Summary of Thermal Conductivity: What is it and Why You Should Care
This article defines thermal conductivity as a material's ability to transfer heat, emphasizing its critical role in cooling electronic equipment from the die to the cabinet. It explains that as power levels rise, managing junction-to-case resistance and heatsink design becomes essential. The text details how total thermal resistance comprises three distinct parts: interfacial resistance (addressed by interface materials), spreading resistance (dependent on heatsink base conductivity), and conduction resistance. Understanding these components is vital for designing effective thermal solutions for modern high-powered devices.
Parts used in Thermal Management:
- Die
- Cabinet
- PCB (Printed Circuit Board)
- Heatsink
- Interface Material
Thermal Conductivity: A measure of the ability of a material to transfer heat. Given two surfaces on either side of a material with a temperature difference between them, the thermal conductivity is the heat energy transferred per unit time and per unit surface area, divided by the temperature difference 1.
Thermal conductivity is a bulk property that describes the ability of a material to transfer heat. In the equation in Figure 1, thermal conductivity is the proportionality factor K. The distance of heat transfer is defined as rate of heat transferred through the material (Q), from temperature T1 to temperature T2, when T1>T2 2.
Thermal conductivity of materials plays a significant role in the cooling of electronics equipment; from the die where the heat is generated to the cabinet where the electronics are housed, conduction heat transfer and, subsequently, thermal conductivity, are the integral components of the overall thermal management process.
The path of heat from the die to the outside environment is a complicated process that must be understood when designing a thermal solution. In the past, many devices were able to operate without requiring an external cooling device like a heatsink. In these devices, the conduction resistance from the die to the board needed to be optimized, as the primary heat transfer path was into the PCB. As power levels increased, heat transfer solely into the board became inadequate. Much of the heat is now dissipated directly into the environment through the top surface of the component. In these new higher-powered devices, low junction-to-case resistance is important, as is the design of the attached heatsink.
To determine the importance of material thermal conductivity in a specific thermal management application (e.g. a heatsink), it is important to separate the overall thermal resistance associated with conduction heat transfer into three parts: interfacial, spreading, and conduction resistances.
Interface Material
An interface material enhances the thermal contact between imperfect mating surfaces. A highly thermally conductive material, with good surface wetting ability, will reduce interfacial resistance.
Spreading Resistance
Spreading resistance is used to describe the thermal resistance associated with a small heat source coupled to a larger heatsink. Among other factors, the thermal conductivity of the base of the heatsink directly impacts spreading resistance.
For More Details: Thermal Conductivity: What is it and Why You Should Care
- What is thermal conductivity?
It is a measure of the ability of a material to transfer heat, defined as the heat energy transferred per unit time and area divided by the temperature difference. - How does thermal conductivity affect electronics cooling?
It is an integral component of the overall thermal management process, moving heat from the die to the cabinet. - Why did heat transfer methods change for newer devices?
As power levels increased, transferring heat solely into the board became inadequate, requiring dissipation through the top surface. - What are the three parts of overall thermal resistance?
The three parts are interfacial resistance, spreading resistance, and conduction resistances. - How do interface materials help thermal contact?
They enhance thermal contact between imperfect mating surfaces and reduce interfacial resistance if they have high conductivity and good wetting ability. - What impacts spreading resistance in a heatsink?
The thermal conductivity of the base of the heatsink directly impacts spreading resistance when coupling a small heat source to a larger sink. - Is thermal conductivity a bulk property?
Yes, it is described as a bulk property that characterizes a material's ability to transfer heat. - What happens when T1 is greater than T2 in the heat equation?
Heat transfers from temperature T1 to temperature T2 through the material.
