Iso Die Package Selection for Compact Surface Mount Assembly
Matching package creepage distance to board pollution degree prevents arc flash failure while maintaining high density surface mount assembly yields.
Isolation Split
Physical Clearance
Printed circuit board layout requires distinct physical separation between different voltage domains to prevent electrical cross-conduction. An isolation split represents the intentional void or gap in copper planes and traces that divides high-power circuits from low-power control sections. This gap must extend through all copper layers of the board.
It establishes electrical safety and ensures that voltage spikes do not cross the boundary.
Routing Rule
Routing signals across the boundary is forbidden unless they pass through an optocoupler, digital isolator, or transformer. Crossing the isolation split with a copper trace creates a path for high voltage to propagate directly into low-voltage circuits. This layout error defeats the safety barrier entirely.
Board designers must bypass the gap only with components rated for the working voltage.
Creepage Boundary
Creepage and clearance regulations specify the minimum dimensions of the gap based on the working voltage and pollution degree of the operational environment. High-voltage power supplies require wider splits than low-power systems. In cases where the standard surface distance is insufficient, a physical slot is routed through the fiberglass substrate.
This slot increases the effective creepage path by forcing any surface currents to travel through the air.
Verification Check
Automated design rule checks verify the integrity of the board layout by scanning for copper violations across the split. Any stray trace or copper fill that approaches the gap closer than the specified limit triggers a violation. Hardware testers audit the fabricated board by measuring the isolation resistance across the split using a megohmmeter.
This test confirms that no residual copper remains from the etching process to bridge the gap, which is necessary before assembling active components that could be destroyed by a short circuit.