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
  • C23C18/18—Pretreatment of the material to be coated
  • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
  • C23C18/28—Sensitising or activating
• • 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
  • H05K3/22—Secondary treatment of printed circuits
  • H05K3/24—Reinforcing the conductive pattern
  • H05K3/244—Finish plating of conductors, especially of copper conductors, e.g. for pads or lands
• • 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
• • 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

Definitions

• the invention relates to a method for coating surfaces on copper or a copper alloy, for example on brass, with a tin or tin alloy layer, further a layer combination including a tin or tin alloy layer and applications of the method for producing solderable even after thermal treatment Surfaces on copper or a copper alloy and for the production of layers to protect such surfaces against corrosion.
• the invention also relates to a bath solution for the electroless deposition of a tin layer or a tin alloy layer.
• tin layers have long been applied in an electroless process in which the base metal dissolves in favor of the deposited tin ions.
• the tin layers can in principle also be deposited on other metals, such as iron.
• the workpiece In order to form a sufficiently thick layer, the workpiece must be treated at 90 to 100 ° C for two to three hours.
• US Pat. No. 2,891,871 A describes a process for the direct coating of workpieces on copper or a copper alloy, in which a tin layer is formed on the workpiece by immersion in a solution of a tin salt, a carboxylic acid and thiourea or a derivative of thiourea by charge exchange becomes.
• US Pat. No. 2,282,511 A describes a process for coating copper surfaces in which a solution is used which contains compounds containing tin (II) ions, dissolved thiocarbamide and a small amount of an alkali metal carbonate. With this solution, too, a tin layer can be formed directly on the copper surfaces.
• such solutions can be used for electroless deposition of tin on the inner surfaces of copper pipes in order to avoid the dissolution of copper.
• US 2,369,620 A also describes an electroless tinning process for the coating of copper surfaces.
• the aqueous coating solution described in this document is acidic and, in addition to a tin-II salt, preferably SnCl 2 , also contains thiourea.
• an aqueous immersion bath for the deposition of tin also contains hypophosphorous acid or its alkali salts in order to improve the stability of the deposition solution and to obtain purer, lighter, denser and more resistant to etching tin layers than with the deposition solutions known hitherto .
• the deposition solution can also contain an organic acid such as acetic acid, citric acid, malic acid, maleic acid and similar aliphatic mono-, di- and tricarboxylic acids.
• This solution also contains thiourea and a wetting agent. With this bath, layers with a thickness of a few ⁇ m could be deposited.
• DE 30 11 697 A1 describes an acidic chemical tinning bath, for example for coating copper surfaces, which contains a source of tin (II) ions, thiourea and, as a further constituent, an inhibitor, an organic sulfonic acid preferably being used as the inhibitor.
• the pH of the solution is kept below 1. This solution also contains a hypophosphite.
• a method is described in US 4,657,632 A in which a part of the copper surfaces on the base material is removed by etching, in that an etching resist is applied to the regions of the copper surfaces which are not to be removed and the parts of the copper surfaces which are to be removed are left free.
• the etching resist layer is formed by electrolessly depositing a tin layer on the copper layers.
• the deposition solution used for this purpose also contains urea or a derivative of urea.
• the solution can also contain a chelating agent, for example amino and hydroxycarboxylic acids, a reducing agent, for example an aldehyde, and an acid.
• a wetting agent may also be present in the solution.
• EP 0 503 389 A2 describes a method for electroless coating of workpieces with surfaces on copper or a copper alloy with tin or a tin / lead alloy.
• the acidic coating bath contains a reducing agent, such as hypophosphite or its acid, and a complexing agent, for example organic carboxylic acids or thiourea or its derivatives.
• EP 0 521 738 A2 describes a solution for electroless plating with tin or with a tin / lead alloy of copper surfaces preferably contained on printed circuit boards, which in addition to tin salts, thiourea, an acid and a reducing agent such as hypophosphite, also one or more nonionic Contains wetting agents, preferably a polyoxyalkyl ether, for example polyoxynonylphenyl ether.
• DE 40 01 876 A1 describes a composition for a bath for electroless coating with tin or with a tin / lead alloy, the alkane or alkanolsulfonic acids and their tin and lead salts and also thiourea and thiourea derivatives and mono-, di-, Contains tricarboxylic acids or their salts as chelating agents for tin and lead.
• the composition is used to coat copper or copper alloys.
• the composition can also contain, inter alia, nonionic wetting agents, for example polyoxyalkylene alcohol ethers.
• the use of tin layers as a solderable layer was also repeatedly tested for the production of printed circuit boards.
• the conductor tracks obtained after the structuring of the copper layers must be solderable for the assembly of components, with the requirement that the exposed metal surfaces have good wettability with the solder, usually tin / lead solder, even after a long storage period of several days to weeks. must have.
• the present invention is therefore based on the problem of avoiding the disadvantages of the prior art and, in particular, of finding a method and a bath solution with which it is possible to add tin and possibly also tin alloy layers to surfaces on copper or a copper alloy form, which are easily wettable with liquid tin / lead solder even after a long storage period.
• This problem is solved by the features of claims 1 and 8, 9, 12 and 13.
• intermetallic phase is responsible for the poor solderability of tin layers on printed circuit boards that have been stored for several days to weeks.
• the storage forms a copper / tin alloy at the phase interface between the copper base and the tin layer, the thicker the longer the printed circuit board is stored and the higher the temperature during storage.
• These intermetallic phases form very quickly.
• the solderability drops rapidly when the entire tin layer, which has a thickness of 0.7 ⁇ m, for example, is converted into the intermetallic phase.
• the electroless plating of tin is closely observed in the first seconds of the plating process, it can be determined that "states" that were already visible on the copper surface before the tin plating are "frozen” by the tin layer.
• the tin or tin alloy layer is deposited more rapidly on certain morphological structures that are located on the copper surface than on locations on the copper surfaces where these structures are not. For example, structures are formed on rinsing water lines or oxidized areas of the copper surfaces that differ at least optically from neighboring areas. Will the
• intermetallic phases form very quickly at these spots. These are more easily oxidized in air than pure tin layers or copper surfaces. When oxidized, these intermetallic phases lose their ability to be wetted with liquid solder.
• the problems described above were solved by the method according to the invention, which has the following essential method steps: a.
• the copper or copper alloy surfaces are treated with a solution which contains at least one noble metal compound in order to deposit noble metal in a first step. Its thickness can be extremely small. For example, it is sufficient to form a layer of precious metal that is not visible to the naked eye. That alone
• step a surfaces coated with noble metal are then treated with a solution which contains at least one tin compound and optionally at least one compound of a further metal to be deposited, at least one acid and at least one complexing agent for copper from the group consisting of thiourea and its derivatives.
• Tin or tin alloy layer Tin or tin alloy layer.
• the bath solution according to the invention for the electroless deposition of a tin layer or a tin alloy layer is characterized in that it a. at least one tin compound and optionally at least one compound of a further metal to be deposited, b. at least one acid, c. at least one complexing agent for copper from the group consisting of thiourea and its derivatives and d. optionally contains at least one wetting agent.
• the precious metal layer is formed by charge exchange, through which copper ions dissolve at the same time as the metal deposition.
• the noble metal coating formed is believed to hinder the further oxidation of copper and the formation of the intermetallic phase between copper and tin. This probably suppresses the further oxidation of the tin layer, so that the wettability of the surfaces with solder is retained even after prolonged heat treatment.
• the tin and precious metal layers are dissolved extremely quickly by the liquid solder. This process proceeds very quickly, so that there is sufficient time between the liquid tin / lead solder and the copper to form the intermetallic tin / copper phase that is typical and desired for the soldering process.
• the copper or copper alloy surfaces are cleaned or etched.
• the workpieces are then brought into contact with an aqueous acid solution. 5. Then tin is deposited without current, preferably at a temperature of about 60 ° C; the treatment time is preferably about 4 minutes to about 30 minutes.
• customary cleaning and etching solutions are used, for example solutions containing wetting agents, which can also contain, for example, hydrogen peroxide and sulfuric acid.
• One or more noble metal compounds from the group consisting of silver, gold, platinum, palladium, ruthenium, rhodium, osmium and iridium are used in the bath used for the noble metal deposition.
• the concentration of the noble metals in the solution is preferably about 0.1 to about 2000 ppm (parts by weight of noble metal per million parts by weight of solution), preferably about 1 to about 100 ppm.
• the circuit boards are only treated briefly in the precious metal bath, for example within a period of about 60 seconds to about 120 seconds. Of course, longer treatment times can also be selected.
• the treatment temperature when depositing noble metal is preferably about 20 to about 30 ° C.
• the plates are brought into contact with an acid solution.
• An acid contained in the tinning bath can preferably be used as the acid.
• Another acid can of course also be used.
• the copper or copper alloy surfaces are prepared for tinning; at the same time, the acid protects the subsequent tin bath from dilution.
• the electroless tin bath must have the highest possible stability against decomposition.
• Mineral acids, organic acids and sulfonic acids are preferably selected as the acids contained in the tin bath.
• the tinning bath is operated at a temperature of about 50 to about 70 ° C. Under these conditions, firmly adhering and uniformly bright tin layers with a thickness of approximately 0.6 to approximately 1.4 ⁇ m can be deposited on copper or a copper alloy.
• a tin / lead alloy can be deposited as the tin alloy.
• the deposition bath additionally contains a lead II salt, for example PbCI 2 or Pb (OCOCH 3 ) 2 .
• the printed circuit boards are immersed one after the other in containers in which the individual treatment solutions are contained. Since the treatment times are extremely short, the circuit boards can also be treated in a continuous system through which the boards are passed in horizontal or vertical orientation and in the horizontal transport direction.
• the method according to the invention is particularly suitable for the production of surfaces on copper or a copper alloy that can be soldered even after thermal treatment, and for the production of layers for protecting surfaces on copper or a copper alloy against corrosion.
• the method can also be used to form the layer combination according to the invention on workpieces other than printed circuit boards, for example for coating pipes against corrosion.
• a wiring board provided with copper structures and in particular with connection points for electrical components was treated with an aqueous solution of sodium peroxodisulfate in a silver complex solution containing 50 ppm silver after 1 minute at room temperature after cleaning and etching the copper. After the plate was rinsed with water and subsequently treated with a solution of 2% by weight acid in water, it was tinned in an electroless tin plating bath at 60 ° C. for 15 minutes.
• the tinning bath had the following composition:
• the tin layer obtained after the treatment with the bath was light metallic and had a thickness of 1.05 ⁇ m.
• the plate was then annealed in air at 155 ° C for eight hours and then subjected to a wave soldering process.
• a fluxing agent a low solid content (2%) no-clean Flux was used (product Kester ® Litton-Kester, USA).
• the soldering result at the connection points was excellent because the wetting behavior on the tinned copper surfaces was flawless.
• the passage of the solder into the drill holes contained in the plate was 80 to 90% flawless (the circuit board was not equipped with components).
• a circuit board pretreated as in Example 1 was coated with platinum in a platinum solution containing 15 ppm of platinum for 1 minute at room temperature and then further treated as in Example 1.
• the bright tin layer obtained had a thickness of 1 ⁇ m after a 30 minute immersion in the tinning bath at 55 ° C.
• the plate was then tempered at 155 ° C. for four hours and subjected to a soldering test analogously to Example 1. There were neither errors in wetting with the liquid solder nor problems with solder penetration in the holes; this was 100%.
• a circuit board pretreated as in Example 1 was treated in a ruthenium solution containing 50 ppm ruthenium for 2 minutes.
• the copper layers, which were covered with the extremely thin ruthenium layer, were in a chemical tin bath of the composition: Tin (II) chloride 5 g
• the tin layer was subjected to a solder spread test.
• the solderability was excellent with 9 ° contact angle.

Landscapes

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

Applications Claiming Priority (3)

Publications (1)

Family

ID=7866016

Family Applications (1)

Country Status (6)

Families Citing this family (9)

Family Cites Families (3)

• 1999
  • 1999-04-15 WO PCT/DE1999/001176 patent/WO1999055935A1/de not_active Application Discontinuation
  • 1999-04-15 CA CA002326049A patent/CA2326049A1/en not_active Abandoned
  • 1999-04-15 KR KR1020007011306A patent/KR20010042625A/ko not_active Application Discontinuation
  • 1999-04-15 CN CN99805208A patent/CN1297490A/zh active Pending
  • 1999-04-15 EP EP99927684A patent/EP1082471A1/de not_active Ceased
  • 1999-04-15 JP JP2000546074A patent/JP2002513090A/ja active Pending

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events