Practically all microelectronic assemblies in use today utilize Sn-Pb eutectic solder for interconnection. Due to the increase in the use of electronic devices within the industry as well as personal use, the usage of solder connections has increased.
Emerging environmental regulations worldwide, most notably in Europe (WEEE) and Japan, have targeted the elimination of Pb usage in electronic assemblies, due to the inherent toxicity of Pb. This has made the search for suitable Pb-free solders an important issue for microelectronics assembly.
In this case Ramani investigated Sn-9Zn and Sn-8Zn-3Bi lead-free solders as potential replacements for the Sn-Pb solder.
She studied the solders characteristics, wetting behaviour, the interfacial reaction, mechanical properties and growth kinetics of solders on Cu substrate. The experiment was adding 3wt% of Bi to the Sn-Zn system which lowered the melting temperature by 3.5°C which is only 12°C higher than Sn-40Pb solder. It improved the wettability on Cu substrate by reducing the surface tension of the molten solder. The y-CusZna phase is the main interface intermetallic formed between Sn-Zn solders and the Cu substrate and this intermetallic thickness increased with time and temperature. The Sn-8Zn-3Bi/Cu solder joint had higher joint strength than Sn-9Zn/Cu and Sn-40Pb/Cu joints but solder joint degradation occurred at 150°C aging temperature. The activation energy for the growth of y-CusZna phase in Sn-9Zn/Cu and Sn-8Zn-3Bi/Cu systems are 44.05 and 55.36 kJ/mol, respectively. The addition of Bi to the Sn-Zn system had retarded the growth of y-CusZna phase by increasing the activation energy for the intermetallic growth.
The direct interface between Cu and Sn-8Zn-3Bi solder should have a temperature limit to be used below 100°C, which is enough for most of the commercial electronics applications.
Author contact:
Universiti Teknologi MARA, Perlis, Malaysia.
Reported by Megawati Omar
Research Management Institute
UiTM
