Rule of thumb: 0.5-1.0 nH per mm of wire length for a single wire in free space. Typical 25 micron gold bond wire, 1 mm long, approximately 0.7 nH. Multiple parallel wires reduce total inductance: two parallel wires with 100 micron spacing approximately 0.4 nH (not exactly halved due to mutual inductance). At 10 GHz, 1 nH = 63 ohms reactance.

Impact on RF circuits?

Source/emitter bond wires add inductance to the ground path, creating negative feedback that reduces gain and improves stability. Gate/drain bond wires are part of the matching network and must be modeled accurately. In GaN HEMT packages, the internal pre-match uses bond wire inductance intentionally as series matching elements. Uncontrolled wire length variation of +/- 100 microns shifts the match point.

Simple: lumped inductor L = 0.7 nH/mm. Better: include mutual inductance between parallel wires. Best: 3D electromagnetic simulation (HFSS, CST) of the wire geometry including proximity to ground plane and adjacent wires. Above 20 GHz, transmission-line effects and radiation become significant. Published models exist for standard wire profiles (JEDEC wire bond geometry).

RF Design

Bond Wire Inductance

Bond Wire Inductance is the parasitic inductance introduced by wire bonds connecting semiconductor dies to package leads or substrates. At approximately 0.5-1.0 nH per mm of wire length, this inductance creates significant reactance at RF frequencies (1 nH = 63 Ω at 10 GHz). It must be accurately modeled in impedance matching networks and is intentionally used as series matching elements in pre-matched RF power transistor packages.

Category: RF Design

Typical: 0.5-1.0 nH/mm

Understanding Bond Wire Inductance

The inductance of a single wire in free space depends on its length and diameter: L ≈ (μ₀/2π)·l·[ln(2l/r) − 1], where l is length and r is wire radius. For 25 μm diameter gold wire, this gives approximately 0.7 nH/mm. The loop height also matters: higher loops increase inductance.

Parallel bond wires share current and reduce total inductance, but mutual coupling limits the reduction. Two wires with 100 μm spacing provide about 60% reduction (not 50%). The ground plane proximity further modifies the inductance through image currents.

Bond Wire Inductance

Single wire:
L ≈ 0.2·l·[ln(2l/r) − 1] nH
l = length (mm), r = radius (mm)

25 μm Au, 1 mm: ~0.7 nH
Reactance at 10 GHz:
X_L = 2πfL = 2π·10×10⁹·0.7×10⁻⁹ = 44 Ω

Wire Configuration Inductance

Configuration	L (nH, 1 mm)	Reduction	Use
Single wire	0.7	Reference	Signal
2 parallel (100 μm)	0.4	43%	Power
4 parallel (100 μm)	0.25	64%	Ground
Ribbon (250 μm)	0.3	57%	High current

Common Questions

Frequently Asked Questions

How much?

0.5-1.0 nH/mm single wire. 25 μm Au, 1 mm ≈ 0.7 nH. Parallel wires reduce but mutual coupling limits gain. At 10 GHz: 44 Ω.

RF impact?

Source wires: negative feedback (gain reduction). Gate/drain: matching element. ±100 μm length variation shifts match. Must model accurately.

Modeling?

Simple: 0.7 nH/mm lumped. Better: include mutual inductance. Best: 3D EM simulation. Above 20 GHz: transmission-line effects.

Related Terms

← Bond Pull Bonded Fin →

RF Packaging

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