# Just Ask Happy: Calculating Trace Temps in a Vacuum

We asked for you to send in your questions for Happy Holden, and you took us up on it! The questions you've posed run the gamut, covering technology, the worldwide fab market, and everything in between. Enjoy.

Q: For space applications (without air), how should we calculate external layer current-carrying traces against the IPC-2221 (formerly IPC-D-275) charts?

A: I have never studied that, so I turned this question over to an expert, my friend Mike Jouppi, former committee chair of IPC-2152 Standard for Determining Current Carrying Capacity in Printed Board Design. This standard will provide many answers to your questions. Mike wrote Chapters 22 and 23 in the seventh edition of the Printed Circuits Handbook, edited by Clyde F. Coombs and me.

Mike answered: I'm a mechanical engineer who worked as a career thermal analyst. The charts in IPC-2152 in almost all cases will be conservative (both air and vacuum environments). The vacuum is for space environments. The purpose behind these charts is misconstrued by most users. My intention when they were developed was to use these charts as a baseline for developing thermal models that could be used to better understand the actual temperature rise of conductors in actual designs, which I did for my own design purposes. The concept did not catch on.

There is a significant difference between the temperature rise in a conductor, tested per IPC-TM-2.5.4.1a, and most PWB design configurations. The reason is that most designs have copper ground and power planes that conduct energy away from the traces. In addition, most designs in space applications have a significant conduction path from the PWB through-bolted fasteners or wedge locks to a sink.

Since the question does not include IPC-2152, I would recommend researching IPC-2152 and accounting for the power dissipations in the traces in the thermal design. I also recommend accounting for the conductor power dissipation in all designs, especially if the designers are not familiar with sizing parallel conductors. Parallel conductors are easily managed with accounting for conductor losses (power dissipation). FYI: It was the power dissipation in conductors that motivated me to lead the development of IPC-2152.

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## Just Ask Heidi Barnes: The Exclusive Compilation

01/15/2021 | I-Connect007 Editorial Team
We asked for your questions for Keysight Technologies' Heidi Barnes, and you took us up on it! We know you all enjoyed reading these questions and answers, so we’ve compiled all of them into one article for easy reference. We hope you enjoy having another bite at the apple.

## TTM’s Approach to Stackup Design: Train the Customer

01/12/2021 | I-Connect007 Editorial Team
In this interview with the I-Connect007 Editorial Team, TTM’s Julie Ellis and Richard Dang drill down into stackup design, detailing some of the common stackup challenges that their customers face when designing for both prototype and volume levels, and offering advice to designers or engineers who are struggling with stackup issues. They also discuss why having too many different prepregs in a stackup can be asking for trouble, and how proper stackup design can optimize both the fabrication and assembly processes.

## Cutting Respins: Journey to the Single-spin PCB

01/07/2021 | Chris Young, The Goebel Company
PCB design is more than a short sprint to the finish line; it is a journey best suited for the prepared adventurer. According to a study by Lifecycle Insights, the average PCB design project requires 2.9 respins. These respins can cost anywhere from tens of thousands to millions of dollars—each! As an engineer/business owner, I find respins frustrating because I would rather spend my time and money applying scientific principles inventing, improving technology, and solving problems. I am not an advocate for perfectionism, but rather I focus on becoming a better adventurer. Sometimes I get to taste the sweet wine that is a single spin PCB. As fellow adventurers, let’s discuss some topics that influence unnecessary return trips on our PCB design journey: simulation, technical reviews, and interest in PCB design.