L
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[Technical article, rfforum Editorial Team]
A via fence around an RFIC looks decisive in a layout review and still fails isolation if the return path, fence pitch, or layer transitions are wrong. Isolation is a return-current problem before it is a "more vias" problem.
1. What the fence is for
The fence shortens the loop for return current between the RFIC ground paddle / exposed pad and the board reference, and it raises the frequency where a slot or cutout starts to radiate. A sparse fence with a long cut in the ground pour is often worse than no fence.
2. Pitch and distance
Rule-of-thumb λ/20 pitch at the highest aggressor frequency is a starting point, not a guarantee. Keep the fence close to the paddle edge; a fence two centimetres away mostly decorates the silkscreen. Stitch every ground layer the RFIC actually references, not only L2.
3. Cuts and connectors
USB, SIM, and board-edge connectors that slice the return plane defeat the fence. If a cut is mandatory, bridge it with dense stitching and treat that bridge as part of the RF review.
4. Habit
- Review return current on the layer stack, not only top-metal keepouts
- Measure isolation or desense before/after fence changes on the same fixture
- Do not add vias into a floating pour and call it grounding
Discussion: for your last Wi-Fi / cellular / UWB module, what via pitch and paddle-to-fence distance survived desense, and did a connector cut force a redesign?
— rfforum 编辑部 / Editorial Team
A via fence around an RFIC looks decisive in a layout review and still fails isolation if the return path, fence pitch, or layer transitions are wrong. Isolation is a return-current problem before it is a "more vias" problem.
1. What the fence is for
The fence shortens the loop for return current between the RFIC ground paddle / exposed pad and the board reference, and it raises the frequency where a slot or cutout starts to radiate. A sparse fence with a long cut in the ground pour is often worse than no fence.
2. Pitch and distance
Rule-of-thumb λ/20 pitch at the highest aggressor frequency is a starting point, not a guarantee. Keep the fence close to the paddle edge; a fence two centimetres away mostly decorates the silkscreen. Stitch every ground layer the RFIC actually references, not only L2.
3. Cuts and connectors
USB, SIM, and board-edge connectors that slice the return plane defeat the fence. If a cut is mandatory, bridge it with dense stitching and treat that bridge as part of the RF review.
4. Habit
- Review return current on the layer stack, not only top-metal keepouts
- Measure isolation or desense before/after fence changes on the same fixture
- Do not add vias into a floating pour and call it grounding
Discussion: for your last Wi-Fi / cellular / UWB module, what via pitch and paddle-to-fence distance survived desense, and did a connector cut force a redesign?
— rfforum 编辑部 / Editorial Team
