Bi-Layered Magnetic Electromagnetic Interference Shields with Thinner Metals

This paper presents the concept of bilayer magnetic materials as electromagnetic (EM) shields. Sputtered shields are becoming a potential solution for molded packages. However, sputtering thick metals creates throughput limitations and also introduces stress. By introducing an underlayer of the ferrite-encased molding compound, the sputtered seed layer can be reduced substantially. The ferrite-layered molding compound can partially replace the traditional silica molding compounds without causing additional thicknesses of the overall package. The first part of the paper addresses the concept of shielding effectiveness (SE) against magnetic field interference in the near field. The second part of the paper discusses the SE of magnetic materials such as steel, cobalt (Co), and nickel (Ni). Finally, the paper investigates the effect of a thin secondary magnetic layer on traditional electromagnetic interference (EMI) shielding materials such as ferrites from magnetic field sources. A thin layer of 1 mu m nickel increases the shielding effectiveness (SE) of a 100 mu m ferrite EMI shield from 25 dB to as high as 60 dB across a 1-100 MHz frequency range. On the other hand, 1 mu m cobalt (Co) on an EMI shield of 100 mu m ferrite improves SE up to 55 dB in the same frequency range. Such simplified bi-layered materials are shown to be superior in their shielding effectiveness compared to monolithic materials and can lower the metal shield burden.