AMD ADA4200DAA5BV Builders Guide - Page 39

31684 Rev. 3.00 September 2004 Builder's Guide for AMD Athlon™ 64 ProcessorBased Desktops and Workstations seam could cause an EMI problem. Spring fingers or foam EMI gasket can be used to seal these gaps or seams. 8. Processor Heatsink Grounding Although grounding of the processor heatsink has not yet been required on any AMD Athlon™ 64 processor-based systems, grounding of the processor heatsink can further lower the harmonic EMI levels of the processor. Many AMD Athlon 64 processor-based motherboards contain grounding pads around the footprint area of the processor. These grounding pads can be utilized to ground the heatsink to the motherboard ground. If excessive system level EMI radiated emissions exist after attempting all the listed EMI reduction techniques, then more extensive remedies may be necessary. First, determine if the emissions emanate from the system I/O cables (including the AC power cord) or from aperture leaks in the system chassis. If EMI emissions emanate from a particular I/O cable, then improved filtering or cable shielding may be required on that cable. If EMI emissions emanate from slots or seams in the chassis enclosure, use copper tape across the apertures to improve shielding effectiveness. If copper tape reduces emission levels to a satisfactory level, then chassis sheet metal changes or conductive EMI gasketing can be added at that location. Chapter 5 EMI Reduction Techniques 39