Autocatalytic Electroless Copper Plating

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Autocatalytic Electroless Copper Plating
Kate Goodwin Department of Chemistry and
Biochemistry University of Massachusetts
Dartmouth, Fall River, MA
Chen-Lu Yang Advanced Technology and
Manufacturing Center University of Massachusetts
Dartmouth, Fall River, MA
University of Massachusetts Dartmouth Chapter of
Sigma Xi, the Scientific Research Society 11th
Annual UMass Dartouth Resarch Exhibition April
26th 27th, 2005
Introduction
Copper is used as a base plating metal onto which
additional metals can be electroplated.
Electrolessly plated copper broadens the range of
base materials that can be used for metal plating
because the material does not have to be
conductive. Copper can be electrolessly plated
onto ABS plastic by first coating the plastic
with an enamel mixture containing aluminum and
carbon black powders. The components of the
mixture are adjusted to optimize adhesion to the
plactic accroding to the tape test. The coated
ABS samples are placed in solution baths
containing different concentrations of CuSO4 and
HF. The enamel and bath parameters are adjusted
to decrease the plating bath time and increase
the consistancy of the plated copper metal. The
consistancy of the plated copper metal surface
can be measured with a 4-wire Ohm meter.
Enamel Coating Tape Test Results
Experimental

• Prepare ABS plastic
• Prepare Enamel Mixture
• Apply Enamel Mixture with Spray Gun
• Preform Tape Test on Enamel Coating
• Smooth Enamel Coating
• Prepare Copper Plating Bath
• Plate Enamel Coated ABS Sample
• Measure Resistance with Ohm meter

Chemical Equations 2Al(s) 3CuSO4(aq) ?
Al2(SO4)3(aq) 3Cu(s) HF(aq) ? H(aq) F-(aq)
Cu(s) ½O2(g) ? CuO(s) CuO(s) 2H(aq) ?
Cu(s) H2O(aq) Copper(II) in solution is
reduced onto the prepared surface by the exposed
aluminum powder. No current is necessary with
autocatalytic plating because the process is a
self initiating redox reaction which is driven by
the transfer of electrons from the aluminum solid
to the aqueous copper. In the redox equation,
the aluminum is the limiting reagent because
there is ample copper(II) in solution. That is
why the percentage of aluminum powder in the
enamel mixture needed to be maximized and the
scouring of the applied seed layer was necessary
in order to expose the aluminum to the copper in
solution. The hydrofluric acid is in solution to
clean the plated surface and to prevent copper
oxide formation.
Conclusions
In conclusion, the first step of substrate
preparation is extremely important for enamel
adhesion. The improved substrate preparation
allowed for a decrease in enamel percentage and
an increase in adhesion. Once the percentage of
enamel in the seed layer was optimized for
maximum adhesion, the percent aluminum was
adjusted to increase the amount of copper reduced
onto the surface of the enamel seed layer. The
composition of the seed layer is more important
than the bath composition since the aluminum
which it contains is the limiting factor. Copper
metal plates onto an anluminum coated surface
when it is placed in a bath containing Cu2 ions
no matter what the percentage. The amount of
copper plated onto the surface and the
consistency of the plated copper depends on the
percent aluminum contained in the seed layer and
the amount of aluminum exposed to the copper in
solution. Baths containing more copper than
hydrofluoric acid plate more consistently and in
general produce samples with lower ohm/cm2
values. The ohm/cm2 value decreases as the plate
time increases until all of the aluminum
contained in the seed layer is consumed an no
more copper can be reduced onto the surface.