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Low-Profile Ethernet Expansion Card

The Low-Profile Ethernet Expansion Card is an ongoing community effort to design a gigabit Ethernet expansion card that fits within the standard Framework expansion card height — roughly 6.8 mm — without protruding below the laptop1. Started by ExplodingWaffle in November 2021, the project has had contributions from multiple community members across 87 posts spanning over four years, and remains an active area of development as of early 20261.

The core challenge: a standard RJ45 connector is 13.8 mm wide and ~12 mm tall, while Framework expansion card slots are only ~6.8 mm tall. The official Framework Ethernet Expansion Card solves this by protruding below the laptop chassis, which some users find undesirable1.

ExplodingWaffle's Design (2021–2022)​

Initial Exploration​

ExplodingWaffle began by investigating compact RJ45 connectors from LCSC and other suppliers, trying to find one that could fit within the expansion card envelope1. Key measurements established early on:

  • Available clearance under the laptop: 3.45 mm (measured by community member Fraoch)1
  • A standard Ethernet cable can plug into an expansion slot opening, but the tab extends below the laptop1

PCB Design​

ExplodingWaffle designed a PCB using a compact RJ45 connector (RCH RC02405) with discrete magnetics (transformers and common-mode chokes) rather than integrated magnetics, which wouldn't fit1. Framework VP nrp reviewed the design and asked about the magnetics solution, which ExplodingWaffle confirmed was feasible with discrete components1.

Hinged/Folding Concept​

The ambitious goal was a folding RJ45 jack — inspired by those used in Fujitsu LifeBook and HP EliteBook laptops — that would fold flat when not in use and pop up when needed1. ExplodingWaffle designed and 3D-printed a prototype with a "live hinge" case1:

  • Result: The assembled prototype measured ~10.6 mm thick — too tall to fit under the laptop
  • Problem: An unexpected 0.85 mm step in the connector wasn't accounted for in initial measurements1
  • Conclusion: The folding concept was "still possible" but required a connector with a smaller top portion than available off-the-shelf1

XJACK Investigation (February 2022)​

ExplodingWaffle purchased a vintage 3Com XJACK PC Card modem (the classic pop-out RJ45 design from the 1990s) and disassembled it to study the mechanism1:

  • The XJACK uses a flat-flex cable between the port and the board
  • The pop-out mechanism is "push-push" (like a ballpoint pen)
  • The whole card is 5 mm thick; the RJ45 jack itself is 4.25 mm thick and 17.6 mm wide
  • The jack is too long to fit within the expansion card's 25 mm depth (USB-C plug to front face) alongside electronics1
  • A gigabit version would be even harder due to larger controllers, more magnetics, and signal integrity concerns over flat-flex1

ExplodingWaffle ultimately concluded that only Framework themselves would have the resources to produce a connector meeting all constraints, and "threw in the towel" on the project1.

Subsequent Community Efforts​

Fujitsu Folding Jack Approach​

Several community members explored using the Fujitsu folding RJ45 jack (part FUJ:CA52303-3751) from LifeBook laptops1. This "origami" style connector folds into the laptop when not in use. The connector was found available from lambda-tek.eu for prototyping, and Steve_Audia purchased a broken Fujitsu LifeBook on eBay to extract the full drawer assembly in October 20251. The assembly takes up most of the expansion card space, confirming the extreme space constraints1.

Jekotia's Parametric Design (February 2026)​

Community member Jekotia revived the project in February 2026, creating a parametric Fusion 360 model that allows testing whether any given RJ45 connector can fit1. Using the Singatron 2RJ1656-000111F half-type connector, Jekotia achieved a theoretical table clearance of just 0.08 mm — essentially flush1. After discovering the Singatron part was unavailable for purchase, Jekotia published the configurable Fusion model so others can test alternative connectors1.

Alternative Approaches Discussed​

ApproachDescriptionStatus
IX Industrial connectorsHirose mini Ethernet connectors, smaller than RJ45Rejected — requires non-standard cables, negating the point1
USB-C to Ethernet cableUSB-C on one end, RJ45 on the otherAvailable commercially but not an expansion card1
Fujitsu folding jackOrigami-style pop-out connector from LifeBookConnector sourced; space constraints remain1
XJACK mechanismVintage 3Com push-push designPatent expired (HP stopped paying); too long for card depth1
Dell folding jackSimilar to Fujitsu, disassembled by Miles_RaymondToo thick for Framework1
Vertical protrusionRJ45 sticking out downward (not sideways)Discussed; sticks out both ways with official card1
Power adapter passthroughEthernet in the power brick, like iMacAcknowledged as a dongle alternative1

Key Technical Constraints​

The thread identified several fundamental constraints for a low-profile Ethernet card1:

ConstraintLimit
Expansion card height~6.8 mm total
Clearance under laptop (FW 13)~3.45 mm from card bottom to desk
Available PCB space above USB-C~1.15 mm (with upside-down 0.8 mm PCB)
Card depth (USB-C plug to face)~25 mm
RJ45 connector width13.8 mm (wider than card is tall)
RJ45 connector height~12 mm (standard)
MagneticsMust fit transformers + common-mode chokes
Signal integrityGigabit through flat-flex is challenging

Framework VP nrp suggested MMCX connectors for antenna connections in similar RF projects and recommended exploring integrated matching/balun parts1.

Footnotes​

  1. Low profile ethernet expansion card (maybe) — Framework Community (ExplodingWaffle et al., November 2021 – February 2026) ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ↩7 ↩8 ↩9 ↩10 ↩11 ↩12 ↩13 ↩14 ↩15 ↩16 ↩17 ↩18 ↩19 ↩20 ↩21 ↩22 ↩23 ↩24 ↩25 ↩26 ↩27 ↩28 ↩29 ↩30 ↩31