Micro Coaxial Cable
is manufactured in two physical formats: round bundle (multi-core) and ribbon (flat). Both formats use the same individually shielded 50 Ω elements — identical conductor, dielectric, shield, and jacket construction at the element level. The difference is how elements are arranged: concentrically in a round cross-section, or side-by-side in a flat plane.
This seemingly simple geometric choice has cascading effects on connector termination, routing flexibility, phase matching capability, manufacturing cost, and application suitability. Choosing the wrong format can add unnecessary cost, complicate assembly, or physically prevent the cable from fitting the intended routing path.
Construction Comparison
Round Bundle (Multi-Core):
Elements arranged in concentric hexagonal close-pack layers. 1 element at center, surrounded by rings of 6, 12, 18, 24, 30, 36, 42, 48 elements. Bound with Kevlar serving tape. Enclosed in round outer jacket. Cross-section is circular.
Ribbon (Flat):
Elements arranged side-by-side in a single plane at controlled pitch (0.40, 0.50, or 0.635 mm center-to-center). Bonded with adhesive film or laminated between polyester carrier tapes. Cross-section is rectangular: width = (element count × pitch), thickness ≈ 1.0–1.5 mm.
| Characteristic | Round Bundle | Ribbon |
| Cross-section shape | Circular | Rectangular (flat) |
| Element arrangement | Concentric layers | Single row, parallel |
| Core count range | 1–512+ | 4–64 (practical max) |
| Pitch control | Not applicable (variable spacing) | Controlled: 0.40/0.50/0.635 mm |
| OD/dimensions (20 core) | ~3.8 mm diameter (42 AWG) | ~10.5 × 1.2 mm (42 AWG, 0.50 pitch) |
| Connector termination | Requires fan-out board or individual solder | Direct ZIF plug-in |
| Routing | 3D: tubes, channels, torsion | 2D: flat paths, hinges, under PCBs |
| Phase matching | Standard capability | Possible but uncommon |
| Flex mode | Omnidirectional bend + torsion | Flat bend only (no twist) |
| Cost (≤ 40 cores) | Higher (bundling, serving process) | Lower (simpler lamination) |
| Cost (> 64 cores) | Lower per channel | Impractical (ribbon too wide) |
Connector Termination — The Decisive Factor
In many Application, the connector interface determines the cable format — not the cable routing or core count.
Round bundle termination: Individual elements must be separated from the bundle, stripped, and individually soldered or welded to connector contacts. For high-pin-count connectors (128+), this requires a "fan-out board" — a PCB that receives the individual cables and routes them to the connector footprint. Fan-out boards add cost, assembly time, and a potential failure point.
Ribbon termination: Elements at controlled pitch align directly with ZIF connector contacts. The ribbon slides into the ZIF actuator and is locked in place — no individual soldering, no fan-out board. Assembly time for a 40-core ribbon ZIF connection: approximately 30 seconds. Assembly time for a 40-core round bundle with individual solder: approximately 45–90 minutes.
Decision rule: If your system uses I-PEX CABLINE, HIROSE DF, JAE FI-X, or any ZIF-style micro coaxial connector, use ribbon cable. If your system uses LEMO, BNC, or custom overmold connectors, use round bundle. If your system has ZIF at one end and a non-ZIF connector at the other, consider a ribbon-to-round transition cable.
Routing Geometry
Round bundle routes through:
- Cylindrical conduits (endoscope insertion tubes, catheter shafts, robot arms)
- 3D cable paths with compound bends and torsion
- Cable chains and drag chains
- Any path where the cable must bend in multiple planes
Ribbon routes through:
- Flat paths between PCBs (inside device housings)
- Hinges and folds (laptop lids, articulating displays)
- Under or between PCBs (stacked board configurations)
- Flat cable tracks in equipment chassis
Critical limitation: Ribbon cable cannot twist. Applying torsion to a ribbon causes element buckling and shielding damage. If your cable path involves any rotational motion (surgical robot wrist, CT gantry, articulating endoscope), round bundle is mandatory.
Critical advantage: Ribbon cable fits in spaces where round bundle does not. A 20-core ribbon at 0.50 mm pitch is 10.5 mm wide but only 1.2 mm thick. The equivalent round bundle is 3.8 mm in diameter. If your routing path has a 2 mm height constraint, only ribbon fits.
Phase Matching Capability
Round bundle: Phase matching is a standard production capability. Elements are TDR-measured, bin-sorted, and assembled from matched bins. The concentric layer arrangement means all elements experience similar mechanical strain during flex — maintaining phase match over the cable's flex life.
Ribbon: Phase matching is possible (same TDR sorting process) but has a practical limitation. In a ribbon, outer elements travel a slightly different path than inner elements during flat bending. Over long ribbon lengths (> 500 mm) with repeated bending, this differential path length can cause phase drift between edge and center elements. For short ribbons (< 200 mm), this effect is negligible.
Recommendation: For phase-matched systems (ultrasound probes, PAUT), use round bundle for the main cable and ribbon only for short transition sections (< 200 mm) at the connector interface.
Application Decision Guide
| Application | Best Format | Why |
| Ultrasound probe main cable | Round bundle | 128–512 ch, phase-matched, 3D routing |
| Ultrasound probe-to-PCB interface | Ribbon | Short (50–200 mm), ZIF connector, flat routing |
| Endoscope insertion tube cable | Round bundle | Cylindrical path, articulation, torsion |
| Laptop display cable | Ribbon | Flat hinge routing, ZIF connector |
| NDT PAUT main cable | Round bundle | Phase-matched, LEMO EPL connector |
| Medical monitor display connection | Ribbon | Internal flat routing, I-PEX CABLINE |
| Surgical robot instrument cable | Round bundle | Torsion, 3D routing, hybrid construction |
| Board-to-board high-speed link | Ribbon | Short, flat, ZIF termination |
| CT gantry cable | Round bundle | Continuous torsion, counter-helical |
| Capsule endoscope internal cable | Ribbon | Flat within capsule housing, minimal height |
Hybrid Approach — Ribbon-to-Round Transition
Many ultrasound probe assemblies use both formats in a single cable system:
Probe tip → fan-out board: Ribbon cable (50–150 mm) from transducer array PCB to fan-out board. ZIF termination at both ends for fast probe assembly.
Fan-out board → console connector: Round bundle (1.5–3.0 m) from fan-out board to console plug. Phase-matched, flexible, 3D routing through probe handle and umbilical.
This hybrid approach combines the assembly efficiency of ribbon termination at the probe tip with the routing flexibility and phase-matching integrity of round bundle for the main cable run.
The transition from ribbon to round occurs at the fan-out board, where individual cable elements from the round bundle are fanned out and routed to ribbon ZIF connector footprints on the PCB.
Cost Comparison
| Core Count | Ribbon Cable Cost | Round Bundle Cost | Ribbon Advantage | Notes |
| 4 | Baseline | 0.3 | Ribbon cheaper | Few cores, simple lamination |
| 8 | Baseline | 0.25 | Ribbon cheaper | |
| 20 | Baseline | +15–20% | Ribbon cheaper | Still simple flat assembly |
| 40 | Baseline | +5–10% | Similar | Crossover zone |
| 64 | Baseline | Similar | Similar | Ribbon handling becomes harder |
| 128 | Not practical | Baseline | Round only | Ribbon too wide (64 mm+) |
| 256 | Not practical | Baseline | Round only | Round bundle is the only option |
At 4–20 cores, ribbon is 15–30% cheaper due to simpler assembly (lamination vs. concentric layering + serving). At 40–64 cores, costs converge. Above 64 cores, only round bundle is practical.
Frequently Asked Questions
Can I convert a round bundle to ribbon at one end for ZIF termination?
Yes — this is the fan-out board approach. The round bundle is opened at the termination end, individual elements are routed and soldered to a PCB that presents ZIF connector footprints. This is standard practice for ultrasound probe manufacturing.
What is the maximum core count for ribbon cable?
Practical maximum: 64 cores. At 0.50 mm pitch, a 64-core ribbon is 32 mm wide — already requiring careful handling during connector insertion. Beyond 64 cores, the ribbon becomes too wide for reliable ZIF termination and too stiff for flat bending.
Can ribbon cable be phase-matched?
Yes, for short lengths (< 200 mm). The TDR sorting process is identical to round bundle. The limitation is at longer lengths with repeated bending, where differential path length between edge and center elements can cause phase drift. For the short ribbon sections used in probe-to-PCB interfaces, this is not a concern.
Is ribbon cable more flexible than round bundle?
In one plane (flat bending), yes — ribbon minimum bend radius can be as low as 3 mm. In other planes (twist, compound bend), no — ribbon cannot handle torsion or out-of-plane bending without damage. Round bundle is omnidirectionally flexible.
Do you manufacture both formats?
Yes. Round bundle from 4 to 512 cores. Ribbon from 4 to 64 cores at 0.40, 0.50, and 0.635 mm pitch. Hybrid ribbon-to-round transition assemblies on request.
Not sure which format — round bundle or ribbon? Share your application, connector type, and routing path — we will recommend the optimal format.
Primary: multi core vs ribbon
Micro Coaxial Cable
, round vs ribbon coaxial, coaxial cable format comparison
Secondary: round bundle coaxial cable, ribbon coaxial cable, flat micro coaxial, when to use ribbon coax, multi core coaxial advantages, coaxial cable routing
Related Products
FRS Technology builds these assemblies to order - core count, gauge, jacket, connector and length to your drawing. Products relevant here:
Not sure which construction fits? Talk to our engineers - share your channel count, frequency and space constraints.
