Abstract: The solderability deterioration of the leads of electronic components often occurs during a longer storage and operation periods in which even more excess of tin layer still remained on the upper part of intermetallics η andε phases formed between the border of Cu and Sn. In this work, hot dipped and electroplated samples with thick tin coating layer more than 120 μm have been investigated by the methods of metallograph, XPS, electrochemical testing and wettability measuring. Some samples have been heat treated at 155 ℃ for 16 h to simulate storage and operation periods. The results indicated that copper rapidly dissolved and diffused deeply into liquid tin phase and also in the solid tin during heat treatment. The dissolved copper accumulated as micro crystals ofηphase suspensing in the tin phase even exposed to the surface of tin coating layer. Close connection of ηSn couples on the tin surface aroused electrochemical corrosion of tin under a moist or acidic atmosphere. The oxidized products deteriorated the solderability of lead wires.

Key words: Cu₆Sn₅, Leads of electronic component, 　Soldering, Solderability