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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

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

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

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

Possible causes: 1.Low grain refiner; 2.High hardener content

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copper_plating.txt · Last modified: 2013/12/14 by dmitri_kopeliovich
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