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

Seeing Clearly: XR Headsets and Flex’s Reference Design at AWE

06/26/2018 | Dan Feinberg, Technology Editor, I-Connect007
At this year’s CES, they announced the launch of an extended reality (XR) reference design for the next generation of XR headsets. As the “sketch-to-scale” solutions provider, as they describe themselves, that designs and builds “intelligent products for a connected world,” they have now introduced an augmented reality (AR or, as we now call it, XR) reference design to reduce time to market for companies wishing to make and market XR devices.

A Not So Surprising Focus for Flex in the XR Realm

03/14/2018 | Dan Feinberg
Dan Feinberg has been covering augmented, virtual, and mixed-reality for I-Connect007 for the last few years. He recently met with Eric Braddom, VP of Extended Reality (XR) Product Management for Flex, a company that is involved in this disruptive technology. In this interview, Dan and Eric discuss the future of augmented, mixed and/or virtual reality, or as Flex calls it, "extended reality."

Should You Be Outsourcing Product Design?

02/01/2018 | Neil Sharp, JJS Manufacturing
While handing over part or all of your manufacturing to a third party can be daunting, it offers a host of benefits. It frees you up to focus on what you do best--whether that's designing, marketing or selling. It reduces your operating costs, and you gain from the range and depth of expertise than an EMS can provide. For OEMs already outsourcing their manufacturing, going to a third party for other services, like product design, could well be the next logical step.



Copyright © 2018 I-Connect007. All rights reserved.