Stainless Steel FeCl₃+HCl

Chemical Etching Formula
SUS309S with FeCl₃+HCl

This page documents the reference wet chemical etching formula for SUS309S using the FeCl₃+HCl system. The recipe below covers a sheet-thickness range of 0.1-0.5 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
46 °Bé Concentration
1.430 Specific Gravity
52 °C Bath Temperature
Through etch (double-sided) Etch Depth Type
0.1-0.5 mm Thickness Range
0.20 mm Typical Thickness
0.12-0.95 m/min Conveyor Speed Range
0.34 m/min Typical Speed
120-600 μm Min Hole Ø Range
100-500 μm Min Line Width Range
19-95 μm Undercut Range
2.62 Etch Factor (EF)
96.4% Typical Yield (95.5-96.7%)

Why FeCl₃+HCl for SUS309S?

On SUS309S, 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 SUS309S etch line runs a variant of this formula.

Process Window & Bath Control

The process window for this FeCl₃+HCl formula centres on 52°C and 46 °Bé. Conveyor speed spans 0.12-0.95 m/min over the 0.1-0.5 mm thickness band; the typical operating point is 0.34 m/min. Every 5°C drop in bath temperature requires roughly a 30% reduction in conveyor speed to hold the same etch depth, so temperature stability is the single biggest lever on consistency.

Design Rules & Tolerances

Feature sizes scale with sheet thickness. For this formula the minimum hole diameter ranges 120-600 μm and the minimum line width ranges 100-500 μm across the 0.1-0.5 mm band, following the industry 1.2× (hole) and 1.0× (line) thickness rules. Single-side undercut ranges 19-95 μm, and the etch factor is about 2.62. Size your photomask by subtracting twice the expected undercut from each finished feature dimension.

Design Rule Summary
• Minimum hole diameter range: 120-600 μm
• Minimum line width range: 100-500 μm
• Single-side undercut range: 19-95 μm
• Typical etch factor (EF): 2.62

Yield & Production Economics

Typical mass-production yield for SUS309S in the FeCl₃+HCl system is 96.4%, within an observed range of 95.5-96.7%. The dominant yield-loss modes are photoresist pinhole defects and rinse-water contamination. Improving incoming sheet quality and photoresist coating consistency gives the highest yield-improvement leverage for this formula.

Typical Applications

Parts produced with the FeCl₃+HCl formula on SUS309S are common in precision shims, encoder discs, RF/EMI shields, surgical and dental components, fuel-cell bipolar plates, and fine filter meshes. The burr-free, stress-free nature of chemical etching makes it the preferred process wherever flatness and edge quality matter more than raw throughput.

More Stainless Steel Formulas

Other formulas in the same material family.

AM350 Stainless Steel FeCl₃+HCl Through etch (double-sided) SUS2205 Duplex Stainless FeCl₃+HCl Through etch (double-sided) SUS2507 Super Duplex FeCl₃+HCl Through etch (double-sided) SUS301 FeCl₃+HCl Through etch (double-sided) SUS301 FeCl₃+HCl Through etch (double-sided) SUS302 FeCl₃+HCl Through etch (double-sided)

Frequently Asked Questions

The typical etch factor for this recipe is 2.62 — vertical etch depth is about 2.62× the single-side undercut. Higher EF means tighter feature tolerance; values near or above 3.0 are close to best-in-class for wet etching, and SUS309S in FeCl₃+HCl sits in the typical production range.

Need a Quote for This Process?

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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