Fabrication and microstructures of sequentially electroplated Au-rich, eutectic Au/Sn alloy solder

• Published in: Journal of materials science. Materials in electronics Vol. 19; no. 12; pp. 1176 - 1183
• Main Authors: Tang, Wenming, He, Anqiang, Liu, Qi, Ivey, Douglas G.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.12.2008; Springer; Springer Nature B.V
• Subjects: Alloys; Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Cross-disciplinary physics: materials science; rheology; Design. Technologies. Operation analysis. Testing; Electrodeposition, electroplating; Electronics; Eutectic temperature; Exact sciences and technology; Gold; Gold base alloys; Integrated circuits; Materials; Materials Science; Methods of deposition of films and coatings; film growth and epitaxy; Microelectronic fabrication (materials and surfaces technology); Optical and Electronic Materials; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Silicon; Solders; Tin; Tin base alloys; Wafers; Alloy Solder; Solder Preform; Vacuum Deposition Technique; Eutectic Zone; Reflow Temperature; Microcrack; Phase composition; Tin alloy; Multiple layer; Annealing temperature; Integrated circuit bonding; Microelectronic fabrication; Gold alloy; Soldered joint; Electrodeposition; Silicon; Microstructure; Wafer; Room temperature; Reflow soldering
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-007-9522-z

An Au-rich, eutectic Au/Sn alloy was fabricated by sequential electroplating of Au and Sn, and reflowing the as-deposited Au/Sn/Au triple-layer film at 320–350 °C. Microstructures and phase compositions for the as-deposited Au/Sn/Au triple-layer film and the reflowed Au-rich, eutectic Au/Sn alloys were studied. Two Si wafers, each with the Au-rich, eutectic Au/Sn alloy solder, were bonded together. For the deposited Au/Sn/Au triple-layer film, reaction between Au and Sn occurs at room temperature leading to the formation of AuSn and AuSn 4 . After reflowing at 320 °C, two phases remain, AuSn and Au 5 Sn, with the AuSn particles distributed randomly in the Au 5 Sn matrix. There are also some micropores and microcracks in the reflowed alloy. If the annealing temperature is increased to 350 °C, the Au/Sn alloy is denser and contains fewer micropores. However, microcracks remain, forming preferentially along the Au 5 Sn/AuSn interface. After reflowing at 320 °C under a pressure of 13 kPa, two Si wafers are joined using the Au-rich, eutectic Au/Sn alloy solder. The solder is in intimate contact with the Si wafers; however, there are some micropores within the solder. After reflowing at 350 °C, the bond is quite good, without microcracks or micropores at the Si wafer/solder interface or within the solder.