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 requiredo not just need "clean"power"; powerthey toneed operateClean withinPower.

tolerance. Electrical noise, voltage

Voltage sags, harmonic distortion, and ground loops are invisiblethe driverssilent ofkillers behind "No Trouble Found" (NTF) test failuresfailures. andIf erratica machinefunctional behavior.tester Thisfails sectiona definesboard 3 times but passes it on the electrical4th architecturetry, requireddo tonot isolateblame sensitivethe logicboard—blame fromthe heavyground inductive loads.reference.

The Single Point Ground (Star Topology) 

ToGround preventloops groundoccur loops—wherewhen current flows between two equipment grounds due to voltage potential differences—differences. This creates noise that mimics logic signals. To eliminate this, the facility must utilizestrictly adhere to a SingleStar PointTopology.

Ground

The Architecture: architecture.

• Requirement:Central Earth Bar: AllEvery SMT linesline and Test RacksRack must referencerun a dedicated ground cable back to a central copper earth ground bar. Daisy-chaining grounds between machines is prohibited.
• Impedance: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 earthEarth groundGround must be < 1.0 Ohm.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

SuddenA UPS is not just for computers. In a thermal process, a power losscut causesis catastrophicnot failuresan ininconvenience; thermalit processingis equipment.a Destructive Event.

Critical Load: The Reflow Oven

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

• ReflowThe Ovens:Failure Mode: MustIf havepower sufficientdies, UPSthe capacityfans tostop keepand the conveyor belthalts. movingThe forheat 15-20has minutes.nowhere to go.
  • Failure Mode:Result: If the belt stops while the oven is hot, FR4 substratesboards inside the tunnel will carbonize (burn),catch andfire). theHeater oven heater elements maycoils warp due to lackthermal of airflow.soak-back.
• PCThe Control:Engineering Requirement: Pick-and-placeThe PCsUPS does not need to run the heaters (too much load). It must havedrive the Conveyor Belt and Control PC for a minimum of 20 minutes.
  • Action: Configure the UPS to allow"Cool forDown aMode"—keep gracefulthe softwarebelt shutdown,moving preventinguntil corruptionthe 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 placement"Graceful programsShutdown" time to save machine state and databases.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

UtilityControl Point	Requirement	CriticalityCritical State
EquipmentGround GroundTopology	Star Topology(Single (< 1 Ohm)Point)	No Daisy Chains
Impedance	HighResistance (Preventsto TestEarth	< Noise)1.0 Ω
Reflow BackupUPS	UPS for Conveyor Drive+ Fans only	CriticalActive (PreventsRun Fire/Damage)
Voltage> Stability20 mins)	± 5% of Nominal	Medium (Machine Uptime)
Harmonics	THD < 5%Monitoring	< 5%
Outlet Testing	MediumPolarity/Ground (MotorCheck	Annual longevity)Scan