UltraCAD Design, Inc

Articles on
Trace Current/Temperature/Power/Resistance



Note: There is a bug in some versions of Adobe Acrobat that sometimes prevents a pdf file from opening. If you have this problem, right-click the link and select "Save Target As...". Then save the file on you local hard drive and open it there.
How Many Volts IS This: The RMS Role  
  Confused about what RMS  voltage means? You're not the only one, as you'll find out when you read this article, from the July 2001, issue.
Trace Currents and Temperatures, Revisited   
  (Minor revision, July, 2015) This paper is the result of a collaboration between our Doug Brooks and Dr. Johannes Adam of ADAM Research (Germany). Dr. Adam has written a sophisticated thermal modeling program that can simulate the thermal performance of traces. They used this program to validate the IPC 2152 trace data. They then formulated a set of equations that very closely fit the IPC curves. Finally, they used the simulations to discover how sensitive the trace/current relationships are to other variables, such as adjacent traces and planes, and material choices. Their extensive research results are reported in this paper. These results have also been incorporated in the new upgrade to UltraCAD's PCB Trace Calculator.
Fusing Currents in Traces  
  (Moderately revised, July, 2015) After Brooks and Adam collaborated on the trace/temperature relationships, they used Dr. Adam's simulation tool to evaluate the fusing current question. First, they used the tool to validate Onderdonk's equation. Then the look at a variety of "real world" trace configurations to see what changes occurred. The results are reported in this paper. The results are also incorporated in the "Fusing" section in UltraCAD's newly upgraded PCB Trace Calculator.
In Search of Preece and Onderdonk
  W. H. Preece and I. M. Onderdonk are credited with first looking at the fusing current of copper conductors question. Preece's work was reported in the Royal Society of London Proceedings back in the 1880's, but until recently copies of his work have been very hard to obtain. We are not aware of any original work published by Onderdonk. This paper provides a little insight about who these people were and what motivated them. We then offer a derivation of Onderdonk's Equation.
Via Currents and Temperatures  
  When we started looking at the relationship between via currents and temperatures we were truly surprised. The conventional wisdom is that the via conducting cross-sectional area must be the same as the trace conducting cross-sectional area. If the via area is smaller, then the typical advice is to use multiple vias. It turns out that the current isn't the controlling factor. The thermal coupling between the trace and the via is so good, it is the trace temperature that controls the via temperature! Read all about it here.
Current Densities in Vias  
  When we were looking at the thermal effects surrounding vias, we noticed a very interesting phenomenon related to the current densities around and through vias. The current density is not as uniform as we might imagine. This paper looks at the current densities as current flows through a single via, multiple vias when the trace continues in a straight line, and multiple vias when the trace turns at an angle. While we find the results (and the pictures) really interesting, we struggle a little to see if there is really any practical implications to what we saw!
Gauging Traces.    
  What is the relationship between AWG wire gauge and trace size? This article, from the January, 2001 issue, explains the relationship and provides a formula for conversion. See also our new companion calculator for making these calculations easier. (Note: This article was revised 7/01 to correct an error in one of the formulas.)
Current Carrying Capacity of Vias; Some Conceptual Observations (Withdrawn)
Skin Effect
            The skin effect is the tendency of high frequency current density to be highest at the surface of
            a  conductor and then to decay exponentially toward the center. Its effect is to reduce the effective
            cross sectional area of a trace, which in turn increases its resistance and reduces its current carrying

   Click on logo to return to UltraCAD's Home Page.