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
  • C23C18/42—Coating with noble metals
  • C23C18/44—Coating with noble metals using reducing agents
• • 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
  • C23C18/1601—Process or apparatus
  • C23C18/1633—Process of electroless plating
  • C23C18/1655—Process features
  • C23C18/166—Process features with two steps starting with addition of reducing agent followed by metal deposition
• • 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
  • C23C18/18—Pretreatment of the material to be coated
  • C23C18/1803—Pretreatment of the material to be coated of metallic material surfaces or of a non-specific material surfaces
  • C23C18/1824—Pretreatment of the material to be coated of metallic material surfaces or of a non-specific material surfaces by chemical pretreatment
  • C23C18/1827—Pretreatment of the material to be coated of metallic material surfaces or of a non-specific material surfaces by chemical pretreatment only one step pretreatment
  • C23C18/1834—Use of organic or inorganic compounds other than metals, e.g. activation, sensitisation with polymers
• • 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
  • C23C18/18—Pretreatment of the material to be coated
  • C23C18/1803—Pretreatment of the material to be coated of metallic material surfaces or of a non-specific material surfaces
  • C23C18/1824—Pretreatment of the material to be coated of metallic material surfaces or of a non-specific material surfaces by chemical pretreatment
  • C23C18/1837—Multistep pretreatment
  • C23C18/1844—Multistep pretreatment with use of organic or inorganic compounds other than metals, first

Definitions

• the present invention relates generally to direct electroless palladium plating on copper substrates.
• Electroless deposition is a process for depositing a thin layer or layers of a material(s) onto a substrate. Electroless deposition is typically accomplished by immersing the substrate in a bath that contains ions of the material to be deposited along with a chemical reducing agent, whereby some of the ions precipitate onto the substrate surface. In contrast to electroplating processes, electroless deposition does not normally require an externally applied electrical field to facilitate deposition. Thus, one advantage of electroless plating processes is that it can be selective, i.e., the material can be deposited only onto areas that demonstrate appropriate electrochemical properties, and thus, local deposition can be performed on areas that have been pretreated or catalyzed.
• a molded interconnect device is an injection-molded thermoplastic element with integrated electronic circuit traces.
• MIDs provide new opportunities for miniaturization of complex devices and integration of functionalities into one component reduces assembly costs and product volume.
• MIDs combine a high temperature plastic substrate (or housing) with circuitry into a single element through selective metallization.
• PCB printed circuit board
• MID manufacturing processes electronic components are bonded to selected bonding areas of a copper structure produced on one or both sides of a substrate. Such interconnection must be reliable in terms of bond strength.
• Wire bonding is one of the preferred processes for connecting the chip in interconnect packages.
• One of the main wire bonding processes used for IC-substrates is gold wire bonding, in which a gold wire is bonded on a layer of electrolytically deposited nickel and gold. Alternatively, gold wire may be bonded onto a surface of nickel, palladium and gold.
• the mechanical reliability of wire bonds in microelectronic packages depends on the formation and development of intermetallic compounds at the interface between the bond wedge and the bond pad on the substrate, which is needed for successful bonding. Bonding either gold or copper-wires onto a copper bond pad surface is difficult mainly because of the tendency of the copper metallization to oxidize.
• Wire bonding portions are typically made of copper. If they remain bare or are externally exposed to the atmosphere and humidity, soldering and wire bonding properties of the copper layers can deteriorate due to oxidation or corrosion of the surface.
• bare or exposed copper layers are typically electroplated or electrolessly plated with nickel.
• the plated nickel layer protects the copper from a corrosive environment for an extended period of time.
• the nickel layer protects the copper from being dissolved by solder during the soldering assembly step by functioning as a diffusion barrier layer.
• the plated nickel layer also acts as an interfacial film for prevention the copper layer and a subsequently plated gold layer, from diffusing into each other.
• ENIG electroless nickel/immersion gold
• palladium final finishes provide ideal surfaces for soldering, wire bonding and molded interconnect devices (MID) applications with the advantage of completely replacing nickel/gold finishes.
• MID molded interconnect devices
• direct electroless palladium plating on copper deposits can be hard to initiate. This has become a major hurdle and has slowed down the process to replace nickel.
• MID molded interconnect devices
• the present invention relates generally to a method of providing an electroless palladium deposit on a copper surface, the method comprising the steps of:
• the electroless palladium, deposit can then be soldered to or wire bonded to.
• the inventors of the present invention have discovered an improved process for catalyzing the copper surface through the use of a pre-dip solution, which as makes direct electroless palladium plating on copper possible.
• the present invention relates generally to a method of providing an electroless palladium deposit on a copper surface, the method comprising the steps of:
• the copper surface may comprise copper or copper alloy and may be a copper or copper alloy surface used in a printed circuit board or molded interconnect device.
• the use of the electroless palladium produces a product that does not contain nickel or nickel alloy and in which the electroless palladium is deposited directly on the underlying copper substrate.
• the use of the electroless palladium as described herein replaces the more commonly used nickel/gold finishes of the prior art.
• the present invention utilizes a pre-dip composition comprising a reducing agent that catalyzes the copper surface for the subsequent deposition of electroless palladium thereon.
• the reducing agent comprises a boron reducing agent selected from the group consisting of alkyl boranes, amine boranes, borane complexes, boron hydride compounds and combinations of one or more of the foregoing.
• phosphorus-based reducing agents including hypophosphorous-acid-based reducing agents and their salts would be usable in the pre-dip composition.
• suitable alkyl boranes include, but are not limited to, trimethylborane, methoxydiethylborane, and dibutylboron triflate.
• suitable amine boranes include but are not limited to dimethylamine borane, t-butylamine borane, pyridine borane, triethylamine borane, tri-ethylamineborane-1,3-diaminopropane complex, ethylenediamine borane, 5-ethyl-2-methylpyridine borane. Of these amine boranes, dimethyamine borane is preferred.
• borane complexes include, but are not limited to, borane-tetrahydrofuran complex, dimethyl sulfide borane, and N,N-diethylaniline borane, morpholine borane, and piperazine borane, among others.
• the reducing agent comprises dimethyamine borane.
• the reducing agent is preferably present in the pre-dip composition at a concentration of between about 2 and about 20 g/L, more preferably between about 5 and 15 g/L and most preferably at a concentration of between about 8 and about 10 g/L.
• the bath of the pre-dip composition is preferably maintained at a temperature of between about 20 and about 30° C., more preferably at about room temperature.
• the copper surface is contacted with the pre-dip composition in the bath for a period of time to catalyze the copper surface which is typically between about 30 seconds and about 2 minutes.
• the copper surface may be contacted with the pre-dip composition by spray coating, curtain coating or immersion. In a preferred embodiment, the copper surface is contacted with the pre-dip composition by immersing the copper surface in the pre-dip composition for the desired period of time.
• the now catalyzed copper surface is contacted with an electroless palladium plating solution.
• the electroless palladium plating solution preferably comprises:
• the source of palladium ions is preferably a palladium salt which typically comprises a salt such as palladium chloride, palladium sulfate, palladium nitrate, palladium nitrite, and palladium acetate, by way of example and not limitation.
• the concentration of the palladium salt in the pre-dip is preferably in the range of about 2 to about 6 g/L, more preferably about 3 to about 5 g/L.
• the one or more complexing agents may typically include one or more nitrogenated complexing agents and suitable nitrogenated complexing agents include primary, secondary and tertiary amines as well as polyamines.
• nitrogenated complexing agents may include, but are not limited to, ethylenediamine, 1,3-diaminopropane, 1,2-bis(3-amino-propyl-amino)-ethane, 2-diethyl-amino-ethylamine, and diethylene triamine.
• nitrogenated complexing agents include diethylene-triamine-penta-acetic acid, nitro-acetic acid, N-(2-hydroxyethyl)-ethylenediamine, ethylenediamine-N,N-diacetic acid, 2-(dimethylamino)-ethylamine, 1,2-diamino-propylamine, 1,3-diamino-propylamine, 3-(methylamino)-propylamine, 3-(dimethylamino)-propylamine, 3-(diethylamino)-propylamine, bis-(3-aminopropyl)-amine, 1,2-bis-(3-aminopropyl)-alkylamine, diethylenetriamine, triethylenetetramine, tetraethylene-pentamine, penta-ethylene-hexamine, and combinations of one or more of the foregoing.
• the nitrogenated complexing agent comprises ethylenediamine.
• concentration of the one or more nitrogenated complexing agents in the electroless palladium solution is preferably in the range of between about 2 to about 8 g/L, more preferably between about 3 to about 6 g/L.
• the one or more complexing agents may also comprise a compound containing a carboxylic acid group.
• the compound containing a carboxylic acid group is preferred because it forms a complex with the palladium ions.
• the compound containing a carboxylic acid group include, but are not limited to, citric acid, acetic acid, propionic acid, lactic acid, ortho-hydroxybenzoic acid, oxalic acid, malonic acid, succinic acid, maleic acid, tartaric acid, ortho-phthalic acid, diglycolic acid, thioglycolic acid, thiodiglycolic acid, glycine, methylglycine, dimethylglycine, anthranilic acid, picolinic acid, quinolinic acid and combinations of one or more of the foregoing.
• the concentration of the one or more complexing agents comprising a carboxylic acid group is preferably in the range of between about 8 and about 25 g/L, more preferably in the range of between about 10 and about 20 g
• the electroless palladium plating solution also preferably comprises a reducing agent and the reducing agent may preferably be a hypophosphite reducing agent.
• the reducing agent may preferably be a hypophosphite reducing agent.
• Other reducing agents such as formaldehyde, hydrazine and boron reducing agents may also be usable in the compositions described herein, depending on the chemistry of the plating bath.
• the electroless palladium plating solution also preferably comprises a pH buffering agent, which may comprise a suitable acid such as formic acid, acetic acid, malonic acid, succinic acid or citric acid.
• a pH buffering agent which may comprise a suitable acid such as formic acid, acetic acid, malonic acid, succinic acid or citric acid.
• various solvents including aliphatic alcohols as well as diols and polyols such as ethylene glycol and glycerine may also optionally, but preferably, be included in the electroless palladium plating solution. Mixtures of such solvents as well as blends with other solvents can also be used.
• the concentration of the solvent may be in the range of about 30 to about 50 g/Lm more preferably, about 35 to about 45 g/L.
• the electroless palladium plating solution may also comprise other additives that are usable in electroless plating solutions, including, but not limited to brighteners, stabilizers, surfactants, by way of example and not limitation.
• the pH of the electroless palladium solution is preferably above 4, more preferably in the range of about 4 to about 10.
• the electroless palladium bath is typically maintained a temperature of between about 45 and about 60° C., more preferably at a temperature of between about 50 and about 55° C.
• the copper surface is contacted with the electroless palladium composition for a period of time to deposit the desired thickness of palladium.
• the copper surface is contacted with the electroless palladium composition for about 2 to about 20 minutes, more preferably for about 5 to about 15 minutes.
• immersion of a copper substrate in the electroless palladium composition for 4 minutes yielded an electroless palladium layer on the copper substrate having a thickness of about 8 microinches.
• the copper substrate is preferably contacted with the electroless plating composition by immersing the copper substrate in the electroless plating composition for the desired period of time at the desired temperature.
• a copper or copper alloy surface is first prepared for plating.
• the copper or copper alloy surface may be prepared by treatment with an acid cleaner and then the surface copper oxides may be removed in a microetch bath.
• the copper or copper alloy surface is contacted with a pre-dip composition comprising about 8 g/L of DMAB and then with an electroless palladium bath as described above in Table 1.
• the copper or copper alloy surface is subjected to the following steps set forth in Table 2 to deposit an electroless palladium layer.
• the copper or copper alloy surface is prepared first prepared for plating.
• the copper or copper alloy surface may be prepared by treatment with an acid cleaner and then the surface copper oxides may be removed in a microetch bath.
• the copper or copper alloy surface is subjected to the following process steps as set forth in Table 3 to apply an ENIG layer on the copper surface.
• the electroless palladium process described in Example 1 has fewer process steps, resulting in shorter production times.
• lower bath temperatures also translate into lower energy costs.
• Parts coated with electroless palladium and parts coated with ENIG were dipped into a tin/lead solder pot maintained at a temperature of 290° C. to check for solder wetting of the surface. Parts coated with electroless palladium and parts coated with ENIG both wet equally well.
• Parts coated with electroless palladium, parts coated with ENIG and parts coated with silver were aged in a steam bath for 8 hours at 100° C. to evaluate the ability of the respective coatings to adhere to the copper surface after an extended period of immersion in the steam bath. All of the coated parts passed the steam aging test, with no delamination of the metallization from the substrate. In addition the electroless palladium coated part passed the same as the ENIG and the silver coated parts.
• the palladium process offers the same advantages as an ENIG final finish.
• the palladium finish gives desirable results for solderability, salt spray, sulfur tarnish, contact resistance, steam aging, paint and RF testing.
• palladium baths are cyanide free, unlike many of the widely used gold baths.
• electroless palladium process described herein the process is simple and costs are significantly reduced due to the removal of expensive gold metal and the running cost of electroless nickel. Finally, production times are reduced by nearly 70% with use of palladium as compared with ENIG.

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)
• Inorganic Chemistry (AREA)
• Chemically Coating (AREA)

Priority Applications (2)

Applications Claiming Priority (1)

Publications (1)

Family

ID=50233532

Family Applications (1)

Country Status (2)

Cited By (7)

Citations (5)

Family Cites Families (3)

• 2012
  • 2012-09-11 US US13/609,705 patent/US20140072706A1/en not_active Abandoned
• 2013
  • 2013-08-20 WO PCT/US2013/055653 patent/WO2014042829A1/fr active Application Filing

Patent Citations (5)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events