Key Technical Specifications
| Parameter | Specification |
|---|---|
| Flow Range (N₂ equivalent) | 5 SCCM – 8 SLM (SEC-4400); up to 5 SLM for SEC-4400MF |
| Accuracy | ±1.0% F.S. |
| Linearity | ±0.5% F.S. |
| Repeatability | ±0.2% F.S. |
| Control Range | 2 – 100% F.S. |
| Response Time | <1.0 s (500 ms typical) |
| Valve Type | Piezo valve, Normally Closed or Normally Open |
| Wetted Materials | M-Type: SUS-316L with metal seals; R-Type: SUS-316L with fluorocarbon (Viton/FKM) seals |
| Leak Integrity (M-Type) | ≤5 × 10⁻¹⁰ Pa·m³/s He |
| Operating Pressure | 14 – 42 psi (96 – 290 kPa) differential |
| Setpoint Signal | 0.1 – 5 VDC |
| Flow Output Signal | 0 – 5 VDC |
| Power Supply | ±15 VDC ±5%, 60 mA |
| Process Fittings | 1/4″ VCR or 1/4″ Swagelok (typical) |
| Operating Temperature | 5 – 50 °C (accuracy guaranteed 15 – 35 °C) |
Product Introduction
The SEC-4400 is the kind of MFC you find inside a CVD or etch tool where ±5% accuracy would mean scrapping an entire wafer lot. HORIBA STEC built this series around a piezo valve and a thermal mass-flow sensor, giving it sub-second response and ±1% F.S. accuracy without needing an external pressure regulator in many installations. The metal-seal M-Type variant is the one you want for ultra-clean or corrosive service (C₂F₆, SF₆, SiF₄, and similar process gases); the R-Type with fluorocarbon seals is for less aggressive gases.Engineers keep this series in spares inventory because the analog 0–5 VDC interface is dead-simple to integrate with legacy PLC analog cards, and the piezo valve does not suffer the coil burnout failures you see on solenoid-based MFCs. One caution: the SEC-4400MF sub-type is specifically rated for corrosive gases and uses all-metal wetted paths — do not substitute a standard R-Type unit on a corrosive gas line. I have seen Viton seals swell and leak within weeks on C₄F₈ service. Also, verify the gas calibration factor. An N₂-calibrated unit will read wrong on Ar or He unless the controller or host system applies the correct conversion.
Quality SOP & Tech Pitfalls
The Lab Report (SOP)Pre-shipment verification should include:
- Visual inspection — check for body damage, fitting thread condition, and nameplate legibility (gas type, flow range, serial number).
- Leak test — helium leak check on all wetted fittings; M-Type must meet ≤5 × 10⁻¹⁰ Pa·m³/s He.
- Live flow test — run on a calibrated flow bench with the correct gas (or N₂ with proper conversion factor), verify 0–5 VDC output tracks setpoint across 10%, 50%, and 100% F.S.
- Piezo valve exercise — cycle valve open/close 20–50 times; confirm no sticking or hysteresis.
- Zero verification — confirm zero output at no-flow condition; perform auto-zero if the sub-type supports it.
- Insulation and supply check — verify ±15 VDC draw is within spec (60 mA) using a Fluke 115 or equivalent.
- ESD-safe packaging — seal with desiccant and tamper-evident label.
Do not skip the gas-specific calibration check. An MFC that passes on N₂ can be 15% off on Argon if the conversion factor is wrong.The Engineer’s Warning (Pitfalls)Two mistakes cause repeat failures:
- Wrong sub-type for the gas. Installing an R-Type (Viton seals) on a fluorinated process gas will destroy the seals. The SEC-4400MF exists for a reason — use it for corrosive service. I once traced a chamber contamination issue back to a swapped MFC with swollen elastomer seals; the gas panel looked fine until we pulled the unit.
- Ignoring differential pressure requirements. The SEC-4400 needs 14–42 psi differential pressure to control properly. Running it at 5 psi delta-P gives you sluggish response and poor accuracy. If your supply pressure has dropped due to a failing regulator, no amount of zeroing will fix it.
Installation & Configuration Guide
Phase 1 — Pre-Installation ️
- Isolate the gas line and purge per site safety procedure. Many SEC-4400 installations handle toxic or pyrophoric gases — do not skip the purge.
- Photograph the nameplate — gas type, flow range, serial number, and fitting orientation matter.
- Verify the replacement unit matches the original gas calibration and flow range.
- Confirm power supply: ±15 VDC ±5%, 60 mA. A single-ended +15 V supply will not work.
Phase 2 — Removal
- Close upstream and downstream isolation valves.
- Vent the line safely through the appropriate scrubber or exhaust.
- Disconnect the electrical connector (pinout varies by STEC connector type — verify before cutting wires).
- Unbolt VCR fittings using proper backup wrenches. Cap all open fittings immediately.
Phase 3 — Installation
- Verify flow direction — the arrow on the MFC body must match process flow. Installing backward destroys the sensor.
- Install new VCR gaskets (nickel for M-Type metal seal). Never reuse VCR gaskets.
- Torque fittings to manufacturer specification. Over-torque deforms the sealing surface.
- Reconnect electrical wiring per the pinout diagram. Typical STEC analog pinout: +15 V, –15 V, SET (+), SET (–), OUT (+), OUT (–), GND/FG. Confirm with the nameplate or STEC manual.
Phase 4 — Power-On & Testing
- Pressurize the line slowly. Check for leaks with a helium sniffer or approved leak-check method.
- Apply ±15 VDC. Verify the output reads near 0 V at zero setpoint.
- Perform a zero adjustment if the sub-type supports it (refer to STEC procedure; some units require a specific zero-check sequence).
- Step the setpoint through 10%, 50%, and 100% F.S. and verify the output voltage and actual flow.
- Document the as-found and as-left readings.
Compatible Replacement Models
| Model | Compatibility Tier | Notes |
|---|---|---|
| SEC-4400 (matching gas/range/suffix) | Drop-in Replacement | Same body, same analog interface, same fittings. Verify gas calibration and NC/NO valve state. |
| SEC-4400MF (corrosive-gas variant) | Drop-in Replacement | All-metal wetted path for corrosive gases. Do not substitute with R-Type on corrosive service. |
| SEC-4500 / SEC-4550 / SEC-4600 | ️ Software Compatible | Same analog interface and accuracy, but higher flow ranges (10–100 SLM). Requires piping resize and requalification. |
| SEC-N100 / SEC-Z700S (digital) | Hardware Mod Required | Digital communication (RS-485, DeviceNet, EtherCAT). Requires new cabling, host configuration, and full requalification. |
Frequently Asked Questions (FAQ)
Can I replace an SEC-4400MC with a standard SEC-4400?
Yes, if the gas type, flow range, valve state (NC/NO), and fittings match. The “MC” suffix typically denotes a specific configuration or customer spec — verify the full part number against your nameplate before swapping.What happens if I use an R-Type MFC on a corrosive gas?
The fluorocarbon (Viton/FKM) seals will degrade. You will get leaks, particle generation, and potential process contamination. Use the M-Type or SEC-4400MF for corrosive gases.Does the SEC-4400 need an external pressure regulator?
Not always. The piezo valve compensates for moderate upstream pressure changes, but you still need to stay within the 14–42 psi differential pressure range. If your supply pressure varies outside that window, add a regulator.Can I use a +24 VDC supply instead of ±15 VDC?
No. The SEC-4400 requires a true ±15 VDC supply. A single-ended 24 V supply will not power the analog circuitry correctly and may damage the unit.How do I verify the MFC is working without removing it from the line?
HORIBA STEC offers the MFT-20 Mass Flow Checker, which drives the MFC in-place and monitors input/output voltages without breaking the piping. It is the safest way to diagnose a suspect unit before pulling it.Is the SEC-4400 still in production?
The SEC-4400 family is considered legacy. HORIBA STEC’s current analog MFC lines include the SEC-E and SEC-400 series. Replacement units on the market are typically surplus or refurbished. For new installations, consider migrating to a current STEC model with documented support.What is the difference between SEC-4400 and SEC-4400MF?
The MF variant is designed for corrosive gases with an all-metal (SUS-316L) wetted path and metal seals. The standard SEC-4400 R-Type uses fluorocarbon seals and is not suitable for aggressive process gases.
