Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/38—Improvement of the adhesion between the insulating substrate and the metal
• • 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
  • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
  • C23C18/22—Roughening, e.g. by etching
  • C23C18/24—Roughening, e.g. by etching using acid aqueous solutions
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/38—Improvement of the adhesion between the insulating substrate and the metal
  • H05K3/381—Improvement of the adhesion between the insulating substrate and the metal by special treatment of the substrate
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
  • H05K1/0313—Organic insulating material
  • H05K1/032—Organic insulating material consisting of one material
  • H05K1/0346—Organic insulating material consisting of one material containing N
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/07—Treatments involving liquids, e.g. plating, rinsing
  • H05K2203/0779—Treatments involving liquids, e.g. plating, rinsing characterised by the specific liquids involved
  • H05K2203/0783—Using solvent, e.g. for cleaning; Regulating solvent content of pastes or coatings for adjusting the viscosity
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
  • H05K3/18—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using precipitation techniques to apply the conductive material
  • H05K3/181—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using precipitation techniques to apply the conductive material by electroless plating

Definitions

• This inv ention relates to the metal plating of plastics and, in particular, to enhancing the adhesion of metal plating to polyetherimide plastics, such as, the plastic sub st rate of elect ronic circu it boards, by conditioning the board p rior to metal plating of the board.
• plastic parts are well-known to be of considerable commercial importance because the desirable characteristics of both the plastic and the metal are combined to offer the technical and aesthetic advantag es of each.
• Such metal plating of plastics is used for a wide range of applications f rom decorative plating to radio f requency shielding.
• These boards vary in design and may have a copper layer on each surface face of the polyetherimide resin (two-sided boards) or they can be multi-layer boards which have a plurality of inter-leaved parallel planar copper and resin layers.
• through-holes in the boards are metal ' plated to facilitate connection between the circuits on the copper layers.
• the problems in plating either the through-holes or other plastic parts of the board are well-known in the art and a number of methods have been developed to improve the adhesion of the metal plating to the plastic substrate. While different uses require different adhesive strengths, in general, it has been established that a minimum peel strength of about 8 lbs. per linear inch (approximately 1.4 kilograms per centimeter) as measured by the Jacquet Peel Test is required to prevent a metal coating from blistering or peeling from a plastic surface during manufacture and use. According to ASEP
• test measures the force needed to peel a one-inch (2.5 centimeters) wide plate strip 37.5 micrometers ⁇ 0.51 thick acting at 90° ⁇ 5° to the substrate surface.
• the measurement is done with an Instron Tensometer programmed to peel the plate strip from the substrate. at the rate of 1.0 + 0.1 inch (2.5 + 0.2 centimeters) per minute.
• the present invention treats the plastic surface before plating to enhance the adhesiveness of the metal plating using a procedure generally known as a swell and etch technique and employs solvents which condition or swell the plastic and oxidants to etch the plastic.
• U.S. Patent No. 3,758,332 discloses the use of chemicals such as methyl ethyl ketone, tetrahydrofuran, dioxane, pyridine, dimethylf orma ide, and an alcohol mixture comprising methyl ethyl ketone, ethanol and methanol as SW ellants for epoxy resin.
• Etchants are oxidizing materials and are generally aqueous solutions containing materials such as sulfuric acid, phosphoric acid, permanganate ions, Cr+6 ions and the like.
• 4,086,128 shows pretreatment of an epoxy resin with an organic solvent comprising alcohols, acids, esters, ketone, nitriles, nitro compounds, and polyhydric compounds such as ethylene glycol, gylcerine and 1, 2-p ropylene gylcol p rior to etching with hydrogen peroxide and sulfu ric acid.
• U.S. Patent No. 3,865,623 shows immersion of expoxy resin in an organic solvent 5 such as dimethylformamide to render the epoxy receptive to an acid etch.
• the method includes first exposing the plastic for a suitable time to a swellant composition comprising a solution of a polar material, preferably having a dielectric constant g reater than about 15 and a
• an acid such as H2S04
• the resultant etched su rface is now in a condition of improved adhesion for any species such as p rinting inks, paints, coatings, and, in particular, for metal coatings, which may be deposited thereon.
• rinsing of the plastic may be performed at any stage of the process and removal of residual etchant or etchant-plastic material may require fu rther treatment if desired.
• the process of using the compositions of the invention in manufactu ring printed circuit boards and,- in particular, boards containing through-holes is a sequ ence of steps comm encing with a laminate or multi-lamin ate m ade f rom, e.g., filled polyetherimide material.
• a predesigned series of through-holes may be formed in the board by injection molding or d rilling.
• the board is then contacted with the swellant composition of the invention and, after water rinsing, the board is etched at an elevated temperatu re with an oxidant such as a solution of H2 S04 and C r03 and w ater rin sed.
• a p referred step is to pretreat the board with a composition such as ENPLATE PC-4459 sold by Enthone, Incorporated to remove hyd rocarbon soils and promote the catalyst and then to contact the board with a composition such as ENPLATE PC-236 to eliminate d rag-in.
• the board is now immersed in a catalyst, such as a tin-palladium solution, which conditions the surface of the resin for electroless copper plating.
• ENPLATE Activator 444 is exemplary of this type of catalyst.
• the board is then immersed in a post activator such as ENPLATE PA-493 to activate the Scatalyst by removing the excess tin and freeing the metal palladium ions on the board, rinsed and immersed in an electroless copper plating solution for a period of time sufficient to plate copper to the desired thickness on the surfaces and to plate the surfaces of the holes to lOform through-hole connections between the laminate surfaces.
• ENPLATE CU-700 and other similar plating compositions may be employed.
• the boards may then be immersed in dilute sulfuric acid followed by electroplating using conventional techniques if a thicker
• Rinsing of the board between steps may be conventionally employed as is well-known in the art.
• the polyetherimide resin contain other materials, preferably a filler or reinforcing material, e.g., glass fibers.
• Other fillers include
• the swellant composition comprises a solution of a polar material and
• 35an organic solvent which composition is essential to provide a swelled plastic capable of being etched and plated with the desired adhesiveness at a high degree of reproducability as will be demonstrated in the examples.
• the polar materials useful herein are those materials having dielectric constants greater than about 15, preferably greater than about 20, most preferably greater than about 30 and dipole moments greater than about 3 D and preferably greater than about 3.5 D. Exemplary of these materials are dimethylformamide, dimethylacet amide, dimethyl sulfoxide, tetrahydrothiophene dioxide, N-methylpyrrolidone, hexa ethylphosphoric triamide, tetramethylurea, and acetonitrile. Other materials of similar structures may also be utilized as the polar materials hereof. Thus, other sulfoxides which are liquid at or near room temperature may be so employed, e.g., those having the formula
• R and Rl may each comprise alkyl groups of from 1 to 4 carbon atoms.
• other sulfones may be so used, e.g., those of the formula
• R2 and R3 may be lower alkyl (1 to 4 carbon atoms) or may be linked to form a tetrahydrothiophene ring.
• the second component of the swellant composition may be any suitable organic solvent selected from the carboxylic acids, ketones, hydrocarbons, ethers, esters. alcohols, polyhydrics, e.g., glycols and polyglycols, including ethers and esters thereof.
• the organic solvent will typically contain less than about 10 carbon atoms, with the proviso that the polar material be soluble in the organic solvent to produce the desired composition.
• Exemplary solvents include acetic acid, n-pentane, ethyl acetate, ethanol, methoanol, and the like.
• the preferred organic solvents because of their demonstrated effectiveness are the polyhydrics such as the glycols, and the ethers and esters thereof. These solvents may be represented by the formula
• RlO(AO)nR 2 wherein Rl and R2 are independently selected from the group consisting of hydrogen atoms, aryl groups and alkyl and acyl groups of 1-4 carbon atoms, A is a straight or branched chain C2 to C4 alkylene group, and n is an integer of 1 to 4.
• solvents include ethylene glycol, ethylene glycol m on om ethyl ether, propylene glycol, propylene glycol monomethyl ether, ethylene glycol acetyl ester, etc.
• the polar material and organic solvent swellant mixture may comprise one or more compounds of each ingredient.
• the swellant composition may also be used in the form of an aqueous solution although it has been found that the water is desirably limited, in weight percent, to less than about 20%, and preferably less than 10% and more preferably less than 5% and even 1%. In general, water decreases the swellant effect of the composition and the adhesiveness of the subsequent metal plating.
• Two particularly preferred polar materials are dim ethylsu If o ide (DMSO) and N-methylpyrr olid one and the preferred solvents are the polyhydrics represented by the formula RlO(AO)nR2.
• compositions of the two components contain, by volume, about 25% to 90% DMSO, preferably 50% to 85% and most preferably 70% to 80%, with the balance being the polyhydric component.
• DMSO dimethyl sulfoxide
• a range of 15% to 70% preferably 20% to 50% and most preferably 20% to 30% may be employed.
• a preferred solvent because of its demonstrated effectiveness is propylene glycol onomethyl ether wherein Rl is H, A is C3, n is 1 and R2 is methyl.
• Suitable additives can be employed in the swellant composition for specific purposes such as wetting agents to enhance the capability of spreading the composition on the resin surface.
• the plastic substrate is contacted with the swellant composition at an elevated temperature for a sufficient time to render the surface receptive to the etching process.
• Contacting procedures may vary widely, e.g., 1 to 60 minutes at temperatures up to about 180°F. (82°C), and preferably 2 to 20 minutes at 140° to 160°F. (60° to 71°C). Satisfactory results for glass-filled polyetherimide resin are provided by immersing the part in the composition for about 5 minutes at 150°F. (65°C).
• the time and temperature will, in general, vary inversely as will be appreciated by those skilled in the art. Other means such as spraying, may be used for treating the plastic part.
• the treated plastic part is then ready for oxidative etching using a chrome containing solution and basically comprises contacting the treated plastic part with the etchant at an elevated temperature for a sufficient time to promote adhesion to the surface. It is preferred to then rinse the etched plastic part to remove excess solution and to remove any chrome residues by neutralization with a material such as sodium bisulfite or chemical reduction using reductants such as hydrazine and oxalic acid.
• An acid such as
• H2S04 is preferably included in the etchant solution and other acids like H3P04 may also be employed.
• a preferred etchant composition is an aqueous solution of H2S04 and Cr03. Suitable additives may also be used such as surfactants, e.g., perf luorinated sulfonates, to insure uniform etching of the conditioned resin surface.
• the concentration of the etchant solution may vary widely with the chromium component added as Cr03 being, by weight, about 100 grams/liter (g/1) to saturation, preferably about 200 to 600 g/1, and most preferably about 300 to 500 g/1.
• the acid component is about 100 to 500 g/1, and more preferably about 200 to 400 g/1.
• a preferred composition contains about 400-450 g/1 Cr03, e.g., 420 g/1, and 250-350 g/1 H2S04, e.g., 300 g/1.
• An important feature of the invention is the temperature of the etching process.
• Conventional etching procedures utilize a temperature which may vary over a broad spectrum from as low as room temperature to the boiling point of the etching solution. It has been found for the conditioned polyetherimide resins however, that temperatu res above about 160°F. (71°C) and p referably above about 170°F. (77°C) are n ecessary and that unexpected adhesive p roperties to the metal coating are p rovided.
• etching time will vary depending on the concentration of the etching solution and temperatu re of the etching p rocess as will be app reciated by those skilled in the art, for the p referred composition of 420 g/1 C r03 and 300 g/1 H2 S04 , an etching time of about 5-15 minutes at 170°F. (77°C) p rovides excellent results. In general, the etching time may be up to about 60 minutes but is typically less than 30 minutes.
• An optional step of removing traces of deposits on the etched resin may now be performed. Rinsing will remove deposits but a p referred p rocedu re is to contact the resin with a suitable reducing ag ent for chromium ions such as NaHS03 , NaOH, and the lik e. Immersion of the etched resin in a solution of 150 g/1 NaHS03 for 5 minutes has p roduced satisfactory results. Typically, exposu re to the reducing agent rang es f rom 30 seconds to 10 minutes at a temperatu re ranging f rom room temperatu re to 160°F. (71°C).
• a smoother metal plated su rface is desired, another optional step is to treat the etched resin to dissolve part of the filler material.
• Materials such as hydrogen fluoride and ammonium bifluoride may be suitably employed.
• ACTANE 70 sold by Enthone, Incorporated has proven very satisfactory for this purpose.
• the etched resin is now prepared for metal plating by known means to render the surface catalytic. Among them are cleaning, applying catalyst promoters, sensitizing using an aqueous tin chloride solution and then activating by means of palladium chloride.
• unitary baths may be employed for such purposes, such as the dispersions of colloidal palladium and tin ions described in Shipley, U.S. Patent No. 3,011,920 or the soluble complexes of noble metals, stannous ion and anions as described in Zeblisky, U.S. Patent No. 3,672,938.
• the surface may now be plated, with a film of metal by ' electroless ' plating.
• the metal layer was tested for adhesion using the Jacquet Peel Test and an ultimate peel strength of greater than 11 lbs/in (2 kilograms/cm) was obtained.
• the peel strength generally increases with time to a maximum (ultimate) value and the ultimate peel strength as used herein represents the adhesion value obtained for the metal layer greater than 3 days after metallization.
• EXAMPLE I was repeated except that the etched board was treated with ACTANE 70 prior to step (g) and a smooth adhesive coating was obtained.
• Step (a) of EXAMPLE I was repeated using 100% DMSO and the plaque's surface was attacked and unsuitable for further processing. Similar results were obtained when 100% N-methylpyrrolidone was used in Step (a).

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Manufacturing & Machinery (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Chemically Coating (AREA)
• Electroplating Methods And Accessories (AREA)
• Manufacturing Of Printed Wiring (AREA)

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• 1986
  • 1986-05-28 EP EP19860903950 patent/EP0227746A4/de not_active Withdrawn
  • 1986-05-28 JP JP61503368A patent/JPS63500249A/ja active Pending
  • 1986-05-28 WO PCT/US1986/001199 patent/WO1987000391A1/en not_active Application Discontinuation
  • 1986-05-28 BR BR8606709A patent/BR8606709A/pt unknown
  • 1986-05-28 AU AU59914/86A patent/AU580433B2/en not_active Ceased
  • 1986-05-28 KR KR870700155A patent/KR880700620A/ko not_active Application Discontinuation
  • 1986-06-04 CA CA000510800A patent/CA1249188A/en not_active Expired
  • 1986-06-05 IL IL79044A patent/IL79044A0/xx unknown
  • 1986-06-23 ES ES556423A patent/ES8800992A1/es not_active Expired

Non-Patent Citations (2)

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