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Effect of Deposition Conditions for Au-Sn and Sn Solder Film on Composition and Bonding Strength
Keywords: Au Sn , solder alloy, fluxless packaging
For high frequency applications, the flip chip interconnection and the chip stacking have been widely paid attention in the industry. These interconnections are commonly used with low temperature polymer materials during assembly process. Especially in optical device packaging process, both requirements of fluxeless and low temperature process had to be satisfied. In addition, the residues of flux after assembly of SIP and MEMS components has seriously damaged to the performance of system. One of the most popular solders is Au-Sn alloy. Up to now, 80wt.%Au and 20wt.%Sn solder has been used in the microelectronic and the photonic industries. The advantage of the alloy, in addition to fluxless assembly, is the excellent fatigue and creep resistance. On the other hand, it has relatively high melting temperature (280C) and very high cost. Many researches have looked into the fluxeless process with low melting temperatures. One of the promising candidates is Sn. The Sn has lower melting temperature than Au-Sn alloy. The Sn oxide is a big obstacle for the applications. Sn oxide is one of the strongest and densest oxides on metal system. In this research, the Au-Sn solder alloys with various compositions, from pure Sn to several tens % Au, were deposited by rf-sputtering system on Si wafer with Ti/Ni adhesion layer. Roughness, composition and deposition rate of solder alloy were critically dependent on the temperature of substrate, the power of rf system and the pressure of Ar in the chamber. As increasing the substrate temperature, the roughness decreased dramatically. While bonding a device on the Ag coated leadframe, the roughness was a critical factor to determine the bonding strength. In addition, the composition effect of solder alloy will be discussed.
Dong-Jin Kim, Graduate Student
Hanbat National University
Daejeon 305-719,
Republic of Korea

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