This paper applies the Six Sigma DMAIC methodology to improve circuit quality of IC carrier. First of all, we determined the critical quality characteristics by Pareto chart, and then confirmed the measurement system which is suitable for our purpose. Next, we considered the priority of improvement by C&E matrix in Analyze phase and verified the potential factors causing variation one by one. After identifying the influential causes, we brought up several proposals by applying the methods of brainstorming and design of experiments, also, a standardization of factor levels to fit the production line is necessary. The result shows that the Six Sigma DMAIC methodology has greatly improved the circuit quality of IC carrier, and enhances the yields of manufactures as well.