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

Print


Suggested Items

SMTA Europe Solder Finish Webinar Addresses Defects Causes and Cures

12/14/2020 | Pete Starkey, I-Connect007
“What is your most common PCB problem?” A survey conducted by Bob Willis had revealed finish solderability to be the predominant contender, and it was clear that the choice of solderable finish applied to surface mount boards could have a significant effect on the assembly yield and cost of the final circuit. SMTA Europe organised an informative and enlightening webinar this month entitled “Guide to PCB Solder Finishes—Process Defects Causes and Cures,” with soldering specialist Bob Willis as presenter.

SMTA Europe Webinar: What Is a Good Solder Joint, and How Can Solder Joints Be Tested?

11/18/2020 | Pete Starkey, I-Connect007
What is a good solder joint? And how can they be tested not only for purposes of process characterisation, optimisation, monitoring, and control but also for ensuring their long-term reliability? Pete Starkey details a webinar organised by the Europe Chapter of SMTA that was presented by Bob Willis, an expert in soldering, assembly technologies, and failure analysis.

This Month in SMT007 Magazine: Robustness Is Not the Same as Reliability

09/02/2020 | I-Connect007 Editorial Team
Bob Neves discusses a disconnect he sees in reliability testing between what’s being tested and what happens out in the field, as well as why most reliability tests these days should instead be considered robustness tests.



Copyright © 2021 I-Connect007. All rights reserved.