Naturally, heat always moves from the higher temperature area or material to the lower in search of equilibrium or a constant temperature throughout and managing the heat transfers on your board is a design requirement. That means managing or controlling the conduction and convection of heat on your board for manufacturing and operation.
Doing so requires that you institute methods to control thermal dissipation and thermal distribution. Both thermal dissipation and distribution management are concerned with the adequate movement of heat. However, dissipation is the process of removing excess heat from the board entirely, while distribution is the process of ensuring that excess heat is not concentrated, but evenly distributed. The table below compares and contrasts this and other attributes of these two thermal properties.
As shown above, thermal dissipation is an issue for operation in the field, while distribution is a concern for board assembly. However, both are managed by controlling thermal resistance. Thermal resistance can be defined as the property of a material to resist the flow of heat.
For dissipation, the materials of primary concern are the traces; including surface routes and thermal vias, which are plated through-holes PTHs specifically placed to pass heat, not current. Additionally, for SMTs thermal reliefs can be used instead of full component pads which are easier for assembly rework. When designing PCBAs, it is important to know the difference between thermal dissipation and thermal distribution and what design choices impact each.
At Tempo Automation , the industry leader in manufacturing high-quality PCBAs, fast, we will work with you to ensure that both of these design concerns are addressed. 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. Tempo Automation Inc. Learn More. Styrofoam is used in coolers, pop can insulators, thermos jugs, and even foam boards for household insulation.
Another solid insulator is cellulose. Cellulose insulation is used to insulate attics and walls in homes. It insulates homes from heat loss as well as sound penetration.
It is often blown into attics as loose fill cellulose insulation. It is also applied as fiberglass batts long sheets of paper backed insulation to fill the spacing between 2x4 studs of the exterior and sometimes interior walls of homes. Another variable that affects the rate of conductive heat transfer is the area through which heat is being transferred.
For instance, heat transfer through windows of homes is dependent upon the size of the window. More heat will be lost from a home through a larger window than through a smaller window of the same composition and thickness. More heat will be lost from a home through a larger roof than through a smaller roof with the same insulation characteristics.
Each individual particle on the surface of an object is involved in the heat conduction process. An object with a wider area has more surface particles working to conduct heat. As such, the rate of heat transfer is directly proportional to the surface area through which the heat is being conducted. A final variable that affects the rate of conductive heat transfer is the distance that the heat must be conducted.
Heat escaping through a Styrofoam cup will escape more rapidly through a thin-walled cup than through a thick-walled cup. The rate of heat transfer is inversely proportional to the thickness of the cup. A similar statement can be made for heat being conducted through a layer of cellulose insulation in the wall of a home. The thicker that the insulation is, the lower the rate of heat transfer.
Those of us who live in colder winter climates know this principle quite well. We are told to dress in layers before going outside. This increases the thickness of the materials through which heat is transferred, as well as trapping pockets of air with high insulation ability between the individual layers.
So far we have learned of four variables that affect the rate of heat transfer between two locations. The variables are the temperature difference between the two locations, the material present between the two locations, the area through which the heat will be transferred, and the distance it must be transferred. As is often the case in physics, the mathematical relationship between these variables and the rate of heat transfer can be expressed in the form of an equation.
Let's consider the transfer of heat through a glass window from the inside of a home with a temperature of T 1 to the outside of a home with a temperature of T 2. The window has a surface area A and a thickness d. The thermal conductivity value of the window glass is k.
The equation relating the heat transfer rate to these variables is. This equation is applicable to any situation in which heat is transferred in the same direction across a flat rectangular wall. It applies to conduction through windows, flat walls, slopes roofs without any curvature , etc. A slightly different equation applies to conduction through curved walls such as the walls of cans, cups, glasses and pipes.
We will not discuss that equation here. To solve this problem, we will need to know the surface area of the window. We will also need to give attention to the unit on thickness d. It is given in units of cm; we will need to convert to units of meters in order for the units to be consistent with that of k and A. Now we are ready to calculate the rate of heat transfer by substitution of known values into the above equation. It is useful to note that the thermal conductivity value of a house window is much lower than the thermal conductivity value of glass itself.
The thermal conductivity of glass is about 0. Glass windows are constructed as double and triple pane windows with a low pressure inert gas layer between the panes. Furthermore, coatings are placed on the windows to improve efficiency. The result is that there are a series of substances through which heat must consecutively pass in order to be transferred out of or into the house. Like electrical resistors placed in series , a series of thermal insulators has an additive effect on the overall resistance offered to the flow of heat.
The accumulative effect of the various layers of materials in a window leads to an overall conductivity that is much less than a single pane of uncoated glass. Lesson 1 of this Thermal Physics chapter has focused on the meaning of temperature and heat.
Emphasis has been given to the development of a particle model of materials that is capable of explaining the macroscopic observations. Efforts have been made to develop solid conceptual understandings of the topic in the absence of mathematical formulas. This solid conceptual understanding will serve you well as you approach Lesson 2.
The chapter will turn slightly more mathematical as we investigate the question: how can the amount of heat released from or gained by a system be measured? Lesson 2 will pertain to the science of calorimetry. Predict the effect of the following variations upon the rate at which heat is transferred through a rectangular object by filling in the blanks.
If the area through which heat is transferred is increased by a factor of 2, then the rate of heat transfer is increased by a factor of 2. If the thickness of the material through which heat is transferred is increased by a factor of 2, then the rate of heat transfer is decreased by a factor of 2.
If the thickness of the material through which heat is transferred is decreased by a factor of 3, then the rate of heat transfer is increased by a factor of 3. He worked on several projects on prevention and control Heat dissipation is a type of heat transfer. Heat dissipation occurs when an object that is hotter than other objects is placed in an environment where the heat of the hotter object is transferred to the colder objects and the surrounding environment.
Heat dissipation occurs in a variety of ways. Heat dissipation is unavoidable and sometimes is considered a negative process in a range of industries and applications. In the corrosion mitigation and prevention industry, heat dissipation can lead to corrosion under insulation.
Heat transfer can also be detrimental to alloy performance , which is a consideration in high temperature environments. Temperature difference is the major factor that determines the mode and rate of heat transfer in a given application. There are other factors relevant to the design, operation and environment that need to be taken into consideration to manage heat dissipation, and aid in the selection of suitable thermal insulation means wherever applicable.
Heat dissipation represents a form of energy dissipation energy transfer. Energy dissipation is a measure of energy lost due to temperature difference and inefficiencies. Using the right type of insulation, depending on the application, reduces the heat loss and costs associated with it, while also increasing efficiency and safety.
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