating, Surprisingly, by the use of ⁇ -amino acids as stabilizers in electroless plating methods this edge weakening effect can be avoided which significantly increases the overall outline accuracy of the plating especially when plating large substrates.
• ⁇ -amino acids having a pK s -value within a range of 4 to 8, preferably within a range of 5 to 7 seems to be suitable in this respect.
• 3-amino propionic acid ⁇ -alanin
• 3-aminobutyric acid 3-amino-4-methyl valeric acid
• 2-aminoethane-sulfonic acid Taurin
• the ⁇ -amino acid can be comprised in the inventive electrolyte within a range of 1 mg/l to 2 g/l, preferably 100 mg/l to 1 g/l, and even more preferred 200 m/l to 400 mg/l.
• reducing agent in the inventive electrolyte a reducing agent of the group consisting of sodium hypophosphite, formaldehyde, dimethylaminoborane, aminoborane, or other organic boranes can be comprised.
• a metal compound of the group consisting metal chloride, metal sulfate, metal acetate, metal nitrate, metal propionate, metal formiate, metal oxalate, metal citrate, and metal ascorbinate can be used.
• the metal compounds having volatile ions like for example metal acetate, metal nitrate, metal propionate, and metal formiate are preferred since the volatile character of the anion those anions leak out from the electrolyte in gaseous form which enables to reduce the amount of anions in the electrolyte. This enables to extend the lifetime of the electrolyte significantly, which under normal conditions is only limited. For example, by the use of volatile anions also at a metal turnover rate of 22 metal layers having internal compressive stress can be deposited.
• the inventive electrolyte comprises a compound of the group consisting of 2-hydroxy propionic acid, propanedioic acid (malonic acid), EDTA, and amino acetic acid.
• the inventive electrolyte comprises a compound of the group consisting of saccharin, hydantoin, rhodanine, or carbamide and its derivates.
• the inventive electrolyte may comprise a metal of the group consisting of nickel, copper, cobalt, boron and gold.
• the metal to be deposited also alloys like for example nickellcobalt-alloys, nickel/phosphor-alloys, cobalt/phosphor-alloys, boron/phosphorus-alloys or the like can be deposited.
• the deposition of nicket/PTFE-tayers or boron carbide/graphite-layers from dispersion bathes is possible by the inventive electrolyte.
• the inventive electrolyte can have a pH-value within a range of pH 3 and pH 12, preferably within pH 3,9 and pH 6.
• the temperature at which the electrolyte is used for deposition may vary between room temperature and 100° C.
• an electrolyte comprising:
• an electrolyte comprising:
• Plastic samples made from ABS etched with chromosulfuric add and activated with a Pd-activator system were brought into contact with an electrolyte comprising:
• a copper layer with a thickness of about 0,4 to 0,6 ⁇ m was plated on the substrate within 20 min at a temperature of 40° C.
• the plating result was fully comparable to the plating result achieved when depositing a copper layer under equal conditions on an ABS plastic substrate from an electrolyte commercially available as Enthone Enplate CU872, wherein Enthone Enplate CU872 comprises heavy metal ions.
• copper sulfate can be replaced by copper chloride in an equal molar amount.
• the resulting electrolyte is not only free of sulfur compounds having an oxidation state between -2 and +5, but entirely free of sulfur.
• Brass samples were degreased in an alkaline degreasing solution and activated in 10% sulfuric acid, rinsed and brought into contact with an electrolyte comprising:
• the quadrol [a N, N, N, N-Tetrakis(2-hydroxypropyl)ethylene diamine] comprised in the electrolyte was exchanged by 15 - 20 g/l of tetra sodium ethylene diamine tetra acetic acid (Na 4 EDTA).
• the plating result was almost the same as by the use of quadrol.
• an electrolyte comprising:
• a copper substrate is brought into contact with an electrolyte having a pH-value of about 10 which comprises:
• the same electrolyte was used to deposit a nickel layer on a brass substrate with the same results achieved when plating copper substrates.
• a copper layer with a thickness of about 0,4 to 0,6 ⁇ m was plated on the substrate within 20 min at a temperat ure of 40° C.
• the plating result was fully comparable to the plating result achieved when depositing a copper layer under equal conditions on an ABS plastic substrate from an electrolyte commercially available as Enthone Enplate CU872, wherein Enthone Enplate CU872 comprises heavy metal ions.
• Plastic samples made from ABS etched with chromosulfuric acid and activated with a Pd-activator system were brought into contact with an electrolyte comprising:
• the plating solution and sodiumhydroxide solution (20 g/l) were counterflowed.
• the flow velocity was 1 -2 lI/(m 2* h) for the plating solution and 0,5 - 1 l/(m 2* h) for the NaOH solution.
• the exchange rate was 7-15 g(NaOH)/(h*m 2 ) (related to the concentration of formiate and carbonate in the bath.

Landscapes

• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemically Coating (AREA)

Priority Applications (11)

Applications Claiming Priority (1)

Publications (1)

Family

ID=41226803

Family Applications (1)

Country Status (1)

Cited By (3)

Citations (7)

• 2009
  • 2009-07-03 EP EP09008744A patent/EP2270255A1/fr not_active Withdrawn

Patent Citations (7)

Similar Documents

Legal Events