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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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Douglas G. Brooks, PhD
When I first got involved in printed circuit board design in the early 1990s, fast rise/fall times were just starting to become an issue. Prior to that we had been pretty much a “connect-the-dots” kind of technology. But as rise times got faster, it became necessary to worry about (electromagnetic) fields. One manifestation of that was EMI, and the increasing need to pass FTC compliance testing.
Douglas Brooks, Consultant, and Johannes Adam, ADAM Research
Most of are aware that when we pass an electrical current through a trace (conductor), the trace will heat up. This temperature increase is caused by the I2R power loss dissipated in the resistance of the trace. The resistance of a copper trace is mostly determined by its geometry (cross-sectional area), and there are lots of studies trying to look at the relationship between the current down a trace (of known size) and the resulting temperature of the trace. But the situation is much more complicated than this. There are physical properties that exist that result in helping to cool the trace. These properties are usually a combination of conduction of the heat away from the trace through the material, convection of the heat away from the trace through the air, and radiation of the heat away from the trace.
Andy Shaughnessy, Design007 Magazine
For this issue on ultra HDI, we reached out to Tara Dunn at Averatek with some specific questions about how she defines UDHI, more about the company’s patented semi-additive process, and what really sets ultra HDI apart from everything else. Do designers want to learn a new technology? What about fabricators? We hope this interview answers some of those questions that you may be having about these capabilities and what it could mean for your designs.