197. AraznaA
نویسندگان
چکیده
Immersion tin is widely used as lead free surface finish in the printed circuit board technology. Tin prevents the underlying copper from corrosion and preserves its solderability during a long storage and lead-free assembly processes. In the paper immersion tin coatings of different thickness (0.2 ÷ 1.5 μm) deposited on copper foil from methanelulphonic bath were investigated. The layers were tested in the state as received and after ageing (4 h at 155oC, in air). Their morphology, solderability and corrosion properties were examined. The SEM studies revealed that thin tin layers have smooth and uniform structure with very small crystals. However, thicker coatings are irregular with a lot pits (cavities) on the surface. It was observed, that corrosion resistance of 0.25 μm thick Sn layer increased after ageing, whereas the corrosion resistance of thicker layers were changed slightly. The tin coatings solderability assessed in a solder spread test was acceptable for as-deposited samples. A significant decrease in the solderability of the aging coatings which had better corrosion protective properties was stated. The changes in corrosion behaviour and solderability of investigated tin coatings were related to tin grain size of tin coatings and intermetallic SnCu phase formation.
منابع مشابه
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