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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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Andy Shaughnessy, PCBDesign007
I had the opportunity to talk with our contributor Doug Brooks recently. He has been doing some research on temperature effects on PCB traces over the last few years, and I wanted to check the status of his latest thermal efforts. He discussed his work with Dr. Johannes Adam, why temperature charts based on a trace in isolation are inaccurate, and how the industry remained so wrong about PCB temperatures for so long.
Craig Armenti, Mentor
A key aspect of HDI technology is the use of microvias. For reference, the IPC HDI Design Committee has identified microvias as any hole equal to or less than 150 microns. Multiple types of HDI stack-ups associated with blind and buried microvias can be used to meet the density and cost requirements for today’s products. Design teams should develop stack-ups in conjunction with the fabricator to minimize cost and meet signal integrity requirements.
Douglas G. Brooks, PhD
Two years ago I entered into a collaboration with Dr. Johannes Adam, from Leimen Germany. Johannes has written a software simulation tool called Thermal Risk Management (TRM). We used it to look at the thermal characteristics of PCB traces under a variety of conditions, and it is hard for me to contain my excitement and enthusiasm for what it does and what we learned about traces using it. Our collaboration resulted in the publication of numerous articles and a book. In this article, I’ll talk about some of the capabilities of TRM that really caught my attention.