MXPA06009327A - Method of electroplating on aluminum - Google Patents

Abstract

This invention is a zincating process of aluminum surfaces for subsequent plating in which the aluminum surfaces are cleaned, contacted with an acidic etching solution comprising a peroxygen compound, the acidic etching solution being substantially free of corrosive nitrate compounds, and contacting the aluminum surfaces with a zincate solution containing 6-60 g/1 zinc and 100-500 g/1 hydroxide ion. The acidic etching solution is substantially free of toxic inorganic fluoride compounds in order to simplify waste treatment. This invention may be understood with reference to Figure 2, in particular Step 6.

Description

METHOD OF ELECTRODEPOSITION IN ALUMINUM BACKGROUND OF THE INVENTION Field of the invention This invention is in the field of electrodeposition in aluminum. More specifically, it relates to methods of galvanization and, in particular, to methods for the formation of holes through electroplating on cards with printed circuit, of multiple layers, which have internal planes of grounding of aluminum.

Introduction to the invention The electrodeposition process in aluminum for aluminum requires a prolonged and expensive pre-fracking process to prepare the aluminum for electrodeposition. The most popular method for the application of electroplating is the zinc coating method that applies zinc dip coating on a clean aluminum surface. In a typical electroplating process of aluminum on aluminum, the aluminum substrate is first cleaned to remove dirt, grease and oils and then eroded to acid to provide an adequate substrate for adhesion of a zinc coating. The acid eroded substrate is then de-sulfurized with nitric acid to remove the aluminum oxide from the surface and the aluminum substrate is then galvanized followed by electrodeposition of metal. The son of Zinc plating is a fugitive cover that disappears in the subsequent metal electrodeposition operation. Typically a double galvanizing process is used where a first zinc coating is de-galvanized by the use of nitric acid and after applying a second coating of zinc to the aluminum substrate. The double zinc coating process applies the first zinc coating followed by immersion in 50% nitric acid in order to dezincize the zinc. Then the second zinc cover is applied, which is much more uniform than the first one. The nitric acid used to de-sulfur the aluminum and for the double galvanizing process would chemically attack the copper in an aggressive manner, so that conventional zinc-plating processes can not be used for the production of printed circuit boards. The standard galvanization process starts with a two stage alkaline chemical attack of an aluminum surface, 1-3 minutes at 77 ° C (170 ° F) in a regulated alkaline cleaning solution, and then 0.50-1 minute at 55 ° C (130 ° F) in a solution of chemical attack by sodium hydroxide. The alkaline chemical attack leaves a soot in the aluminum, which is removed by strong acids, such as 50% nitric acid solution or 25% hot sulfuric acid followed by 50% nitric acid solution or a solution of 3%. parts of nitric acid and 1 part of hydrofluoric acid. After removing the soot, an aluminum surface is covered with zinc by immersion in a zinc coating solution. The zinc coating solutions typically contain 120-500 g / l of sodium hydroxide, 20-100 g / l of zinc oxide, 1 0-60 g / l Rochelle salt (potassium sodium tarrate) or other complexing organic acid salts, such as gluconates and salicylates and additives such as sodium nitrate, copper, iron or nickel salts. Printed circuit cards with alias component density per unit area require a means to dissipate heat. The problem increases in complexity as the semiconductor industry places more functionality and electronic processing in smaller packages. One of the most important problems is the attraction of heat away from the components and the printed circuit board and the maintenance of a reliable connection between the components and the printed circuit board. The two most common approaches are the heat sink, passive, external and the term, active, internal dissipater. The external passive term dissipater is a metal plate attached to the exile of the printed circuit board. The metal plate is either aluminum or copper. The thermal dissipation depends on the material of the heat sink, the thickness of the material and the properties of formic dissipation of the connection material between the ferrous dissipator and the card with printed circuit. The plans of the external passive heat sink require designs with a low density of holes through electroplating, which is a major disadvantage. The internal active heatsink planes can function as either a ground plane or a heatsink thermal. Copper plates that are used as internal grounding planes and heat sinks can be laminated, drilled and electrodeposited easily into printed circuit boards to provide double support for electrical and thermal needs. However, the thick copper plates required for adequate heat dissipation are heavy and of limited use in weight-sensitive applications. La Pateníe by E. U. No. 4,601, 91 6 (Arachíingi) describes a card with an aluminum core printed circuit. The aluminum core is laminated on both sides with pre-impregnated metallized sheet. The holes are drilled through the copper metallization and the aluminum core. The aluminum surface exposed on the walls of the holes is electrophoretically coated with an epoxy resin and a pattern of printed wiring and holes through electroplating formed by conventional techniques. The aluminum core is a passive support, since there is no way, in the Arachtingi process, to make a hole through the electroplated that has an electrical connection to the aluminum core. U.S. Patent No. 5,538,616 (Arai) refers to a process for producing printed circuit boards, such as a multilayer printed circuit board with an internal aluminum conductor, the aluminum conductor being connected through a hole through the Electroplated. In the Arai process, a multi-layered laminate provided with holes is equipped with a palladium / tin caíalizador. Then, the laminate is subjected to alkaline and acidic cleaning solutions for the chemical attack of the exposed aluminum surface. After the acid cleaning solution, the laminate is treated with an acid solution containing nickel and sodium nitrate. Arai proposes that this heat transfer of nickel acidic nickel causes the aluminum surface to be replaced with fine nickel in submicron preservatives. Esfe nickel is a basis for further development by electrodeposition of nickel without electrons. After the electrodeposition of nickel without electrodes, the holes were electrodeposited by means of conventional copper electrodeposition. Acid acidic cleaning solution is 20% nitric acid and 50 g / l aluminum bifluoride. The nickel substitution process is also an acidic nitric oxide. Nitric acid solutions strongly attack copper surfaces, such as copper metallized laminates, chemically attacking and oxidizing the copper surface and generating noxious nitrogen oxide fumes. Arai does not show the concealment of copper surfaces before the electrodeposition of nickel without electrons. Unless these surfaces are hidden from the deposition of nickel without electrons, the outer surfaces of copper would be electrodeposited with nickel without electrons. The concealment and de-galvanized posiérior of the masks would add exfra efapas to the process. If the copper outer surfaces are not hidden, the surface conductive patterns must be chemically attacked through a layer of nickel without electrons. Chemical etching through nickel without electrons in fine patterns, as required in multilayer printed circuit boards, is extremely difficult due to the strong etching agents needed to attack the nickel layer and the corrosion cell established between the nickel and copper strata. Acidic fluoride solutions, such as ammonia bifluoride, are very toxic and special precautions should be taken in their use and in the treatment of waste solutions containing them. For these reasons, the Arai process has not gained acceptance in the printed circuits industry.

BRIEF DESCRIPTION OF THE INVENTION An object of this invention is to provide a process for the galvanization of an aluminum substrate.; avoiding the process the use of nitric acid and acidic fluorides that are not environmentally friendly and can be difficult in the treatment of waste. This invention is a process of galvanizing aluminum surfaces for subsequent electrodeposition, in which the aluminum surfaces are cleaned, contact with an acidic etching solution comprising a peroxide compound, the acidic etching solution being substantially free of corrosive nitrate compounds and coniacing the aluminum surfaces with a galvanizing solution It contains 6-60 g / l of zinc and 100-500 g / l of hydroxide ion. The acidic etching solution can be substantially free of toxic inorganic fluoride compounds in order to simplify the disposal of waste. In one aspect, the invention is a manufacturing method of a circuit with printed circuit on an organic laminate, the printed circuit length having an aluminum conductive layer and orifices made of copper electroplated. The method comprises the proportion of a laminate having at least one aluminum conductor and orifices contacting the aluminum conductor; cleaning the walls of the holes and the exposed aluminum conductor; the contamination of the walls of the holes and the exposed aluminum conductor with an acidic etching solution, the acidic etching solution being substantially free of corrosive nilrates; the contact of the exposed aluminum conductor with a zinc coating solution, the zinc coating solution containing 6-60 g / l zinc and 100-500 g / l hydroxide ion; electrodeposition of the exposed aluminum conductor with copper in an alkaline electrodeposition solution; metallization of the walls of the holes; electrodeposition of the orifice walls to form holes through the copper electroplating and the processing of the laminate having holes through the copper electroplating to form a finished printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by the drawings in which Figure 1 is a diagram of the general process flow for the production of multilayer printed circuit cards, according to the invention. Figure 2 is a diagram that shows the process flow for copper electroplating and electroplating on aluminum substrates. Figure 3 is a schematic cross-section of an orifice through the electroplated in a multi-skewed printed circuit board having an aluminum ground plane.

DETAILED DESCRIPTION OF THE INVENTION The zinc coating process according to this invention initiates with a chemical etching of an aluminum surface in an alkaline cleaning solution followed by either a short etching in a sodium hydroxide etching solution or an acidic cleaning solution. These treatments leave a soot on the aluminum surface that is de-galvanized in a de-galvanizing solution without nitric acid. The non-nitric degalvanizer is an aqueous solution of a peroxide compound, such as persulfates or peroxysulfates. One such de-galvanizer is 25 g / l of potassium peroxymonosulfate. Potassium peroxymonosulfate is available from DuPont as Oxone ™ and Degussa Corp., Parsippany, NJ as Caroaí ™. The de-galvanizer or chemical attack solution is followed by a rinse. A potassium peroxymonosulfate degalvanizer typically contains 10 to 100 g / l of potassium peroxymonosulfate; the preferred concentration is 20 to 30 g / l. After desulphurization, an aluminum surface is covered with zinc by immersion in a zinc coating solution. The zinc coating solutions typically contain 120-500 g / l of sodium hydroxide, 20-100 g / l of zinc oxide, 10-60 g / l of Rochelle's salt (potassium sodium tarrate) or other organic complexing salts. , such as gluconates and salicylates and other additives such as sodium nitrate, copper, iron or nickel salts. The product and the manufacturing methods of the product of the invention are applicable to cards with printed circuit, double-sided, single, and cards with printed circuit with at least one aluminum conductor layer or having an aluminum core. However, the invention is especially suitable for multi-layer, high-density printed circuit boards with a plurality of signal layers and one or more ground planes and / or aluminum heatsink. In the manufacture of a multi-layer card having an aluminum ground plane, the internal signal planes are prepared in a conventional manner by etching the desired pattern onto copper metallized substrate. Signal planes and outer copper metallized layers are laminated to the ground plane of aluminum, in the same way that it is used when rolling to a copper ground plane. After rolling, the required holes are drilled through the copper metallized strata, external, the signal wires and the aluminum ground plane. Any hidden path required is also drilled. In order to form holes through electroplating with a heat sink / aluminum grounding piano, it is necessary to electrodeposite the aluminum as well as the copper conductors and the dielectric insulate between the conductor strata. A process for the production of multiple strata of aluminum core is outlined in Figure 1. A team of internal conductive strata eroded to acid, pre-impregnated sheets, aluminum extruded and external copper metallized esyrates, is assembled and laminated together. The multi-layer laminate is drilled for holes. After drilling, the holes for electrodeposition are prepared, as shown in Figure 2. In the first stage, the multi-layer panels are loaded onto electrodeposition supports. Stage 2 is immersion in an alkaline cleaning solution. The alkaline cleaning solution can be stirred by means of a recycling pump. The alkaline cleaning solutions, suitable, are well known and widely available; one such solution contains Atotech Basiclean LP ™ at a concentration of 35-45 g / l at a temperature of 55 ° C (1 30 ° F). Atotech ™ products are available from Atotech USA Inc., 1750 Overview Drive, Rock Hill, South Carolina. After a rinse, Step 3, the multi-layer panels are immersed in an acidic cleaning solution, Figure 2, Step 4. A suitable acidic cleaner is Atotech Acid Cleaner AF ™, at a concentration of 145-225 g / l and at a temperature of 43 ° C (1 10 ° F). Stage 5 is a rinse; the rinse can be agitated by air. Stage 6 is a de-galvanizing solution without citric acid. The non-nitric degalvanizer can be operated at ambient temperature and stirred by a recycling pump. The non-niric degalvanizer is an aqueous solution of a peroxy compound, such as persulfairs or peroxysulfates. One such de-galvanizer is 25 g / l of potassium peroxymonosulfate. Potassium peroxymonosulfate is available from DuPont as Oxone ™ and from Degussa Corp., Parsippany, NJ as Xaroat ™. The de-galvanizer or chemical bath solution is followed by a rinse, which can be agitated by air, Figure 2, Step 7. A potassium peroxymonosulfate de-galvaniser typically contains 10 to 100 g / l potassium peroxymonosulfate; the preferred concentration is 20 to 30 g / l. The concentration of copper in the degalvanizer will increase with time. The de-galvaniser is less effective when the copper concentration is greater than 4 g / l, and preferably the copper concentration is controlled at less than 3 g / l.

Figure 2, Step 8 is the galvanization solution. A technician practicing this invention will select a suitable electroplating solution for use on aluminum surfaces that have been brought with a de-oiling solution which is substantially free of nitric and / or hydrofluoric acids. The technician will also select a galvanizing solution that applies an adequate zinc coating without the use of a "double galvanizing" process using a nitric acid de-galvanizer. Although a "double zinc plating" process can be used with a de-galvanizer without nitric acid, a single-plated process is preferred. The galvanizing solution can be selected from those available from commercial suppliers for the metal finishing industry. The preferred zinc coating solution contains 5-50 g / l of zinc oxide, 50-125 g / l of hydroxide ion. The most preferred zinc coating solutions contain 6-15 g / l of zinc oxide, 55-80 g / l of hydroxide ion. A suitable commercially available zinc coating solution is Optibond ™ A &; B from Taskem, Inc., 4629 Van Epps Road, Brooklyn Heighs, OH. The Opiibond solution can be used at 32-38 ° C (90-1 00 ° F) with concentrations of zinc oxide and sodium hydroxide of 6-12 g / l and 10-160 g / l, respectively, and mixed by a recycling pump. As shown in Figure 2, Step 8, the zinc coating step is followed by a rinse (Step 9) and then in Step 10 the galvanized aluminum is electrodeposited in an alkaline copper electrodeposition bath. The electrodeposition bath Alkaline copper, preferred, is a copper cyanide bath. Electrodeposition baths of copper cyanide contain 30-75 g / l of copper cyanide, 50-100 g / l of sodium cyanide (or 60-120 g / l of potassium cyanide), 30-60 g / l of sodium carbonate (or carbonaio de poíasio) and 30-100 g / l of Rochelle salts. A good alkaline copper discharge formulation is 40 g / l of copper cyanide, 90 g / l of sodium cyanide, 25 g / l of sodium carbonate and 80 g / l of Rochelle salts. This copper discharge bath can be used at a temperature of 60 ° C (140 ° F) and a current density of 1 .3 A / dm2 (12 A / ft2). The copper deposit in the discharge bath should be 2-5 μm (0.1-0.2 mil) thick. As shown in Fig. 2, the alkaline copper discharge is followed by rinsing, drying and disassembly, EIApas 1 1, 12, 13 and 14. The EIAPA 1 1 is normally a loss per wash or rinse without circulation. The Elapa 12 must be a running rinse that operates at room temperature. Optionally, after Step 12, the alkaline copper discharge may be reinforced by an acid copper discharge, as shown in Figure 1. Brilliant acid copper electrodeposition solutions are commonly used in the printed circuit board industry. One such bright acid copper electrodeposition bath is Atotech BLCT from Atotech USA Inc., 1750 Overview Drive, Rock Hill, SC. The discharge tank of the shiny acid copper bath can also be 2-5 μm (0.1 -0.2 mil) thick. The multi-layer printed circuit board now experiences conventional circuit processing printed, as shown in Figure 1. The measurement of the dielectric layers of the holes for conductivity through the holes can be carried out by means of a graphite treatment, catalysis and electrodeposition of copper without electrodes or direct electrodeposition on a palladium-traced surface, according to the EU-No. 4,683,036 (Morrissey et al.). After the holes are metallized, the circuit image patterns are formed on the outer copper strata with a dry film resnce. The holes and the external circuit pattern are electrodeposited electrolytically with bright acid copper and followed by electrowinning electrodeposition. A selective chemical resnce is then applied to the exothermic circuit pads that leave the countertop areas exposed. The spheno / lead plate is de-galvanized from the condensation areas. After the pigeon / lead pigeon is laughed at, the conjoint areas are electroplated with nickel and gold. The exposed areas and edges of the aluminum base can optionally also be electrodeposited with nickel or nickel and gold. The resnce is de-galvanized and the outer copper strata erode to the acid to form the surface conductors. The preferred acid erosion agent is the copper ammonium acid erosion agent commonly used in the printed circuit board industry. The electrodeposited solder surfaces are fused to return the tin / lead plate to a uniform, shiny finish. Multi-layer panels are cut to size; HE protects the exposed aluminum, by electroplating by gold brush or Chemcoat, and the final inspection is given. Figure 3 illustrates a transverse section of an orifice through the aluminum core electroplated in a multi-layer printed circuit board, with the orifice copper electroplated firmly attached to the aluminum housing. In Figure 3, the dielectric epoxy of the multi-layered laminate is designated 1; the hole is 2. 3 designates the aluminum layer and 4 are copper conductors in the internal strata. The conductive acid-eroded copper payroll on the exoerne is marked as 5, while the copper deposited from the alkaline copper discharge bath is shown as 6. The copper-plated orifice galvanoplasty is marked as 7 and the Welded electroplating is shown as 8. Multi-printed circuit boards with an inferno aluminum conductive screen can also be made by using an electron-free nickel discharge instead of the alkaline copper plate (Figure 2)., Stage 1 0). The walls of the hole are cleaned and the exposed aluminum is treated with a non-nitric de-galvanizing solution (Figure 2, Stage 6); it is rinsed; it is treated with a zinc coating solution (Figure 2, Stage 8); it is rinsed and then electrodeposited with nickel without electrons. Since copper metal is not catalytic for electrodeposition of nickel without electrons, external copper outlets are not electrodeposited with nickel. If necessary, to insure against activation accidentally from the outer strata of copper, the strata can be covered with a mask or given a positive electrical derivation to avoid nickel deposition. Conventional processing is followed after the discharge of nickel without electrons to produce the finished multi-layer printed circuit board. The multi-layer printed circuit board can also be produced with hidden pathways, only with copper or other metal surfaces by appropriate process modifications. These modifications are well known to those experts in the field.

Claims (12)

1. CLAIMS 1. A method of galvanizing aluminum surfaces for subsequent electrodeposition, characterized in that it comprises cleaning the aluminum surfaces; contacting the aluminum surfaces with a solution of acidic chemical aiaque comprising a peroxygen compound, the acidic etching solution being substantially free of corrosive nitrate compounds; and 'contacting the aluminum surfaces with a zinc-plating solution, the solution containing zinc plating .6-60 g / l zinc and 100-500 g / l hydroxide ion.
2. 2. The method according to claim 1, characterized in that the acidic etching solution is substantially free of inorganic fluoride compounds.
3. The method according to claim 1, characterized in that the peroxygen compound is selected from a group consisting of peroxydisulfuric acid, peroxysulfuric acid, peroxydisulfuric acid salts and peroxysulfuric acid salts.
4. 4. The method according to claim 3, characterized in that the peroxygen compound is sodium persulfate or potassium monopersulfate.
5. 5. The method according to claim 1, characterized in that the zinc coating solution contains 5-50 g / l of zinc oxide and 50-125 g / l of hydroxide ion, preferably wherein the solution of zinc coating contains 6-1 5 g / l zinc oxide and 55-80 g / l hydroxide ion.
6. 6. The method according to claim 1, characterized in that the aluminum surfaces are part of a printed circuit board, with multiple lines, in a row with printed, laminated, organic circuit which has at least one aluminum conducting channel.
7. The method of manufacturing a printed circuit board having an aluminum conductor strip according to claim 6, characterized in that it comprises: providing a laminate having at least one aluminum conductor and holes that contact the aluminum conductor; clean the walls of the holes and the exposed aluminum conductor; coníacíar the walls of the holes and the conductive aluminum exposed with a solution of chemical acidic acid, finding the solution of acid chemical acid substantially free of corrosive nitrafos; confact the exposed aluminum conductor with a zinc coating solution, the zinc coating solution containing 6-60 g / l zinc and 1 00-500 g / l hydroxide ion; Electrodeposiíar aluminum with copper in an alkaline electroplated solution; metallize the walls of the holes; electrodeposing the walls of the hole to form holes through the copper electroplating; and process the laminate which is orifices through the copper electroplating to form a card with finished printed circuit.
8. 8. The method according to claim 7, characterized in that the cleaning of the walls of the orifice and the exposed aluminum conduit comprises the condensation with an alkaline cleaning solution.
9. 9. The method according to claim 8, characterized in that the cleaning of the walls of the hole and the exposed aluminum conductor also comprises the contact with an acid cleaning solution. The method according to claim 7, characterized in that the alkaline electrodeposition solution comprises an electrodeposition bath of copper cyanide. eleven . The method according to claim 7, characterized in that the orifice walls are electrodeposited with a copper layer of an acidic copper sulfate electrodeposition bath to form holes through the copper electroplating. The method of manufacturing a printed circuit board having an aluminum conductive pattern according to claim 7, characterized in that it comprises: providing a laminate having at least one aluminum conductor and holes that contacted the conductor aluminum; clean the walls of exposed aluminum holes and conductor; contact the walls of the holes and the exposed aluminum conductor with a solution of acidic chemical ayaque, the acidic etching solution being substantially free of corrosive liquids; connect the exposed aluminum conductor with a galvanizing solution, the zinc solution containing 6-60 g / l zinc and 1 00-500 g / l hydroxide ion; Electrodeposite the aluminum conductor exposed with nickel in a solution of nickel electrodeposition without electros; meíalizar the walls of the holes; Electrodeposing the hole walls to form the holes through the copper electroplating; and processing the laminate having holes through the copper electroplating to form a finished printed circuit board.