A fluxless process of producing tin-rich gold-tin joints in air

Ricky W. Chuang, Dongwook Kim, Jeong Park, Chin C. Lee

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)


A soldering process performance in ambient air without the use of any flux is reported. We believe that this is the first time fluxless soldering process is successfully done in air without prior fluorine treatment. The fluxless process is implemented using Au-Sn binary system. It is based on Au-Sn multilayer design that is substantially tin-rich, namely, with 95 at.% Sn (91.8 wt.% Sn) and 5 at.% Au (8.2 wt.% Au). Over the past 15 years, we have developed numerous fluxless bonding processes. These processes require environments such as H2 or N2 during the bonding process to inhibit solder oxidation. This requirement is not compatible with the pick-and-place bonding machines widely employed in the industry. Thus, fluxless processing in air has been our lifelong endeavor. After many attempts, we finally achieved some initial success. The bonding process is carried out at 225°C. The resulting joints are nearly void-free as confirmed by scanning acoustic microscopy (SAM). To study the microstructure and composition of the samples, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) spectroscopy was performed on the joint cros-section. The results show that the joint is composed of AuSn4 intermetallic grains embedded in a Sn matrix. Re-melting temperatures of the solder joint were measured to range from 214°C to 220°C, which are consistent with data on the Au-Sn phase diagram.

Original languageEnglish
Pages (from-to)177-181
Number of pages5
JournalIEEE Transactions on Components and Packaging Technologies
Issue number1
Publication statusPublished - 2004 Mar

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering


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