Effect of a high-temperature pre-bake treatment on whisker formation under various thermal and humidity conditions for electrodeposited tin films on copper substrates

The effect of high-temperature pre-bake treatment on whisker formation was studied under various thermal and/or humidity and plating conditions for thin tin films on thick copper substrates. The pre-bake treatment was performed at 180 °C for 1 h. In tests conducted at 85 °C/85% relative humidity and ambient atmosphere, whisker formation was suppressed considerably when a pre-bake treatment was applied. After the pre-bake treatment, Cu3Sn intermetallic compounds were formed at the tin-copper interface. Cu3Sn IMCs play an important role in the formation of regular-shaped Cu6Sn5. Cu3Sn IMCs were also formed after temperature cycling and under conditions of 85 °C/85% RH. Irregular-shaped Cu6Sn5 IMCs were formed under all test conditions except for pre-baked samples in ambient atmosphere. A pre-bake treatment at 180 °C is advantageous for the inhibition of whisker formation and allows for planar and regular-shaped Cu3Sn to be produced.