초미세 SAC305 나노입자를 사용한 저온 코팅법으로 제조된SAC305 코팅 Cu의 솔더 젖음성

SAC-coated Cu specimens were fabricated by novel pad finish process using a phenomenon that metal nanoparticles less than 20 nm in diameter melted at a temperature lower than the melting point of bulk metal, and their wettabilities were evaluated. The thickness of SAC305 layer coated at low temperature of 160oC using SAC305 ink was extremely thin as the level of several nanometers. It was analyzed by Auger electron spectroscopy that Cu6Sn5 intermetallic layer with a thickness of 10~100 nm and Cu3Sn intermetallic layer with a thickness of 50~150 nm were sequentially formed under the SAC305 coating layer. The thickness of formed intermetallic layers was thicker in electroplated Cu than rolled Cu, which attributed to improved surface roughness in the electroplated Cu. The improved surface roughness induces the contact, melting, and reaction of a larger number of SAC305 nanoparticles per the unit area of Cu specimen.
In the wetting angle test using SAC305 solder balls, the Cu coated with SAC305 through the low temperature process presented evidently low wetting angles than those in non-coated Cu, indicating that only a few nanometer-thick SAC305 coating layer on Cu could also cause the enhancement of wettability.