Issue link: https://iconnect007.uberflip.com/i/1449048
54 DESIGN007 MAGAZINE I FEBRUARY 2022 functions, enabling faster identification of the defects whether component level or defects related to the assembly process (Figure 2). Additionally, the test engineer may request that the circuit board designer provide a means of disabling on-board clock functions. e pur- pose of furnishing this disabling capability is to expedite testing and improve test efficiency. In-Circuit Testing (ICT) To certify absolute assembly quality the industry commonly implements a more sophisticated electrical testing solution. e fixtures developed for in-circuit testing employ dedicated spring probe fixtures that interface with test systems pre-programmed to measure every net within the circuit board. Preparing for assembly level testing on the board, the panel must first be furnished with tooling holes. A mini- mum of two non-plated tooling holes are needed to maintain a fixed position of the board under test. Tooling hole requirements: • At least two non-plated tooling holes must be furnished on the PCB • Ideally, the tooling holes are located at diagonal corners of the board • Position components and test probe lands away from tooling holes Programming for ICT is designed to mea- sure overall functionality, identify any compo- nent termination locations needing attention, confirm that the values specified for all passive devices are correct, and that semiconductors are functioning properly. In-Circuit Net Access To enable the in-circuit test system to func- tion without compromise, 100% test probe access must be provided for every "net," the common interface between all component terminals. Anything less than the 100% net access will compromise test coverage. e example furnished in Figure 3 represents a high-density SMT assembly requiring two- side test probe access. Figure 2: Circuit partitioned for focused functional access. Figure 3: In-circuit test fixture with two-sided probe access.