NCKU researchers invent aluminium bonding wires

National Cheng Kung University (NCKU) researchers’ latest invention, of aluminium bonding wires used in semiconductor packaging, is poised to revolutionize the industry by providing a cheaper alternative to gold, silver and copper, materials science professors Hung Fei-yi and Lui Truan-sheng said.

Due to their superior conductivity and ductility, gold, silver or copper bond wires are used to make the ball bonds that connect 90 per cent of the world’s LED and IC semiconductor devices to their casing or frames, the researchers said.

However, the high prices those metals command make mass production expensive, with gold valued at about NT$2 million (US$61,862) per kilogram, silver at NT$40,000 per kilogram and copper at the much lower, but still pricey, NT$220 per kilogram, they said.

In contrast, aluminium trades at about NT$60 per kilogram, and its use in semiconductors could greatly reduce production costs if scientists could overcome the material’s naturally low conductivity and strength, they said.

They have worked on making aluminium wires that could be used in ball wire bonding for the past four years and have finally solved the problem, they said.

The aluminium wires Hung and Lui’s team made are 1.8 micrometers thick, heat-treated for improved strength and elasticity, and crucially, they have been plated with zinc using nanotechnology, which provides the final product with the necessary wire-bonding qualities.

The professors credited two of their students, master’s degree candidate Chu Kuan-ming and doctoral candidate Tseng Yi-wei, with realizing that the zinc electroplating on the wires was responsible for their failure to assume the proper ball shape during the bonding process.

When subsequent analysis confirmed that the students were correct by showing that the electroplating method had led to unwanted formation of oxidized zinc on the wire surface, the team replaced the process with nanoplating, which perfected the bonding wire, Hui and Lui said.

The researchers said that the government had issued a patent for their aluminium bond wire and that they have also applied for a patent in China.

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