Surface finish and treatment on iron substrates for electronic packaging

Iron (Fe) with small percentage of carbon (less than 0.2%) is known as low carbon steel. It has numerous industrial applications since the Iron Age. It possesses high strength, high melting point, and low CTE. It is very inexpensive. The downside is fair thermal conductivity, which can be compensated using thinner substrates and thinner solder layer. The other downside is that it rusts easily and its oxides dissolve in water. In this research, we explored techniques to treat its surfaces to achieve finishes compatible with electronic packaging processes. These methods include electroplating of nickel (Ni), tin (Sn), respectively. With these finishes, we demonstrated that Si chips can be strongly bonded to Fe substrates using Sn without any flux.