Chulalongkorn University Theses and Dissertations (Chula ETD)

Other Title (Parallel Title in Other Language of ETD)


Year (A.D.)


Document Type


First Advisor

Napassavong Osothsilp


Faculty of Engineering (คณะวิศวกรรมศาสตร์)

Department (if any)

The Regional Centre for Manufacturing Systems Engineering (ศูนย์ระดับภูมิภาคทางวิศวกรรมระบบการผลิต)

Degree Name

Master of Engineering

Degree Level

Master's Degree

Degree Discipline

Engineering Management




According to the company's current situation, the case study company has been encountered with a large amount of non-wetting defects within the production process leading to a higher defect rate and cost over a several years. Therefore, this research is aimed to reduce non-wetting defective rate of location L7 on PCBA during Surface Mount Technology (SMT) process by applying Six Sigma DMAIC methodology accompanying with quality control tools and focus on experimental design. There are separated into five significant phases. The first is Define phase, which related to the studying of current process of manufacturing PCBA and also gathering historical data of defects for one year in order to use as a basic data to analyse in this research. Moreover, this phase is also set scope of the research and the purpose. The second is Measure phase that is brainstorm to find factors affecting non-wetting defect by using cause-and-effect diagram. In addition, using cause-and-effect matrix to prioritize the factors. Attribute Agreement Analysis (AAA) also has been applied to determine the accuracy and precision of the operators in order to judge the non-wetting defect. The third is Analyse phase which is mainly related to applying Design of Experiment (DOE). This research has been applied full-factorial with centre points design to test the significance of selected factors and find the optimal setting parameters. Then, conduct experiment and collect experimental data. Analyse the results of experiment and find the optimal setting parameters and make conclusion. The fourth phase is Improve phase which is to confirm experiment using the optimal setting in a real production for one month and summary result of improvement by comparing non-wetting on L7 defective between before and after improvement. Finally, Control phase is to create action plan, control chart, and control plan in order to maintain the results after improvement. The result of DOE illustrates the defective rate of non-wetting on L7 is decreased from 65.36% to only 15.04% and resulting in the scrapped cost to be decreased from 6,947,244 baht per year to only 1,393,152 baht per year for non-wetting defect of L7 on PCBAs.



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