Intermetallic growth and void formation in Au wire ball bonds to Al pads

Tomohiro Uno, Kohei Tatsumi

研究成果: Article

10 引用 (Scopus)

抄録

In order to clarify the reliability of Au wire bonds to Al pads, void formation and diffusion behavior were investigated using bonds annealed at various temperatures (423-573 K). We investigated the effects of the annealing environments, Al pad thickness, and bonding conditions on void formation. Voids became larger only when Au-Al intermetallics grew non-uniformly, whereas deleterious voids were not observed in the bonds annealed in vacuum. Oxide film on the surface of Al pads acts as a diffusion barrier at the interface. Optimized bonding conditions (applied pressure, ultrasonic energy) broke up the oxide film, resulting in reduction of void formation. Au5Al2 phase grew dominantly in the early stage of diffusion, then it transformed into Au4Al phase because the Al layer was completely consumed. The activation energy Q of transmission velocity at the Au/Au4Al boundary was 0.85 eV (82 kJ/mol). This is similar to the activation energy of the bond failure by annealing. These results indicate that void formation has a great correlation with the Au4Al growth. It is predicted that the non-uniform diffusion behavior causes vacancies to pile-up and these vacancies coalesce to form several types of voids in the interface.

元の言語English
ページ(範囲)828-837
ページ数10
ジャーナルNippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
63
発行部数7
出版物ステータスPublished - 1999
外部発表Yes

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Intermetallics
intermetallics
balls
voids
wire
Wire
Oxide films
Vacancies
Activation energy
Annealing
Diffusion barriers
Piles
Ultrasonics
oxide films
Vacuum
activation energy
annealing
piles
ultrasonics
Temperature

ASJC Scopus subject areas

  • Metals and Alloys

これを引用

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abstract = "In order to clarify the reliability of Au wire bonds to Al pads, void formation and diffusion behavior were investigated using bonds annealed at various temperatures (423-573 K). We investigated the effects of the annealing environments, Al pad thickness, and bonding conditions on void formation. Voids became larger only when Au-Al intermetallics grew non-uniformly, whereas deleterious voids were not observed in the bonds annealed in vacuum. Oxide film on the surface of Al pads acts as a diffusion barrier at the interface. Optimized bonding conditions (applied pressure, ultrasonic energy) broke up the oxide film, resulting in reduction of void formation. Au5Al2 phase grew dominantly in the early stage of diffusion, then it transformed into Au4Al phase because the Al layer was completely consumed. The activation energy Q of transmission velocity at the Au/Au4Al boundary was 0.85 eV (82 kJ/mol). This is similar to the activation energy of the bond failure by annealing. These results indicate that void formation has a great correlation with the Au4Al growth. It is predicted that the non-uniform diffusion behavior causes vacancies to pile-up and these vacancies coalesce to form several types of voids in the interface.",
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AB - In order to clarify the reliability of Au wire bonds to Al pads, void formation and diffusion behavior were investigated using bonds annealed at various temperatures (423-573 K). We investigated the effects of the annealing environments, Al pad thickness, and bonding conditions on void formation. Voids became larger only when Au-Al intermetallics grew non-uniformly, whereas deleterious voids were not observed in the bonds annealed in vacuum. Oxide film on the surface of Al pads acts as a diffusion barrier at the interface. Optimized bonding conditions (applied pressure, ultrasonic energy) broke up the oxide film, resulting in reduction of void formation. Au5Al2 phase grew dominantly in the early stage of diffusion, then it transformed into Au4Al phase because the Al layer was completely consumed. The activation energy Q of transmission velocity at the Au/Au4Al boundary was 0.85 eV (82 kJ/mol). This is similar to the activation energy of the bond failure by annealing. These results indicate that void formation has a great correlation with the Au4Al growth. It is predicted that the non-uniform diffusion behavior causes vacancies to pile-up and these vacancies coalesce to form several types of voids in the interface.

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