High Frequency Induction Focused Soldering Method and Solder Joint Quality Control

Abstract

As the electronic industrial production toward high density, high integration, and multi-function, the differentiation in the needs of various modules in integrated circuits has become a more pressing issue, among these, the problem of local heating and soldering of heat-sensitive components has gotten a lot of attention lately. High-frequency induction heating methods are considered suitable and commonly employed in the production of integrated circuits because of its great efficiency, cheap cost, high power, and skin effects. However, the limitations of the induction heating are increasing, mainly because the alternating magnetic fields around the coil are not easy to control, which causes unexpected heating in the adjacent space.This research suggests a focused induction soldering approach with a conical magnet to tackle this problem. Combining finite element simulation to develop a high-frequency focus induction heating model, the magnetic field distribution and temperature field distribution of the system are analyzed, and the accuracy of simulation results is validated with soldering experiment. Based on the soldering of power transistors on a 2mm thick PCB, we compared the effects of traditional induction soldering and high-frequency focused induction heating.The findings reveal that, compared to traditional induction heating, high-frequency focused induction heating can efficiently concentrate the magnetic field spread around the coil, increasing the maximum magnetic flux density from 0.08 T to 0.27 T, the maximum magnetic flux density is increased by a factor of 3.4. The magnetic field lines are gathered at the tip of the ferrite, and the maximum position of the magnetic field is moved from the coil to the tip of the ferrite, which realizes the control of the position of the maximum magnetic flux density. Furthermore, within the same 2.4-second heating period, high-frequency focused heating and traditional induction heating raise the maximum temperature of tin ring to 238 °C and 70 °C, respectively, and the heating efficiency was increased by about 3.5 times. This implies that the addition of tapered ferrite can improve the heating effect, and it also proves that the addition of ferrite can effectively increase the local magnetic field strength.