Investigation of a server shows the heatsink of the CPU module as a primary component of the EMI coupling path. In order to identify the specific noise source and coupling path to the heatsink, a series of experiments were defined to provide support for one source and eliminate others. Based on experiments with two different versions of the CPU module, a stack-up related design guideline is proposed: a ground layer should be the first entire plane (as opposed to Vcc) on the active component side of the board. If there are known IC sources that switch significant currents with the outputs unloaded at nanosecond rise and fall times on both sides of the board, then ground should be the first entire plane on both sides of the board when feasible.
S. Radu et al., "An Impact of Layer Stack-up on EMI," Proceedings of the IEEE International Symposium on Electromagnetic Compatibility (1998, Denver, CO), vol. 2, pp. 828-833, Institute of Electrical and Electronics Engineers (IEEE), Aug 1998.
The definitive version is available at http://dx.doi.org/10.1109/ISEMC.1998.750314
IEEE International Symposium on Electromagnetic Compatibility (1998: Aug. 24-28, Denver, CO)
Electrical and Computer Engineering
Electromagnetic Compatibility (EMC) Laboratory
Keywords and Phrases
CPU Module; EMI; EMI Coupling Path; IC Sources; PCB; Coupling Path; Currents Switching; Electromagnetic Interference; Heat Sinks; Heatsink; Integrated Circuits; Layer Stack-Up; Primary Component; Printed Circuits; Server; Specific Noise Source; Switching
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Article - Conference proceedings
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