I organize certain things with a reportedly alarming neuroticism. In grad school, there was a line of demarcation between the edge of my side of the desk and the pile of sample containers and papers that began on my neighbor’s side. This same tendency, though annoying to deskmates and boyfriends, especially since it doesn’t extend to bathrooms, makes me an ace at optimizing component placement on PCBs. Not only does this keep things neat, it also improves the electrostatic discharge protection for the entire board.
The obvious implication of good component placement is that it affects routing on the board. That means your routing determines how any ESD effects will be spread across PCB and into your sensitive or unprotected components. As you arrange your components, there are several basic guidelines to help you improve your routing to best protect your PCB and sensitive ICs.
Place components in the safest place possible
Sometimes, design requirements keep you from using protection circuits for all of your sensitive components. When that’s the case, there are steps you can take to improve the odds for those ICs.
Keep unprotected circuits away from the traces between a TVS protection circuit and a connector input, or any other location where ESD is anticipated. This way, you minimize the risk of exposing the component to any current induced by rapidly changing EM fields resulting from an ESD pulse.
Component placement can help protect your ICs from ESD, even if you can’t put them on a protected line.
Even devices that are on a protected can benefit from some forethought regarding their placement. Sensitive components that are on a protected line should be placed closer to the center of the board. That helps to balance the parasitic inductance for the best performance of the protection circuit.
Minimize the length of your lines
Long traces and wires act like little antennas. They can both transmit and receive unintentional emissions. If you do have an ESD pulse, these guys can receive “output” from the spike, and pass it along their entire length.
One of the easiest first steps for minimizing line length is to place all the components with lots of interconnects close to each other. This helps you to minimize the length, and hopefully the number, of interconnecting lines. And good organizers know you should keep similar stuff together
I know I’ve said it before, but minimize circuit loops. Circuit loops over large areas increase the amount of your board that’s exposed to EMI generated by an ESD pulse. They can undo all of the other protection you’ve implemented, and are really bad news. And while you’re at it, use a properly designed ground plane.
Mind your edges
Maybe you’re a rebel and put books on different subjects next to each other on the shelf. Be warned, though, your rampant disregard for order can have serious repercussions for your PCB if you let different signal traces simply go where the autorouter sends them.
Don’t run sensitive tracks along the edge of the board. This is particularly true for supply tracks. You want to minimize radiation from these tracks, as well as their exposure to crosstalk from other tracks, whether it’s from a noisy signal, or ESD-induced interference. Keeping your noisy tracks away from everything sensitive is good design practice, anyway.
You don’t want an ESD pulse from handling your board to go straight into your most sensitive components.
PCB layout can be incredibly tedious to get right. Using the right PCB tools, like Altium’s unified design environment, can make the difference between a neat, functional board with good protections, and a rat’s nest of routing that keeps you up a night. They can help you get started now, so you have more time to get everything else in order!
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