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enter image description here On the picture, the yellow is a keepout. Why is this necessary? Wouldn't it be better to have a larger ground plane?

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    \$\begingroup\$ A schematic of the circuit would probably help us give you a better answer. \$\endgroup\$ – The Photon Aug 30 '16 at 3:46
  • \$\begingroup\$ @tommy, please read the tour as it will help you to improve your question. electronics.stackexchange.com/tour \$\endgroup\$ – user98663 Aug 30 '16 at 8:57
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A keep-out can be used for many reasons, some (but not all) of them being:

  • Forcing an automatic pour to keep away from fixed copper art.
  • A small bit of high voltage, for which the designer wanted a nice area of larger distance. (With clearance rules you sometimes get ghastly little tips and nicks)
  • In a place where a complex shape creates many hard strange shapes that may drive up the cost of production in an automated check.
  • To force the designer to not put any components there, or no comonents of a type (you set it up early in the design so that you can't accidentally do something stupid).
  • To force the designer to not route anything there, or not route specific signals.
  • To force a warning about objects above the component - keep-out's can also operate in the space above the copper.
  • To create an area where ground isn't, because that's required for characteristic impedances.

etc etc etc.

Which one it is? I don't know, because you have cleverly not given me anything to go by in that regard.

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    \$\begingroup\$ Given the part in question looks to be an 8-pin SOIC, it seems somewhat likely the circuit is an op-amp or in-amp amplifier of some kind and the keep-out is to reduce parasitic capacitance from some node(s) to ground. Quite why 5 pins need the keep-out under them, though, I can't guess. \$\endgroup\$ – The Photon Aug 30 '16 at 3:57
  • \$\begingroup\$ @ThePhoton I thought of that, but there's a lot of copper fill in there still... \$\endgroup\$ – Asmyldof Aug 30 '16 at 22:44
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A keepout is for a part that's bigger than just the pins where it connects to the board.

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    \$\begingroup\$ This is a little short for an answer and would be better as a comment. \$\endgroup\$ – David Aug 30 '16 at 6:55
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    \$\begingroup\$ But it gets to the point, which the other answers don't. \$\endgroup\$ – Nicole Hamilton Aug 30 '16 at 8:56
  • \$\begingroup\$ I think in this case though, keepout may be referring to the ground plane. \$\endgroup\$ – Tom Carpenter Aug 30 '16 at 14:02
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I see a layout assuming the conventional pins for an 8pin INA, which I visualized below. enter image description here

The ref to VCM must be Common Mode Voltage used for high impedance guarding to reduce signal capacitance and common mode noise. The entire VIN(-) and feedback path is a keep out zone from ground capacitance ( bottom layer)

Judging by the two series feedback R's, my guess is two large standard values (eg 10M) to increase gain at the expensive of high impedance and great sensitivity to stray capacitance of a couple pF to (perhaps floating) ground noise.

Hence the reason why ground is used every around except under these parts.

Short answer is keep out GROUND, guessing to reduce patient noise, Not their complaints ;)

Pin 4 being low Z (Vee) does not matter for keepout.

Gain is controlled by R between Pin 1&8 yet only pin 1 is used with R between Vin(-)pin2 and pin 1, resulting in basically just common mode buffer and no differential gain.

It might be used for EKG or EEG such as as Right LEG driver.

schematic

simulate this circuit – Schematic created using CircuitLab

... Subject to change without notice... :)

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  • \$\begingroup\$ A keep-out can reduce noise, why need add a copper pour ? \$\endgroup\$ – tommy Aug 31 '16 at 0:43

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