Effect of isothermal aging on the interfacial reactions between Sn-0.4Cu solder and Cu substrate with or without ENIG plating layer

摘要

The interfacial reaction between the Sn-0.4 wt.% Cu solder and two different kinds of substrates (Cu and ENIG (electroless nickel-immersion gold)) during isothermal aging at 150 degrees C were studied. In case of the Cu substrate, two IMCs (intermetallic compounds) of Cu6Sn5 and Cu3Sn formed at the interface after aging for 250 h. After aging at 150 degrees C for 1000 h, crack occurred along the interface between the Cu3Sn IMC and Cu substrate. In case of the ENIG substrate, the solder/electroless Ni-P interface exhibited a duplex structure of (Cu,Ni)(6)Sn-5 and (Ni,Cu)(3)Sn-4 after aging at 150 degrees C for 24 h. Many discontinuous (Cu,Ni)(6)Sn-5 IMCs formed on (Ni,Cu)(3)Sn-4 IMC layer. The presence of P in the electroless Ni-P layer caused complicated interfacial reactions such as formation of a P-rich Ni (Ni3P) and Ni-Sn-P layers. The growth of the Cu-Sn IMC layer formed on the Cu substrate was much faster than that of the Cu-Ni-Sn IMC ((Cu,Ni)(6)Sn-5 and (Ni,Cu)(3)Sn-4) layer formed on the ENIG substrate. In addition, the formation of the Cu-Ni-Sn IMC layer retards the consumption of the Ni from the electroless Ni-P layer. Results of this study showed that the ENIG plating layer acts as a good diffusion barrier for the Sn-0.4Cu solder. (c) 2005 Elsevier B.V. All rights reserved.