Intermetallic reactions in a Sn‐51In solder BGA package with immersion Ag surface finish

Chao‐Chi Jain Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan, R. O. C.

Shiuan‐Sheng Wang Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan, R. O. C.

Hui‐Min Wu Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan, R. O. C.

Tung‐Han Chuang Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan, R. O. C. Phone: 886–2–23929635 Fax: 886–2–23929635 E-mail: [email protected])

Abstract

Intermetallic compounds formed in Sn‐51In solder ball grid array (BGA) packages with Ag/Cu pads are investigated. After reflow, the Ag thin film dissolves quickly into the solder matrix, and scallop‐shaped intermetallic layers with compositions of (Cu_0.89Ag_0.11)(In_0.79Sn_0.21)₂/η‐Cu₆(Sn_0.54In_0.46)₅ appear at the interfaces between the Sn‐51In solder balls and Cu pads. Aging at 75°C and 100°C caused the η‐Cu₆ (Sn_0.54In_0.46)₅ intermetallics to replace the (Cu_0.89Ag_0.11)(In_0.79Sn_0.21)₂ at the solder/pad interfaces. The thickness of η‐ intermetallic versus the square root of reaction time (t ^1/2) shows a linear relation, indicating that the growth of intermetallics is diffusion‐controlled. Ball shear tests show that the strength of these Sn‐51In solder joints is initially 1.9 N, decreasing to 1.7 N and 1.6 N after aging at 75°C and 100°C, respectively.

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Corresponding author. (Tel: 886–2–23929635; Fax: 886–2–23929635; Email: [email protected])

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Intermetallic reactions in a Sn‐51In solder BGA package with immersion Ag surface finish

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Intermetallic reactions in a Sn‐51In solder BGA package with immersion Ag surface finish

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