7.2 Power Quality & Grounding

Modern SMT equipment and test instrumentation require "clean" power to operate within tolerance. Electrical noise, voltage sags, and ground loops are invisible drivers of "No Trouble Found" (NTF) test failures and erratic machine behavior. This section defines the electrical architecture required to isolate sensitive logic from heavy inductive loads.

7.2.1 The Single Point Ground (Star Topology) 

To prevent ground loops—where current flows between two equipment grounds due to potential differences—the facility must utilize a Single Point Ground architecture.

• Requirement: All SMT lines and Test Racks must reference a central earth ground bar. Daisy-chaining grounds between machines is prohibited.
• Impedance: Resistance to earth ground must be < 1.0 Ohm.

7.2.2 Uninterruptible Power Supply (UPS) Strategy

Sudden power loss causes catastrophic failures in thermal processing equipment.

• Reflow Ovens: Must have sufficient UPS capacity to keep the conveyor belt moving for 15-20 minutes.
  • Failure Mode: If the belt stops while the oven is hot, FR4 substrates inside the tunnel will carbonize (burn), and the oven heater elements may warp due to lack of airflow.
• PC Control: Pick-and-place PCs must have UPS to allow for a graceful software shutdown, preventing corruption of placement programs and databases.

Final Checklist