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.

Meeting Name

IEEE International Symposium on Electromagnetic Compatibility (1998: Aug. 24-28, Denver, CO)


Electrical and Computer Engineering

Research Center/Lab(s)

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

International Standard Book Number (ISBN)


International Standard Serial Number (ISSN)


Document Type

Article - Conference proceedings

Document Version

Final Version

File Type





© 1998 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Aug 1998