Effect of polyethylene glycol additives on pulse electroplating of SnAg solder

Hsiao Yun Chen*, Chih Chen, Pu-Wei Wu, Jia Min Shieh, Shing Song Cheng, Karl Hensen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Eutectic Sn-3.5wt.%Ag alloy is one of the most promising lead-free solders in low temperature processes for wafer bumping. Near eutectic composition of deposited alloy films could be readily acquired by pulse electroplating with a proper combination of active ingredients including K 4P 2O 7, KI, Sn 2P 2O 7, and AgI, as well as polyethylene glycol (PEG), with molecular weights of 200, 600, 2,000, and 4,000, as an inhibitive agent. Pulse electroplating was carried out with current in alternating polarity to conduct electroplating and electropolishing sequentially. As a result, alloy films with grains of less than 1 μm and uniform surface morphology can be obtained. The addition of PEG was necessary for the stabilization of the plating baths to promote a wider process window for the desirable eutectic composition. Electrochemical characterization established that PEG with molecular weight of 4,000 exhibited the strongest inhibition behavior. In contrast, PEG with molecular weight of 200 demonstrated the least interference. Energy dispersive X-ray and differential scanning calorimeter data confirmed the formation of eutectic alloy as a function of deposition current density. X-ray diffraction results indicated that a biphasic structures of β-Sn and ε-Ag 3Sn was present in the as-deposited film.

Original languageEnglish
Pages (from-to)224-230
Number of pages7
JournalJournal of Electronic Materials
Issue number2
StatePublished - 1 Feb 2008


  • Electroplating solder
  • Packaging
  • Pb-free solder

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