In-Circuit Test Vector Synthesis for High Density Assembly Modifications
Vector synthesis for modified assemblies requires delta netlist verification, BSDL timing re-validation, and algorithmic backdrive current bounds.
Unprobed Nets
Meaning
Electrical pathways within a complex assembly remain unreachable by automated probes when design constraints prevent the placement of test pads. Relying on unprobed nets forces manufacturers to use functional testing or optical inspection to verify the integrity of the hidden connections. These signals represent a gap in the automated diagnostic capability of the production line.
Probing Limitation
Internal signals remain completely isolated.
Diagnostic Limitation
Identifying the root cause of a failure becomes more difficult when the internal state of the board is not fully visible. For unprobed nets, the test system must infer the status of the connection by observing the behavior of nearby components. This indirect method increases the time required to debug a faulty assembly during the manufacturing process.
Software models of the circuit can help simulate the expected behavior to narrow down the possible locations of a defect.
Quality Assurance
Alternative inspection methods like x ray imaging are often used to check the solder joints of hidden nodes. This ensures that even the hidden parts of the board meet the required standards for mechanical and electrical reliability. Balancing the number of testable points with the size of the board is a constant challenge for layout designers.