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72 PCB007 MAGAZINE I JULY 2019 Feature by Todd Kolmodin GARDIEN SERVICES USA Some people think of the PCB manufactur- ing process as a black box: design data goes to the manufacturer (fabrication house), and magically, the finished PCB is produced. While it may have been like that in the past—such as manufacturing in the '80s, which now looks archaic and sometimes unbelievable—in actu- ality, fabricating PCBs today is quite a ballet of processes. All of the complex steps must be taken in place and in sync to deliver a success- ful product. The challenge is to identify and feed back as-built testing information to help optimize the design data over time. Today, as in years past, the OEM design is sent to the manufacturer for processing. There, the design data is massaged to produce the re- quired PCB within the fabrication modes and methods of the manufacturer while still pro- ducing the required end product. Now, howev- er, this same design data is also used in other processes throughout the manufacturing pro- cess in addition to creating the photo-imaging data and CNC drill/route programs. This same design data drives other quality control processes too. There are tools and soft- ware programs in the verification processes that utilize this same customer supplied data to drive the quality control feedback loop. The design data is used to verify inner layer and outer layer circuits, such as in the AOI and AVI processes (automated optical and visual In- spection). The design data also drives electri- cal test (ET) processes. Now, in the PCB manufacturing arena, the ET game has changed considerably. To close the quality feedback loop, even more checks must be included with the board design's tool- ing. And the new ET results data requires new presentation methods for an efficient response from the inspectors. Getting Here From There Back in the '80s, most ET was done by means of "self-learning" a board and then comparing it to the rest of the lot; there was no such thing as netlist test. The risk was extreme with this method because the testing standard relied on a "known good board" to use as the master. If there was no gold-standard board to use, then How to Feed Test Data Back to Engineering for Process Improvement

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