Analysis of Defects Generated by the Reflow Soldering in SMT (Surface Mount Technology) Assembly Applying the Six Sigma Method


  • Ana C. Bueno
  • Maíra P. Shiki
  • Valdemir R. de Lima
  • Luis G. Brandão
  • Maurício M. Oka



DMAIC methodology, reflow soldering, Six Sigma, SMT


The Six Sigma method using the DMAIC methodology is being applied for analyzing the reflow soldering process in an SMT assembly line. The Define phase (D) and Measure phase (M) were concluded, the Analysis (A) phase is being implemented, and the Improve (I) and Control (C) phases will be the next ones. Defects generated during the reflow process were classified and measured both on assembled memory modules and on virgin laminates that were passed through the oven during the reflow of these modules. Spots of solder and flux were found on the edge connector of the modules and also on the surface of the virgin laminates. It was found that these defects are generated inside the reflow oven, indicating that the oven is contaminated. Two solder pastes were analyzed and consequently, two temperature profiles were used. The amount of defects generated by the oven was found to be independent on the temperature profile. On the other hand the amount of defects depends on the solder paste that is used. The FMEA (Failure Mode and Effect Analysis) was also accomplished. As a result, the main failure modes of the reflow process were determined, namely, the heating rate, the soak temperature, the conveyor velocity, the reflow temperature, the reflow time, and the cooling rate.