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Non-cyanide Electroplating of Au-Sn Alloy

Author: ZhangFuShun
Tutor: HuangMingLiang;WangLai
School: Dalian University of Technology
Course: Materials Science
Keywords: Au-Sn eutectic non-cyanide plating co-electroplating lead-free solder
CLC: TQ153
Type: Master's thesis
Year: 2008
Downloads: 243
Quote: 1
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LEDs were applied in many fields as a long-life,energy efficient,environmentally friendly and multi-use light source in modem life.The flip-chip technology improved the thermal dissipation and luminescence efficiency of High-power LEDs,but higher requirements were submitted to the packaging technology.Our purpose was to develop an Au-Sn bumping process on high-power LED flip-chip technology.This paper focused on the influence of non-cyanide plating solution stability,the electroplating parameters on the thickness of cladding,and the preparation of Au70Sn30 eutectic bump.The main results indicated that:1.A new non-cyanide co-electroplating solution for Au-Sn alloys was developed based on D. G.Ivey’s solution which was stable at room temperature.NaSO3 and EDTA were used as golden complexing agent,potassium pyrophosphate as stannous complexing agent,pH value was adjusted from 6.0 to 8.0.The high-temperature stability of this solution was improved(it was still stable after heating to 50℃).2.When the NaAuCl4·2H2O concentration in bath was 4,10,15,20g/L respectively,a peak of growth rate appeared for 10g/L under T=45℃.When NaAuCl4·2H2O concentration was 4g/L, heavy current made the plating films porous;as NaAuCl4·2H2O concentration increasing,the plating solution stability became worse.The suitable NaAuCl4·2H2O concentration in bath was 10g/L.3.The plating temperature had an obviously effected on the surface topography of Au-Sn films.When the temperature was in the range from 35℃to 65℃,the lower the temperature the rougher the films;but the higher temperature also made the films rough owing to scorch of the films,and lowered the quality of Au-Sn alloys.The suitable plating temperature was 45℃.4.While Jwas set at 1,2,3,4,5,6,6.5,7,8,8.5,10mA/cm2 separately,the tin content was 16%for Au5Sn at 1mA/cm2 and the tin content was nearly 50%for AuSn when the current was higher than 3mA/cm2,the tin content of Au-Sn alloys was 30%(at.%)at 2mA/cm2.The morphologies of Au-Sn films became coursing with the increasing J value,and then the grain became rough.The growth rate of Au-Sn alloys increased firstly and then reduced,the fastest growth rate achieved 24μm/h when J=7mA/cm2.5.Two methods were performed to preparate Au70Sn30 alloys using co-electroplating in this study.The sequential electroplating Au5Sn and AuSn multi-layers had a lower growth rate because of the lower growth rate of the AusSn.However,the co-deposition of 30%tin content film had a faster growth rate under a varied impulse current,which can reach 13μm/h at 6.05mA/cm2,T=45℃.

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