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SMT-Nov2017

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76 SMT Magazine • November 2017 by Stephen Las Marias I-CONNECT007 American Computer Development Inc. (ACDi) started approximately 30 years ago as a PCB design and layout service bureau. Today, the company does about 350 to 400 unique PCB layouts per year for a variety of customers across different industries, including medical and in- dustrial fields. Around 15 years ago, ACDi acquired a lo- cal manufacturing plant, enabling it to ramp up into design, layout, and prototype assembly. Five years ago, the company purchased another facility in North Carolina for production-type runs. Garret Maxson is the manager of engineer- ing services at ACDi. He currently oversees 11 direct reports, and most of them are PCB layout designers, AutoCAD drafters, and component librarians. In this interview Maxson discuss- es the PCB assembly challenges when dealing with high-density interconnect (HDI) boards, parameters to consider, and strategies to help facilitate a smooth assembly process when using HDI boards. Stephen Las Marias: What are the challenges in PCB assembly when it comes to dealing with HDI boards? Garret Maxson: As the boards get denser and denser, obviously we get into high-density in- terconnect boards. There are a variety of via structures due to the pitches of the parts, and how small the IC manufacturers are making them. What that often leads to is new via tech- nologies, whether they're buried vias or blind vias, or microvias—a lot of companies will start putting them in the pad, which can lead to is- sues if the assembly is not done properly. When you put a via in a pad that is going to get sol- dered, you typically want to fill that via, with either a non-conductive or conductive epoxy, and use some sort of plating over the barrel of the via so that you get a smooth pad that you are assembling the part to without a whole lot of surface deviation. The flatter the pad, the eas- ier it is to print solder on the board, and to as- semble the part. As it pertains to assembly, the via-in-pad is one of the larger concerns of the HDI. Other than that, you are mostly concerned with the FEATURE INTERVIEW

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