In Circuit Test Fixture Coverage and Unprobed Assembly Netlist Limits
Unprobed netlists drop structural fault coverage, requiring integrated boundary scan vectors and adjusted warranty reserves to cover escape risks.
Parallel Path Leakage
Measurement Distortion
In-circuit measurement of board-level components can be distorted by an electrical measurement error that occurs when current bypasses the target component through alternative routing on the circuit board. This circuit phenomenon, known as parallel path leakage, yields inaccurate resistance or capacitance readings because the tester cannot distinguish between current flowing through the device under test and current flowing through surrounding connected networks. Whenever a circuit designer places parallel resistors or feedback loops on a board, the test engineer must account for these parallel paths during test program development.
Neglecting this phenomenon leads to false failures and unnecessary board reworks.
Path Identification
Analyzing the schematic is the first step in identifying these alternative loops. Tester software scans the CAD netlist to find all closed loops containing the target node, but some paths are highly complex and hard to trace manually. High-density designs with multiple pull-up and pull-down resistors often exhibit parallel path leakage at almost every test node.
This issue is resolved during the test step by calculating the net impedance or by using physical guarding pins to block the extra current paths.
Guarding Resolution
When guarding is unavailable, the tester must rely on alternative test frequencies or dual-measurement algorithms to isolate the component. These methods add to the test cycle time.