I have a 2 layer PCB that carries a microcontroller (Particle Electron), connects to a sensor with an ADC reading, has an ADC comparator IC, a watchdog timer IC, a PNP switch, an power bus and I2C lines.

To protect the Analog reading line from EMI, should I be removing the ground pour around certain areas/ICs? For example, I am thinking of removing the ground pour around the watchdog timer IC because it may be introducing some noise. Does removing ground pour in this situation help, or hurt?

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  • \$\begingroup\$ How is the sensor connected? How far away from ADC ? Are there any inductive noise sources?? Active guarding is best practice but you may not need this. \$\endgroup\$ – Sunnyskyguy EE75 Apr 23 at 21:01
  • \$\begingroup\$ The sensor is on a seperate PCB and its analog reading output is connected through a cable. I dont know about much about inductive noise sources. \$\endgroup\$ – Tapatio Sombrero Apr 23 at 21:11
  • \$\begingroup\$ Most of those BLUE lines can be made 2x or 3X shorter. Do so. This lets you use much more of the BLUE as a PLANE to capture Efield flux, etc. Instead of one LONG Blue line, use 2 or 3 or 4 very short jumpers, and make most of the BLUE become RED, separated by very short red traces. \$\endgroup\$ – analogsystemsrf Apr 24 at 3:51

You don't remove copper pour to reduce noise. An unconnected copper pour will have more noise than no copper pour, but having a grounded copper pour tends to reduce noise or at least keep it the same compared to no copper pour.

You remove copper pour to get rid of parasitic capacitance for sensitive circuits like oscillators an RF, and leakage currents for really high impedance circuits which operate on miniscule currents. And even then, it's not a universal rule since the right copper connected to ground can help things in instances with leakage currents.

If you're that worried about EMI, you should be using a 4-layer board with a ground plane.

  • \$\begingroup\$ I am using the ADS1015 as a ADC to wakeup my microcontroller out of a sleep state. Since this IC contains an oscillator, should I remove the ground pour around this IC? \$\endgroup\$ – Tapatio Sombrero Apr 23 at 21:09
  • 1
    \$\begingroup\$ No, if the oscillator is inside the IC it won't care about parasitics. I was referring to crystal oscillator circuits where you have very small discrete capacitors so it's very sensitive to parasitics in the PCB. \$\endgroup\$ – DKNguyen Apr 23 at 21:11

Does removing ground pour in this situation help, or hurt?

It probably doesn't make a difference. You could think of an unconnected copper pour as a capacitor with one end ungrounded/unconnected as a 1"sq area would have ~10-30pF of capacitance. The area could function like an antenna or resonator, but only at very high frequencies due to the low parasitics that form the antenna.

There are a few designs where one would definitely be wise to remove an ungrounded/unconnected copper pour, if the design is going into a high radiation environment, the copper needs to be removed because it can slowly collect a charge in the thousands of volts and then break down in an ESD event.

If your worried about it remove it, or ground it.

  • \$\begingroup\$ Interesting. It collects the charge even if the copper pour is grounded? \$\endgroup\$ – DKNguyen Apr 23 at 21:13
  • \$\begingroup\$ No, if it's floating \$\endgroup\$ – Voltage Spike Apr 23 at 21:13
  • \$\begingroup\$ Ah, okay. The way your post is worded it is not clear, but I saw you just edited it. \$\endgroup\$ – DKNguyen Apr 23 at 21:14

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