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
• • 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
  • H05K3/382—Improvement of the adhesion between the insulating substrate and the metal by special treatment of the metal
  • H05K3/385—Improvement of the adhesion between the insulating substrate and the metal by special treatment of the metal by conversion of the surface of the metal, e.g. by oxidation, whether or not followed by reaction or removal of the converted layer
• • 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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
  • C23C22/52—Treatment of copper or alloys based thereon
• • 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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/82—After-treatment
  • C23C22/83—Chemical after-treatment

Definitions

• the present invention relates to a treatment solution and method for copper surfaces on printed circuit boards. More particularly, the present invention relates to a solution and method for improving copper-to-dielectric bond integrity by increasing the chemical resistance of organometallic conversion coatings that are formed on the surface of copper pads and traces on printed circuit boards.
• Multilayer circuit boards typically consist of alternating layers of copper and dielectric material, which are laminated together.
• MLBs There are a variety of MLBs on the market today. Depending on the materials they are made of, they can be rigid (if formed from rigid materials such as glass-reinforced epoxy-resin, BT, CE, PTFE, etc.), flexible (if formed from flexible materials such as polyester or polyimide) or they can be a combination, (i.e., so-called "rigid- flex”). If the alternating layers of copper and dielectric are applied one onto another in a sequential process rather than laminated simultaneously into a single package, they are classified as Sequential Build-Up (SBU) Boards. The integrity of MLB depends upon a reliable bond being formed between the copper and dielectric. In conventional MLB manufacturing processes, copper layers are treated using a hydroxide/chlorite based treatment solution. This so-called
• Black Oxide Process provides an enhanced copper-to-dielectric bond.
• Examples and details of the Black Oxide Process are set forth in, for example, U.S. Patents 4,358,479; 4,409,037; 4,512,818; 4,844,981 and 4,969,958.
• the Black Oxide Process suffers from various limitations including the following: 1. The process can be carried out only in an aggressive strongly alkaline solution at about 160-170 °F.
• the processing time is long, thereby creating bottlenecks in the manufacturing sequence.
• the Black Oxide coating readily dissolves in acids, which makes it susceptible to acid attack in subsequent processing steps. This frequently results in an undesirable phenomenon commonly referred to as “pink ring” and sometimes can even result in "wedge voids” and ultimately delamination between the copper and adjacent dielectric layer. 4.
• the initially high bond strength between the Black Oxide coated copper and the dielectric material usually deteriorates rapidly as the MLB passes through subsequent thermal excursions during the fabrication and assembly processes.
• a reliable copper-to-dielectric bond is especially important for flex and SBU circuit boards.
• Polyimides which are used for flexible boards, and photo-imageable dielectrics used for SBU circuit boards, are known to exhibit lower copper-to-dielectric bond strength than conventional epoxy-glass based rigid circuit boards.
• the Black Oxide coating comprises a mixture of cupric and cuprous oxides. This coating exhibits poor chemical resistance on the basis that it is predominantly formed of cupric oxide. Unlike cupric oxide (black) which is easily attacked by acids, cuprous oxide (red to brown) is relatively chemically inert.
• the first type is based on a reduction process as disclosed in, for example, U.S. Patents 4,642,161; 4,902,551; 5,006,200; 5,076,864; 5,147,492; 5,382,333; 5,492,595; 5,556,532 and 5,721,014.
• the second Black Oxide post-treatment type is based on partial dissolution of the oxide coating as described in, for example, U.S. Patents 4,717,439; 4,775,444; 5,106,454; 5,261,154; 5,289,630 and 5,501,350.
• the first mechanism is a reduction process, which partially converts the cupric oxide into a mixture of cuprous oxide and metallic copper.
• the second mechanism is a dissolution process, which selectively dissolves cupric oxide, thereby leaving cuprous oxide on the surface. Both processes convert Black Oxide (predominantly cupric) into a surface rich in cuprous oxide.
• Black Oxide reduction and dissolution post-treatments do eliminate "pink ring" and improve the acid resistance of the coating to some extent, they do not solve all of the above mentioned problems associated with the Black Oxide performance.
• organometallic conversion coating (OMCC) on the copper surface.
• organometallic conversion coatings are the product of a chemical reaction between metal ions (in single or multiple valency states) and organic compounds. As such, they are readily distinguished from inorganic Black Oxide.
• the OMCC comprises a film of metal ions tied into a complex or otherwise bonded with one or more organic materials. Such processes for forming an OMCC are disclosed in U.S. Patents 5,800,859 and 5,869,130.
• the organometallic conversion coating that forms during this process is much more acid resistant than Black Oxide coatings. It is not, however, completely impervious to chemical attack since it still contains a portion of a cupric-based organometallic compound in its composition.
• the MLB panels are drilled. During the drilling operation, vibration of the drill bit can create microfractures in the copper/dielectric interface. Solvent conditioners then can get absorbed into the microgaps between the copper and the dielectric. Subsequent treatment with permanganate solution will oxidize, i.e. remove, this already swelled resin creating a "wedge". Microetch solution will attack the copper and widen the gap. Pre-dip and activator solutions typically are fairly concentrated hydrochloric acid based solutions, which will further remove the copper treatment layer. If electroless copper fails to completely seal the "wedge", the chemical attack will continue when the article is immersed in acid cleaner, microetch solution, acid dip and acid copper.
• the present invention relates to a treatment solution and process that overcomes the problems associated with known methods for enhancing the copper to dielectric bond during MLB manufacture. More particularly, the present invention relates to a method for enhancing the bond integrity by increasing chemical resistance of the adhesion promoting copper coating by converting cupric-based organometallic compounds on the copper surface into cuprous-based organometallic conversion coatings. This is achieved by reduction and/or by partial dissolution of the organometallic coating, and optionally applying a copper oxidation inhibitor at the same time.
• the basis of the present invention is to significantly improve chemical resistance of an organometallic conversion coating (OMCC) making it resistant to chemical attack during the desmear, electroless copper and acid copper electroplating processes, thereby eliminating "pink ring", "wedge voids” and a propensity towards delamination due to chemical attack and enhancing the bond integrity.
• OMCC organometallic conversion coating
• Improved chemical resistance can be accomplished by converting most of the cupric-based organometallic compound on the surface into a cuprous-based organometallic conversion coating. This conversion can be achieved by reduction and/or by dissolution.
• Post-treated OMCC can be easily differentiated from either reduced or partially dissolved Black Oxide. The latter is claimed to consist primarily of metallic copper.
• Reduced OMCC remains an organometallic complex in which most of the divalent copper is reduced to monovalent.
• partially dissolved Black Oxide is still a mixture of cuprous and cupric oxides
• partially dissolved OMCC is an organometallic complex based primarily on monovalent copper.
• the composition can contain a copper oxidation inhibitor or a combination of several inhibitors in order to prevent re-oxidation of the OMCC in subsequent processing steps.
• the resulting cuprous-based OMCC is substantially more resilient and resistant to subsequent MLB processing steps, than either post-treated Black Oxide or untreated OMCC.
• DMAB dimethylaminoborane
• other aminoboranes e.g. diethylaminoborane, morpholine borane, etc.
• reducers that can be utilized for this application are: ammonium, alkali and/or alkaline earth metal borohydrides, hypophosphites, sulfites, bisulfites, hydrosulf ⁇ tes, metabisulfites, dithionates, tetrathionates, thiosulfates, thioureas, hydrazines, hydroxylamines, aldehydes (including formaldehyde and glyoxal), glyoxylic acid and reducing sugars. Electric current can be used for the reduction as well.
• any of the known cupric ion chelators can be utilized for this application.
• these include EDTA, HEEDTA, NTA, DTP A, DCTA, Quadrol, organic phosphonates (Dequests), organic acids (citric, tartaric, gluconic, glutamic, sulfamic, glycolic, glycine, malic, maleic, salicylic, ascorbic, formic, etc.), inorganic acids (hydrochloric, hydrofluoric, hydrobromic, nitric, chromic acids, etc.), and/or their ammonium, alkali, alkaline earth metal and/or amine salts, amines (MEA, DEA, TEA, TMAH, EDA, DETA, TETA, TEPA, etc.), ammonium hydroxide, pyrophosphates, etc.
• copper oxidation inhibitors may optionally be used as well.
• one or more of the following copper oxidation inhibitors can be incorporated into the composition: unsubstituted and/or alkyl-, aryl-, alkylaryl-substituted azole derivatives, (including halogen substituted derivatives thereof), e.g.
• benzotriazol BTA
• tolyltriazol TTA
• 5- methylbenzimidazole 2-bromobenzyl benzimidazole, 2-chlorobenzyl benzymidazole, 2- bromophenyl benzimidazole, 2-chlorophenyl benzimidazole, 2-bromoethylphenyl benzimidazole, 2-chloroethylphenyl benzimidazole and 2-undecyl-4-methylimidazole.
• benzotriazol and tolyltriazol are preferred.
• Cationic, amphoteric, anionic and/or non-ionic surfactants can also be utilized to enhance the effectiveness of the post-treatment solution.
• a combination of a reducer (or any number of reducers) with a dissolution agent (or any number of dissolution agents) can be used as well.
• the pH, temperature, concentration and processing time should be adjusted appropriately to insure effective reduction and/or dissolution of the cupric ion.
• this solution may contain an oxidation inhibitor or a combination of several inhibitors.
• Example 1 A piece of 1 oz. DSTFoil (available from Polyclad Laminates) and an epoxy-glass laminate panel clad with the same DSTFoil on both sides (Polyclad Laminates) were processed through the sequence of the following steps:
• PC 7036 Microetch (available from Alpha PC Fab) 90°F, 1 min.
• the foil was laid-up with two layers of Polyclad 1080 B -stage pre-preg (available from Polyclad Laminates) and two layers of Polyclad 7628 pre-preg on one side, treatment layer facing the 1080 pre-preg.
• the DSTFoil clad copper/epoxy-glass laminate was laid-up with two layers of Polyclad 2313 on each side. Both lay-ups were then pressed at 370°F temperature and 350 psi pressure for 60 minutes.
• the laminated foil panel was masked with 1/8 inch wide tape and the exposed copper was etched off in 500 g L ferric chloride solution at 130°F. The panel was rinsed, dried and the masking tape was removed. The adhesion of the copper foil to the cured epoxy resin was then tested by peeling back the 1/8 inch wide copper strips using CECO TA 620-30 Peel Tester. The adhesion was found to be 6.76 Lb/in.
• the laminated copper clad panel was cut into 2 inch wide strips, which were subsequently immersed into PC 7457 HASL flux (available from Alpha PC Fab) and then into the molten solder at 500°F. Every minute a strip was taken out of the solder and checked for signs of delamination. The time-to-delamination was found to be 9 minutes.
• PC 7457 HASL flux available from Alpha PC Fab
• Example 1 was repeated with the exception that the DSTFoil and the copper clad laminate after the treatment in PC 7023 Adhesion Promoter were immersed in the solution made up from 6 g/L DMAB and 7.5 g/L KOH at 105°F for 2 minutes. The adhesion was found to be 7.36 Lb/in and the time-to-delamination was 9 minutes and 30 seconds.
• Example 3
• Example 4 A piece of standard 1 oz. foil was taped to a circuit board panel and processed using the same steps as in Example 1 in Coates-ASI horizontal conveyorized wet processing spray machine. The tape was removed and the foil was laminated and tested for adhesion as in Example 1. The adhesion was found to be 4.6 Lb/in.
• Example 4 A piece of standard 1 oz. foil was taped to a circuit board panel and processed using the same steps as in Example 1 in Coates-ASI horizontal conveyorized wet processing spray machine. The tape was removed and the foil was laminated and tested for adhesion as in Example 1. The adhesion was found to be 4.6 Lb/in. Example 4
• Example 3 was repeated with the exception that after the processing in the horizontal equipment the foil was immersed in 5% (vol.) HCL for 1 min. at ambient temperature. The adhesion was 5.1 Lb/in.
• Example 5
• Example 4 was repeated with the exception that 38 g/L NajEDTA solution was used as the post-treatment at 130°F, pH 4.1 for 6 min. The adhesion was 6.2 Lb/in.
• Example 6
• Example 4 was repeated with the exception that 76 g/L Na ⁇ EDTA solution was used as the post-treatment at 130°F, pH 4.1 for 1 min. The adhesion was 6.6 Lb/in.
• Example 7
• Example 4 was repeated with the exception that 10% (vol.) Versene 100 (EDTA solution available from Dow Chemical) solution was used as the post-treatment at 130°F, pH 10 for 1 min. The adhesion was 6.8 Lb/in.
• EDTA solution available from Dow Chemical
• Example 4 was repeated with the exception that 10% (vol.) Versene 100 solution was used as the post-treatment at 130°F, pH 13 for 1 min. The adhesion was 6.9 Lb/in.
• Example 9 is the same as the post-treatment at 130°F, pH 13 for 1 min. The adhesion was 6.9 Lb/in.
• Example 4 was repeated with the exception that 10% (vol.) Quadrol (ethoxylated/propoxylated ethylene diamine derivative available from BASF) solution was used as the post-treatment at 130°F, pH 10 for 1 min. The adhesion was 6.9 Lb/in.
• 10% (vol.) Quadrol (ethoxylated/propoxylated ethylene diamine derivative available from BASF) solution was used as the post-treatment at 130°F, pH 10 for 1 min.
• the adhesion was 6.9 Lb/in.
• Example 4 was repeated with the exception that 10% (vol.) Quadrol solution was used as the post-treatment at 130°F, pH 13 for 1 min. The adhesion was 6.9 Lb/in.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Metallurgy (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Manufacturing Of Printed Wiring (AREA)
• Chemical Treatment Of Metals (AREA)
• Chemically Coating (AREA)
• Manufacturing Of Printed Circuit Boards (AREA)

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Citations (3)

• 1999
  • 1999-07-01 CA CA002335816A patent/CA2335816A1/en not_active Abandoned
  • 1999-07-01 EP EP99933653A patent/EP1097618B1/en not_active Expired - Lifetime
  • 1999-07-01 JP JP2000558701A patent/JP4242566B2/ja not_active Expired - Lifetime
  • 1999-07-01 KR KR1020017000009A patent/KR100592746B1/ko not_active Expired - Lifetime
  • 1999-07-01 WO PCT/US1999/014983 patent/WO2000002426A1/en not_active Ceased
  • 1999-07-01 AT AT99933653T patent/ATE235796T1/de not_active IP Right Cessation
  • 1999-07-01 DE DE69906301T patent/DE69906301T2/de not_active Expired - Lifetime

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