copper electroplating

RANDHIR KUMAR SINGH

ASST PROFESSOR

OPJIT

COPPER ELECTROPLATING

Copper plating Copper plating is a process of copper deposition over a part immersed into

an electrolyte solution and used as a cathode, when the copper anode is being

dissolved into the electrolyte in form of the copper ions traveling through the

solution and depositing on the cathode surface.

Phosphorized copper (0.04-0.08% P)is recommended for the anodes in

Copper plating [Acid copper sulfate bath] and Acid copper fluoborate bath.

High purity oxygen-free copper is used for the anodes in Cyanide copper

bath and Copper pyrophosphate bath. Less pure anodes form sludges on their

surfaces.

The sludge particles may increase the deposit roughness.

Anode-to-cathode area ratio is kept within the range between 1 and 2.

The copper electrolyte solutions are normally agtated by the solution flow,

oil-free air or by the oscillating cathodes.

The solutions are continuously filtered through a 1-5 μm filters at a flow 1-3

turnovers/hour (at least).

Discuss:

Properties of copper deposites

Cyanide copper bath

Copper pyrophosphate bath

Acid copper sulfate bath

Acid copper fluoborate bath

Properties of copper deposites

High electrical conductivity. The most popular application of the electroplated copper is copper plating of Printed Circuit Boards (PCB).

Copper substrate is easy to plate therefore copper deposit is widely used as an undercoat for over-deposits.

High thermal conductivity. Copper deposits are used as thermal conductors.

Copper deposit over steel surface may serve as a diffusion barrier. Copper coatings are used as stop-off preventing diffusion of carbon or/and Nitrogen during selective Case hardening.

There are numerous elctrolyte solutions and electro-deposition techniques for copper plating.

Copper deposits possess excellent decorative appearance.

Copper is relatively inexpensive metal.

Cyanide copper bath

Cyanide copper (particularly strike bath) provides excellent adhesion of the copper deposit. Cyanide baths are used for applying strike adhesion coatings and for wire plating

CuCN NaCN KCN Na2CO3 NaOH KOH Rochelle salt Cu Free cyanide

Bath oz/gal g/l oz/gal g/l oz/gal g/l oz/gal g/l oz/gal g/l oz/gal g/l oz/gal g/l oz/gal g/l oz/gal g/l

Strike 2.0 15 3.7 28 2.0 15 1.4 10.5 1.5 11

Rochelle

salt 3.5 26 4.6 35 4 30 to PH=12.3 6 45 2.5 19 0.8 6

High

speed 8 60 12.5 94 2 15 5.6 42 5.6 42 1.0 7.5

Compositions of cyanide copper baths

Operation conditions of cyanide copper baths

Temperature Cathode current

density

Anode current

density (max.)

Cathode

efficiency

Max.deposit

thickness Agitation Filtration

Bath °F °C A/ft2 A/dm2 A/ft2 A/dm2 % mil μm

Strike 120-

145 49-63 10-30 1-3 10 1 30-60 0.1 2.5 Solution flow Continuous

Rochelle

salt

130-

160 54-71 20-40 2-4 30 3 50 0.2 5.0 Solution flow Continuous

High speed 170-

180 77-82 30-60 3-6 50 5 100 0.3-2.0 7.5-50

Solution flow,

mechanical, air Continuous

Cyanide copper bath troubleshooting guide Problem: Poor adhesion (blistering or peeling)

Possible causes:

1.Poor cleaning treatment (Surface preparation)

2.Contaminated rinsing water

Problem: Low current efficiency due to the anode polarization (black or green deposit on anodes)

Possible causes:

1. Low free cyanide

2.Insufficient agitation

3.High anode current density

4.High operation temperature

5.Organic contamination

Problems: Roughness

Possible causes:

1.Suspended solid particles in the solution

2.Rough substrate surface

3.High current density


Cyanide copper bath troubleshooting guide

Problem: Turbide solution Possible causes: 1.Low free cyanide

2.Insoluble particles in the solution

Problem: Dull deposit Possible causes: 1.Low brightner


Problem: Dark deposit with yellow tarnish Possible causes: 1.Low copper

2.High free cyanide

Problem: Spongy deposit Possible causes: 1.Low free cyanide

2.Low Rochelle salt

Copper pyrophosphate bath

Copper pyrophosphate baths provide high throwing power and ductile copper deposition. They are used in electroforming, plating on plastics, printed circuit boards, and as stop-off in selective Case hardening of

steel. Copper pyrophosphate is a weak alkaline process.

Composition of copper pyrophosphate bath

Copper Pyrophosphate Nitrate Ammonia

Weight

ratio

P2O7/Cu

oz/gal g/l oz/gal g/l oz/gal g/l oz/gal g/l

3.5 26 25 188 1.5 11 0.13 1 7-8.5

Operation conditions of acid copper pyrophosphate

bath


density

Cathode

efficiency Voltage PH Filtration Agitation

°F °C A/ft2 A/dm2 % V

100-140 38-60 10-70 1-7 95-100 2-5 8-8.5 Vigorous

air

Continuous

1 turnover/hr

Copper pyrophosphate bath troubleshooting guide

Problem: Poor adhesion (blistering or peeling) Possible causes: 1.Poor cleaning treatment (Surface preparation);


Problem: Poor throwing power Possible causes: 1.High copper metal;

2.Insufficient agitation;

3.Low copper/pyrophosphate ratio;

4.High operation temperature;


Problems: Roughness Possible causes: 1.Suspended solid particles in the solution;

2.Rough substrate surface;

3.High current density;

4.Metallic contamination

Copper pyrophosphate bath troubleshooting guide

Problem: Brittle deposit

Possible causes:

1.High brightner content;

2.Organic contamination;

3.Excessive ammonia

Problem: Dull deposit

Possible causes:

1.Low brightner;

2.Organic contamination;

3.Low ammonia

Problem: Burnt copper deposit

Possible causes:

1.Low copper;


3.Low operation temperature;

4.low pyrophosphate

Problem: Buildup of orthophosphate in solution.

Possible causes:

1.High operation temperature;

2.Low copper/pyrophosphate ratio

Acid copper sulfate bath

Copper sulfate baths provide high throwing power. The plating process

and the waste treatment are relatively inexpensive. Copper sulfate copper

plating is widely used in electronics (printed circuit boards,

semiconductors), electroforming and for application undercoats.

Copper sulfate

CuSO4*5H2O

Sulfuric acid

H2SO4

Chloride ion

Cl-

Bath oz/gal g/l oz/gal g/l ppm

General 27 200 9.3 70 75

High throw 10 75 25 188 60

High speed 50 375 8 60

Compositions of acid copper sulfate baths

Operation conditions of acid copper sulfate baths

Temperature Cathode

current density

Anode current

density (max.)

Anode/

cathode

area ratio

(min.)

Agitation Filtration

Bath °F °C A/ft2 A/dm2 A/ft2 A/dm2

General 70-100 21-38 40 4 40 4 1 Vigorous air Continuous

3 turnover/hr

High

throw 70-90 21-32 15-50 1.5-5 7-25 0.7-2.5 2

Air or

mechanical

Continuous

2 turnover/hr

High

speed 64-113 18-45 50-200 5-20 20-100 2-10 2

Vigorous air

or

mechanical

Continuous

2 turnover/hr

Acid copper sulfate bath troubleshooting guide Problem: Poor adhesion (blistering or peeling)

Possible causes: 1.Poor cleaning treatment (Surface preparation);


Problem: Poor throwing power Possible causes: 1.High copper metal; 2.Low acid;

3.Low brightner content

Problems: Roughness Possible causes: 1.Suspended solid particles in the solution; 2.Rough substrate surface;

3.High chloride;

4.Low brightner content; 5.High rectifier ripple

Acid copper sulfate bath troubleshooting guide

Problem: Anode polarization Possible causes: 1.High chloride;

2.Insufficient anode area;


4.Low temperature;

5.High acid;

6.Low copper

Problem: Burnt deposit Possible causes: 1.Low copper;

2.High acid;

3.Low chloride;



Problem: Pitting Possible causes: 1.Low chloride;


Acid copper fluoborate bath

Copper fluoborate baths provide high plating speed. They are used

in printed circuit boards, electroforming, plating on plastic.

Copper fluoborate

Cu(BF4)2 Copper metal

Fluoboric acid

HBF4

Boric acid

H3BO3

Bath oz/gal g/l oz/gal g/l oz/gal g/l oz/gal g/l

Low

concentrat

ion

30 225 8 60 2 15 2 15

High

concentrat

ion

60 450 16 120 4 30 4 30

Compositions of acid copper fluoborate baths

Operation conditions of acid copper fluoborate baths


density

Cathode

efficiency Agitation Filtration

Bath °F °C A/ft2 A/dm2 %

Low

concentration 80-170 27-77 75-125 7.5-12.5 95-100

Air or

mechanical

Continuous

carbon

High

concentration 80-170 27-77 125-350 12.5-35 95-100

Air or

mechanical

Continuous

carbon

Acid copper fluoborate bath troubleshooting guide

Problem: Poor adhesion (blistering or peeling) Possible causes: 1.Poor cleaning treatment (Surface preparation);


Problem: Poor throwing power Possible causes: 1.High copper metal; 2.Low acid;

3.Low operation temperature;

4.High current density

Problems: Roughness Possible causes: 1.Suspended solid particles in the solution;

2.Rough substrate surface;

3.Low brightner content; 4.High rectifier ripple

Acid copper fluoborate bath troubleshooting guide

Problem: Low deposit hardness Possible causes: 1.High temperature; 2.High acid; 3.Low current density

Problem: Brittle deposit Possible causes: 1.Chloride contamination; 2.Organic contamination

Problem: Coarse deposit Grain structure Possible causes: 1.Low grain refiner; 2.High hardener content

copper electroplating

Documents

copper anode

copper deposits

copper coatings

electroplated copper

copper ions

copper substrate

phosphorized copper

copper electrolyte solutions