Bath Composition and Operating Variables

The compositions and analyses given in Tables 1, 2, 3, and 4 for cyanide, noncyanide alkaline, pyrophosphate, and acid copper plating baths may be varied within the control limits to satisfy requirements for specific applications.

Current density can be altered to effect more efficient control and to increase the deposition rate of copper. The data in Table 6 can be used as a guide to the selection of current density.

Table 6 Estimated time required for plating copper (valence 1) to a given thickness at 100% cathode efficiency

Cyanide baths contain copper with a valence of 1. For baths containing copper with a valence of 2, such as noncyanide alkaline, sulfate, pyrophosphate, and fluoborate baths, double the time values given in this table. Values must be corrected for losses in cathode efficiency by adding the difference between the actual cathode efficiency and 100%; for example, for 70% cathode efficiency, add 30% to values in table to determine estimated time.

Table 6 Estimated time required for plating copper (valence 1) to a given thickness at 100% cathode efficiency

Cyanide baths contain copper with a valence of 1. For baths containing copper with a valence of 2, such as noncyanide alkaline, sulfate, pyrophosphate, and fluoborate baths, double the time values given in this table. Values must be corrected for losses in cathode efficiency by adding the difference between the actual cathode efficiency and 100%; for example, for 70% cathode efficiency, add 30% to values in table to determine estimated time.

Thickness

Plating time,

• (a) min

of plate

at current density, A/dm2 (A/ft2)

^m

mils

1.0 (10)

1.5 (15)

2.0 (20)

2.5 (25)

3.0 (30)

3.5 (35)

4.0 (40)

4.5 (45)

2

0.08

4

3

2

2

2

1

1

1

5

0.2

11

8

6

5

4

3

3

2

10

0.4

23

15

11

9

8

6

6

5

20

0.8

45

30

23

18

15

13

11

9

30

1.2

68

45

34

27

23

19

17

14

40

1.6

90

60

45

36

30

26

23

18

50

2.0

113

75

57

45

38

32

28

23

60

2.4

136

90

68

54

45

39

34

27

70

2.8

158

106

79

63

53

45

40

32

80

3.1

181

120

90

72

60

52

45

36

(a) To nearest whole value

(a) To nearest whole value

Impurities. The degree of control required to protect copper plating baths from impurities varies with the type of bath and the method of processing used. Known causes of roughness in copper deposits are:

• Dragover from cleaners, which results in the formation of insoluble silicates in the electrolyte

• Poor anode corrosion

• Insoluble metallic sulfides because of sulfide impurities

• Organic matter in the water used for composition, especially in rinse tanks

• Insoluble carbonates because of calcium and magnesium in hard water

• Oil from overhead conveyors

• Airborne dust or particles

If the level of impurities reaches a critical point, causing poor results, a batch carbon treatment or circulation through a carbon-packed filter may be required. For the noncyanide processes, a sulfur-free carbon pack must be maintained on the bath and changed weekly. Lead and cyanide are contaminants to these systems and tend to cause a black smutted deposit. When converting a plating line from a cyanide system to a noncyanide electrolyte, all associated equipment must be cleaned and thoroughly washed to ensure no cyanide contamination.

Caution: Cyanide remains in the system. Acids can be used only after all traces of cyanide have been eliminated.

Purity of Water Used in Composition. The purity of the water used in the composition of the baths is important for all plating operations. Iron in the water causes roughness in the deposit if the pH of the electrolyte is above 3.5 where iron can be precipitated. Chlorides in concentrations greater than about 0.44 g/L (0.05 oz/gal) promote the formation of nodular deposits. Calcium, magnesium, and iron precipitate in the bath. Organic matter may cause pitting of deposits.

When plating in sodium or potassium, high-efficiency electrolytes and distilled, deionized, softened, or good quality tap water may be used for solution composition and for replenishment. Tap water with high contents of calcium and/or iron should not be used, because it may cause roughness of the deposit. Softened water should be used with care, especially in plating baths where chloride contents are critical, such as bright copper sulfate baths.

Agitation during plating permits the use of higher current densities, which create rapid deposition of copper. The amount of increase permissible in current density varies for the different baths. Preferred methods of agitation for the types of baths are:

Cyanide baths

Cathode movement, air agitation, or both

Pyrophosphate baths

Air agitation

Acid baths

Cathode movement, air agitation, or both

Noncyanide baths

Vigorous air agitation

When air agitation is used, all airline pipes should be made of inert material or coated with an inert material to prevent attack by the electrolytes. The air used for agitation must be clean to avoid bath contamination. Filtered air from a low-pressure blower is required.

Ultrasonic vibration also has been used for the agitation of copper plating baths. This method does not largely improve the properties or appearance of electroplates, but it can improve plating speed by permitting an increase in the current density without the hazard of burning the parts. Increased plating speed does not necessarily justify the increased cost and complexity of ultrasonic operation, because the high-speed baths can usually be operated with a fairly high current density at nearly 100% efficiency.

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