Comparison between Magnetic Fields and Electric Fields of Microwave Radiation for Heating the Solder Used to Connect a Transistor to a Printed Circuit Board

We demonstrated soldering of an electrical component (the metal-oxide semiconductor field effect transistor (MOSFET)) on a printed circuit bord (PCB) via solder paste heated by microwave irradiation. The behavior of the object soldered with solder heated in a microwave magnetic field and electric field were evaluated by using various microwave resonators. In the magnetic field, the solder paste was selectively heated by microwave irradiation. We confirmed that the MOSFET was connected onto the PCB without any damage and that the MOSFET operated normally. However, in an electric field, the solder paste cannot be heated by microwave irradiation because the edges of the PCB were selectively heated. Consequently, the MOSFET could not be connected onto the PCB. The strengths of the electromagnetic fields produced by different microwave resonators were numerically simulated to determine the optimal positions for microwave soldering. Based on the simulation results, microwave heating with separate magnetic and electric fields was carried out and we investigated the heating characteristics of the samples. The appearance and cross sections of the samples were observed by using scanning electron microscopy and energy dispersive X-ray spectroscopy. To estimate any damage by microwave irradiation of the MOSFET, we evaluated the output and transfer characteristics of the MOSFET. We conclude that microwave heating in a magnetic field was superior to heating with an electric field.