Statistical-based simulation and reflow profile optimization for improving self-alignment performance − an experimental study

Purpose There are three major processes in the surface mounting technology (SMT) manufacturing line, namely, printing, mounting and reflowing. During the reflow process, the printed solder pastes are melted into liquid and cooled down into solid again, forming the solder joint. During this process, because of the combined force of the liquid solder, the components will move from the placed location to the final location. This is known as the self-alignment performance in the reflow process. From the comparable studies, it is known that the reflow process with a longer time above the liquidus (TAL) results in better self-alignment performance, as well as higher peak temperatures of the reflow profiles. The TAL and the peak temperatures are influenced by multiple factors, but the experimental designs from the comparable studies kept the same ramping and cooling slopes to modify the TAL and the peak temperature. The purpose of this study is to study on the multiple factors influencing the TAL and the peak temperatures (ramping slope, cooling slope and peak temperature) by conducting designed experiments for each of the factors. Design/methodology/approach In this study, the TAL-influencing features are studied independently, including ramping slope, cooling slope and peak temperature; designed and conducted an experiment to reveal the relationship between the self-alignment and each of the three features; the statistical-based model for the combination of the three features for optimal self-alignment performance; and proposed a statistical-based simulation model for the offset after reflow. Findings The authors conducted a case study validating the mounter optimization model previously proposed. As a result, the optimized reflow profile improved the self-alignment performance by at least 10%, and the simulation within the error of 15 µm. Research limitations/implications This research is statistical-based, which is limited to component types and sizes used in the design of experiments (DOE). The model proposed in this study can suggest a new reflow profile that can increase the self-alignment performance, which is critical to the solder joint quality, especially long-term quality. Practical implications This study can suggest a new reflow profile that can increase the self-alignment performance, which is critical to the solder joint quality, especially long-term quality. Social implications This study can suggest a new reflow profile that can increase the self-alignment performance, which is critical to the solder joint quality, especially long-term quality. Originality/value The proposed statistical-based soldering reflow target profile optimization model offers a novel and practical approach. The soldering profile provided by the manufacturer contains recommended and acceptable ranges in the critical features. This study provides the optimal setting within the ranges.