Carbon & Tool Steel FeCl₃+HCl

Chemical Etching Formula
SUP9 Spring Steel with FeCl₃+HCl

This page documents the reference wet chemical etching formula for SUP9 Spring Steel using the FeCl₃+HCl system. The recipe below covers a sheet-thickness range of 0.1-0.3 mm and is configured for through etch (double-sided). Every value is drawn from operational process records rather than theoretical calculation, and is provided as a starting point for your own process development.

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.

FeCl₃+HCl Etchant System
42 °Bé Concentration
1.390 Specific Gravity
48 °C Bath Temperature
Through etch (double-sided) Etch Depth Type
0.1-0.3 mm Thickness Range
0.20 mm Typical Thickness
0.2-1.02 m/min Conveyor Speed Range
0.36 m/min Typical Speed
120-360 μm Min Hole Ø Range
100-300 μm Min Line Width Range
18-55 μm Undercut Range
2.72 Etch Factor (EF)
96.6% Typical Yield (96.3-96.8%)

Why FeCl₃+HCl for SUP9 Spring Steel?

On SUP9 Spring Steel, the ferric chloride system attacks the alloy's oxide layer continuously while ferric ions drive dissolution. It is regenerable, compatible with standard photolithography, and produces clean burr-free edges — which is why nearly every SUP9 Spring Steel etch line runs a variant of this formula.

Process Window & Bath Control

Bath control for SUP9 Spring Steel in FeCl₃+HCl: temperature 48°C, concentration 42 °Bé, specific gravity 1.390. The recipe is tuned for through etch (double-sided). Conveyor speed is the primary throughput control, ranging 0.2-1.02 m/min across the supported thickness range. Check specific gravity each shift with a calibrated hydrometer and correct with fresh make-up or water as needed.

Design Rules & Tolerances

Feature sizes scale with sheet thickness. For this formula the minimum hole diameter ranges 120-360 μm and the minimum line width ranges 100-300 μm across the 0.1-0.3 mm band, following the industry 1.2× (hole) and 1.0× (line) thickness rules. Single-side undercut ranges 18-55 μm, and the etch factor is about 2.72. Size your photomask by subtracting twice the expected undercut from each finished feature dimension.

Design Rule Summary
• Minimum hole diameter range: 120-360 μm
• Minimum line width range: 100-300 μm
• Single-side undercut range: 18-55 μm
• Typical etch factor (EF): 2.72

Yield & Production Economics

Expect a yield in the 96.3-96.8% range for SUP9 Spring Steel with FeCl₃+HCl, with 96.6% typical on a well-controlled line. Most rejects trace back to upstream coating and exposure rather than to the etch bath itself, so tightening photolithography control is usually the fastest path to a higher number.

Typical Applications

Typical applications for SUP9 Spring Steel processed with FeCl₃+HCl include spring elements, blades, shim stock, and stamped-replacement flat parts. The formula's tolerance band and yield make it well suited to medium-to-high-volume precision flat parts.

More Carbon & Tool Steel Formulas

Other formulas in the same material family.

50CrV4 Spring Steel FeCl₃+HCl Through etch (double-sided) 65Mn Spring Steel FeCl₃+HCl Through etch (double-sided) 65Mn Spring Steel FeCl₃+HCl Half etch (single-sided) DT4 pure iron FeCl₃+HCl Through etch (double-sided) SK2 Tool Steel FeCl₃+HCl Through etch (double-sided) SK3 Tool Steel FeCl₃+HCl Through etch (double-sided)

Frequently Asked Questions

Across the supported 0.1-0.3 mm thickness range, conveyor speed runs from 0.2-1.02 m/min. A typical mid-range setpoint is 0.36 m/min for 0.20 mm stock. Thinner sheets run faster and thicker sheets slower, roughly in inverse proportion to thickness.

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WET Etched runs production wet chemical etching lines using the FeCl₃+HCl chemistry. Send us your part drawing and quantity for a full process quote.

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