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52 DESIGN007 MAGAZINE I MARCH 2022 electrostatic coupling or conduction. Here are four tips for reducing EMI from your design: 1. Choose surface mount device (SMD) components over through-hole parts. Generally, the leads on the through-hole parts create higher levels of inductance and thus an opportunity to create EMI. 2. Design with multilayers, adding a ground plane on the layer directly below the external signals (2 and n-1). e presence of these planes near the signal will effectively reduce the return path, keep signals clean, and reduce EMI emission. Connecting decoupling or bypass capacitors to these planes offers another effective technique for reducing EMI because you are creating short and logical return paths. 3. Limit the operating current and/or the rise times of the signals to help reduce larger fluctuations in current. is creates lower EMI emission rates. 4. Match the impedance on signals. is is a critical design practice, especially at higher signal speeds that will reduce the opportunity for signal reflection, harmonics, ringing, and overshooting digital signals, all of which increase the EMI radiation. 3. Manage Heat If not properly managed and miti- gated in the design phase, heat can diminish board performance and durability. Most electronic compo- nents generate heat during use. Most have some tolerance threshold beyond which they can fail. To manage heat effectively, identify which components generate the most heat in your design. You should dis- tance them from other heat generators and any heat-sensitive components during layout. Use design components such as heat sinks, cooling fans, or thermal vias to remove the excess heat from the board. If you are unsure of heat tolerances, the information on heat generation and sensi- tivity to heat can usually be found on the com- ponent datasheets. 4. Component Placement Aer considering functionality, signal sepa- ration, EMI, and heat, it's time to place compo- nents on your layout. Here are several impor- tant placement considerations: • Seek to optimize component placements from a design integrity standpoint and increase the assembly yields. • Shorten the distance of the trace runs as much as possible. is results in less signal loss, faster speeds, and a cleaner overall signal. • Orient parts in a similar fashion and perpendicular to at least one edge of the PCB if possible and consider the height and width of components. • When it is feasible, use a stair-step approach to placement to avoid trapping a short component between two taller components. • If you can, place all SMD components on one side of the PCB unless you really need to use both sides. • Place all through-hole components on the top side.