Design for testability of printed circuit board assemblies

It is widely recognised that decisions taken at the early design stages holds the key to product profitability. Providing the designer with information on product manufacturability and testability can avoid costly design changes and reduce manufacturing costs. It is estimated that test activities account for a third of total manufacturing costs of printed circuit board assemblies (PCBAs). In-circuit test is the method most commonly used to locate faults on PCBAs; this test method has become very difficult to apply with the use of very small, fine pitch surface mount components. At the University of Salford, EPSRC sponsored research aims to integrate physical testability considerations into the design environment at the PCB layout stage. A prototype, demonstrating this integration, is known as DICTA-Design for In-circuit Test Advisory system. DICTA analyses a PCBA layout description to identify potential test problems. The results of the analysis are presented in a graphic way and linked to screens explaining the implications of the guidelines violated. The DICTA system also produces an outline design for a suitable in-circuit test fixture. In this way, the PCB designer is supported in determining a layout which is easier to test and in reducing fixturing costs and lead times. The DICTA prototype demonstrates the benefits of linking a critiquing system to a graphic rule explanation and reporting facility to increase the designer´s awareness of downsteam issues. Further work involves including PCB manufacture and assembly guidelines within the design environment