电子元件覆锡铜引线的腐蚀机制

Corrosion Mechanism of Tin Coated Leads of Electronic Component

电子元件覆锡铜引线的可焊性常因储存时间的延长而大大恶化.本文通过金相、XPS、电池断路电位和润湿性测定等方法判断可焊性恶化的机制是:铜—锡金属间化合物η相(Cu6Sn5)微晶向锡表面扩散,与锡形成微电池对,遇到空气中的水份与酸气氛构成电化腐蚀所致.

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.