What is Thermal Design (dissipation / insulation of heat) ?
The density of heat generation is tend to increase, as electric devices are getting compact and thinner, as well as the electric components are closely built-up.
Thermal design is to lower the temperature of the element by using heat-releasing material, and/or by transferring the heat from the heat-generating part to the cooling surface of the chassis.
Necessity of Thermal Design (dissipation / insulation of heat )
Heat Design (dissipation / insulation of heat) is essential to solve the following problems,.
Many electric devices are constructed with PCB, and various electrical parts mounted on the PCB generate heat while electricity passes through.
The generated heat causes the following problems
- Functional problems: the life of the elements is shortened
- Mechanical problems: the damage caused by the chemical change, such as the malformation due to expansion from heat
- Interpersonal problems: Human contact to the high heat area of the electrical device
Heat Transfer Basics
There are three forms of heat flow.
- Thermal Transfer: The fact that the steel conducts heat from hot to cold places
When the tip of a spoon is roasted, the handle gets hot.
- Convectional thermal transfer: The heat is transferred to the fluid that is in contact with the object
When a frying pan is heated on a stove, the air above gets warm.
- Thermal radiation: The phenomena that the heat energy travels in an electro-magnetic wave.
The sun light. The heat from the sun is not transferred through the air, but it is travelling through the atmosphere in an electro-magnetic wave.
Thermal Design (dissipation / insulation of thermal) is performed under the consideration of the above mentioned heat behavior.
Thermal conductivity and thermal Resistance
Basic formula of heat calculation
Fourier’s equation: Q=λ×((ΔT・S)/d)
Q: Amount of Heat (W), λ：thermal conductivity (W/m・K)、ΔT: Temperature difference, S: Surface area, d: distance
The thermal conductivity
<< the ease of thermal conductivity within the material >>
- Even if the mounting conditions of the equipment is changed, the value stays the same
- Reducing the thickness results in smaller temperature difference
λ(thermal conductivity）=(Q・d)/(ΔT・S) ※d/ΔT=fixed
What is Thermal Resistance?
<< Difficulty of transferring the heat >>
- the distance from the heat source, degree of adhesion, and the area change the resistance amount, even when the same heat transferring pad is applied.
- When greater area, high-thermal conductive material, smaller distance (thickness) are applied, the resistance gets smaller.
Thermal Design (dissipation / insulation of heat ) is performed under the consideration of thermal conductivity rate and thermal resistance.