Aqueous based copper electroplating seems the mostreliable, flexible, cost effective method to create a copperlayer on stainless steel coupler devices; this however,doesn’t imply a straightforward application, assubcomponents geometry is complex and tolerances aretight. At CERN, two existing copper electroplating bathswere tested to evaluate the feasibility of plating threecouplers subcomponents within the demanded dimensionaltolerances. COMSOL Multiphysics® ElectrodepositionModule was used to optimise the counter electrodegeometry with the objective of achieving an as even aspossible copper layer thickness, as well as obtaining theplating parameters such as applied current density andplating time.
Introduction
Physics
Metal electrodes obey to Ohm’s law:
Current density vector: , with
Electrolyte in excess and vigorous agitation:
Current density vector: , with
Electrode kinetics are not negligible, but do not induce significate electrolyte concentration variations between the
bulk and the electrode surface. Electrode/Electrolyte interface: ,
The relation between current density and overpotential (h)can be described by the Butler-Volmer or Tafel equation,and also directly through experimental data obtained frompolarisation curves.
Model creation
Components geometry:
CEC (hollow geometry)Copper plating tolerances:10 +/- 5 µm Surface to be plated: Internal
WEC (hollow geometry)Copper plating tolerances:10 +/- 5 µm Surface to be plated: Internal
WIC (hollow geometry)Copper plating tolerances:20 +/- 10 µm Surface to be plated: External
Electrochemistry
Copper sulfate plating bath:CuSO4.5H20 75 g/lH2SO4 (96%) 100 ml/lCl (NaCl) 0.075 g/lConductivity 22.6 S/m
at 23 °C
Copper sulfate plating reactions:
CuCN 26 g/lNaKC4H4O6 60 g/lNa2CO3 15 g/lNaOH 12 g/lNaCN 42 g/lConductivity 10.6 S/m
at 45 °C
Copper cyanide plating bath:
cathodic reaction
cathodic reaction
anodic reaction (Ti/Pt anode)
anodic reaction (Ti/Pt anode)
Copper cyanide plating reactions:
-200
-100
0
100
200
-2 -1 0 1 2 3
Cur
rent
den
sity
(A
.m-2
)
Overpotential (V)
Cyanide plating bath anodic branch Cyanide plating bath cathodic branch
Sulfate plating bath anodic branch Sulfate plating bath cathodic branch
Copper plating baths polarisation curve
Conclusions
The work developed with Comsol allowed to evaluate the feasibility of platingcomplex geometries such as the ones of the couplers subcomponents. Thedata acquired from the different simulations allowed to: chose the mostinteresting operating bath; define, within a few iterations, an optimum workinggeometry for the CEC and WEC anode; define, the optimum workingparameters, current density and plating time, which allows to achieve thecopper layer thickness within the specified tolerances. Concerning the WICgeometry, simulation data showed that the copper sulfate plating bath wasn’table to respect the specified copper layer thickness specifications withoutlong plating times; on the other hand, the copper cyanide bath, was capableof doing it within the existing bath and anodes setup.
Physics interface:Electrodeposition, Secondary (edsec)
Results
CEC with copper sulfate bath:
CEC current density distribution with a
non-optimised anode
CEC current density distribution with an optimised anode
0
20
40
60
80
100
120
140
0
10
20
30
40
50
60
0 0.5 1 1.5 2
Pla
ting
time
(min
)
Pla
ted
thic
knes
s (µ
m)
Applied current density (A/dm2)
Minimum MaximumCopper thickness Plating time
Optimum platingparameters
WEC with copper sulfate bath:
WEC current density distribution with an optimised anode
0
20
40
60
80
100
120
140
160
0
10
20
30
40
50
60
0 0.5 1 1.5 2
Pla
ting
time
(min
)
Pla
ted
thic
knes
s (µ
m)
Applied current density (A/dm2)
Minimum Maximum Copper thickness Plating time
Optimum platingparameters
WIC:
0
100
200
300
400
500
600
0
20
40
60
80
100
120
140
0 0.2 0.4 0.6 0.8 1 1.2
Pla
ting
time
(min
)
Pla
ted
thic
knes
s (µ
m)
Applied current density (A/dm2)
Minimum Maximum Copper sulfate
Copper cyanide Time copper sulfate Time copper cyanide
Optimum platingparameters
Copper sulfate bath (green & black line) had very longplating times for the WIC geometry, thus the choice went tothe copper cyanide as plating bath (orange & grey line).
References
1. http://www.comsol.com/electrodeposition-module
COMSOLConferenceGrenoble 2015
COMSOLConferenceGrenoble 2015
Excerpt from the proceedings of the 2015 COMSOL Conference in Grenoble
