Investigation on cracked inductors based on finite element analysis

I-type ferrite inductors are prone to cracking easily after undergoing cooling and heating cycles. It is necessary to work out a method to improve reliability of the device, even if the cracking does not damage the device directly. In this paper, one failure case on product line is investigated deeply by combining finite element analysis, environmental tests and failure analysis methods. Analysis results show the internal fillet radius R of the inductor affects the stress distribution directly. When the radius size gets smaller, the stress is more concentrated, and the cracking occurs easily. The key stress will decrease by 60-90Mpa when R increases from 0.02mm to 0.7mm, which will greatly improve the reliability of the device. Moreover, the results also show the filler material of the inductor is one of key factors of improving cracking phenomenon. So it can improve the stress distribution to select the optimal filler material. To optimize the entire device, it is necessary to use the existing optimization design method of multivariate nonlinear to synthetically optimize parameters of various materials and size parameters of the device and to find out the best materials and sizes that are suitable for the current process.