A study of grounded-heatspreader for EMI mitigation of ASIC IC package

The thermal Heat Spreader (HS) is an essential part of an Integrated Circuit (IC) package. At SerDes dat rates the physical dimensions of heat spreader and that of the package are comparable to the operating clock frequencies. These structures behave as unintentional radiators and contribute to EMI. In this paper we investigate the radiated emissions of a high-speed SerDes IC package when its HS is grounded to its grounded plane. Using a Transmission Line Matrix based full wave EM solver, it is shown that EMI radiation can be reduced by increasing the number of grounding posts. A 32 grounding post design reduces the total radiated power by 20+ dB in the frequency range of 1 – 15 GHz when compared to a non-grounded heat spreader case. It is also shown that the effectiveness of the grounded lid decreases as we increase the resistance of the posts.