Precious Metals Aqua Regia (3:1 HCl:HNO₃)

Chemical Etching Formula
Au Pure Gold with Aqua Regia (3:1 HCl:HNO₃)

For engineers selecting an etching chemistry for Au Pure Gold, the Aqua Regia (3:1 HCl:HNO₃) formula shown here defines the bath composition, temperature window, and achievable feature sizes across a 0.03-0.1 mm thickness band. Typical mass-production yield for this recipe is 98.4%, with a typical conveyor speed of 2.26 m/min at 28°C.

Formula Summary

The table below summarizes every parameter that defines this etching formula. Values listed as ranges scale with sheet thickness across the supported band.

Aqua Regia (3:1 HCl:HNO₃) Etchant System
— °Bé Concentration
1.150 Specific Gravity
28 °C Bath Temperature
Through etch (double-sided) Etch Depth Type
0.03-0.1 mm Thickness Range
0.05 mm Typical Thickness
0.8-4.87 m/min Conveyor Speed Range
2.26 m/min Typical Speed
36-120 μm Min Hole Ø Range
100 μm Min Line Width Range
46160 μm Undercut Range
2.75 Etch Factor (EF)
98.4% Typical Yield (98.3-98.4%)

Why Aqua Regia (3:1 HCl:HNO₃) for Au Pure Gold?

Aqua Regia (3:1 HCl:HNO₃) earns its place as a Au Pure Gold etching formula through repeatability. The bath can be titrated and corrected each shift to hold concentration (as specified) and specific gravity (1.150) within a tight band, which keeps the etch factor near 2.75 and yield near 98.4% run after run.

Process Window & Bath Control

Hold the bath at 28°C with concentration as specified (specific gravity 1.150). Across the 0.03-0.1 mm thickness range, conveyor speed runs from 0.8-4.87 m/min — thinner sheets move faster, thicker sheets slower, in roughly inverse proportion to thickness. A typical mid-range setpoint is 2.26 m/min for 0.05 mm stock. Use redundant PID temperature control to hold the bath within ±1.5°C, and titrate at least once per shift.

Design Rules & Tolerances

Feature sizes scale with sheet thickness. For this formula the minimum hole diameter ranges 36-120 μm and the minimum line width ranges 100 μm across the 0.03-0.1 mm band, following the industry 1.2× (hole) and 1.0× (line) thickness rules. Single-side undercut ranges 46160 μm, and the etch factor is about 2.75. Size your photomask by subtracting twice the expected undercut from each finished feature dimension.

Design Rule Summary
• Minimum hole diameter range: 36-120 μm
• Minimum line width range: 100 μm
• Single-side undercut range: 46160 μm
• Typical etch factor (EF): 2.75

Yield & Production Economics

This formula delivers a typical yield of 98.4% (range 98.3-98.4%). At that rate, per-part economics are driven mostly by fixed photomask and setup cost for small batches and by sheet utilisation for large runs. The chemistry itself does not change with quantity, so the same recipe serves prototype and production volumes.

Typical Applications

Au Pure Gold etched with this recipe typically ends up in fine jewelry components, electrical contacts, and decorative inlays. Because chemical etching applies no mechanical or thermal load, the finished features are free of work-hardening and heat-affected zones — a decisive advantage over stamping or laser cutting for these uses.

More Precious Metals Formulas

Other formulas in the same material family.

Ag Pure Silver HNO₃(30%) Through etch (double-sided)

Frequently Asked Questions

Run the bath at 28°C. Holding much above 33°C can degrade photoresist adhesion and erode feature edges; running below 23°C slows the etch and forces a conveyor-speed reduction. Production lines hold 28°C within ±1.5°C using redundant PID control.

Need a Quote for This Process?

WET Etched runs production wet chemical etching lines using the Aqua Regia (3:1 HCl:HNO₃) chemistry. Send us your part drawing and quantity for a full process quote.

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