Abstract: Hermetical packaging in CSP component is increasingly investigated. In order to realize the hermetic interconnection between Kovar cap and ceramic substrate, the electroplating method was used and Au/Sn/Au sandwiched layers were fabricated on the HTCC substrate. Through the eutectic reaction between Au and Sn, a hermetic interconnection was realized. In this paper, the influence of Au/Sn/Au electroplated layer quality and soldering parameter on the packaging quality of Au-Sn eutectic solder was systematically investigated. It is found that the Au/Sn/Au electroplated layer thickness and interlayer bonding would directly determine the packaging results. During the soldering process, Sn electroplated layer firstly melted and a molten pool thus formed. The molten Sn then dissolved the surrounding Au electroplated layer and the Au-Sn eutectic reaction occurred. The shorter soldering time was better for the Au-Sn eutectic packaging. When the soldering temperature was 330 ℃ and holding time was set to 30 s, the (Au, Ni)Sn—ζ phase—(Au, Ni)Sn delaminated eutectic microstructures formed due to Au-Sn eutectic reaction and a reliable hermetical packaging between Kovar cap and HTCC substrate was eventually realized.