266
Fundamentals of Corrosion
8.2.1.2 Gold Coatings
Gold electrodeposits are primarily used to coat copper in electronic applications to protect the copper connectors and other copper components from
corrosion. It is desirable to obtain the corrosion protection with the minimum thickness of gold because of the cost of the gold. As the thickness of
the electrodeposit decreases, there is a tendency for the deposit to provide
inadequate coverage of the copper. For this reason it is necessary that there
be a means whereby the coverage of the copper can be determined. Such
a test using corrosion principles as a guide has been developed. In a 0.1 M
NH 4 Cl solution, gold serves as the cathode and copper serves as the anode.
At a high cathode/anode surface area fraction, the corrosion potential is linearly related to the area fraction of copper exposed, as shown in Figure 8.5.
By measuring the corrosion potential of the gold-plated copper in a 0.1 M
NH 4 Cl solution, the area fraction of copper exposed is determined.
Gold coatings can also be deposited by means of electroless plating.
Borohydride or DMAB is used as the reducer with a stable gold cyanide complex. Thin gold coatings can be deposited on plastics by an aerosol method
using gold complexes with amines and hydrazine as a reducer. A relatively
thick coat can be obtained.
–100
–80
–60
–40
–20
Corrosion Potential, mV (vs SCE)
Bath 0.1 M NH 4 Cl
20
40
10 –7
10
–6
10
–5
Area Fraction Copper
10
–4
10
–3
0
FigurE 8.5
Data showing that the fractional exposed area of copper in a copper-gold system is linearly
related to the corrosion potential at low exposed copper areas.
Fundamentals of Corrosion
8.2.1.2 Gold Coatings
Gold electrodeposits are primarily used to coat copper in electronic applications to protect the copper connectors and other copper components from
corrosion. It is desirable to obtain the corrosion protection with the minimum thickness of gold because of the cost of the gold. As the thickness of
the electrodeposit decreases, there is a tendency for the deposit to provide
inadequate coverage of the copper. For this reason it is necessary that there
be a means whereby the coverage of the copper can be determined. Such
a test using corrosion principles as a guide has been developed. In a 0.1 M
NH 4 Cl solution, gold serves as the cathode and copper serves as the anode.
At a high cathode/anode surface area fraction, the corrosion potential is linearly related to the area fraction of copper exposed, as shown in Figure 8.5.
By measuring the corrosion potential of the gold-plated copper in a 0.1 M
NH 4 Cl solution, the area fraction of copper exposed is determined.
Gold coatings can also be deposited by means of electroless plating.
Borohydride or DMAB is used as the reducer with a stable gold cyanide complex. Thin gold coatings can be deposited on plastics by an aerosol method
using gold complexes with amines and hydrazine as a reducer. A relatively
thick coat can be obtained.
–100
–80
–60
–40
–20
Corrosion Potential, mV (vs SCE)
Bath 0.1 M NH 4 Cl
20
40
10 –7
10
–6
10
–5
Area Fraction Copper
10
–4
10
–3
0
FigurE 8.5
Data showing that the fractional exposed area of copper in a copper-gold system is linearly
related to the corrosion potential at low exposed copper areas.