# Stop Relating Trace Temperature to Current Density

Many design engineers and even many software suppliers make the significant mistake of equating changes in trace or via temperature with current density. This is incorrect at best and dangerous at worst. There is little if any correlation between temperature and current density. Current and trace dimensions (among other things) are the relevant variables, but current density is not. I hope by the end of this article you will see why. Here are four illustrations that will help you understand this.

1. Current Density Is Not an Independent Measure

We can understand that the change in trace (and via) temperatures are a function of other variables. Thus, we can formulate the following as two possible relationships (all other things equal). Let:

C = current
J = current density
w = trace width
th = trace thickness
ΔT = change in trace temperature

Then, we can suggest the following:
Equation 1: ΔT = fn(C, w, th)
Equation 2: ΔT = fn(J, w, th)

Now, the question is, “Are both of these relationships true, or, if not, is either one true?” We know from the extensive experimental evaluations reported in IPC-2152 that Equation 1 is true, so is Equation 2 also true? From Equations 1 and 2, it follows that:

Equation 1a: C = fn(ΔT, w, th)
Equation 2a: J = fn(ΔT, w, th)

To read this entire article, which appeared in the September 2020 issue of Design007 Magazine, click here.

## What Happens When You Assume?

07/05/2022 | I-Connect007 Editorial Team
What is design with manufacturing and what does true DWM look like in operation? In this interview, I-Connect007 columnist Dana Korf explains what it will take to achieve total communication among all the stakeholders in the PCB development cycle. He also stresses the need for everyone involved in PCB design and manufacturing to stop making assumptions, even at the risk of being labeled as “that guy” who asks too many questions.

## Book Excerpt: 'The Printed Circuit Designer’s Guide to… High Performance Materials,' Chapter 2

06/03/2022 | I-Connect007 Editorial Team
Chapter 2 of 'The Printed Circuit Designer’s Guide to… High Performance Materials' explores the varieties of woven glass fabrics and their components, and why spread glass is in such high demand for high-speed digital PCB designs. Download this book for a clearer picture of what to know when selecting which material that is most desirable for upcoming products, and obtain a solid knowledge base for making material selection decisions.

## Altium Invests in Future Designers

04/13/2022 | Andy Shaughnessy, Design007 Magazine
While at IPC APEX EXPO, I stopped by the Altium booth to visit with Rea Callender, vice president of education at Altium. Rea shared information about the company’s recent design competition for students around the world, as well as a new curriculum that is drawing interest from some unique locations.