JPH0333797B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for forming copper plating directly on aluminum. In addition, in this specification, "aluminum" shall collectively refer to all intermediate products and final products made of aluminum and aluminum alloys. In addition, "aluminum pretreatment" refers to the degreasing and degreasing that is usually performed prior to aluminum plating.
It means at least one process such as pickling, neutralization, and water washing. Prior Art and Its Problems One of the methods for directly copper plating aluminum is the "zincate treatment method," in which aluminum is zinc-plated and then copper-plated. However, in this method, after galvanizing, the zinc layer is dissolved and removed by etching, galvanizing is carried out again, and then copper plating is carried out, which requires a great deal of effort and cost. The zincate treatment solution must also be updated frequently. Furthermore, the time required for the etching process is extremely short, and because this short time must be precisely controlled, it is difficult to automate the etching process, and as a result, it is also impossible to automate the entire plating process. It is. Furthermore, since the copper plating layer formed on aluminum by this method has insufficient adhesion, it is necessary to perform heat treatment to improve it, but the degree of improvement is also satisfactory. isn't it. .
Furthermore, since cyanide compounds are used, wastewater treatment requires a large amount of cost. Therefore, the zincate treatment method has only been applied to a very limited number of aluminum products. Another method of directly plating copper on aluminum is the copper pyrophosphate plating method, but this method also has many practical problems as described below. (1) Poor adhesion between aluminum and copper plating layer. As a method for improving adhesion, a method has been proposed that targets aluminum alloys of a specific composition (Japanese Patent Laid-Open No. 1983-92236), but this method is of course not suitable for high-purity aluminum and general aluminum. Not applicable. (2) If the adhesion between the aluminum and copper plating layer is low and the copper plating is made thicker, it will peel off easily. (3) Increasing the current density may cause cracks or
It becomes easy to peel off. (4) Since plating takes a long time, the cost is high. Another method for improving adhesion is to heat an aluminum product on which a copper plating layer has been formed using the copper pyrophosphate plating method in a non-oxidizing atmosphere.
A method of annealing has been proposed (Japanese Patent Application Laid-Open No. 1983-
158018, Japanese Patent Application Laid-Open No. 61-84338). However, since such a method requires a non-oxidizing atmosphere furnace for annealing, it is inevitable that the product will be expensive. In addition, when using a reducing gas atmosphere as a non-oxidizing atmosphere, it is necessary to replace the product with an inert gas such as nitrogen gas to prevent explosions when loading and unloading products before and after annealing, which reduces productivity. This results in a lower cost and further increases in cost. In addition, if commercially available nitrogen gas is used as is as a replacement gas, the trace amount of oxygen contained as an impurity will cause oxidation and discoloration of the surface of the copper plating layer, which not only impairs the appearance but also makes it difficult to continue the process. It may also interfere with soldering operations that may occur. In addition, this method requires complicated steps, so it is not possible to automate the entire process. Means for Solving the Problems The present inventor has conducted various studies in view of the current state of the technology as described above, and has found that, quite unexpectedly, a specific amount of phosphoric acid and/or Alternatively, it has been found that the problems of the prior art can be significantly alleviated when a phosphate is added, the aluminum is directly plated, and then heat treated. That is, the present invention provides a method for directly plating copper on aluminum as follows: After pretreating aluminum, phosphoric acid and/or
Or to aluminum, characterized in that copper plating is performed at a current density of 0.1 to 2.0 A/2 m ² using a copper pyrophosphate plating bath containing 10 to 500 g of phosphate, and then the aluminum is heat treated. direct copper plating method. The method for direct copper plating on aluminum according to item 1 above, wherein oil is applied to the plating portion of the copper-plated aluminum and held at 140 to 250°C for 1 to 60 minutes. The method for direct copper plating on aluminum according to item 1 above, wherein the copper-plated aluminum is immersed in oil heated to 140 to 250°C for 1 to 60 minutes. The method for direct copper plating on aluminum according to item 1 above, wherein the copper-plated aluminum is immersed in boiling water for 2 minutes or more. 2. The method for directly copper plating aluminum as described in item 1 above, wherein the copper-plated aluminum is brought into contact with water vapor for 2 minutes or more. As a result of further research, the inventor of the present invention found that when the amount of phosphoric acid and/or phosphate salt in a known copper pyrophosphate plating bath is within the range of 100 to 250 g, heat treatment is not necessary. It has been found that the same excellent effects as above can be achieved. That is, the present invention also provides the following method for directly plating copper on aluminum: After pretreating aluminum, phosphoric acid and/or
Or, a method for direct copper plating on aluminum, characterized in that copper plating is performed at a current density of 0.1 to 2.0 A/dm ² using a copper pyrophosphate plating bath containing 100 to 250 g of phosphate. The composition of aluminum that is the object of the present invention is not particularly limited, and includes substantially all aluminum materials from high purity aluminum to various aluminum alloys. Also in the method of the present invention, the aluminum to be plated is pretreated prior to copper pyrophosphate plating. This pretreatment may be carried out according to a conventional method, and is not particularly limited, but depending on the state of oxidation or dirt on the aluminum surface, for example, alkaline degreasing → washing with water, cleaning with a surfactant → washing with water, etc.
Processes such as alkaline degreasing → water washing → pickling → water washing, surfactant cleaning → water washing → alkaline degreasing → water washing → pickling → water washing may be adopted as appropriate. Direct copper plating onto the pretreated aluminum is then performed using a copper pyrophosphate plating bath. When heat treatment is performed after plating, phosphoric acid and at least one kind of phosphate is added to a known copper pyrophosphate plating bath as a copper pyrophosphate plating bath.
The amount added is about 500g/more preferably about 10 to 400g/. Phosphoric acid and its salts added to the copper pyrophosphate plating bath are not particularly limited, and include water-soluble phosphoric acids such as ortho and meta and their salts, and more specifically, the following are exemplified. Ru. *Orthophosphoric acid (H ₃ PO ₄ ) * Primary salt of orthophosphoric acid: KH ₂ PO ₄ , NaH ₂ PO ₄ ,
(NH ₄ )H ₂ PO ₄ *Second salt of orthophosphoric acid: K ₂ HPO ₄ , Na HPO ₄ ,
(NH ₄ ) ₂ HPO ₄ *Tertiary salt of orthophosphoric acid: K ₃ PO ₄ , Na ₃ PO ₄ ,
(NH ₄ ) ₃ PO ₄ * Metaphosphoric acid (HPO ₃ ) * Salts of metaphosphoric acid: KPO ₃ , NaPO ₃ , (NH ₄ )PO ₃ The above phosphates contain not only anhydride but also water of crystallization. It's okay. The amount of phosphoric acid and/or phosphate added is 10g/
If the amount is less than 500 g/g, the desired effect will not be fully achieved, while if it is more than 500 g/g, the cathode efficiency for copper plating will be markedly reduced, and the plating operation may be inhibited. Components other than phosphoric acid and/or phosphate in the copper plating bath may be the same as those in known copper pyrophosphate plating baths, and are not particularly limited. Some examples are as follows. Copper pyrophosphate 75-105g / Potassium pyrophosphate 280-370g / Metallic copper 26-36g / Ammonia water (specific gravity 0.88) 2-5ml / Brightener 1-4ml / P ratio 6.4-9.0 PH 8.5-9.0 Copper pyrophosphate 65- 105g / Potassium pyrophosphate 230-370g / Copper metal 22-36g / Aqueous ammonia (specific gravity 0.88) 1-2ml / Potassium nitrate 15-25g / P ratio 6.4-7.0 PH 8.5-9.0 Copper pyrophosphate 65-105g / Potassium pyrophosphate 240 ~450g/ Metallic copper 22-36g/ Ammonia water (specific gravity 0.88) 1-2ml/ Brightener 1-2ml/ Potassium nitrate 15-15g/ P ratio 7.0-8.0 PH 8.2-8.8 Copper pyrophosphate 90g/ Potassium pyrophosphate 345g/ Ammonia Water (specific gravity 0.88) 3 ml / Brightener 2.5 ml / P ratio 7.0 PH 8.6 ~ 9.0 The conditions for the copper direct plating process on aluminum are usually a temperature of about 50 ~ 60 ℃, a current density of 0.1
~20A/ ^dm2 , time: approximately 10 minutes to 1 hour. If the current density exceeds 2A/ ^dm2 ,
This is not preferable because it reduces adhesion. Therefore,
In order to form a thick copper plating layer, plating may be performed for a sufficient amount of time, or a thin copper plating layer may be formed in a short time and then normal copper plating may be performed again. The aluminum on which the copper plating layer has been directly formed is then subjected to heat treatment. The heat treatment method, conditions, etc. are not particularly limited, but some examples are as follows. (b) The aluminum with the copper plating layer formed thereon is washed with water, dried, and the copper plating area is coated with oil and fat.
After heating in the air at a temperature of about 140 to 250°C for about 1 to 60 minutes, it is allowed to cool. The fats and oils to be used are not particularly limited, as long as they become liquid at a temperature of about 140 to 250°C. in particular,
Vegetable oils such as castor oil, linseed oil, tung oil, funnel oil, coconut oil, olive oil, palm oil, peanut oil, rapeseed oil, cottonseed oil, soybean oil; Mineral oils such as machine oil, quenching oil; silicone oil, glycerin, etc. Examples include synthetic oil. During the heat treatment, it is preferable to take into consideration the above temperature and time ranges, such as shortening the time when the temperature is high and lengthening the time when the temperature is low. The oils and fats applied to the surface of the plated part can be removed in a short time of about 10 to 20 seconds, for example, by electrolytic degreasing, which is usually carried out in plating factories. Note that if the above heat treatment process is performed without applying oil or fat to the copper plating part, oxygen will diffuse into the plating layer from the pinholes on the surface of the copper plating layer, and the metal at the interface between the aluminum and the plating layer will is oxidized, which actually reduces the adhesion. (b) The aluminum on which the copper plating layer has been formed is washed with water, dried, and then immersed in oil heated to a temperature of about 140 to 250°C, held for about 1 to 60 minutes, and then left to cool in the atmosphere. do. The oils and fats used are
The same as in case (a) above may be used. Further, the relationship between temperature and time during heat treatment may be considered in the same manner as in the case (a) above. The method for removing the used fats and oils may be the same as in the case of (a) above. (c) The aluminum on which the copper plating layer has been formed is heat treated by keeping it in boiling water for about 2 minutes or more. (d) The aluminum on which the copper plating layer has been formed is brought into contact with water vapor for 2 minutes or more. On the other hand, if heat treatment is not performed after copper plating, a known copper pyrophosphate plating bath to which 100 to 250 g/at least of at least one of phosphoric acid and phosphate is added is used as the copper pyrophosphate plating bath. do. Types of phosphoric acid and phosphate salts used;
The plating conditions and the like are the same as above. It is currently unclear why the heat treatment step can be omitted only when the amount of phosphoric acid and/or phosphate salt added to the copper pyrophosphate plating bath is about 100 to 250 g. Effects of the Invention According to the present invention, the following remarkable effects are achieved. (1) If ordinary copper pyrophosphate plating equipment and technology are available, it can be carried out as is. (2) Unlike the zincate treatment method, which is almost the only practical copper plating method for aluminum, wastewater treatment is easy because it does not contain cyanide compounds. (3) Since no atmosphere control is required during heat treatment, the entire process can be automated. (4) When heating is performed in hot water or boiling water, cleaning after copper plating formation and degreasing cleaning after heat treatment are unnecessary. Therefore, it is particularly advantageous when further performing nickel plating, chrome plating, etc. after copper plating. (5) Since plating is performed at low current density, a uniform copper plating layer can be formed even on irregularly shaped products. (6) There are no restrictions on the composition of the target aluminum, and it can be applied to a wide range of materials, from high-purity aluminum to various aluminum alloys. (7) The adhesion between the base material and the copper plating layer of the final aluminum product is extremely good, and the appearance is beautiful. On such a copper plating layer, other metals such as nickel and chromium can be further plated. (8) When the amount of phosphoric acid and/or phosphate added to the copper pyrophosphate plating bath is 80 g or more, the stability of the plating bath is significantly improved. (9) When the amount of phosphoric acid and/or phosphates added to the copper pyrophosphate plating bath is in the range of 100 to 250 g, it is particularly advantageous in terms of the process since there is no need to perform heat treatment after copper plating. . Examples Examples will be shown below to further clarify the features of the present invention. In addition, each determination in the examples shown in Table 1 is as follows:
I did it as follows. *Peeling (): Bend the aluminum plate on which the copper plating layer has been formed 180 degrees and visually observe whether the copper plating layer has peeled off. *Cracks (): Bend the aluminum plate with the copper plating layer 180 degrees and visually observe whether or not cracks have occurred in the copper plating layer. Microcracks ()...If the above cracks are not observed, use a magnifying glass (10x magnification) to observe whether microcracks have occurred in the copper plating layer. Example 1 A high-purity aluminum plate measuring 20 mm x 50 mm x 0.5 mm was immersed in a 3% aqueous sodium hydroxide solution, then washed with water and degreased. )Made by Murata)
A bath (p
Electroplating was carried out for 46 minutes at a current density of 1 A/dm ² and a temperature of 55° C. while stirring. The thickness of the copper plating layer formed was about 10 μm. Next, castor oil was applied to the copper-plated parts and heat treated in air at 250°C for 5 minutes. Table 1 shows the results. In addition, in order to confirm the effect of heat treatment, a copper plating layer was formed on two aluminum test pieces under the same conditions, one of which was subjected to a bending test as is, and the other was subjected to a bending test after heat treatment.

【table】

[Table] From the results shown in Table 1, it is clear that the resistance to bending after heat treatment is improved by setting the concentration of orthophosphoric acid in the copper pyrophosphate plating solution to a range of 10 to 400 g/. . In addition, in the case of samples 2, 3, 4, 8, and 9, small cracks were generated even after heat treatment, but this was due to the harsh conditions of 180 degree bending, and it is of no practical use. This should not be a hindrance. In addition, instead of castor oil, linseed oil, tung oil, funnel oil, coconut oil, olive oil, palm oil, peanut oil, rapeseed oil, cottonseed oil, soybean oil, machine oil,
Substantially similar results were obtained using quenching oil, silicone oil, and glycerin, respectively. In addition, the heat treatment conditions were 150℃ x 60 minutes,
Almost the same results as above were obtained when the temperature was 170°C for 5 minutes, 170°C for 10 minutes, 190°C for 3 minutes, and 250°C for 1 minute. Example 2 A high-purity aluminum plate on which a copper plating layer was formed in the same manner as in Example 1 was immersed in castor oil heated to 150° C. for 60 minutes, and then a bending test similar to that in Example 1 was conducted. As a result, no peeling of the copper plating layer occurred, and neither cracks nor microcracks occurred in the copper plating layer. Similar good results were also obtained when a similar test piece was immersed in castor oil heated to 250°C for 1 minute. Example 3 A high-purity aluminum plate on which a copper plating layer was formed in the same manner as in Example 1 was immersed in glycerin heated to 200° C. for 5 minutes, and then a bending test similar to that in Example 1 was conducted. In this case as well, no peeling of the copper plating layer occurred, and neither cracks nor microcracks occurred in the copper plating layer. Example 4 A high-purity aluminum plate on which a copper plating layer was formed in the same manner as in Example 1 was immersed in pre-boiled water for 5 minutes, and then subjected to the same bending test as in Example 1. Ta. In this case as well, no peeling of the copper plating layer occurred, and neither cracks nor microcracks occurred in the copper plating layer. Example 5 A high-purity aluminum plate on which a copper plating layer was formed was brought into contact with water vapor in the same manner as in Example 1 except that a matting bath containing orthophosphoric acid in the proportions shown in Table 2 was used. A bending test similar to Example 1 was conducted. For contact treatment with water vapor, the sample and a beaker containing water are placed inside a cylindrical stainless steel pressure-resistant container with a diameter of 30 cm and a length of 50 cm, equipped with a heater (temperature can be controlled from the outside). , the pressure was reduced, the air was replaced with nitrogen gas, and then the pressure was reduced again. Thereafter, the sample was taken out after heating to a predetermined temperature and holding it for 5 minutes. The results were as shown in Table 2.

[Table] Reference Example 1 Samples were prepared under the same heat treatment conditions as the samples judged to have good peeling resistance in each of the above examples, and the following soldering test was conducted. First, when we soldered the copper-plated surfaces of two samples and then forcibly peeled them off, we found that in most cases the solder surface was peeled off, and the copper-plated surface was peeled off at the copper-aluminum interface. There were very few things. From this, the 180 degree bending test conducted in each example is appropriate as a method for confirming the adhesion of the product of the present invention, and the product of the present invention has excellent adhesion and can be used as a base for soldering. That is clear. Reference Example 2 After preparing samples under the same heat treatment conditions as those of the samples that were judged to have good peeling resistance in each of the above examples, nickel was coated on the copper plating layer of each of the obtained samples in accordance with a conventional method. It has been plated. As a result, plating could be easily performed in the same way as plating a normal copper plate. In addition, when the nickel plated surface was observed using a differential interference microscope, beautiful interference colors were observed.
It was confirmed that a uniform plating layer was formed. Further, when nickel plating and chrome plating were applied to the copper plating layer of each sample according to a conventional method, the operations were also easy to perform. When the surface of this chrome plating layer was observed using a differential interference microscope in the same manner as above, beautiful interference colors were observed, confirming that a uniform plating layer was formed.

Claims (1)

[Claims] 1. After pre-treating aluminum, phosphoric acid and/or
Alternatively, copper plating is performed at a current density of 0.1 to 2.0 A/dm ² using a copper pyrophosphate plating bath containing 10 to 500 g of phosphate, and then the aluminum is heat treated. Direct copper plating method. 2. The method for direct copper plating on aluminum according to claim 1, wherein oil is applied to the plating portion of copper-plated aluminum and held at 140 to 250°C for 1 to 60 minutes. 3. The method for directly copper plating aluminum according to claim 1, wherein the copper-plated aluminum is immersed in oil heated to 140 to 250°C for 1 to 60 minutes. 4. The method for directly copper plating aluminum according to claim 1, wherein the copper-plated aluminum is immersed in boiling water for 2 minutes or more. 5. The method for directly copper plating aluminum as set forth in claim 1, wherein the copper-plated aluminum is brought into contact with water vapor for 2 minutes or more. 6 After pre-treating aluminum, phosphoric acid and/or
Or, a method for direct copper plating on aluminum, characterized in that copper plating is performed at a current density of 0.1 to 2.0 A/dm ² using a copper pyrophosphate plating bath containing 100 to 250 g of phosphate.