How to Streamline PCB Thermal Design


Reading time ( words)

Thermal issues with a PCB design are mostly determined during the component selection and layout phases. After this point, only remedial actions are possible if components are found to run too hot. Addressing thermal issues early in PCB design, starting at the system or enclosure level to understand the flow environment critical for air-cooled electronics, can streamline the process. Assumptions about the airflow uniformity in early design that subsequently prove unachievable can have a disastrous effect on the commercial viability of the product and meeting the market window.

Begin Before Placement and Layout

Substantial work can be done well before layout is completed within the electrical design flow. A simple representation of the enclosure can provide information about the air flow profile over the board. Start by smearing the total board power over the total board surface, which will provide a temperature map that will show any hot regions that are caused by a badly distributed air flow. Treat the board as a block with an isotropic conductivity of between 5 W/mK and 10 W/mK to optimize enclosure-level air flow ahead of the PCB design.

Components inject heat locally into the board so the heat flux density into the board below a component will be higher than the average for the board. As a result, the local board temperature will be higher than that predicted in the simulation. Refine the model before using the board temperature to estimate component temperatures. If the board temperature at any point is close to the maximum component case temperature, this limit will be exceeded once the component heat sources are represented discretely.

Guesstimate Component Power

At this stage, make a best-guess estimate of the individual power budgets for the main heat dissipating components that will be used in the design and the approximate size of those packages. This will enable describing them as footprint heat sources in the simulation, smearing the remainder of heat uniformly over the board surface.

Before Selecting the Package, Use 3D Component Models

Include some form of 3D component model in the simulation before the component selection is finalized. By feeding the thermal results back before this milestone is reached, the thermal performance will more likely be considered in the package selection criteria. Some ICs are available in more than one package style, and not all package styles perform equally well from a thermal point of view. The need for a heatsink later may be eliminated by appropriate package selection.

Component temperature, either in the form of a case temperature or junction temperature depending on how the manufacturer has specified the component, is the key measure used to indicate whether the design is thermally acceptable.

Read The Full Article Here

Editor's Note: This article originally appeared in the March issue of SMT Magazine.

Share




Suggested Items

Assemblers Play the ‘Revise or Wait’ Game With Designers

06/22/2022 | Nolan Johnson, I-Connect007
Nolan Johnson recently spoke with Duane Benson at Milwaukee Electronics and Screaming Circuits. Duane was pointing out a trend in moving designs into production, which he termed “revise or wait.” This excerpt provides a preview of our exploration of similar topics involving supply chain issues, lead times, and proceeding forward despite the supply challenges.

How Will Emerging Chiplet Technology Affect PCBs?

06/01/2022 | I-Connect007 Editorial Team
In a recent conversation with Ventec’s Alun Morgan, the I-Connect007 Editorial Team discussed, among several topics, semiconductor packaging developments. Industry insiders will know that, when you get Happy Holden and Alun Morgan talking about emerging technology trends, there will be insights shared.

Getting Involved Earlier in the Test Process

04/18/2022 | Andy Shaughnessy, I-Connect007
At SMTA Dallas, Andy Shaughnessy stopped by the booth for The Test Connection, to find out from Bert Horner why the company has evolved into spending more time educating and consulting with their customers when it comes to testing new designs.



Copyright © 2022 I-Connect007 | IPC Publishing Group Inc. All rights reserved.