DE2104873A1 - Process for galvanic copper deposition - Google Patents

Description

Metal finishing companies are currently paying particular attention to the treatment of their waste solutions. Most depositors use copper cyanide baths in which the provision and the degradation of cyanide as a result of the extraordinarily lent toxic nature of the same entail particularly strict and costly treatment procedures.

Furthermore, when copper is applied to a more electronegative metal such as e.g. steel or zinc, is electroplated, then the copper has the tendency to initially deposit, that it displaces part of the metal on its surface. The electrodeposition achieved in this way is almost always loose and non-sticking and prevents the subsequent galvanic deposition of a good copper coating. this makes the application of an initial, thin strike-coating of copper from a separate one Copper bath with a very low copper ion -

109842/1580

concentration required. The electroplated copper deposition is then substantially removed by a normal electroplating bath causes higher copper ion concentrations.

Although Kupferbäaer with gyanide as the main complexing agent for the copper ion lead to the best galvanic precoatings as well as normal coatings of copper it is highly desirable because of the disadvantages associated with the use of cyanide-based baths Use of equally effective baths without cyanide -

to develop salary.

Copper plating without cyanide is not new. Approaches based on copper sulfate and copper fluorate are used in acidic copper plating, and pyrophosphate baths are used in the alkaline copper plating industry used. However, these baths which do not use gyanide ar compared to the cyanide-containing baths Do not bathe the same performance. Solutions of copper sulfate and sulfuric acid cannot be used as a solution for The thin galvanic precoating of steel can be used because of the galvanic effect that results in a non-adhesive galvanic deposition leads. In addition, these acidic solutions attack the zinc surface of zinc and zinc alloys quickly and change the dimensions of the object to be coated. Both fluoborate and pyrophosphate baths require an initial thin galvanic precoating with copper for steel and zinc castings a cyanide bath to get a consistent, good, normal copper plating from both baths. You can Reduce the use of gyanide, but has not turned it off.

In previously known processes for galvanic copper deposition on a metal substrate, lemon

109842/1580

acid or a salt thereof as an additive to the copper plating solutions used to expand the permissible range of cathode current density, the conductivity of the bath, to increase the gloss of the cathode deposit, the tolerance of the bath with respect to To increase impurities as well as to support the anode corrosion.

Citric acid and its salts have often been used as additives, but never before have they come as Main complexing agent for copper in electroplating baths.

In contrast to the previous technology, surprisingly found that copper can be electrodeposited on an object, which thereby becomes the cathode was made to be an aqueous copper (II) salt solution at a pH of about 0.4 to 8.9, the solution was about 16 to 64 g per liter of copper (II) ions and contained about 48 to 192 grams per liter of citric acid, and a current density of about 10.76 to about 430 Apply amps per m (1-40 amp./seuare foot) to the desired To obtain coating.

Where the object to be coated with copper is made of a metal that is more electronegative than copper is, which means that there are always non-adherent galvanic deposits of the copper on the object, a thin pre-coating of copper is first applied to the object made before the normal copper plating galvanically is deposited on the object, again surprisingly it has been found that the thin electroplated precoat with copper in the object can be made by placing it in an aqueous copper-II-salt solution gives at a pH of about 1 to 12,

109842/1580

the solution being about 3 to 16 g per liter of copper (II) ions and contains about 20 to 100 g per liter of citric acid, and a current density of about 10.76 to about 430 Am-

x 2

pere pro m applies to the desired coating

to obtain.

Thus, citric acid can be used as the main complexing agent for copper in precoating and plating solutions with results that with the results for gyanide and acid plate ie riaigs baths are comparable, but in which the disadvantages associated with their use are avoided.

A major advantage of the method of the present invention is the elimination of gyanide and pyrophosphate ions in the electroplating bath and the rinsing water used afterwards. The elimination of waste is there therefore relatively easy in that the citrates are easily biodegradable.

Another advantage is that the copper deposit is given a gloss at the same time, in contrast to similar deposits that are common when using unspecific copper electroplating solutions can be obtained.

Yet another advantage of the present invention is the elimination of the need for a cyanide bath To be used for galvanic pre-coating. at other copper plating baths such as Fluoborate or pyrophosphate-based baths, a precoating with a cyanide bath is required before a corresponding adhesion of the copper coating is achieved can be. Thanks to the present invention it is possible

109842/1580

lent to adjust the citrate and copper salt quantities so that both precoating and electroplating can be carried out.

It is also based on electroplating solutions of citric acid the effect of storage is unimportant with regard to the galvanic consisting of copper Coating that is subsequently obtained using these solutions.

In accordance with the present invention, shiny, adherent and dense copper coatings can be applied to an object be electrodeposited by the fact that the object stood as a cathode in an aqueous copper (II) salt solution brings, in citric acid the main complexing agent for the copper is in solution. The process steps according to the invention are usually provided for carrying out the process steps according to the invention Anode copper metal.

The object to be electroplated can be made of any suitable metal, such as aluminum, Steel, zinc, brass or other metals and their alloys are made. If the item consists of a Metal, which is more electronegative than copper, results in galvanic deposits without the use of any current density Type on the surface of the object. Have deposits obtained by immersion processes usually not of good quality and will not adhere so that a poor quality copper plating will result if then the current load takes place. This creates the need for the object with a first To provide copper plating as a thin galvanic pre-layer ("strike coating") is known, and by the one

109842/1580

obtain a first adherent coating and prevent the formation of a desirable galvanic type coating will. It is therefore necessary to apply a thin galvanic pre-layer of copper where the to be galvanized Item is made of steel or zinc, both of which are more electronegative than copper; with one made of brass a thin galvanic pre-coating is not necessary. Surprisingly it was found, however, that the galvanic-type coatings in which citric acid is the main complexing agent for the Copper in solution adheres better than the coatings normally used in which other complexing agents are used be used. This copper coating is probably caused by galvanic displacement by the Copper and can also be produced by chemical reduction.

While any water-soluble Kuofer II or I salts can be used in the practice of the present invention, it is preferred to use copper (II) salts, especially copper (II) sulfate (e.g., CuSOi and CuSO ₄ .5H ₂ O ) or copper-II-carbonate / "eg 2 CuCO ₃ .Cu (OH) ₂ and CuCO ^ .Cu (OH) ο_7 ^to use, as they are easy to access and inexpensive.

The temperature of the electroplating baths can vary from room temperature to the boiling point of the solution; Conveniently, the temperature is kept (about 20-30 ⁰ C) at room temperature.

The optimal current density depends on the other electrolysis conditions and the composition of the bath. Current densities from about 10.76 to about 430 amps per meter are found to be satisfactory.

109842/1580

The amount and quality of the copper coatings obtained depend to a large extent on the relative concentrations of the copper ions and citric acid as well as the pH of the galvanizing solution away. It is preferred to use citric acid in practicing the invention, whether the same this does not exclude the use of citrates. The preferred concentration of citric acid in normal copper plating baths this is about 48 to 192 g per liter, 160 to 192 g is best used per liter. In the baths for the thin galvanic pre-charging with copper, there is a concentration preferred to citric acid of about 20 to 100 g per liter.

A copper-II-ion concentration becomes pure normal electroplating farmers from about 16 to 65 grams per liter preferred; a concentration of 50 to 64 g per liter becomes most preferred. A copper (II) ion concentration is used for the baths for the thin galvanic precoating preferred from about 5 to 16 g per liter. A copper (II) ion concentration of about 12 big is particularly important 16 g per liter preferred when copper (II) carbonate is used, and a concentration of about 3 to 5 g per liter, if copper (II) sulfate is used.

The preferred pH with respect to the deposited copper quality varies somewhat depending on the concentrations of the bath components. The pH value for maximum copper ergal vani Sizing baths can be about 0.4 to &.9, with a pH value from 0.4 to 1.2 if copper (II) sulfate is used is, and from 7 to 8, if copper (II) carbonate is used, preferably wira. For baths for galvanic precoating en with copper, the pH value can be around 1 to 12 if copper (II) sulfate is used, and a pH value of 9 to 12 is preferred when copper-II-carbon

1098A2 / 1580

nat came to use.

Although it is not essential to the practice of the invention Sodium sulfate or ammonium citrate can be added to the conductivity of the galvanizing bath to improve, and boric acid can be added as a buffering agent, also a base (e.g. MILOH, NaOH or the like.) to control the pH value. Of course, this does not preclude the use of other common additives for improvement the conductivity of the bath or controlling the pH of the bath.

In a preferred embodiment of the invention, an aqueous copper solution is used for thin galvanic precoating, which contains about 96 g per liter of citric acid, 20 g per liter of CuCO ^ Cu (OH) ₂ , the pH value being reduced to about 11.6 is set, a current density ύοώ. about 215 to about 430 amperes per m (20-40 amps / square foot) and a plating time of 5 minutes.

In another preferred embodiment of the invention, an aqueous copper solution is used for thin galvanic precoating at a pH of about 1.6, which contains about 24 g per liter of citric acid, 16 g per liter of CuSO ₄ .5HpO, 6 g per liter of sodium sulfate, and 20 g per liter of boric acid, the current density being approx.

* · 2

10.76 to about 32.3 amps per m and a Q-galvanizing

time of 5 minutes.

Yet another preferred embodiment of the invention consists in that an aqueous copper-G-al vanisierungslösung used at a pH of about 0.8, which is about 192 g per liter of citric acid and 250g per

109842/1580

Liters OuSO..5H _o 0, whereby the current density at et-

wa 215 to about 430 ampires per m and a G-alvanizing

time of 60 minutes must be observed.

Finally, a further preferred embodiment of the invention consists in the use of an aqueous copper-galvanizing solution which contains about 192 g per liter of citric acid, 95 g per liter of OuCO, .Ou (OH) ₂ , the pH being by Addition of MILOH is adjusted to about 8 and a current density before. approx. 215

s ρ

up to approx. 430 amperes per m as well as an electroplating time

of 120 minutes must be adhered to.

The following examples serve to further illustrate the invention.

Example 1:

A standard Hull test cell was used as the electrolyzer used. The cathode consisted of a standard steel plate 101.6 mm long, one Width of 63.5mm and a thickness of 0.25 now. Further a pure copper anode was used.

The cathode has been cleaned and prepared according to normal electroplating procedures, i.e. degreased, Alkaline cleaned and carefully rinsed with water before galvanizing.

Fun the cathode was placed in an aqueous solution for thin galvanic precoating with copper, which had a pH value of 1.6 and 24 g per liter of citric acid, 16 g per liter of CuS0 _A .5Hr> 0.6 g per liter of BTa -

109842/1580

- ίο -

trium sulfate and 20 g per liter of boric acid. the Solution was kept at room temperature; the current density

* 2 was approximately 10.76 to 32.3 amps per m. The cathode was Immersed for 5 minutes, removed from the solution and carefully rinsed with water; you got a shiny, thin, adherent pre-electroplating coating made of copper.

Example 2:

The steel plate of Example 1, coated with copper by the galvanic precoating process, was then placed as a cathode in an aqueous copper electroplating solution which contained 95 g per liter of CuCO ^ .Cu (OH) ₂ and 192 g per liter of citric acid, and the pH became adjusted to 8 by adding NH * OH. The solution was kept at room temperature while the current density was approximately 215 to 430 amperes per m. After an immersion time of 120 minutes, the steel plate was removed from the electroplating solution and a shiny, dense and adherent copper coating was obtained.

Example 3:

A standard brass plate for the Hull test cell was cleaned and prepared according to normal electroplating procedures. Then si erungslö solution at a pH of 0.4 was added as the cathode in an aqueous copper Galvani, which contained 250 g per liter of GuSO ^ .5H ₂ O and 192 g per liter of citric acid, namely at one

ο *

Temperature of 66 C and a current density of about 10 amperes.

109842/1580

- li -

After an immersion time of three minutes, a good copper coating was found on the brass plate in the Hull test cell achieved. Similar results were obtained with a current density of approx. 215 to 430 amperes per m and a pH value of 0.8 in larger baths during a longer immersion time.

Example 4:

Satisfactory results were obtained following the procedure of Example 3 with the difference that the electroplating bath had a pH of 1.2 and 63 g per liter of GuSO ₄ . 5HgO and 48 g per liter of citric acid, with a current density of about 430 amperes

2
m and that the immersion time is 60 minutes

wore.
Example 5t

Satisfactory results were obtained according to the procedure of Example 3 with the difference that the G-galvanizing bath had a pH value of 8.9 and contained 250 g per liter of CuSO..5H ₂ O and 192 g per liter of citric acid, was maintained at a current density of about 215 amps per m, and that the immersion time was 120 minutes.

Example 6;

Similar results were obtained following the procedure of the example 1 with the difference that the solution for

109842/1580

thin galvanic precoating had a pH of 9 »2 and contained 29 g per liter of CuCCU.Cu (OH) ₂ , 86 g per liter of citric acid and 61 g per liter of ammonium citrate,

ρ held at a current density of approx. 430 amperes per m

and that the immersion time in a larger bath was 60 minutes.

Example 7;

Similar results were obtained using the method of Example 1, with the difference that the solution for the galvanic precoating contained 20 g per liter of CuCO ^ Cu (OH) ₂ and 96 g per liter of citric acid, and the pH was adjusted to 12 by adding NaOH was established that

ν 2

Current density was kept at about 215 to 430 amperes per m, and the immersion time in a larger bath was one minute fraud.

Example 8:

In this example the throwing power was determined.

Steel plates for Hull test cells were used as test plates. According to the normal galvanizing process four panels were coated, two in conventional baths and two in copper citrate plating solutions. The plates for the conventional bath were subjected to a galvanic thin-film precoating process with the Solution composition CNST subjected una either with the Copper cyanide Rochelle salt solution (CNRO) or the acidic Copper sulfate solution (ACID) coated. The plates T3 and T4 were galvanically thin in the solutions (V) and (H)

109842/15 80

layers and galvanized in solutions (A) and (Q). The details of the solution conditions are from Table I can be seen. The galvanic thin-film pre-coating process was in two liter vessels at a voltage of 3 volts for one minute at room temperature carried out. The plating was in Hull cells at 21.5 amps and room temperature for five minutes long made.

The thickness was measured using an electronic thickness tester according to Kocour, model 955 »determined using the appropriate anodic stripping solution. The test device x-jurde first adjusted and the sensitivity was determined. Then it was against standard plates the thickness of the copper deposit on steel substrates calibrated. The thickness tests were performed on Hull cell plates made in places that give a reference to the current

poems.

ρ ρ

densities of approx. 43 amps per m and approx. 430 amps per m

The measurement of the encroachment was achieved by

that the deposit strength is about 430 and about 43 amps

2
per m reading. The ratio normally to be expected would be a deposit ratio of 10 to 1. The calculation of the overlap as primary and metal ratio was carried out as follows:

Primary ratio - Metal ratio _{χ 10Q} _ Primary ratio ~

The primary ratio was based on the current densities at which the two thickness numbers were measured, i.e. in present case 10. The metal ratio was based on

109842/1 580

- 14 -

the thickness actually obtained at these current densities. For example, in Table I, it was found to be
Plate Tl has a thickness ratio for the two current densities of 19 to 7 »di 2.7. This gives a percentage improvement in throw of 73 %. In other words, is
the wraparound is a measure of the derivative in the actual lYietall distribution from the expected primary distribution based on current density.

In Table I, the compositions of the solutions and the results of the throw-around tests are shown. The at
the percentage improvement achieved the highest values
obtained from the copper cyanide Eochelle salt electroplating bath. The results obtained with the acidic copper sulphate solution and the citrate solutions were in the range of

1098A2 / 1580

plate Together- PH value Around;;· Table I: CNRO Copper strong Percentage
Improve
tion iietall-
varhalts No. setzg. d.
Solution the solution riff - Teut 2 2
b. 45 amp./m
(mm) 73 2.7 Tl CNST &
GNiiO Galvan. Before-
coating Galvanized 0.0018 58 4.2 T2 GNST &
ACID 11.88 Galva
nisier b. 430 amps / m
(mm)
en ^ ' 0.0015 56
50 4.4
5.0 Τ3
Τ4 V & A
H & Q 11.88 10.28 0.0048 0.0013 _o
0.00076 1.69
11.68 0.48 0.0053 ill O GNST 0.75
7.83 0.0056
0.0038 9842 / OO
σ

0.2 M copper cyanide 0.7 M sodium cyanide 0.05 M sodium hydroxide pH value - 11.9

0.2 M Kupi'ercyanicl
0.7 M sodium cyanide
0.5 M sodium carbonate
0.16 iiochelle salt
pH = 10.3

0.0o4 M copper sulfate 0.125 M citric acid 0.042 M sodium sulfate 0.52 M boric acid pH = 1.7

OO --J CO

Table I (continued)

ACID

0.8 M copper sulfate 0.5 M sulfuric acid pH value * 0.5 1.0 M citric acid
1.0 M copper sulfate
pH value «0.8

cn oo ο

0.5 M citric acid 0.09 M copper carbonate

pH · value «11.6, adjusted by

Addition of sodium hydroxide (Q)

1.0 M citric acid
0.43 M copper carbonate

pH = 7.8, adjusted by adding sodium hydroxide

Remarks"

Copper sulfate means CuSO. «5H _? 0 copper carbonate means CuCO, .Cu (OH) ₂

oo -j co

Example 9: Thickness and Adhesion Tests.

Additional panels were prepared by following conventional and experimental procedures, as described above Electrolyzed solutions for thin galvanic pre-coating. The plates were standard 0.25 mm thick plates for Hull lines that are fused into curved cathodes to achieve varying current densities along the immersed cathode. Formed by this arrangement areas of high and low current density to calculate the throwing power, which is the ability of the Means solution for depositing a relatively uniformly thick layer on a surface.

The panels were cleaned according to normal procedures and at 3 to 5 volts and room temperature for one minute precoated in solutions GNST, (V) and (H). They were then made using the solution compositions CNRO, ACID, (A) and (Q) at approx. 215 to 430 amps

ρ
galvanized per m at room temperature for 30 minutes.

The details of the experiment are shown in Table II.

The coated panels were then about 12.7 mm from the side opposite the bent cathode end, bent to an angle of 90 ° and the point of the bend was observed for the release of the cover. Afterward the plate was bent further 90 degrees in the same direction and then bent back to its original flat position.

10984 2/1580

The bent part of the cathode of these same plates has now been flattened, and thickness tests were taken under Using the Kocour tester described in Example 8 above. To measure the thickness were five locations are selected within a range from high to low current density. These places for measurement the thickness are indicated in Table II as numbers 1, 2, 5, 4 and.

Table II shows the results of the test for measuring thickness and adhesion. The five for each Plate thickness results obtained were averaged and converted to give a plating speed received in mm per hour. A slightly higher result was obtained with the conventional electroplating baths than expected. The citrate plating baths had a considerably slower plating rate than the conventional electroplating bath. The speed obtained in the solution composition (A) was about half the speed of the conventional plating baths, whereas the speed obtained with the solution composition (Q) was about a quarter that of conventional electroplating baths.

The adhesion tests from the copper citrate solutions galvanized deposits were not as satisfactory as the values of the tests performed on the conventional ones Copper plating solutions were obtained. Of the ten tests undertaken, only two survived the three bends. These were electroplated from solution compositions (Q). All electroplated from the solution additive (A) Plates failed at some point. An additional

109842/1580

One factor in these results is that the solution composition (Q) deposits are thinner are as the deposits from the solution composition (A).

Example 10:

An adherent galvanic copper coating was on a steel substrate using an aqueous solution composed of 0.064M copper sulfate, 0.24M Citric acid, 0.042 di sodium sulfate, and 0.32 M boric acid duration. The coating developed in 3-5 seconds at a pH of 1.6 and a temperature of 22 ° C. the Adhesion of the deposit was determined by rubbing with a finger as well as with an eraser. Non-adherent galvanic Deposits have been observed with similarly composed solutions that use one instead of citric acid Contained oxalate or citrate.

109842/1580

Together
setting ά.
solution adhesion
from the
storage number 1
(mm) Tabel II: No. 4
(mm) - No. 5
(mm) Avg chni 11-
galvanized
tion so-called fast
speed (mm / hour). plate CNST &
ACID Well 0.0345 Thickness- 0.0277 0.0569 0.0716 Mr. CNST &
CNRO Well 0.0323 No. 2
(mm) vpid adhesion test 0.0269 0.0323 0.0723 Bl H-Gi lifted off at
5th bend 0.0071 0.0452 No. 3
(mm) 0.0043 0.0009 . 0.0147 B2 V-A lifted off at
2nd + 5th bend 0.0170 0.0460 0.0147 0.0099 0.022 0.0330 B3 HA lifted off at
2. bend 0.0229 0.0104 0.0437 0.0188 0.0363 0.0483 B4 V-Q lifted off at
2. bend 0.006g. 0.0252 0.0046 0.0056 0.0132 "0.0157 B5 V-A lifted off at
all bend. 0.0170 0.0285 0.0074 0.0114 0.0328 0.0371 BÖ CNST
& ACID Well 0.0218 0.0076 0.0137 0.0140 0.0325 0.0447 B7 CNST &
CNHO Well 0.0259 0.0208 0.0058 0.0239 0.0512 0.0564 ΒΘ V-A lifted off at 0.0140 0.0310 0.0104 0.0081 0.0208 0.0269 B9 0.0262 0.0127 BIO 0.0173 0.0325 0.0071

all Bends

ro σ oo co

Table II (continued):

Plate Kr.

BIl B12

B13

bra

Composition d. solution

- A T-A

Adhesion of the deposit

good Good

thickness

Kr. (Mm)

0.0081 0.0099

lifted 0.0112 at the 2nd bend

lifted 0.0069 at 3rd bend

No. (mm) Kr. 3
(mm)

Kr.4
(mm)

Kr. 5
(mm)

0.0104 0.006l 0.0064 0.0142

0.0119 0.0076 0.0058 0.0165

0.0145 0.0066 0.0061 0.0163

0.0117 0.0053 0.0046 0.0152

Average plating speed (mm / hour)

0.0180
0.0208
0.0218

0.0173

Purely for the composition of the solution: see! Table

Claims (6)

Claims; Process for galvanic copper deposition an object, characterized in that this object as cathode in an aqueous copper (II) salt solution at a pH of about 0.4 to 8.9, which brings about 16 to 64 g per liter of copper (II) ions and about 48 to 192 g per liter of citric acid, and a current density of approx. 2
wa 10.7 to about 430 amperes per m is allowed to act until the desired copper film has deposited on the object. 2. The method according to claim 1, characterized in that that the object is stronger in an electroplating bath is electronegative than copper, and before the method is applied according to claim 1, a thin copper pre-electroplating coating is thereby applied to the object that the object at a pH of about 1 to 12 as Cathode in an aqueous copper (II) salt solution to thin galvanic precoating brings about 3 to 15 g of copper (II) ions and about 20 to 100 g of citric acid per liter and a current density of about 10.7 to about • v 2 430 amperes per m so long to act until the desired Pre-electroplating copper plating deposited on the item has been. 3 * The method according to claim 1 or 2, characterized in that there is used as copper-II-salζ GuSO ^ .5H ^ O, the copper (II) ion concentration about 64 g per liter and 1 098Λ2 / 1580 the citric acid concentration is about 192 g per liter, the pH is about 0.8, and the current density "is about 215 to about 4 30 amperes per m. 4. The method according spoke 1 or 2 »characterized in that CuGO, .Ou (OH) _{2 is} used as the copper (II) salt, the copper (II) ion concentration is about 55 g per liter and the citric acid concentration is about 192 g per liter , the pH is adjusted to about 8 by adding NH ^ OH, and the current density is about 215 to about 430 amperes per m. 5. The method according to claim 2, characterized in, that as a solution for the thin galvanic coating an aqueous CuCO ^ .Ou (OH) g solution, whose pH was adjusted to about 11.6 by adding HaOH, the copper (II) ion concentration used 12 g per liter, the citric acid concentration about 96 g per Liters, and the current density about 215 to about 430 amperes per m. 6. The method according to claim 2, characterized in that there is a solution for the thin galvanic Pre-coating an aqueous CuSO..5HgO-LOsUHg with a pH of about 1.6 is used, which contains about 6 g per liter of sodium sulfate and 20 g per liter of boric acid, with 109842/15 80 the copper-II-ion concentration about 4 g per liter, the Citric acid concentration at about 24 g per liter and the Current density is about 10.7 to about 32.3 amperes per m. Pure: Pfizer Ine. Lawyer 10 9 8 4 2/1580