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28 The PCB Design Magazine • November 2017 by Craig Armenti MENTOR High-density interconnect (HDI) technol- ogy is often used to meet the requirements of today's complex designs. Smaller component pitches, larger ASICs and FPGAs with more I/O, and higher frequencies with shrinking rise- times all require smaller PCB features, driving the need for HDI. Beyond some of the more obvious electrical effects of the microvias used on HDI designs, there is also an impact to the power integrity the PCB. This includes different effects of mounted inductances of decoupling capacitors, changes in plane performance due to reduction in perforation from chip pinouts, and the inherent plane-capacitance changes from using dielectrics of various thicknesses. HDI Primer HDI can be a confusing topic, especially for new engineers and designers, or those not well versed in the subject matter. Although this ar- ticle is not intended to be an in-depth tutorial on HDI technology, a quick review of the key aspects is appropriate. HDI is a technology that, through a combi- nation of high density attributes, allows for a higher wiring density per unit area as compared to traditional PCB technology. In general, HDI PCBs contain one or more of the following: reduced trace width and spacing, microvias including blind and buried, and sequential lamination. Current generation HDI designs are typical- ly found in mobile phones, digital cameras, lap- tops and wearables to name just a few. Basically, whenever a product needs to be compact and/ or lightweight, then HDI technology will most likely be applied. The benefits of HDI technol- ogy include: • Reduced space requirement using smaller vias, reduced trace width and reduced trace spacing, all of which allow components to be placed in closer proximity • Reduced layer count as a result of increased routing channels on internal layers • Improved signal integrity due to shorter distance connections and lower power requirements • Improved power integrity due to ground planes closer to the surface parts and improved distribution of capacitance • Potential to lower fabrication and assembly costs by consolidating multiple PCBs into a single PCB FEATURE

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