Modern consumer electronics developers continually strive to reduce a product’s “SWaP-C” – its Size, Weight, Power, and Cost. As the industry continues to further miniaturize each generation of electronics and drive budgets down, the thermal design challenges increase.
Most major electronics brands have struggled with thermal design at some point. Think phones, tablets, laptops, gaming consoles, and mobile gaming decks. Even the most experienced brands worldwide have launched devices with overheating issues stemming from insufficient thermal design management. Rapid product development cycles can drive teams to neglect or overlook thermal performance results until it’s too late in the development cycle.
But good news! With a product-oriented design lifecycle and the right team of experienced and enthusiastic product development engineers, success with thermal design is always possible.
Oak Griffith, a Mechanical Engineer with AC Product Development presents today’s TechTalkTM.
From his experience in thermal design and simulation, Oak describes how to incorporate thermal engineering techniques and analysis from the earliest stages of product development to create a successful thermal design management strategy.
Avoiding the Consequences of Poor Thermal Design
Although thermal management is always challenging for product miniaturization, it’s worth doing it right. The consequences of poor thermal performance are serious because they are costly and create a lasting negative impression on consumers.
When a product overheats, in addition to the immediate frustrations of unexpected shutdowns and poor overall performance, the expected service life of the components is significantly reduced. Whether a product’s thermal performance drops suddenly or over time, the result is the same – loss of consumer confidence.
And the greater the design flaw, the more focus it gets in the market. Negative reviews emerge, and word of mouth cautions spreads. Sales drop, or worse yet, consumers run to competing brands to avoid a performance issue that isn’t even a brand differentiator.
Then there’s the costly redesign work to fix the source of the overheating issue. Developers return to the original design to investigate and resolve the root cause. Additional engineering, hardware, or software solutions creates added costs. Developers eventually relaunch the product, but winning back lost sales and consumer confidence may take time and even more marketing investment. Even when the issue is solved, some aggravated consumers vow never to return to a brand they once loved.
So, yes, it’s always worth doing thermal design correctly – and right from the start of the project.
Using Heat Transfer to Inform Thermal Design Solutions
So, what’s a product design engineer to do? We start with our thorough understanding of thermal design and management basics. It’s crucial to include a thermal analysis in the product’s roadmap right from the very beginning of the concept. With that in mind, let’s explore some of the basic first principles of thermal design to understand how we use that to develop better products earlier.
Heat Transfer Methods
Electronics all produce heat, from the basic transistor to the Ryzen Threadripper – and computation is expensive (in terms of heat)!
As design engineers, we aim to move that heat, typically from the component that’s generating it, out to the ambient environment as efficiently as possible. Seems simple enough, right?
The three main methods for heat transfer are convection, conduction, or radiation.
> Convection is the transfer of heat from one material, typically a solid, to a second fluid, typically air.
> Conduction is heat moving between the contact of two solid materials.
> Radiation is heat transfer through electromagnetic waves, most dominantly in the infrared spectrum at ambient environmental temperatures.
As a rule of thumb, convection and conduction dominate almost all consumer electronics thermal transfer. However, radiation is a factor for products that operate without active cooling components, like fans, or with direct exposure to sunlight.
Designing for thermal success boils down to understanding incoming and outgoing heat. To calculate accurately, we start with specific design goals and product specifications. Chiefly, we ask: how much power does your product generate and dissipate? We also identify heat factors from the operating environment.
As an example, let’s imagine a smart doorbell. Based on hypothetical product requirements, it requires 3 watts of energy for all its electronic functions and operates outside in an uncontrolled environment. So, in addition to managing the 3 watts of required power, we must also account for the temperature of the environment and possible solar heat.
With this basic but crucial understanding, it’s time for us to start managing heat transfer.
Keeping it Cool – Thermal Design with Heat Exchangers
Modern electronics typically mitigate heat using a heat exchanger. Heat exchangers usually have many fins made from a conductive metal and are designed to move cool air over as large a surface area of that hot metal as possible.
A fan is often combined with the heat exchanger to ensure we remove the proper amount of heat from the system. That heat exchanger can be mounted directly to the component generating heat. If the design is space-constrained, a heatpipe rapidly moves heat from one area to another very efficiently by taking advantage of the thermal properties of a phase-changing material.
Heat Sink Options & Related Costs
There are plenty of options for heat extraction and system cooling. We aim to ensure optimal thermal resistance to achieve efficient heat dissipation from the component.
For example, laptops and desktops PCs have drastically different strategies for thermal management, even though they’re both performing essentially identical duties.
A laptop uses complex custom heat pipes and high-velocity, low-profile blower fans to keep all components as cool as possible and running efficiently.
A desktop PC has the added flexibility of a larger chassis, constant wall power supply, and higher noise allowance. Because of the focus on performance, we use liquid cold plates.
For each specific application, we balance factors like the heat sink material, its size and shape, fin density (when applicable), airflow, component power, heat output, and mounting and interface materials to select the right heat sink solution.
Fins and heat sinks are the most common, but some designs require a more complex approach and warrant higher costs per unit.
Proving the Thermal Design Transfer Path
Once we define the operational and functional requirements and a likely path for the thermal design transfer, it’s time to do some math.
In the early stages of the design, this begins with hand calculations. At the most basic level, we perform a thermal calculation at a reduced complexity by using a resistive modeling approach.
Heat Flow Modeling & Mapping
By creating a two-dimensional model of the flow of heat, it’s possible to map resistances to thermal transfer along the way. In the image below, theta_sa represents the thermal resistance of the heatsink to the ambient environment.
If you usw an off-the-shelf heatsink, this thermal resistance variable can be found in a product data sheet. However, this value will be an unknown for a custom heatsink design. It must be estimated when using this simpler model. To be confident in the accuracy of our results, we need a more thorough model and advanced calculations.
Heat Flow Model & Resistance Map
As the product’s design matures, we must also improve the accuracy and granularity of our thermal simulations. There are ways to calculate thermal systems very accurately by hand. But at some point, we’ll be stuck solving the Navier-Stokes equations by hand, and that’s really no fun.
To fully characterize the thermal performance of a product, we need to perform a full computational fluid dynamics (CFD) thermal analysis as early and accurately as possible.
There are dozens of great CFD software packages available today for modeling anything from internal combustion engines to whole server rooms. It’s essential to find a package that is appropriate for each use case. The most common software packages used for consumer electronics are Ansys IcePak, Siemens Flowtherm, Dassault Abaqus, and Cadence Celsius EC Solver (formerly 6SigmaET).
Remember that these simulations are only as accurate as the information we give them, magnified by the assumptions we make along the way. Garbage in, garbage out, as the saying goes.
There is much more to explore around thermal simulations and computational fluid dynamics. If you’re ready for more content on product development thermal design, let us know!
AC Thermal Design Expertise & Thermal Simulation Support
AC Product Development engineers are ready to support your product development cycle with thermal design management from concept to manufacturing.
Perhaps you’re already deep into your product development cycle and just now realizing you need additional support for thermal design and analysis.
Whatever your needs, at any point in your product’s journey, we can help.
Speak with an AC engineer, today.