Controlled-impedance flex holds the characteristic impedance of a trace to a target value so high-speed and RF signals travel without reflections that corrupt the link.
FlexiPCB models every stackup with a 2D field solver, builds 1-10 layer flex on Dk 3.2-3.5 polyimide, and TDR-verifies every production panel to ±5% (±3% on request).
On flex the dominant variables are dielectric thickness (held ±10% by lamination control) and trace width (held ±10% by etch compensation) — not the laminate brand alone.
Send the target impedance, signal standard, and bend zones so the stackup is modeled before fabrication and the trace geometry survives the fold without an impedance discontinuity.
High-speed signals do not tolerate impedance discontinuities. When your flex circuit carries LVDS, USB 3.x, PCIe, MIPI, automotive Ethernet, or RF signals above 100 MHz, controlled impedance is not optional — it is a fundamental design requirement. FlexiPCB manufactures impedance-controlled flex circuits from 1 to 10 layers, using calibrated polyimide substrates with known dielectric constant (Dk 3.2-3.5 at 1 GHz) and tightly controlled copper trace geometry. We model every impedance stackup with 2D electromagnetic field solvers before production begins, then verify every panel with time-domain reflectometry (TDR) testing to confirm your target impedance within ±5% tolerance. Whether you need a single-ended 50-ohm microstrip for an RF antenna feed, a 100-ohm differential pair for USB 3.2, or a coplanar waveguide for 5G mmWave, our process controls — dielectric thickness ±10%, etch factor compensation, and coverlay registration — ensure consistent impedance from first article through volume production.
USB 3.x, PCIe Gen 4/5, HDMI 2.1, and DisplayPort require controlled-impedance differential pairs with tight coupling and length matching. Our flex circuits maintain 90/100-ohm differential impedance across dynamic bend zones without discontinuities — critical when routing high-speed buses through hinges, sliders, and folding mechanisms.
100BASE-T1 and 1000BASE-T1 automotive Ethernet over flex circuits demand 100-ohm differential impedance with strict return loss requirements. FlexiPCB manufactures impedance-controlled flex harnesses for camera modules, radar interconnects, and LiDAR sensor chains that meet AEC-Q100 reliability and IATF 16949 process standards.
Antenna feeds, filter interconnects, and RF front-end modules require 50-ohm controlled impedance with minimal insertion loss. Our coplanar waveguide and microstrip designs on low-loss polyimide deliver consistent impedance from sub-GHz ISM bands through 5G mmWave frequencies at 28 GHz and beyond.
Ultrasound transducer arrays and CT scanner interconnects require impedance-controlled flex circuits with dozens to hundreds of matched channels. We manufacture multi-layer flex with controlled impedance on every signal layer, biocompatible materials, and cleanliness levels suitable for Class II and Class III medical devices.
MIPI CSI-2 and DSI interfaces in smartphones, tablets, and automotive cameras use impedance-controlled flex cables with 100-ohm differential pairs. Our ultra-thin constructions (total thickness under 0.15mm) maintain impedance accuracy through 180-degree fold zones with bend radii as small as 1.5mm.
Oscilloscope probes, signal analyzers, and ATE (automated test equipment) require broadband 50-ohm impedance-controlled flex interconnects. Our TDR-verified flex circuits deliver ±3% impedance tolerance with characterized insertion loss from DC to 40 GHz for precision measurement applications.
Our signal integrity engineers import your impedance requirements and model the optimal stackup using 2D electromagnetic field solvers. We calculate trace width, spacing, and dielectric thickness for each impedance target, accounting for polyimide Dk variation across frequency, etch compensation factors, and coverlay dielectric effects.
We select polyimide laminates with characterized dielectric properties (Dk, Df) at your operating frequency. Every incoming lot is verified for dielectric thickness, copper foil thickness, and surface roughness — all parameters that directly affect impedance. Adhesiveless laminates are specified when dielectric tolerance is critical.
Trace geometry is the primary impedance variable. We use LDI (laser direct imaging) for ±10 µm registration accuracy and tightly controlled etch processes to maintain trace width within ±10% of target. Etch factor compensation is pre-calculated in the CAM data to account for copper undercut during wet etching.
Multi-layer impedance flex requires precise dielectric thickness between signal and reference planes. Our vacuum lamination process controls prepreg flow and final dielectric thickness within ±10% of nominal — the single most critical parameter for impedance accuracy.
Every production panel includes impedance test coupons that replicate your actual trace geometries. We measure these coupons with calibrated TDR equipment per IPC-TM-650 2.5.5.7, generating impedance traces that verify compliance with your target ±5% (or ±3%) tolerance. TDR data is included in your quality documentation package.
Completed flex circuits undergo full electrical testing (open/short, isolation), dimensional inspection, and visual inspection per IPC-A-610. The impedance test report — including TDR waveforms, measured values, and statistical analysis — ships with every order as part of our standard quality documentation.
We do not guess trace widths from lookup tables. Every impedance stackup is modeled with 2D field solvers using your actual material properties, layer construction, and soldermask/coverlay — and we share the modeling report before production begins.
Impedance compliance is not sampled — it is verified on every production panel via TDR test coupons that replicate your actual trace geometry. Calibrated equipment, traceable standards, and full test reports included with delivery.
Our dielectric thickness control (±10%), trace width control (±10%), and process repeatability deliver ±5% impedance tolerance as standard. For precision RF and measurement applications, we achieve ±3% with material selection and tighter process windows.
From automotive Ethernet at 100 MHz to 5G mmWave at 28 GHz to test equipment at 40 GHz — we have manufactured impedance-controlled flex circuits across the frequency spectrum. Our material database includes characterized Dk/Df data at your operating frequency.
Targets, frequency, and bend data let engineering model the stackup before fabrication, not after.
Gerber, layer stackup, and the impedance targets (single-ended and differential) with which layers carry them
Signal standard or data rate (USB 3.x, PCIe, MIPI, automotive Ethernet, RF band) and operating frequency
Required tolerance (±5% standard or ±3%) and whether a pre-production impedance model is needed for sign-off
Bend radius, static versus dynamic flex, fold count, and cycle expectation for any impedance traces in a bend zone
Surface finish, layer count, MOQ, forecast, and required reports: TDR waveforms, coupon data, electrical test
The response is written for signal-integrity, quality, and procurement review.
Pre-production 2D field-solver impedance model with trace width, spacing, and dielectric thickness per target
Recommended stackup keeping reference planes continuous and impedance traces clear of the bend zone
Quotation with MOQ, lead time, tooling, and the cost impact of ±3% versus ±5% and added layers
TDR impedance report per IPC-TM-650 2.5.5.7 with waveforms, measured values, and statistical analysis
Production release checklist for drawing revision, coupon design, lot traceability, and repeat-order control
Two steps. Before fabrication, we model your stackup with a 2D electromagnetic field solver using the real polyimide Dk at your frequency, the copper geometry, and the coverlay effect, then set trace width, spacing, and dielectric thickness to hit the target. During fabrication, the two variables that move impedance are dielectric thickness, which we control to ±10% through lamination profiling, and trace width, which we control to ±10% with etch-factor compensation pre-calculated in CAM. Then we measure TDR coupons that replicate your actual geometry on every production panel. You get the modeling report up front and the TDR report with delivery.
On rigid FR4 the dielectric is thick and dimensionally stable. On flex the dielectric is thin polyimide, so a small absolute change in thickness during lamination is a large percentage change in impedance, and the coverlay over the trace adds a dielectric layer that shifts the result. Bending adds a second issue: a via, pad, or thickness change in a bend zone is an impedance discontinuity that also becomes a mechanical crack risk. We address both by tightly controlling dielectric thickness, accounting for coverlay in the model, and keeping reference planes continuous and discontinuities out of the bend zone.
Yes, with the geometry designed for it. We keep the signal trace and its reference plane continuous through the bend, avoid vias and width changes in the fold, and place the impedance layers near the neutral axis so the geometry that sets impedance does not deform as the part flexes. For MIPI and camera-module flex we have held 100Ω differential through 180-degree folds at bend radii as small as 1.5mm in constructions under 0.15mm total thickness. Send the bend radius, fold count, and cycle expectation with your impedance target so the stackup is designed to keep impedance and survive the flex.
Public references provide context; your drawings and purchase specifications control production acceptance.
Characteristic impedance is the property of a transmission line that, when matched, prevents reflections; it is the value controlled-impedance flex is built to hold.
TDR is the measurement method used to verify the impedance of fabricated trace coupons against the target tolerance.
IPC-6013, IPC-2223, and IPC-TM-650 2.5.5.7 are the design, performance, and TDR-test references for controlled-impedance flex.
Written for OEM signal-integrity and procurement teams evaluating controlled-impedance flex suppliers.
FlexiPCB manufacturing and sourcing specialist
Hommer Zhao has supported flexible and rigid-flex fabrication for OEM teams since 2008. For controlled-impedance flex, the review focuses on pre-production field-solver modeling, dielectric-thickness and trace-width control, TDR verification on every panel, and keeping impedance traces and reference planes continuous through the bend zone.
Capability
Single-ended 25-120Ω, differential 80-120Ω; microstrip, stripline, CPW, broadside; 1-10 layers; DC to 40+ GHz
Process control
2D field-solver model before build, dielectric ±10% and trace width ±10%, TDR coupon on every production panel
Case evidence
A camera-module flex held 100Ω differential through a 180-degree fold at a 1.5mm bend radius in a sub-0.15mm construction
Standards
IPC-6013 Class 2/3, IPC-2223, IPC-TM-650 2.5.5.7, ISO 9001
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