2.2 Power Quality & Grounding

Electricity is the fuel of the factory, but "dirty" fuel destroys the engine. Modern SMT equipment and high-precision test instrumentation do not just need "power"; they need Clean Power.

Voltage sags, harmonic distortion, and ground loops are the silent killers behind "No Trouble Found" (NTF) test failures. If a functional tester fails a board 3 times but passes it on the 4th try, do not blame the board—blame the ground reference.

The Single Point Ground (Star Topology)

Ground loops occur when current flows between two equipment grounds due to voltage potential differences. This creates noise that mimics logic signals. To eliminate this, the facility must strictly adhere to a Star Topology.

The Architecture:

• Central Earth Bar: Every SMT line and Test Rack must run a dedicated ground cable back to a central copper earth bar.
• Prohibited: Daisy-chaining grounds (connecting Machine A to Machine B, then Machine B to Wall) is an engineering violation. This creates an antenna for noise.
• Impedance Standard: Resistance to Earth Ground must be < 1.0 Ω.

Pro-Tip: Use insulated ground cables (green/yellow) for the run to the central bar. Bare copper touching the building steel frame creates unintentional "ground loops" and defeats the Star Topology.

Uninterruptible Power Supply (UPS) Strategy

A UPS is not just for computers. In a thermal process, a power cut is not an inconvenience; it is a Destructive Event.

Critical Load: The Reflow Oven

The Reflow Oven is the highest-risk asset during a blackout.

• The Failure Mode: If power dies, the fans stop and the conveyor halts. The heat has nowhere to go.
  • Result: FR4 boards inside the tunnel carbonize (catch fire). Heater coils warp due to thermal soak-back.
• The Engineering Requirement: The UPS does not need to run the heaters (too much load). It must drive the Conveyor Belt and Control PC for a minimum of 20 minutes.
  • Action: Configure the UPS to "Cool Down Mode"—keep the belt moving until the tunnel temperature drops below 100°C.

Secondary Load: SMT Logic

• Pick-and-Place: Sudden power loss corrupts placement databases and calibration files.
• Strategy: UPS provides 5 minutes of "Graceful Shutdown" time to save machine state and park the gantry.

Power Quality Standards

Do not assume the grid is stable. Monitor the "Quality of Supply" at the main breaker.

• Voltage Stability: ± 5% of Nominal (e.g., 230V ± 11.5V).
• Harmonics (THD): Total Harmonic Distortion must be < 5%. High harmonics cause motors (in chillers and compressors) to overheat and fail prematurely.

Final Checklist