Issue link: https://iconnect007.uberflip.com/i/1350598
MARCH 2021 I PCB007 MAGAZINE 57 nario if the fixture test causes damage, it would be caught at the inspection interval. If we had 15 boards, we could catch it aer board 5, or board 10. Although it could result in a loss of product it would be limited due to the inspec- tion interval. It may be your local process to in- spect all boards in that size of order and this is fine. e question really is based on large or- ders. We should still inspect the first and last board but if we wait until the middle of a large order, we could lose a significant amount of product, especially if the order is 100 piec- es or larger. Here is where QMS discretion is advised. e matrix could break down the or- der by percentage and create an interval for in- spection or it could simply state that on orders of X pieces or larger, every X board needs to be inspected. is allows containment quick- ly should a fatal error occur during test. It must also be noted that there should be a referee inspection done during these inspection in- tervals. is is simply referred to as a "buddy check." It is proven that the second set of eyes may capture a witness mark defect that is over- looked by the primary inspector. Repeatedly inspecting small pads and lines can be monoto- nous and pattern recognition fatigue can cause the visual senses to tire. So now we have a setup process and a good understanding of the inspection process, and how, where and when to do it. Again, this all is part of the continuous improvement and quality assurance discipline. We need to own our processes and live them as well. Having integral steps in a process where it requires more than one person during a KPI check or inspection is always beneficial. is is by no means a knock to the primary operator but as humans, we can get tired, fall into repetition, and with that comes an increased margin for error. As newer technologies emerge the ultimate solution would be to add AVI (automated vi- sual inspection) to the final FA process. Even though we are inspecting the boards at regular intervals there remains a margin for error. Us- ing a process where the test is performed and then an AVI is used to scan the surface of the board and sort by "pass" and "fail' would cap- ture any and all surface defects. Line = ET Tester + AVI Inspection + Auto sort pass/fail. Another item to mention is where the mark may be placed. Many specifications call out the probing area "allowed." Many times, mechani- cal drawings may state a "pristine area" of the pad. is cannot have any marks whatsoever. It can be difficult many times, but when it's un- avoidable, the absolute lightest contact must be made. In Figure 3, we show very light con- tact in a high-density BGA. Figure 3: Very light contact in a high-density BGA.