In this study we consider the effect of separately adding 0.5 wt.% to 1.5 wt.% Zn or 0.5 wt.% to 2 wt.% Al to the eutectic Sn-3.5Ag lead-free solder alloy to limit intermetallic compound (IMC) growth between a limited volume of solder and the contact metallization. The resultant solder joint microstructure after reflow and high-temperature storage at 150°C for up to 1000 h was investigated. Experimental results confirmed that the addition of 1.0 wt.% to 1.5 wt.% Zn leads to the formation of Cu-Zn on the Cu substrate, followed by massive spalling of the Cu-Zn IMC from the Cu substrate. Growth of the Cu 6 Sn 5 IMC layer is significantly suppressed. The addition of 0.5 wt.% Zn does not result in the formation of a Cu-Zn layer. On Ni substrates, the Zn segregates to the Ni 3 Sn 4 IMC layer and suppresses its growth. The addition of Al to Sn-3.5Ag solder results in the formation of Al-Cu IMC particles in the solder matrix when reflowed on the Cu substrate, while on Ni substrates Al-Ni IMCs spall into the solder matrix. The formation of a continuous barrier layer in the presence of Al and Zn, as reported when using solder baths, is not observed because of the limited solder volumes used, which are more typical of reflow soldering.

In this study, we will consider the effect of adding 1–1.5wt.% of Al and Zn to SAC alloy solders in order to limit IMC growth between the solder and the contact metallization. The Al and Zn react strongly with the surfaces on the electronic component and the substrate metallizations that are to be joined. At the solder joint interface, the IMC layer continues to grow at high temperatures and, being brittle, becomes the weakest link in the solder joint. In present work, the interfacial reaction studies were carried out on Cu and Ni(P) substrates. The resultant solder joint microstructure after reflow and isothermal aging at 150 °C up to 500h were investigated under scanning electron microscopy (SEM) with energy-dispersive x-ray analysis (EDX) for phase identification and optical microscopy (OM) for qualitative and quantitative analysis. Our experimental results have confirmed that addition of Al and Zn alloys forms Al-Cu and Cu-Zn on Cu substrate and Al-Ni on Ni(P) substrate respectively. In addition, results have confirmed that addition of Zn alloys plays a crucial role in the composition of IMCs. Addition of Zn (>1wt.%) into basic SAC solder alloy, leads to massive spalling on Cu substrate during reaction. It has been found that additions of Zn into SAC solder alloy can significantly suppress the IMC growth during the aging treatment.

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