Positioning A Esp32 Module On A Base Board - Espressif Systems ESP8266 Series Hardware Design Manuallines

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The third layer is the POWER layer where only power lines can be placed. It is
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acceptable to place some signal lines under unavoidable circumstances.
The forth layer is the BOTTOM layer. Only signal lines can be laid. Placing
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components on this layer is not recommended.
Below are the suggestions for a two-layer PCB design.
The first layer is the TOP layer for signal traces and components.
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The second layer is the BOTTOM layer, where power traces are routed. Placing any
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components on this layer is not recommended. Do not route any power or signal
traces under or around the RF and crystal oscillator, and so that there is a complete
GND plane, which is connected to the Ground Pad at the bottom of the chip.

1.6.2. Positioning a ESP32 Module on a Base Board

If users adopt on-board design, they should pay attention to the layout of the module on
the base board. The interference of the base board on the module's antenna performance
should be reduced as much as possible.
It is recommended that the PCB antenna area of the module be placed outside the base
board while the module be put as close as possible to the edge of the base board so that
the feed point of the antenna is closest to the board.
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Espressif
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Figure 1-13. ESP32 Module Antenna Position on Base Board
13 " /30
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Base Board
1. ESP8266EX
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2018.12