Enhancing Thermal-Shock Reliability of a Sleeveless Power Inductor Assembly upon Reflow Soldering

Employing magnetic resin in between the upper and bottom flange of a drum core is proven design in boosting the performance of a power inductor. The optimum core design and magnetic resin characteristic were investigated to improve the thermal shock reliability of the component upon reflow soldering. Finite element modelling (FEM) was utilised to simulate the response of the assemblies to the variations of the core inner radius (rc), upper flange thickness (t) and the coefficient of thermal expansion of magnetic resin (CTEmr). The assessment of those designs was conducted at a reflow oven, modelled by the computational fluid dynamic technique (CFD), on sixteen designs generated by the orthogonal array. The results showed that the inner radius of the drum core was the most vital parameter in designing a drum core in preventing core crack upon reflow soldering. The optimum design of the drum core was obtained at 0.5 mm inner radius of drum core, 0.3 mm upper flange thickness and 2.8 ppm/K coefficient thermal expansion of magnetic resin. Those findings may be used as a reference for designing a similar drum core of a power inductor.