Overview

Diaphragm chemical etching forms the sensing element of a pressure device by removing metal chemically instead of pressing or spinning it. A thin foil is laminated with photoresist, exposed to the diaphragm profile on both faces, developed and etched until the concentric convolutions, the clamping rim and the centre pad are cut through or recessed to depth. Because the metal is never struck, bent or rolled, the foil keeps its original grain structure: no cold work is introduced, no residual stress is locked into the flexing zone, and the deflection under a given pressure stays where the design put it.

The practical value shows up in repeatability. Two diaphragms etched from the same foil, on the same panel, with the same dwell time have the same thickness in the active area and therefore the same spring rate. That is hard to guarantee with stamped diaphragms, where die wear gradually changes the convolution radius. Stainless 301 and 302, nickel 201, titanium grade 2 and beryllium copper are the usual substrates, running from 0.02 mm to 0.25 mm.

Parameter Window

• Available Materials: stainless 301/302, 316L, nickel 201, titanium grade 2, beryllium copper
• Material Thickness Range: 0.02–0.25 mm
• Tolerance: ±0.02 mm on profile and concentricity; ±8% on active-area thickness
• Minimum Feature: 0.05 mm slot width and 0.10 mm convolution radius at 0.05 mm foil
• Surface Options: stress-relief anneal, passivation, nickel or gold plating, black oxide, laser marking
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Response Review — Read the pressure range, deflection target and spring rate from the drawing, and check whether the foil thickness and active diameter can deliver them.
2. Foil Selection — Choose alloy, temper and rolling direction; thickness is verified across the strip, because a 5% drift in foil gauge moves the spring rate by roughly the same amount.
3. Stress-Relief Pre-Anneal — Relax the incoming foil before patterning so the diaphragm does not drift after it is clamped into the housing.
4. Cleaning and Double-Sided Lamination — Degrease and laminate both faces, aligning the resist so front and back patterns register to the same centre.
5. Double-Sided Exposure — Expose the convolution profile from both sides through matched film, keeping the rims concentric to within the drawing callout.
6. Development and Inspection — Wash out the resist, then check rim width and convolution definition under magnification before any metal is removed.
7. Controlled Etching — Etch in a chemistry matched to the alloy, with bath temperature and dwell logged per panel; half-etched convolutions are stopped on depth, through-cut outlines on breakthrough.
8. Strip, Anneal, Measure — Remove resist, vacuum anneal to restore ductility, then measure profile, flatness and, on request, deflection at a reference pressure.

Core Advantages

1. No cold work in the flexing zone: Chemical removal leaves the grain structure intact, so fatigue life is not shortened by the work hardening a stamping operation would introduce.
2. Repeatable spring rate: Thickness in the active area is held within ±8%, and the etch recipe is logged, so batch-to-batch response stays inside the sensor's calibration window.
3. Burr-free edges: A rolled or punched edge creates a stress riser where cracks start; an etched edge has no roll-over, which matters on a part that flexes millions of cycles.
4. Convolutions without a die: Concentric rings, spiral profiles and asymmetric pads are all a film change, so a new pressure range does not need new tooling.
5. Half-etch or through-cut in one pass: Rim stiffening ribs can be recessed while the outline is cut through, removing a secondary operation and a handling step on very thin foil.
6. Clean foil handling: Parts stay supported on the panel until the last operation, which keeps 0.02 mm foil from creasing before it reaches the assembly line.

Typical Applications

• Pressure sensors: Stainless diaphragms with concentric convolutions for transmitters that must hold calibration over temperature.
• Automotive MAP and fuel sensors: Thin nickel and stainless diaphragms that see vibration and fuel vapour.
• Medical infusion devices: Small titanium diaphragms separating fluid from the sensing cavity.
• HVAC differential switches: Beryllium copper diaphragms with a defined snap point for on/off pressure control.
• Flow and level instruments: Large-area foils with shallow convolutions for low-pressure measurement.
• Acoustic and pump membranes: Etched nickel membranes where mass distribution across the dome sets the resonant frequency.

Design Notes & Process Considerations

1. State the spring rate, not only the shape: Pressure range, active diameter and thickness together define response; giving all three lets the supplier confirm the design before film is made.
2. Keep convolution radius above foil thickness: A radius smaller than the foil gauge cannot be formed cleanly and will read as a crack initiation site in fatigue testing.
3. Specify single-sided or double-sided etch: Etching from both faces halves the taper and holds rim width, but requires tighter front-to-back registration.
4. Call out the anneal: Stress-relief temperature and atmosphere affect final flatness and hardness; leaving it to default may leave the diaphragm too stiff or too soft.
5. Define the clamping area: The rim that sits in the housing should be flat and free of etch taper, otherwise the seal loads unevenly and zero-point drift appears.
6. Qualify by deflection, not by drawing: Approve the first article on measured deflection at a reference pressure, then hold that number as the acceptance criterion for diaphragm chemical etching lots.