Non-cyanide Electroplating of Gold-Tin Eutectic Alloy for Flip-Chip Packaging of LED

Abstract

A high stability non-cyanide gold-tin alloy electroplating solution was developed to prepare Au-Sn bumps in flip-chip packaging of light-emitting diode. 5, 5- Dimethyl hydantoin (DMH) was used as the main complexing agent for Au(III) and Sn(IV) was used as the main salt of tin. The additions of complexing agents stabilized the Sn(IV) and improved the stability of electroplating solution. To obtain eutectic composition of Au-Sn coating, the ratio of Au (III) to Sn(IV) was determined to be 1:10. The polarization potential of tin ion was positively shifted, which was approaching to the deposition potential of gold ion. The deposition potential of Au-Sn coating was −0.93 V. The stirring rate had an effect on the content of tin atom in Au-Sn coating. Energy dispersive X-ray spectrometer results showed that the tin content decreased with increasing stirring rate. Scanning electron microscope images showed that the Au-Sn coating became denser with increasing stirring rate. The optimal stirring rate was 100 rpm under a current density of 40 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The content of tin atom in the Au-Sn coating increased when the current density was increased in the range of 20~55 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Voids and larger grains of Au-Sn coating formed at high current density.