1400nH Conical Inductor Ultra Wideband Radio Frequency Choke 20MHz - 40GHz

HALT60005 Ultra-Broadband Conical Inductor 1400nH Micro-Wire Bias Tee RF Choke Ultra-Wideband Performance 20MHz-40GHz

Product Overview

The HALT60005 is a broadband conical inductor optimized for bias tee DC injection networks operating from 20 MHz to 40 GHz. It provides 1400 nH of nominal inductance via a tapered conical winding with 0.05 mm oxygen-free copper wire, supporting 200 mA of continuous DC bias current across a -55°C to +125°C temperature range. An optional 0.08 mm wire configuration is available on custom order for applications requiring higher current handling.

Technical Specifications

Bias Tee Circuit Configuration

In a bias tee, the choke inductor sits between the DC supply and the RF through-line. Its role is twofold: conduct DC bias current to the active device, and present high RF impedance across the signal bandwidth to prevent RF energy from leaking into the DC supply. The HALT60005 is designed for this specific operating condition.

Circuit Nodes:

• RF Through-Path: 50-Ω microstrip or coplanar waveguide connecting Port 1 to Port 2. The narrow apex end of the inductor is soldered directly to this trace.
• DC Bias Input: The wide base end connects to a DC feed pad. A broadband bypass capacitor network (100 pF in parallel with 10 nF ceramic, with an optional 1 µF for low-frequency decoupling) shunts residual RF to the ground plane.
• Isolation Mechanism: At RF frequencies, the 1400 nH inductance generates >2.0 kΩ of impedance. At DC, the winding presents only its copper resistance (~2.0 Ω typical), passing bias current with minimal voltage drop.

DC Bias Current Handling & Thermal Analysis

Passing 200 mA through a 0.05 mm conductor requires careful thermal design. The HALT60005 manages this through the following:

• Conductor Quality: Oxygen-free high-conductivity copper (OFHC, 99.99% Cu) minimizes DC resistance. Typical DCR at 25°C is approximately 2.0 Ω, yielding ~80 mW of I²R dissipation at rated current.
• Thermal Margin: Temperature rise is limited to ΔT ≤ 15°C. Copper resistivity has a positive temperature coefficient of +0.39%/°C. The 15°C limit prevents the positive-feedback loop where higher temperature increases resistance, which increases dissipation, which further raises temperature.
• Cooling Mechanism: The exposed air-core construction radiates and convects naturally. No potting compound traps heat. A 0.5 mm air gap around the coil body is sufficient for rated operation.
• Insulation Headroom: The polyimide enamel is rated for 200°C continuous operation, providing substantial margin above the worst-case junction temperature at +125°C ambient with 15°C self-heating.
• Zero Core Loss: Unlike ferrite chokes, there is no hysteresis or eddy-current heating from RF power. All dissipation is predictable from DC copper loss alone.

Detailed Assembly & Mounting Procedure

Proper mounting is essential to achieve the rated RF performance. The following SOP has been validated on characterized microstrip test fixtures:

Step 1 — Physical Alignment

• Position the small end (apex) of the conical inductor pointing downward, perpendicular (≈90°) to the RF transmission microstrip line.
• Off-perpendicular mounting introduces asymmetric field coupling that degrades S11 return loss above 15 GHz.

Step 2 — Apex Lead Connection

• Solder the apex flying lead directly to the 50-Ω microstrip trace.
• Trim the lead between the solder fillet and the first winding turn as short as possible. Target: ≤0.3 mm. At 40 GHz, even 0.5 mm of excess lead contributes approximately 0.3 nH of parasitic series inductance—enough to measurably shift the input match.

Step 3 — Base Lead to DC Node

• Solder the wide base lead to the DC bias input pad.
• Place bypass capacitors (100 pF || 10 nF) within 1 mm of this pad. This minimizes the inductive loop area between the choke and the RF ground reference.

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, not optional. Without epoxy fixing, the air-core coil can vibrate due to acoustic or mechanical excitation. These micron-scale vibrations modulate the turn spacing (microphonic effect), introducing phase noise into the RF signal.
• Do not encapsulate the full coil—excess dielectric adds unwanted shunt capacitance.

Step 5 — Soldering Thermal Profile

• Iron tip temperature: 280–320°C.
• Dwell time: ≤3 seconds per joint. The ultra-fine 0.05 mm copper reaches soldering temperature almost instantly; prolonged heating can anneal the copper and alter the precision taper geometry.
• Lead-free compliance: Fully compatible with SAC305, AuSn eutectic, and PbSn solder alloys.

Environmental Reliability

• Temperature Cycling: No CTE mismatch stress points. The copper winding is the sole structural material; there is no ferrite-to-copper or ceramic-to-copper interface to crack under thermal cycling.
• Vibration Resistance: When epoxy-stabilized, the assembly passes MIL-STD-202 Method 204 (vibration) and Method 213 (mechanical shock). The <5 mg coil mass keeps mechanical resonance far above typical excitation spectra.
• Humidity: Store at 40–60% RH. The gold/tin-plated leads resist oxidation during the 12-month rated shelf life.
• Outgassing: Epotek H70E meets ASTM E595 low-outgassing requirements for hermetic optical packages.

Application Scenarios by Market

Frequently Asked Questions

Q: How do I choose between the 0.05 mm and 0.08 mm wire options?
A: The 0.05 mm (standard) wire provides the widest bandwidth with the lowest parasitic capacitance, rated to 40 GHz at 200 mA. The 0.08 mm custom option reduces DCR for higher current applications but trades off approximately 5 GHz of upper bandwidth due to increased inter-turn surface area. Choose based on whether your design is current-limited or bandwidth-limited.

Q: Can this component be assembled using automated wire bonding equipment?
A: Yes. The straight, gold/tin-plated copper flying leads are compatible with automated thermosonic wedge bonding and precision automated micro-soldering, suitable for high-volume hybrid microcircuit assembly lines.

Q: What is the failure mode if the epoxy stabilization step is omitted?
A: Without epoxy fixing, microphonic modulation of the turn spacing introduces phase noise sidebands on the RF carrier. In high-vibration environments, the unsupported coil can fatigue at the lead exit points over time. Epoxy stabilization is part of the qualified assembly procedure and is required for rated performance.

Q: How does this model compare to the HALT60005A variant?
A: The core inductor specifications are identical. The HALT60005 documentation provides application-specific guidance for bias tee circuit design, thermal analysis for continuous DC bias operation, and a detailed step-by-step assembly SOP. The HALT60005A documentation emphasizes the electromagnetic physics of the conical geometry, comparative topology analysis, and general-purpose integration. Select the variant whose documentation best matches your workflow.