L
Admin
[Technical article / FAQ, rfforum Editorial Team]
A shield can is drawn as a quiet box. On the bench, seam gaps, lid contact resistance, and sparse via fences turn the can into a cavity whose resonance can sit inside the product band and look like a mysterious coupling or EMI peak.
1. What the cavity actually does
- Seam gaps and poor lid contact set aperture coupling; a can that "passes" with copper tape can fail after production lid torque
- Via fence pitch under the can wall sets how well the board closes the cavity; sparse vias leak and shift resonance
- Absorbing foam or board-level loss can damp a mode — removing it for cost without re-checking EMI is a method change
2. Freeze list before you blame the IC
- Can PN / dimensions, lid contact method, and whether the failing unit still had production gaskets / screws
- Via fence pitch and stitch under the can footprint on the same sheet as the EMI / coupling plot
- Whether the resonance moves when you press the lid or tape the seam (diagnostic for contact vs board)
- Near-field / cavity probe note if you claim a board-level fix without opening the can
3. Habit
Archive can contact and via-fence notes next to every in-can spurious or coupling claim. A layout spin that only moved a filter can still leave the cavity mode untouched.
Discussion: on your last in-can spur or coupling peak, did the fix land in lid contact, via fence density, or an absorber — and do you require a lid-press / seam-tape check before redesigning the RF chain?
— rfforum 编辑部 / Editorial Team
A shield can is drawn as a quiet box. On the bench, seam gaps, lid contact resistance, and sparse via fences turn the can into a cavity whose resonance can sit inside the product band and look like a mysterious coupling or EMI peak.
1. What the cavity actually does
- Seam gaps and poor lid contact set aperture coupling; a can that "passes" with copper tape can fail after production lid torque
- Via fence pitch under the can wall sets how well the board closes the cavity; sparse vias leak and shift resonance
- Absorbing foam or board-level loss can damp a mode — removing it for cost without re-checking EMI is a method change
2. Freeze list before you blame the IC
- Can PN / dimensions, lid contact method, and whether the failing unit still had production gaskets / screws
- Via fence pitch and stitch under the can footprint on the same sheet as the EMI / coupling plot
- Whether the resonance moves when you press the lid or tape the seam (diagnostic for contact vs board)
- Near-field / cavity probe note if you claim a board-level fix without opening the can
3. Habit
Archive can contact and via-fence notes next to every in-can spurious or coupling claim. A layout spin that only moved a filter can still leave the cavity mode untouched.
Discussion: on your last in-can spur or coupling peak, did the fix land in lid contact, via fence density, or an absorber — and do you require a lid-press / seam-tape check before redesigning the RF chain?
— rfforum 编辑部 / Editorial Team
