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In a typical interconnect, there lie multiple places where capacitance plays a factor in the signal integrity. This includes the driver and receiver output/input capacitance, as well as the packages, vias, and the transmission lines. Failing to optimize these parameters can often lead to unwanted reflections, excessive radiated and or conducted emissions, and sometimes failure of components and systems.
Reflections can occur anytime there is an impedance mismatch on the line. Sources of mismatches are plentiful and include trace width changes, vias, stubs, reference plane changes, and even the so-called fiber weave effect. In this case, a trace can encounter a different dielectric constant depending on whether it is routed over glass or the epoxy resin in the dielectric material.
In this investigation, it is the capacitive contribution of the different components that are of interest, and how they affect the characteristic impedance the driver sees.
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Tamara Jovanovic, Happiest Baby
When I was a sophomore in college, I had an amazing professor for Physics II: Electricity and Magnetism. He made a series of complex topics fun to learn, and his personality and way of teaching were almost tailor-made for the way I like to learn. He explained new concepts through practical examples, and always kept students engaged throughout the class, making sure everyone understood the lectures. Physics II was an engineering prerequisite, and I didn’t mind taking the class since I really enjoyed the material. However, I did find myself wondering a few times, “Will I ever use any physics in real life?” It turns out that the answer to the question was yes.
Cherie Litson, CID+, Litson1 Consulting
HDI—high-density interconnect—designs require some different thinking on the part of the designer. One of the first things to consider is whether you need HDI, and if so, how much. The HDI option comes into play as soon as you purchase any components with 0.5 mm pin pitch. The number of these components and other specifications of your design will determine the amount of HDI you will need. Here’s a quick list of HDI options.
I-Connect007 Editorial Team
We’ve seen many changes over the past few years, and nowhere are they more evident than in the world of sourcing components. Sourcing has become one of the biggest challenges facing PCB designers and design engineers today. Gone are the days of procuring parts from a single source, and communication between stakeholders and distributors is critical. But as we learned in a conversation with I-Connect007 columnist Kelly Dack, PCB designers can use certain layout strategies to plan for the unexpected, such as leaving extra real estate so that smaller components can be replaced by larger, readily available parts if the originals become “unobtainium.”