Effects of adding stitches on PCB safety and decreasing EMI

The return planes in electronic equipments usually include one or more connections between them and metal system chassis that are known as stitches. They can play a positive role in decreasing PCB emissions and in increasing PCB immunity too. Also these connections between return plane and chassis can change intended resonance frequencies of created cavity between system chassis and return plane. Adding some resistance to these connections, shift resonance frequencies but adding an optimum resistance to these stitches can decrease resonances more and more. In this paper, first we study increasing PCB immunity especially in ESD case, with adding stitches between PCB return plane and chassis. Then we examine how the cavity resonance frequencies shift with adding some resistance to stitches and study damping these resonances with adding optimum resistance to stitches.