Brooks' Bits: Internal Trace Temperatures—More Complicated Than You Think

Co-authored by Dr. Johannes Adam, founder of ADAM Research

IPC-2152, published in 2009, was the most thorough study of trace current and temperature relationships ever undertaken. It contains over 90 pages and charts that examine the relationships from numerous directions. Before IPC-2152, the industry used a set of charts that went back to a National Bureau of Standards (NBS) Report #4283 published in 1956. The charts were first published as a part of MIL-STD-1495 in 1973. They were later published in a subsequent series of standards that culminated in MIL-STD-275E in 1984. Further, the charts were published as part of IPC standard IPC-D-275, and IPC-2221A in 2003.

One of the most interesting findings in IPC-2152 was that internal traces are cooler than external ones for the same size and current. Independent experimentation was not done on internal traces in earlier charts. Internal traces were merely assumed to be hotter than external traces, and the external trace data was derated by 50% by that assumption.

Traces are heated by Joule, or I2R, heating. They are cooled by a combination of conduction through the dielectric, convection through the air, and radiation. It had previously been assumed that convection conducted heat away from the traces and cooled the traces more efficiently than conduction through the dielectric. Hence, the assumption that internal traces were hotter than their external trace counterparts. It turns out that dielectrics cool traces more efficiently than does convection plus radiation, and internal traces are relatively cooler.

One question is, “Is there a predictable relationship between the external temperature of a trace and the internal temperature of the same trace carrying the same current?” That is, is the internal trace 10% cooler, 20% cooler, or is there another predictor we can use to predict internal temperatures? The data in IPC-2152 makes it possible to explore this question. Internal and external temperature curves are provided for 1.0-, 2.0-, and 3.0-oz. traces and a variety of trace widths, so these relationships can be explored directly.

To read this entire column, which appeared in the October 2018 issue of Design007 Magazine, click here.

Back

2018

Brooks' Bits: Internal Trace Temperatures—More Complicated Than You Think

12-06-2018

One of the most interesting findings in IPC-2152 was that internal traces are cooler than external ones for the same size and current. Independent experimentation was not done on internal traces in earlier charts. Internal traces were merely assumed to be hotter than external traces, and the external trace data was derated by 50% by that assumption. Traces are heated by Joule, or I2R, heating. They are cooled by a combination of conduction through the dielectric, convection through the air, and radiation. It had previously been assumed that convection conducted heat away from the traces and cooled the traces more efficiently than conduction through the dielectric. Hence, the assumption that internal traces were hotter than their external trace counterparts.

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2014

Electromagnetic Fields, Part 2: How They Impact Propagation Speed

11-13-2014

In Part 1, Doug Brooks suggested that thinking in terms of what the electromagnetic field looks like around our traces might offer significant insight into how circuits might be performing. In this column, he makes similar observations about signal propagation speed.

View Story

Electromagnetic Fields, Part 3 - How They Impact Coupling

04-30-2014

In Part 1 and Part 2 of this series, Doug Brooks talked about how helpful it can be to recognize what the electromagnetic field looks like around a conductor or trace and how that field may change as the stackup or trace parameters are changed. In Part 3, he looks at how changes in the electromagnetic field relate to changes in coupling between traces or between a trace and the outside world.

View Story

Brooks' Bits: Electromagnetic Fields, Part 3 - How They Impact Coupling

04-30-2014

In Part 1 and Part 2 of this series, Doug Brooks talked about how helpful it can be to recognize what the electromagnetic field looks like around a conductor or trace and how that field may change as the stackup or trace parameters are changed. In Part 3, he looks at how changes in the electromagnetic field relate to changes in coupling between traces or between a trace and the outside world.

View Story
Back

2013

Electromagnetic Fields, Part 2: How They Impact Propagation Speed

11-13-2014

In Part 1, Doug Brooks suggested that thinking in terms of what the electromagnetic field looks like around our traces might offer significant insight into how circuits might be performing. In this column, he makes similar observations about signal propagation speed.

View Story

Electromagnetic Fields, Part 3 - How They Impact Coupling

04-30-2014

In Part 1 and Part 2 of this series, Doug Brooks talked about how helpful it can be to recognize what the electromagnetic field looks like around a conductor or trace and how that field may change as the stackup or trace parameters are changed. In Part 3, he looks at how changes in the electromagnetic field relate to changes in coupling between traces or between a trace and the outside world.

View Story

Brooks' Bits: Electromagnetic Fields, Part 3 - How They Impact Coupling

04-30-2014

In Part 1 and Part 2 of this series, Doug Brooks talked about how helpful it can be to recognize what the electromagnetic field looks like around a conductor or trace and how that field may change as the stackup or trace parameters are changed. In Part 3, he looks at how changes in the electromagnetic field relate to changes in coupling between traces or between a trace and the outside world.

View Story
Back

2012

Electromagnetic Fields, Part 2: How They Impact Propagation Speed

11-13-2014

In Part 1, Doug Brooks suggested that thinking in terms of what the electromagnetic field looks like around our traces might offer significant insight into how circuits might be performing. In this column, he makes similar observations about signal propagation speed.

View Story

Electromagnetic Fields, Part 3 - How They Impact Coupling

04-30-2014

In Part 1 and Part 2 of this series, Doug Brooks talked about how helpful it can be to recognize what the electromagnetic field looks like around a conductor or trace and how that field may change as the stackup or trace parameters are changed. In Part 3, he looks at how changes in the electromagnetic field relate to changes in coupling between traces or between a trace and the outside world.

View Story

Brooks' Bits: Electromagnetic Fields, Part 3 - How They Impact Coupling

04-30-2014

In Part 1 and Part 2 of this series, Doug Brooks talked about how helpful it can be to recognize what the electromagnetic field looks like around a conductor or trace and how that field may change as the stackup or trace parameters are changed. In Part 3, he looks at how changes in the electromagnetic field relate to changes in coupling between traces or between a trace and the outside world.

View Story
Back

2011

Current Flow on Traces, Part 2: Common Mode and Mode Shift

12-07-2011

If we have a differential trace pair, and the signal on the return trace is exactly equal and opposite to the signal on the forward trace, there is no common-mode component. If they are not exactly equal and opposite, there will be a common-mode component to the currents on the trace. Let's carry that idea further.

View Story

Coupling's Effect on Impedance: Why is Zdiff Less Than 2*Zo?

11-09-2011

Assume we have a trace (T1) with a controlled impedance equal to Zo. Now bring a second trace (T2) near it (and parallel to it) so that the signal on T2 couples into T1. Consider this statement: The impedance of T1 (Zo) changes as a result of that coupling. Why is this true, and why do we only worry about it in the case of differential-mode or common mode-signals?

View Story

Current Flow on Traces, Part 1: Transmission Lines

10-12-2011

Current propagates down transmission lines by utilizing the distributed capacitance between the lines and the return path. There will always be reflections from impedance discontinuities along, and at the end of, the line. Do we care about such reflections? We may care, depending on the relationship between the propagation time down the trace and the rise time of the signal flowing on the trace. By Doug Brooks.

View Story

Rise Times and Harmonics: Introducing Mr. Fourier

08-31-2011

In very general terms, frequency relates to information and rise time relates to how quickly we can process that information. A circuit only needs to have a rise time fast enough (and not faster) to process the information flow. Bandwidth refers to how wide a frequency range a circuit (or PCB) needs to handle without distortion. So, how wide a bandwidth do I need to pass my signals?

View Story

Rise Time vs. Frequency: What's the Relationship?

06-07-2011

A circuit must have a fast enough rise time to accommodate the signal being processed. If it does not, information in the waveform or circuit timing may be lost or distorted. But here is the clincher: a circuit does NOT have to have a faster rise time than is required by the waveform. Faster is not necessarily better!

View Story

Propagation Speed in Microstrip: Slower Than We Think

05-11-2011

How fast is propagation speed in microstrip? First of all, we must remember, the propagation speed is not determined by how fast the current can travel down a wire; it is determined by how fast the electromagnetic field can propagate in the medium it is in. And propagation times are much more controllable in a stripline environment.

View Story

What Does Voltage Refer To, and Why Do We Care?

04-20-2011

If you do a search for voltage on the Web, you will find lots of definitions. For our purposes here, we can consider it to be the force that causes current to flow. Since current is the flow of electrons, and since electrons are negatively charged, we can consider voltage to be the difference in charge between two points. Remember that for the quiz!

View Story
Back

2010

Current Flow on Traces, Part 2: Common Mode and Mode Shift

12-07-2011

If we have a differential trace pair, and the signal on the return trace is exactly equal and opposite to the signal on the forward trace, there is no common-mode component. If they are not exactly equal and opposite, there will be a common-mode component to the currents on the trace. Let's carry that idea further.

View Story

Coupling's Effect on Impedance: Why is Zdiff Less Than 2*Zo?

11-09-2011

Assume we have a trace (T1) with a controlled impedance equal to Zo. Now bring a second trace (T2) near it (and parallel to it) so that the signal on T2 couples into T1. Consider this statement: The impedance of T1 (Zo) changes as a result of that coupling. Why is this true, and why do we only worry about it in the case of differential-mode or common mode-signals?

View Story

Current Flow on Traces, Part 1: Transmission Lines

10-12-2011

Current propagates down transmission lines by utilizing the distributed capacitance between the lines and the return path. There will always be reflections from impedance discontinuities along, and at the end of, the line. Do we care about such reflections? We may care, depending on the relationship between the propagation time down the trace and the rise time of the signal flowing on the trace. By Doug Brooks.

View Story

Rise Times and Harmonics: Introducing Mr. Fourier

08-31-2011

In very general terms, frequency relates to information and rise time relates to how quickly we can process that information. A circuit only needs to have a rise time fast enough (and not faster) to process the information flow. Bandwidth refers to how wide a frequency range a circuit (or PCB) needs to handle without distortion. So, how wide a bandwidth do I need to pass my signals?

View Story

Rise Time vs. Frequency: What's the Relationship?

06-07-2011

A circuit must have a fast enough rise time to accommodate the signal being processed. If it does not, information in the waveform or circuit timing may be lost or distorted. But here is the clincher: a circuit does NOT have to have a faster rise time than is required by the waveform. Faster is not necessarily better!

View Story

Propagation Speed in Microstrip: Slower Than We Think

05-11-2011

How fast is propagation speed in microstrip? First of all, we must remember, the propagation speed is not determined by how fast the current can travel down a wire; it is determined by how fast the electromagnetic field can propagate in the medium it is in. And propagation times are much more controllable in a stripline environment.

View Story

What Does Voltage Refer To, and Why Do We Care?

04-20-2011

If you do a search for voltage on the Web, you will find lots of definitions. For our purposes here, we can consider it to be the force that causes current to flow. Since current is the flow of electrons, and since electrons are negatively charged, we can consider voltage to be the difference in charge between two points. Remember that for the quiz!

View Story
Back

2009

Current Flow on Traces, Part 2: Common Mode and Mode Shift

12-07-2011

If we have a differential trace pair, and the signal on the return trace is exactly equal and opposite to the signal on the forward trace, there is no common-mode component. If they are not exactly equal and opposite, there will be a common-mode component to the currents on the trace. Let's carry that idea further.

View Story

Coupling's Effect on Impedance: Why is Zdiff Less Than 2*Zo?

11-09-2011

Assume we have a trace (T1) with a controlled impedance equal to Zo. Now bring a second trace (T2) near it (and parallel to it) so that the signal on T2 couples into T1. Consider this statement: The impedance of T1 (Zo) changes as a result of that coupling. Why is this true, and why do we only worry about it in the case of differential-mode or common mode-signals?

View Story

Current Flow on Traces, Part 1: Transmission Lines

10-12-2011

Current propagates down transmission lines by utilizing the distributed capacitance between the lines and the return path. There will always be reflections from impedance discontinuities along, and at the end of, the line. Do we care about such reflections? We may care, depending on the relationship between the propagation time down the trace and the rise time of the signal flowing on the trace. By Doug Brooks.

View Story

Rise Times and Harmonics: Introducing Mr. Fourier

08-31-2011

In very general terms, frequency relates to information and rise time relates to how quickly we can process that information. A circuit only needs to have a rise time fast enough (and not faster) to process the information flow. Bandwidth refers to how wide a frequency range a circuit (or PCB) needs to handle without distortion. So, how wide a bandwidth do I need to pass my signals?

View Story

Rise Time vs. Frequency: What's the Relationship?

06-07-2011

A circuit must have a fast enough rise time to accommodate the signal being processed. If it does not, information in the waveform or circuit timing may be lost or distorted. But here is the clincher: a circuit does NOT have to have a faster rise time than is required by the waveform. Faster is not necessarily better!

View Story

Propagation Speed in Microstrip: Slower Than We Think

05-11-2011

How fast is propagation speed in microstrip? First of all, we must remember, the propagation speed is not determined by how fast the current can travel down a wire; it is determined by how fast the electromagnetic field can propagate in the medium it is in. And propagation times are much more controllable in a stripline environment.

View Story

What Does Voltage Refer To, and Why Do We Care?

04-20-2011

If you do a search for voltage on the Web, you will find lots of definitions. For our purposes here, we can consider it to be the force that causes current to flow. Since current is the flow of electrons, and since electrons are negatively charged, we can consider voltage to be the difference in charge between two points. Remember that for the quiz!

View Story
Back

2008

Current Flow on Traces, Part 2: Common Mode and Mode Shift

12-07-2011

If we have a differential trace pair, and the signal on the return trace is exactly equal and opposite to the signal on the forward trace, there is no common-mode component. If they are not exactly equal and opposite, there will be a common-mode component to the currents on the trace. Let's carry that idea further.

View Story

Coupling's Effect on Impedance: Why is Zdiff Less Than 2*Zo?

11-09-2011

Assume we have a trace (T1) with a controlled impedance equal to Zo. Now bring a second trace (T2) near it (and parallel to it) so that the signal on T2 couples into T1. Consider this statement: The impedance of T1 (Zo) changes as a result of that coupling. Why is this true, and why do we only worry about it in the case of differential-mode or common mode-signals?

View Story

Current Flow on Traces, Part 1: Transmission Lines

10-12-2011

Current propagates down transmission lines by utilizing the distributed capacitance between the lines and the return path. There will always be reflections from impedance discontinuities along, and at the end of, the line. Do we care about such reflections? We may care, depending on the relationship between the propagation time down the trace and the rise time of the signal flowing on the trace. By Doug Brooks.

View Story

Rise Times and Harmonics: Introducing Mr. Fourier

08-31-2011

In very general terms, frequency relates to information and rise time relates to how quickly we can process that information. A circuit only needs to have a rise time fast enough (and not faster) to process the information flow. Bandwidth refers to how wide a frequency range a circuit (or PCB) needs to handle without distortion. So, how wide a bandwidth do I need to pass my signals?

View Story

Rise Time vs. Frequency: What's the Relationship?

06-07-2011

A circuit must have a fast enough rise time to accommodate the signal being processed. If it does not, information in the waveform or circuit timing may be lost or distorted. But here is the clincher: a circuit does NOT have to have a faster rise time than is required by the waveform. Faster is not necessarily better!

View Story

Propagation Speed in Microstrip: Slower Than We Think

05-11-2011

How fast is propagation speed in microstrip? First of all, we must remember, the propagation speed is not determined by how fast the current can travel down a wire; it is determined by how fast the electromagnetic field can propagate in the medium it is in. And propagation times are much more controllable in a stripline environment.

View Story

What Does Voltage Refer To, and Why Do We Care?

04-20-2011

If you do a search for voltage on the Web, you will find lots of definitions. For our purposes here, we can consider it to be the force that causes current to flow. Since current is the flow of electrons, and since electrons are negatively charged, we can consider voltage to be the difference in charge between two points. Remember that for the quiz!

View Story
Back

2007

Current Flow on Traces, Part 2: Common Mode and Mode Shift

12-07-2011

If we have a differential trace pair, and the signal on the return trace is exactly equal and opposite to the signal on the forward trace, there is no common-mode component. If they are not exactly equal and opposite, there will be a common-mode component to the currents on the trace. Let's carry that idea further.

View Story

Coupling's Effect on Impedance: Why is Zdiff Less Than 2*Zo?

11-09-2011

Assume we have a trace (T1) with a controlled impedance equal to Zo. Now bring a second trace (T2) near it (and parallel to it) so that the signal on T2 couples into T1. Consider this statement: The impedance of T1 (Zo) changes as a result of that coupling. Why is this true, and why do we only worry about it in the case of differential-mode or common mode-signals?

View Story

Current Flow on Traces, Part 1: Transmission Lines

10-12-2011

Current propagates down transmission lines by utilizing the distributed capacitance between the lines and the return path. There will always be reflections from impedance discontinuities along, and at the end of, the line. Do we care about such reflections? We may care, depending on the relationship between the propagation time down the trace and the rise time of the signal flowing on the trace. By Doug Brooks.

View Story

Rise Times and Harmonics: Introducing Mr. Fourier

08-31-2011

In very general terms, frequency relates to information and rise time relates to how quickly we can process that information. A circuit only needs to have a rise time fast enough (and not faster) to process the information flow. Bandwidth refers to how wide a frequency range a circuit (or PCB) needs to handle without distortion. So, how wide a bandwidth do I need to pass my signals?

View Story

Rise Time vs. Frequency: What's the Relationship?

06-07-2011

A circuit must have a fast enough rise time to accommodate the signal being processed. If it does not, information in the waveform or circuit timing may be lost or distorted. But here is the clincher: a circuit does NOT have to have a faster rise time than is required by the waveform. Faster is not necessarily better!

View Story

Propagation Speed in Microstrip: Slower Than We Think

05-11-2011

How fast is propagation speed in microstrip? First of all, we must remember, the propagation speed is not determined by how fast the current can travel down a wire; it is determined by how fast the electromagnetic field can propagate in the medium it is in. And propagation times are much more controllable in a stripline environment.

View Story

What Does Voltage Refer To, and Why Do We Care?

04-20-2011

If you do a search for voltage on the Web, you will find lots of definitions. For our purposes here, we can consider it to be the force that causes current to flow. Since current is the flow of electrons, and since electrons are negatively charged, we can consider voltage to be the difference in charge between two points. Remember that for the quiz!

View Story
Back

2006

Current Flow on Traces, Part 2: Common Mode and Mode Shift

12-07-2011

If we have a differential trace pair, and the signal on the return trace is exactly equal and opposite to the signal on the forward trace, there is no common-mode component. If they are not exactly equal and opposite, there will be a common-mode component to the currents on the trace. Let's carry that idea further.

View Story

Coupling's Effect on Impedance: Why is Zdiff Less Than 2*Zo?

11-09-2011

Assume we have a trace (T1) with a controlled impedance equal to Zo. Now bring a second trace (T2) near it (and parallel to it) so that the signal on T2 couples into T1. Consider this statement: The impedance of T1 (Zo) changes as a result of that coupling. Why is this true, and why do we only worry about it in the case of differential-mode or common mode-signals?

View Story

Current Flow on Traces, Part 1: Transmission Lines

10-12-2011

Current propagates down transmission lines by utilizing the distributed capacitance between the lines and the return path. There will always be reflections from impedance discontinuities along, and at the end of, the line. Do we care about such reflections? We may care, depending on the relationship between the propagation time down the trace and the rise time of the signal flowing on the trace. By Doug Brooks.

View Story

Rise Times and Harmonics: Introducing Mr. Fourier

08-31-2011

In very general terms, frequency relates to information and rise time relates to how quickly we can process that information. A circuit only needs to have a rise time fast enough (and not faster) to process the information flow. Bandwidth refers to how wide a frequency range a circuit (or PCB) needs to handle without distortion. So, how wide a bandwidth do I need to pass my signals?

View Story

Rise Time vs. Frequency: What's the Relationship?

06-07-2011

A circuit must have a fast enough rise time to accommodate the signal being processed. If it does not, information in the waveform or circuit timing may be lost or distorted. But here is the clincher: a circuit does NOT have to have a faster rise time than is required by the waveform. Faster is not necessarily better!

View Story

Propagation Speed in Microstrip: Slower Than We Think

05-11-2011

How fast is propagation speed in microstrip? First of all, we must remember, the propagation speed is not determined by how fast the current can travel down a wire; it is determined by how fast the electromagnetic field can propagate in the medium it is in. And propagation times are much more controllable in a stripline environment.

View Story

What Does Voltage Refer To, and Why Do We Care?

04-20-2011

If you do a search for voltage on the Web, you will find lots of definitions. For our purposes here, we can consider it to be the force that causes current to flow. Since current is the flow of electrons, and since electrons are negatively charged, we can consider voltage to be the difference in charge between two points. Remember that for the quiz!

View Story
Back

2005

Current Flow on Traces, Part 2: Common Mode and Mode Shift

12-07-2011

If we have a differential trace pair, and the signal on the return trace is exactly equal and opposite to the signal on the forward trace, there is no common-mode component. If they are not exactly equal and opposite, there will be a common-mode component to the currents on the trace. Let's carry that idea further.

View Story

Coupling's Effect on Impedance: Why is Zdiff Less Than 2*Zo?

11-09-2011

Assume we have a trace (T1) with a controlled impedance equal to Zo. Now bring a second trace (T2) near it (and parallel to it) so that the signal on T2 couples into T1. Consider this statement: The impedance of T1 (Zo) changes as a result of that coupling. Why is this true, and why do we only worry about it in the case of differential-mode or common mode-signals?

View Story

Current Flow on Traces, Part 1: Transmission Lines

10-12-2011

Current propagates down transmission lines by utilizing the distributed capacitance between the lines and the return path. There will always be reflections from impedance discontinuities along, and at the end of, the line. Do we care about such reflections? We may care, depending on the relationship between the propagation time down the trace and the rise time of the signal flowing on the trace. By Doug Brooks.

View Story

Rise Times and Harmonics: Introducing Mr. Fourier

08-31-2011

In very general terms, frequency relates to information and rise time relates to how quickly we can process that information. A circuit only needs to have a rise time fast enough (and not faster) to process the information flow. Bandwidth refers to how wide a frequency range a circuit (or PCB) needs to handle without distortion. So, how wide a bandwidth do I need to pass my signals?

View Story

Rise Time vs. Frequency: What's the Relationship?

06-07-2011

A circuit must have a fast enough rise time to accommodate the signal being processed. If it does not, information in the waveform or circuit timing may be lost or distorted. But here is the clincher: a circuit does NOT have to have a faster rise time than is required by the waveform. Faster is not necessarily better!

View Story

Propagation Speed in Microstrip: Slower Than We Think

05-11-2011

How fast is propagation speed in microstrip? First of all, we must remember, the propagation speed is not determined by how fast the current can travel down a wire; it is determined by how fast the electromagnetic field can propagate in the medium it is in. And propagation times are much more controllable in a stripline environment.

View Story

What Does Voltage Refer To, and Why Do We Care?

04-20-2011

If you do a search for voltage on the Web, you will find lots of definitions. For our purposes here, we can consider it to be the force that causes current to flow. Since current is the flow of electrons, and since electrons are negatively charged, we can consider voltage to be the difference in charge between two points. Remember that for the quiz!

View Story
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