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Study of Sn-Zn Based Solders for Low-temperature Aluminum Soldering in Electronic Packaging

Author: LiuLiangZuo
Tutor: ZhangXinPing
School: South China University of Technology
Course: Materials Processing Engineering
Keywords: Electronic packaging Aluminum soldering Sn-Zn solder Wettability Corrosion resistance
CLC: TG425
Type: Master's thesis
Year: 2011
Downloads: 189
Quote: 1
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Abstract


The aluminum soldering technology in electronic packaging has attracted much attention in recent years, because aluminum and its alloys show many advantages in applications, such as low density, good thermal and electrical conductivity, excellent corrosion-resitance, as well as low cost. However, compared with copper solderding in electronic packaging there is limited work available about the solders used for soldering aluminum and its alloys. In this thesis study, the effect of adding element Ag to Sn-Zn based lead-free solders on the melting temperature, microstructural features, wettability, corrosion resistance, surface tension and mechanical properties of the solders has been characterized; and further the effect of addition of elelment Al and Ga on surface tension of Sn-15Zn based lead-free solders was investigated.The results from Sn-xZn series solders show that:(1) The wettability of hypereutectic Sn-Zn solders deteriorates with increasing Zn content. In contrast, hypoeutectic Sn-Zn solders show good wettability; for example hypoeutectic Sn-1.5Zn solder exhibits better wettability than eutectic Sn-9Zn solder; (2) The corrosion resistance of Sn-xZn solder joints increases with Zn content, and hypereutectic Sn-Zn solder joints exhibit better corrosion resistance, in term of a longer immersion time (for 5 to 7 days) in a 3.0%NaCl solution without failure, than hypoeutectic Sn-Zn solder joints which generally show a short lifetime (only 1 to 2 days).The results from Sn-1.5Zn-xAg (x=0～2.5%) solders indicate that:(1) Sn-1.5Zn-xAg solders exhibit better wettability than Sn-3.0Ag-0.5Cu lead-free solder. The addition of Ag into Sn-1.5Zn can increase the maximum wetting force (Fmax) of the solder, while increasing the wetting time to. (2) The increase of Ag content in Sn-1.5Zn-xAg solders results in decrease in shear strength of the joints. (3) Finally, it has been shown that Sn-1.5Zn-xAg solder joints exhibit the increased corrosion resistance in a 3wt.% NaCl solution, despite still worse than that of Sn-3.0Ag-0.5Cu solder joints.Moreover, the results from Sn-15Zn-xAg (x=0-2.0%) solders manifest that for the solders with a low Ag content (less than 1.5%) the increase of addition amount of Ag to the solder can improve the wettability of the solder and increase corrosion resistance of the joints.In addition, the interface bonding quality and interfacial microstructures of Sn-15Zn-xAg/Al joints were characterized by using a scanning electron microscope (SEM). It has been seen that there exist dark particle phase, as confirmed being Al (Zn,Sn) solid solution, and white Sn phase at the interfacial area, and a clear diffusion layer also formed at the interface. The microanalysis results also show that no Ag-Al intermetallic compound was found at the interface, this is different from those reported by others. This may be the reason that the addition of Ag in Sn-Zn based solders has not shown the effect of improving the corrosion resistance of the solder joints.Furthermore, the effect of adding element Al and Ga to Sn-15Zn based solders on surface tension of the solders was also studied. The results show that the addition of both Al and Ga can increase the surface tentsion value of the solders, accordingly deteriorate the wettability of the solders, but improve the antioxidation of the solder alloy.Finally, a comprehensive consideration on processing performance, mechanical and anti-corrosion properties, and the cost of the solders suggests that Sn-15Zn-0.1Al-0.5Ga may be the best candidate among these studied in this thesis research, for the possible application in the future.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding materials > Brazing materials
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