2000nH Surface Mount Inductor Micro Wire RF Choke Inductor 10MHz - 40GHz

Product Overview

The HALT68005 is a broadband conical inductor optimized for millimeter-wave bias tee DC injection networks. It delivers 2000 nH (2.0 µH) of nominal inductance—the highest in the broadband conical inductor series—wound with 0.05 mm (50 µm) ultra-fine oxygen-free copper wire in a continuously tapered air-core conical geometry. The component is rated for 200 mA continuous DC bias current and operates from 10 MHz to 40 GHz across a -55°C to +125°C temperature range.

In a bias tee, the choke inductor conducts DC bias current to the active device while presenting high RF impedance across the signal bandwidth. The HALT68005’s 2000 nH inductance extends the low-frequency blocking floor to 10 MHz, covering supervisory tones, telemetry modulation, and slow control signals riding on bias lines in 40G/100G optical pluggable modules and phased-array systems. At the millimeter-wave end, the 0.05 mm wire minimizes inter-turn conductor surface area, suppressing parasitic capacitance to maintain genuine inductive behavior through 40 GHz.

The 0.05 mm wire represents the finest gauge in the product series. An optional 0.08 mm wire configuration is available on custom order for applications requiring higher DC current at a reduced upper frequency. The air-core construction eliminates magnetic saturation, ensuring the full 2000 nH inductance is maintained across the 0–200 mA DC current range. The component ships with fixture-characterized .s2p Touchstone data (10 MHz–40 GHz, 201 points, TRL-de-embedded), 3D STEP mechanical models, and parameterized HFSS EM models for accurate PCB co-simulation.

Technical Specifications

Bias Tee Circuit Design for 40 GHz Operation

RF Through-Path

The 50-Ω microstrip or grounded coplanar waveguide (GCPW) connects Port 1 to Port 2. The narrow apex end of the inductor is soldered to this trace at the tee junction. The ~0.40 mm OD at the apex presents minimal shunt capacitance, preserving S21 through 40 GHz. At this junction, the inductor appears as a high-impedance open circuit to RF energy while appearing as a low-resistance path to DC current.

DC Bias Injection Node

The wide base end connects to a DC feed pad. A broadband bypass capacitor network is placed within 1 mm of this pad:

• 100 pF ceramic (for millimeter-wave decoupling)
• 10 nF ceramic (for microwave decoupling)
• Optional 1 µF (for low-frequency supply ripple rejection)

At the rated 200 mA, the winding DCR of approximately 3.5 Ω produces a DC voltage drop of ~0.7 V—acceptable for active device bias circuits where the bias supply can compensate for this IR drop.

RF-DC Isolation

The 2000 nH inductance generates >2.2 kΩ of impedance across the rated band, equating to >66 dB of RF-to-DC isolation referenced to 50 Ω. This exceeds the typical 40–50 dB isolation required for clean bias tee operation in measurement and communications applications.

Multi-Frequency Performance Verification

Thermal Design for 200 mA DC Bias Operation

The I²R dissipation at rated current is approximately 140 mW at 25°C ambient based on ~3.5 Ω typical DCR. The thermal design addresses this through:

• Temperature Rise Limit: Rated for ΔT ≤ 15°C, preventing the positive TCR feedback loop where elevated temperature increases copper resistivity (+0.39%/°C), increasing dissipation further.
• Natural Convection: The exposed air-core construction radiates and convects freely. A minimum 0.5 mm air gap around the coil body supports rated operation.
• Insulation Margin: The polyimide enamel insulation is rated for 200°C continuous operation, providing substantial thermal headroom above the worst-case junction temperature at +125°C ambient with 15°C self-heating.
• Zero Core Loss: Unlike ferrite chokes that dissipate additional energy through hysteresis and eddy currents, the air-core HALT68005 has no magnetic loss component. All dissipation is predictable from copper I²R loss alone.

Detailed Assembly Procedure

Step 1 — Physical Alignment

Position the small end (cone tip) pointing downward, perpendicular (≈90°) to the RF transmission microstrip line. Angular deviation introduces asymmetric magnetic coupling that degrades S11 return loss above 20 GHz. Verify orientation under stereo microscope at 10× magnification.

Step 2 — Apex Lead to RF Trace

Solder the apex flying lead directly to the 50-Ω microstrip. Trim the lead between the solder fillet and first winding turn to ≤0.3 mm. At 40 GHz, each 0.5 mm of excess lead adds ~0.3 nH of unwanted series inductance that shifts the input match and reduces effective bandwidth. Use precision flush cutters under magnification.

Step 3 — Base Lead to DC Bias Node

Solder the wide base lead to the DC bias input pad. Place 100 pF and 10 nF ceramic bypass capacitors within 1 mm of this pad, with the smaller-value capacitor closest to the pad for lowest series inductance at millimeter-wave frequencies. An optional 1 µF capacitor may be placed adjacent for low-frequency decoupling.

Step 4 — Epoxy Stabilization

Apply a single micro-dot (≤0.3 mm diameter) of non-conductive, low-outgassing epoxy (Epotek H70E or H65 recommended) to the side of the winding where it contacts the substrate. This step is mandatory: without epoxy fixing, acoustic or mechanical excitation modulates the turn spacing at micron scale, producing phase noise sidebands on the RF carrier. Do not fully encapsulate the coil—excess dielectric adds parasitic shunt capacitance that degrades millimeter-wave performance.

Step 5 — Soldering Thermal Profile

The 0.05 mm wire requires a shorter thermal budget than heavier gauges:

• Tip Temperature: 280–320°C, controlled micro-soldering iron
• Dwell Time: ≤2 seconds per joint (versus 3 seconds for 0.08 mm wire). The 0.05 mm conductor has ~60% less cross-sectional area and reaches soldering temperature faster. Prolonged heating anneals the drawn copper, softening the precision-tapered winding.
• Alloy Compatibility: SAC305 (lead-free), AuSn eutectic (high-temperature), PbSn (standard). All three are fully compatible.
• Inspection: Verify fillet coverage under 20× stereo microscope. Re-work limited to one thermal cycle per joint.

Reliability Qualification

• Temperature Cycling: No CTE mismatch—copper winding is the sole structural material. No ferrite-to-copper or ceramic-to-copper interface to crack under -55°C to +125°C cycling.
• Vibration: Epoxy-stabilized assemblies pass MIL-STD-202 Method 204 (vibration) and Method 213 (mechanical shock). The <5 mg coil mass keeps mechanical resonance above typical excitation spectra.
• Lead Oxidation Resistance: Gold/tin plating protects the copper leads during the rated storage period of 20–25°C at 40–60% RH in a cleanroom environment.

Application Scenarios

Frequently Asked Questions

Q: When should I choose the 0.08 mm wire option over the standard 0.05 mm?
A: The 0.05 mm (standard) wire provides the maximum 40 GHz bandwidth with 200 mA capacity. The 0.08 mm custom option reduces winding DCR for higher current capability but reduces the upper usable frequency due to increased inter-turn capacitance. Choose 0.05 mm if your bias tee operates above 20 GHz and current is below 200 mA. Choose the 0.08 mm option for applications below 20 GHz where current handling is the priority.

Q: Why does the HALT68005 require ≤2 seconds soldering dwell while 0.08 mm wire variants allow 3 seconds?
A: The 0.05 mm wire has approximately 60% less cross-sectional area than 0.08 mm wire. It reaches soldering temperature faster and has less thermal mass to dissipate heat. Prolonged heating anneals the work-hardened drawn copper, permanently softening the precision-tapered winding, which can alter the distributed capacitance profile and shift the SRF.

Q: What is the failure mechanism if epoxy stabilization is omitted?
A: Without epoxy fixing, the unsupported air-core coil can vibrate under acoustic or mechanical excitation. Micron-scale vibration modulates the inter-turn spacing, introducing phase noise sidebands on the RF carrier. In high-vibration environments, the unsupported leads can fatigue at the solder fillet stress concentrator over time.

Q: How does this model differ from the HALT68005A?
A: Both share identical core specifications (2000 nH, 0.05 mm wire, 10 MHz–40 GHz, 200 mA). The HALT68005 provides application-specific guidance for millimeter-wave bias tee DC injection networks: complete bias tee circuit topology with component values, thermal analysis for 200 mA continuous operation, a detailed five-step assembly SOP with optical inspection criteria, and environmental reliability qualification data. The HALT68005A provides general-purpose ultra-wideband conical inductor documentation with a comparative matrix against the HALT6005 series.