Suppression effects of electromagnetic radiation from inner-lead portion molded by ferrite-resin composite

This paper describes the suppression effects of electromagnetic waves radiating from the inner-lead portion of lead terminals molded by ferrite-resin composite in semiconductor devices. First, using composites in molded cylindrical form having various ferrite powder content, the complex relative permeability and complex relative permittivity were measured using the Nicolson-Ross, Weir method. Next, the impedance of the inner-lead portion of the lead terminal specimens, molded by the same ferrite-resin composite, was measured. Following this, each of the lead terminal specimens was mounted on a printed wiring board settled in a shield box, and electromagnetic radiation from the inner-lead was measured in an anechoic chamber, while terminating one end of the lead terminal to a 50 ohms resistor and feeding a high frequency signal through the other end. The results of these experiments showed that electromagnetic radiation from the inner-lead portion can be effectively suppressed by molding the lead terminal by ferrite-resin composite having a ferrite powder content of 80 weight-% or greater.