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Copper plating

Dr. Dmitri Kopeliovich

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).

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.

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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

Compositions of cyanide copper baths
	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

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; 4.Organic contamination

Problem: Turbide solution

Possible causes: 1.Low free cyanide; 2.Insoluble particles in the solution

Problem: Dull deposit

Possible causes: 1.Low brightner; 2.Organic contamination

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

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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 stopp-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
Temperature		Cathode current 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); 2.Contaminated Rinsing water

Problem: Poor throwing power

Possible causes: 1.High copper metal; 2.Insufficient agitation; 3.Low copper/pyrophosphate ratio; 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; 4.Metallic contamination

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; 2.Insufficient agitation; 3.Low operation temperature; 4.low pyrophosphate

Problem: Buildup of orthophosphate in solution.

Possible causes: 1.High operation temperature; 2.Low copper/pyrophosphate ratio

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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.

Compositions of acid copper sulfate baths
	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

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); 2.Contaminated Rinsing water

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

Problem: Anode polarization

Possible causes: 1.High chloride; 2.Insufficient anode area; 3.Organic contamination 4.Low temperature; 5.High acid; 6.Low copper

Problem: Burnt deposit

Possible causes: 1.Low copper; 2.High acid; 3.Low chloride; 3.Insufficient agitation; 4.Organic contamination

Problem: Pitting

Possible causes: 1.Low chloride; 2.Organic contamination

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Acid copper fluoborate bath

Copper fluoborate baths provide high plating speed. They are used in printed circuit boards, electroforming, plating on plastic.

Compositions of acid copper fluoborate baths
	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 concentration	30	225	8	60	2	15	2	15
High concentration	60	450	16	120	4	30	4	30

Operation conditions of acid copper fluoborate baths
	Temperature		Cathode current 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); 2.Contaminated Rinsing water

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

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

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Copper plating

Properties of copper deposites

Cyanide copper bath

Copper pyrophosphate bath

Acid copper sulfate bath

Acid copper fluoborate bath

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