Effect of plating stubs of BGA packages on spurious EM radiation

A one-metal layer Micro Star BGA package was used for the analysis of spurious EM radiation characteristics of the package conductors. These conductors were modeled as monopole antennas with an FDTD simulation tool. The effect of plating stubs of the package leads on radiation characteristics was investigated by S-parameter measurements. It was observed that the length and shape of plating stubs will affect the magnitude and frequency of the resultant radiation. However, the effect is negligible in the frequency range of current digital ICs. Based on the theoretical analysis of EMI sources, power spectrum analysis and SPICE simulation, a design idea of constructing the package built-in low pass LC filter was proposed, which makes use of the parasitic inductance and capacitance of the package leads to filter off high frequency harmonics that are sources of EM radiation from the digital signal path between IC chip and PC board.