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80 SMT Magazine • November 2017 HDI CONSIDERATIONS: INTERVIEW WITH ACDI'S GARRET MAXSON Maxson: Anytime you had a component that you are going to be designing the layout for, you consult the SMT engineers, with respect to the footprint. We consult regularly with our in- house SMT engineers. A kind of a perk of hav- ing inhouse manufacturing is we can bounce ideas off them. And you will see most of the package types before, so they will have recom- mendations as to how we can adjust the art- work at the layout level, so it helps us facilitate a smoother assembly process, or help improve their yield. A strong line of communication at the upfront design level between our design group and our SMT engineers help ensure a reli- able design making it out to the manufacturing floor, and improved product yield. Las Marias: One of the problems with assem- blies on HDI boards is the limited access to in- circuit tests. How do you address that? Maxson: We see less and less request for ICT test with the emergence of flying probe tech- nology. We have an in-house flying probe tes- ter that we use, that the requirements for lay- ing out the board for a DFT standpoint is dras- tically reduced. You go from needing a 25-mil round target pads for ICT fixtures down to 4-mil round pads for the flying probe. From a DFT standpoint, obviously the flying probe works great for your prototype runs, but you still need to get that production type run where ICT still has the niche. And as far as designing an HDI board for that, you are going to run into space constraints. There's not as much space on the board, so you may have not as much nodal coverage as you would typically do on an ICT fixture. You must have a certain amount of space between the probe and, if your whole exercise is making the boards smaller and more com- pact, obviously you are going to have to sacri- fice somewhere. And that sacrifice is usually the smaller nodal coverage percentage. Las Marias: Is there anything that we haven't talked about that you think we should be talk- ing about? Maxson: I think from a layout perspective, it re- ally comes down to whether someone is run- ning out of routing room or running out of placing room; that kind of dictates which inter- connects we use, whether it's blind, buried, or microvias. With pitches of the ICs, when you get down to below a 0.65 mm pitch part, you tend to have to get creative with your HDI. Las Marias: Great, thank you very much Gar- rett. Maxson: Thank you. SMT I-Connect007 is excited to announce the release of the first book in our new micro eBook assembly series: The Printed Circuit Assembler's Guide to… Conformal Coatings for Harsh Envi- ronments. Authored by Phil Kinner of Electrolube, this free mi- cro eBook addresses a myriad of conformal coating materials and process considerations for achieving reliable performance in harsh environments. To download the book, click here. I-Connect007 Launches The Printed Circuit Assembler's Guide to...Conformal Coatings for Harsh Environments Micro eBook