Wetting Properties of and Interfacial Reactions in Lead-free Sn-Zn Based Solders on Cu and Cu Plated with an Electroless Ni-P/Au Layer

Abstract

The wetting time, wetting force, contact angle and interfacial reaction of Sn-8.55Zn-0.45Al-XAg (mass%) and Sn-9Zn (mass%) lead-free solders on Cu and Cu/Ni-P/Au substrates have been investigated. The Ag content, X, of the solders investigated was 0-3 mass%. The results indicate that the wettability of Sn-8.55Zn-0.45Al-XAg solders decreases with increasing Ag content. The Sn-8.55Zn-0.45Al-XAg solders containing low Ag content, less than 1mass%, exhibit better wettability than the eutectic Sn-9Zn solder. Furthermore, it was also found that the wettability of Sn-Zn based solders on Cu substrate is better than that on Cu/Ni-P/Au substrate. The when used on Cu and Cu/Ni-P/Au, Sn-9Zn solder forms Cu₅Zn₈ and AuZn₃ respectively, while the Al-containing solders form Al_4.2Cu_3.2Zn_0.7 and Al₂(Au, Zn). Further addition of Ag gave rise to AgZn₃ particles attached to the underlying intermetallic compound.