Issue link: https://iconnect007.uberflip.com/i/1460418
86 PCB007 MAGAZINE I MARCH 2022 argued that in the end the overall drilling time is insignificant, as you may still be using the same fixture drilling time to build the multi- pass headed pin fixture as you would to build the music wire single pass fixture. e hard- ware cost ultimately will be less as no redun- dancy testing is required with the single pass vs. the multi-pass fixture. Now, with the fixture testers themselves, there are some challenges with the legacy uni- versal grid machines. ese machines typi- cally presented a 0.100-inch grid configuration and had only one active test matrix. is only allowed single-side fixtures or wired clamshell combinations. Although still viable equipment, they present challenges when testing today's PCBs. Double-sided universal grid machines with the 0.100-inch grid configurations are also still available through various aermarket venues. ese provide less costly alternatives but still can present challenges. Most univer- sal grid testers used today are of the double- density or tighter grid configurations. ese are better suitable for music wire fixtures and allow higher success rates for maintaining sin- gle-pass test solutions. Now with that said, let's get back to the question as to whether the universal fixture is dead. We know that flying probes can provide many solutions to today's requirements. ey can even provide automated tests that histori- cally required fixtures, either universal or hard- wired. However, one very important aspect of the fixture tester vs. flying probe that will never be successfully met by the flying probe is pro- viding "simultaneous test" of the PCB. What I mean here is the ability to stimulate or interro- gate all nodes of the PCB at the same time. Fly- ing probes use an "adjacency window" where isolation or shorts testing is done node-to-node based on the adjacency of one node or network to another. Other nodes or nets outside the adjacency window are not tested for shorts to that primary node. With fixture testers this iso- lation or shorts test is provided simultaneously to all nets to one another. Further, the conti- nuity test on a flying probe, regardless of how many arms are available is only testing a finite number of nets at a time. e fixture tester will test them all at the same time. Yes, it's still just the continuity test and both machines do the same thing, but the fixture tester does this all at once, giving it a major speed advantage. e other significant item to note is that many aerospace, medical, and high reliability products have requirements that state, "Simul- taneous test required." is statement alone in a customer specification or procurement doc- ument negates the use of flying probe, period. ere is no viable argument that a flying probe can provide a simultaneous test of all nets to one another in one single pass. Only the fixture tester with its full parametric test can provide this solution. erefore, the fixture tester will live on. Whether it be a universal grid or wired dedicated, the simultaneous test will aways require a fixture tester of some flavor. Also, the fixture tester will always have the advantage in high volume applications. Although the fly- ing probe has made electrical test costs signif- icantly lower, it will never be able to compete in high volume theatres against tight deadlines. Long live the fixture. PCB007 Todd Kolmodin is VP of quality for Gardien Services USA and an expert in electrical test and reliability issues. To read past columns or contact Kolmodin, click here. The hardware cost ultimately will be less as no redundancy testing is required with the single pass vs. the multi-pass fixture.