Almost everyone would agree that the discovery of how to create fire is one of the greatest inventions in all of human history. Yet, fires can get out of hand and also be one of the most damaging hazards that we can face. From this perspective, perhaps acquiring the ability to regulate and control heat is at least as important as having heat.
Controlling heat is certainly one of the most important aspects of circuit board development and operation. For board development, the ability to control and remove heat is essential during manufacturing, especially PCB assembly. However, design choices, such as the components to include, the type of surface finish to protect the board, and thermal resistance management options—including the heat dissipation materials you choose—greatly impact the success of your thermal management.
Why is Heat Dissipation Important?
Thermal management to control the effects of temperature is a perennial concern for electronics systems. This is due to a fundamental chemical reaction that occurs in any material electric current flows from or through. In order for electrons that have a negative polarity to flow, energy is required to release electrons from their valence level. This energy change produces radiation that is either emitted or absorbed by the material. In either case, heat is generated that must be controlled for proper component, circuit or system function.
There are two methods for controlling or managing heat on circuit boards: thermal dissipation or distribution. Both methods are important, as they prevent components from overheating and forming hot spots, or concentrated areas of elevated temperature, on the board. These contingencies, if sufficiently severe, can result in short circuits, component or board damage, or sparks that can ignite fires on or near the PCBA.
Additionally, distribution and dissipation are important during PCB manufacturing and operation. For example, the even distribution of solder is necessary to ensure the formation of high-quality joints, while excessive concentrated high heat can cause delamination and board warping. Good thermal distribution depends almost exclusively on the selected board material. For the effective removal of excess heat, common dissipation techniques include mounting heat sinks on high energy devices, such as processors, thermal vias, and even cooling fans for better ventilation. However, board material selection can also be instrumental for dissipation.
How Board Material Affects Heat Dissipation
In many cases, it is tempting to simply choose FR-4 for your board material without considering if it is the best choice. Fortunately, in many situations you can get by with this; however, there are times when design-specific material selection is required to avoid fault modes after installation that can be traced to excessive heat and ineffective thermal dissipation. Examples of these include: shorts, delamination, component and trace damage, excessive EMI and surface arc tracking.
To avoid contingencies like component and board damage, material selection should be based on design type and rely on material characteristics such as the following: coefficient of thermal expansion (CTE), the rate at which the substrate will expand w.r.t. changes in temperature; glass transition temperature (Tg), the point at which the board material begins to soften and deform; and thermal conductivity (k), the speed at which heat is transferred through the material.
Making the best material selection requires an understanding of the electrical, mechanical and thermal properties of your PCBA, the specific values of which are defined by the material(s) selected. In addition to understanding board properties, you can aid your board’s thermal dissipation ability by following a few simple guidelines, as listed below.
Guidelines for Heat Dissipation Material Selection
- Know the important board temperature parameters
A good understanding of all board properties can help you create better designs in all cases. However, for the best heat dissipation, you should be familiar with the thermal properties and their acceptable values for the environment in which your board will operate.
- Perform thermal analysis
In addition to material property knowledge, you should model your board’s thermal behavior during design. This analysis should include nominal power distribution (PDN) evaluation, as well as specific design cases, such as high voltage or high current applications. The results of these analyses should be used to modify your component selections, heat dissipation elements—heat sinks, for instance—and board layout. Include location and number of thermal vias, if necessary, to improve thermal dissipation.
- Choose materials based on board type
When choosing the materials for your PCBA, board type and dimensions should always be considered and integrated into your final selection: for example, high-speed PCBAs where dielectric constant, dk, dissipation factor, df, and dielectric loss are important considerations.
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By following these simple steps, you can improve the material selection aspect of PCBA design and reduce the probability of board failure due to excessive heat. At Tempo Automation, the industry leader in building high-quality PCBAs for prototyping and low-volume production, we will partner with you on day one of design to aid in ensuring your design intent is accurately represented in your manufactured boards.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on heat dissipation materials and how to make the best selection for your design, contact us.