Abstract
A comparison study on the reliability of gold (Au) and copper (Cu) wire bonding is conducted to determine their corrosion and oxidation behavior in different environmental conditions. The corrosion and oxidation behaviors of Au and Cu wire bonding are determined through soaking in sodium chloride (NaCl) solution and high temperature storage (HTS) at 175 °C, 200 °C and 225 °C. Galvanic corrosion is more intense in Cu wire bonding as compared to Au wire bonding in NaCl solution due to the minimal formation of intermetallics in the former. At all three HTS annealing temperatures, the rate of Cu-Al intermetallic formation is found to be three to five times slower than Au-Al intermetallics. The faster intermetallic growth rate and lower activation energy found in this work for both Au/Al and Cu/Al as compared to literature could be due to the thicker Al pad metallization which removed the rate-determining step in previous studies due to deficit in Al material.
Highlights
Au wire thermosonic bonding has been a mainstream semiconductor packaging process for many decades [1].The inert properties of Au make it an excellent choice for use when reliable manufacturing and applications in microelectronics packaging are required
The thin Al metallization in previous works could be the rate-determining step in preventing faster intermetallic formation and resulted in higher activation energy calculated since the thinnest intermetallic layer that is formed in Cu/Al at the mildest high temperature storage (HTS) condition is already 0.58 μm
The following conclusions can be drawn from this study: (1) Uniform pitting corrosion occurs on the Al pad in the absence of wire bonding
Summary
Au wire thermosonic bonding has been a mainstream semiconductor packaging process for many decades [1].The inert properties of Au make it an excellent choice for use when reliable manufacturing and applications in microelectronics packaging are required. The self-passivation of Cu worsens in an acidic environment where the Cl− ions in mold compounds act as a catalyst in the presence of moisture. This increases the corrosion rate of Cu by making the ranges of stable pH for Cu much narrower. The intermetallic growth mechanisms of Cu on Al pad metallization has been studied by a few researchers [2,3,6]. To address the shortfall in the corrosion studies conducted in halide environment, and the intermetallic growth mechanisms of Au and Cu, this paper focuses on these two aspects in Au/Al and Cu/Al wire bonding. Comparison studies between Au/Al and Cu/Al will be carried out to examine the difference in their corrosion behaviors and intermetallics formation
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