Application and reliability of Au-Sn electroplated layer on the CSP hermetical packaging

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.