Reliability of Cu Wire Bonding to Al Metallization

Role of process parameters on bondability and pad damage indicators in copper ball bonding

“…The pad splash is defined as the Al pad material being squeezed outside the BB contact perimeter. Although it is not an indication of failure [25], it generally causes localized pad thinning [17], which reduces the bond reliability and is also an indication of pad damage risk.…”

Fine pitch copper wire bonding in high volume production

“…It is assumed that one of the Al-Cu IMCs is attacked leading to the formation of Al 2 O 3 and eventual ball lifting, i.e., an electrical open. The mechanism is not yet entirely proven [1,15,25]. The propensity for oxidation and corrosion has fostered the development of alternative wires based on palladium (Pd) coating of Cu wire [8,26].…”

Corrosion Study and Intermetallics Formation in Gold and Copper Wire Bonding in Microelectronics Packaging

“…The steep increase in Au prices has triggered the demand for high volume wire bonding process that can utilize Cu wire [2]. Barriers need to be overcome in Cu wire bonding due to the high oxidation rate and hardness of Cu wires.…”

“…However, the potential difference between the Au wire and Al pad may pose an issue which can lead to severe galvanic corrosion in the Al pad, and subsequently to Au ball detachment. The intermetallic growth mechanisms of Cu on Al pad metallization has been studied by a few researchers [2,3,6]. The activation energy reported varies from a wide range of 10.71 kJ/mol to 60.9 kJ/mol.…”

“…As shown in the figure, the intermetallic thickness of Au can range from 3 to 5 times higher than Cu. To calculate the intermetallic growth rate and the activation energy for intermetallic formation, the following two Equations [2] are used: (4) where X = IMC thickness (μm) t = Annealing time (s) K = Reaction rate of IMC formation (μm 2 /s)…”