Thermal Coupling Method For Reflow Soldering Process
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Date
2013
Authors
Lau, Chun Sean
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Reflow soldering is one of the most significant factors in development of surface mount technology (SMT), especially toward the lead-free and miniaturization of the advanced ball grid array (BGA) package. Moreover, an inadequate reflow profile causes the reliability issues in manufacturing assembly process. The purpose of this study is to develop a thermal coupling method that uses to investigate the temperature and thermal stress responses of electronic boards (at board and package level) during the reflow soldering process. The numerical method comprises the computational fluid modeling of the internal flow of the reflow oven and the structural heating/cooling modeling of the BGA assembly. The Mesh-based Parallel Code Coupling Interface (MpCCI) was used as the coupling software. The model was validated with experimental measurements and previous studies. From the results of board-level analysis, the cold region and temperature uniformity (ΔT) increased with increasing complexity of the electronic boards. The cold region was occurred in two possible locations on the board. A suitable conveyor speed of 1.0 cm/s was determined to maintain ΔT below 10 °C and prevent overheating of the thermally critical package. Apart from that, the quality characteristics such as the thermal stress, peak temperature, reflow time and package-level ΔT of lead-based solder were determined from the package-level analysis, and had a good agreement with maximum error of 6% compared to the experiment results. The effect of lead-free soldering and solder joint arrangements during the cooling stage of the reflow process has been discussed, and showed that the lead-free solder (SnAgCu) was qualified soldering material for replacement of lead-based solder. Besides, the maximum von-Mises stress of the critically affected joint was influenced by joint arrangement patterns and not by the number of solder joints. A recommendation was made to increase the fracture time by changing joint arrangement pattern, which successfully improved by 49.9%. This numerical method was extended and combined with a grey-based Taguchi method for optimizing the multiple performances of the lead-free reflow soldering process. This hybrid combination study aims to minimize the solder joint defect rate of a BGA package. Various factors and quality characteristics of batch-type and conveyor continuous-process ovens were considered. The Taguchi orthogonal array was performed, and the optimal parameter settings of each oven were determined. Both case studies expressed the cooling stage of lead-free reflow process was most influential factor to solder joint reliability. The confirmation test results showed that the grey relational grade of Case studies 1 and 2 significantly increased by 117.4% and 46.6%, respectively. On the whole, the newly developed approach greatly reduced solder joint defects and provided a design guideline to lead-free reliability issues in the electronics manufacturing industry.
Description
Keywords
reflow soldering , manufacturing