LimeSDR USB RF-Shielded CNC Case

A two-part aluminum enclosure for LimeSDR USB focused on:

• mechanical protection,
• efficient passive cooling,
• RF section shielding with separated RF/control zones.

Why this project exists

After buying LimeSDR USB, I found that the only ready-made heatsink case with full SMA breakout was Lime AC Tetra Case.
However, it does not separate RF and control areas despite the firewall concept present on the board.

I ordered that case through Crowd Supply, paid, and waited for two months, but shipping was repeatedly postponed.
After refunding the order, I designed and tested this case myself.

Design goals

• Protect LimeSDR USB mechanically for daily bench and field usage.
• Improve heat transfer from high-dissipation components to the enclosure.
• Preserve/extend RF shielding strategy with dedicated firewall geometry.
• Keep the design manufacturable by common CNC services (tested with JLCCNC).

Thermal design notes

• Thermal transfer pads are provided for the main hot components.
• One support/thermal island is placed on the PCB bottom side to support heat removal in the RF chip area.
• The case is designed for 1.0 mm thermal interface pads (soft thermopad recommended).
• Depending on location, compressed pad deflection is roughly 0.4 to 0.7 mm.

Use a soft thermopad to avoid PCB stress or damage.

Fan support

• Top surface has a mounting area for 4010 fan (40x40x10).
• Includes a 6 mm cable access hole to route fan wires to the onboard LimeSDR fan header.
• LimeSDR fan output is 3.3 V and not intended for high current.

Passive cooling has been sufficient in my receive-only usage; observed temperature stayed near 34C without a fan.

Cable recommendations

RF side (SMA-IPEX):

• Recommended: RG113, length 75 mm
• Quantity: 10 pcs for RF ports
• Avoid RG178 here (too stiff; risks damaging IPEX connectors)
• 100 mm on RF side can work, but also makes enclosure assembly noticeably harder

Clock side (CLOCK IN/OUT):

• RG178 is acceptable, 75 to 100 mm
• 100 mm works but makes enclosure assembly noticeably harder

Fasteners and assembly

• Case halves: M4x30
  • Threads are not pre-modeled in the CAD files
  • User should tap threads in the top half during assembly
  • Bolts inserted from bottom
  • Bolt heads act as enclosure feet
• LimeSDR PCB mounting: M3x4, flat head required
• Fan mounting: M2.5 or M3
  • Holes are modeled for M2.5 and can be tapped to M3 if needed

Manufacturing experience

Pilot build was ordered from JLCCNC.

• CNC + sandblasting + anodizing + laser marking: $233.06 (shipping excluded)
• SMA-IPEX cables (AliExpress): EUR 6.42

Typical flow:

1. Upload top.step and bottom.step
2. If port engraving is needed, enable laser marking option and upload Laser_Marking.dwg
3. Wait for engineering review and quotation
4. Pay and wait for production (my case took ~10 days)

Revisions after pilot build

After receiving and testing, the design was updated:

• Increased lower-half PCB lip for 1.7 mm PCB thickness (instead of 1.6 mm)
• Extended RF side to improve connector and screw clearance
• Shortened heatsink fins to reduce machining cost
• Increased top ceiling thickness in CPU/control area

Files in this repository

• top.step
• bottom.step
• top.f3d
• bottom.f3d
• Laser_Marking.dwg
• images/ (pilot build photos)

Photos

Pilot photos (selected highlights; full set is available in images/):

License

This project is licensed under Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0).

• You may use, copy, and modify the design.
• Commercial use and resale are not allowed without separate permission.
• See LICENSE for full terms.