Boundary Scan Test Coverage Calculations and Fault Diagnostics in High Density Boards
Boundary scan test coverage calculations require explicit PCOLA-SOAMI net weighting to yield verifiable structural fault isolation in HDI board assemblies.
JTAG Emulation Test
Debugging Interface
Controlling the internal state of a processor through a dedicated port allows for the verification of both hardware and low level software. A jtag emulation test uses the joint test action group standard to halt execution and inspect registers or memory during the assembly verification phase. This method is effective for testing boards where physical access to signal traces is blocked by high density packaging.
Operational Flow
The test hardware connects to the small header on the board and takes control of the system bus. Through this connection, a jtag emulation test can load small snippets of code into ram to exercise peripherals like flash memory or ethernet controllers. It allows the engineer to verify that the processor is correctly soldered and can communicate with its environment before the final firmware is loaded.
This process is useful for identifying assembly errors like cold solder joints on bga pins that are not visible to cameras. The software provides real time feedback on the health of the core and its ability to execute instructions.
Boundary Limit
This technique requires the silicon to be functional and the power rails to be stable to operate. It cannot diagnose faults in the power delivery network itself.