Cause analysis on the unqualified pull-out force between the bushing and PCB pad in DC-DC converters for new energy vehicles

For new energy vehicles, the DC-DC converter is a key component to realize the electricity conversion between different voltage networks. In the DC-DC converter described in this paper, the copper-substrate bushing was specially designed to fix the PCB onto the aluminum radiator, and thereby the heat generated by the components on the PCB could be successfully dissipated. However, during the ejection tests after reflow soldering, the pull-out force between the bushing and PCB pad was unqualified. To find out the failure causes, the comprehensive characterization analysis and failure analysis were carried out and the analysis objects included the material quality, solder paste printing, reflow soldering process, soldering void and morphology characteristics. Through systematical investigation, the causes of the unqualified pull-out force between the bushing and PCB pad after reflow soldering were finally determined, and some countermeasures were put forward as well. Hopefully, the achievements of the paper could not only provide useful references for avoiding the recurrence of similar problems, but also improve the product quality in the future manufacturing process.