Issue link: https://iconnect007.uberflip.com/i/1507822
96 PCB007 MAGAZINE I SEPTEMBER 2023 solder mask, oxides, or etching residue in and around PCB holes, which act to insulate/ short test probes from the holes. At SPCF, soware in the host computer allows ET operators to halt the test system when an open is detected, though electrical stimulus is still applied to the test points in question. By briefly reactivating the fixture in the test system, while observing status indicators, electrical contact to the PCB can usually be achieved. A key on the operator's terminal instructs the host computer to discard the error, and the test con- tinues. rough detecting and discarding phan- tom errors during the test process, time is saved in troubleshooting and retesting. An estimated average of 15% of all errors reported in finished boards are phantom errors. Testing in Panel Form Testing in panel form refers to testing PCBs before they are routed out of the panel that con- tains them. A number of pro- ductivity advantages are real- ized in this way. Phantom errors are nearly alleviated because the boards have not yet been through a solder mask opera- tion. Test throughput can be greatly increased by using mul- tiple image fixtures oriented to the stepped and repeated PCB images in the panel. A number of boards are then tested at the same time as a single board. It is much easier to troubleshoot and repair boards before solder mask and graphics are applied. If a board cannot be repaired (i.e., due to inner layer shorts), it is scrapped before additional downstream costs are invested in it. e geographical location of defects in a panel gives impor- tant clues to upstream causes. Test systems capable of logging and corre- lating detected errors are just now becoming available. Systematic errors most oen point to artwork or design problems (i.e., close traces, narrowing line widths, scratches, dust, etc.). ey also indicate tooling problems such as misregistration and drill skew. e nature of random errors indicates process prob- lems such as whiskers and voids, but the assumption of random errors should be proven by statistical testing 1 . Phantom Errors A phantom error is an electrical open/ short which is reported by a test system but does not exist in the PCB being tested. Phantom errors are caused by the presence of Figure 5: Sample report including part information, lot information, current and historical defects, and specific defect analysis.