1. What is the effective thermal conductivity of a PCB?
The "effective thermal conductivity" represents the ability of a material to conduct heat. When we talk about the effective thermal conductivity of a PCB, we are talking about the ability of the PCB to transfer the heat generated by the device to the surrounding area. The effective thermal conductivity is expressed in Keff and is measured in W/m-K.
In PCB design, the effective thermal conductivity is an important parameter used in thermal modelling and analysis to help engineers predict the thermal conductivity of a PCB full of devices based on specific assumptions and models. As the size of electronic modules continues to shrink, designers should pay attention to the effective thermal conductivity. 2.
2. Factors affecting the effective thermal conductivity of a PCB
A PCB contains conductive materials, insulators and mounted devices, and each material used in a PCB has a different thermal conductivity. The different thermal conductivities are taken into account when deriving the effective thermal conductivity of a PCB.
Various studies have been carried out in the industry to analyse the thermal conductivity of PCBs. Different studies have used different types of models and assumptions. For the designer, the effective thermal conductivity of a PCB depends on several factors.
Device size
As devices become smaller, the ability to dissipate heat naturally decreases. For example, a MOSFET in a SOT-23 package will have a smaller thermally conductive spacer area than a MOSFET in a TO-220 package. Therefore, the size of the device mounted on the PCB will affect its ability to dissipate heat.
Thermal vias
Thermal vias are holes that are intentionally placed to dissipate heat away from the device. This is similar to giving hot steam more opportunity to escape from porridge rather than trapping it in a container. Therefore, the more thermal vias there are in an area, the higher the effective thermal conductivity of the PCB.
The density of thermal vias affects the effective thermal conductivity of a PCB.
Internal layers
The presence of an internal copper layer also changes the speed and direction of heat dissipation. The thermal conductivity of copper is 355 W/m-K compared to 0.25 m-K for FR-4. If there are multiple copper inner layers, the effective thermal conductivity of the PCB decreases. Of course, thermal vias help to transfer the heat to the inner layers more efficiently.
Alignment geometry
If the copper alignment is continuous from end to end, the effective thermal conductivity of the PCB will be high. However, if the alignment is interrupted, the effective thermal conductivity may drop, which happens in real PCBs. 3.
3. Is the effective thermal conductivity useful for accurate thermal modelling of PCBs?
The effective thermal conductivity is easy to calculate and is therefore the preferred choice for analysis. This parameter is usually based on a homogeneous PCB model. However, PCBs are rarely homogeneous, especially multi-layer PCBs, where the arrangement of devices, alignments, copper surfaces, vias and pads can be different on each layer.
Therefore, the derivation of the effective thermal conductivity from conventional models is subject to errors. In order to estimate the effective thermal conductivity more accurately, each layer of the PCB needs to be analysed in depth. The surface is then analysed pixel-wise for better prediction.
The accuracy of the effective thermal conductivity of a PCB depends on the modelling and, regardless of the technique used, the accuracy of the modelling depends on the software tool used.
Company Profile
Zhejiang NeoDen Technology Co., Ltd. has been manufacturing and exporting various small pick and place machines since 2010. Taking advantage of our own rich experienced R&D, well trained production, NeoDen wins great reputation from the world wide customers.
In our global Ecosystem, we collaborate with our best partners to deliver a more closing sales service, high professional and efficient technical support.
We believe that great people and partners make NeoDen a great company and that our commitment to Innovation, Diversity and Sustainability ensures that SMT automation is accessible to every hobbyist everywhere.
Add: No.18, Tianzihu Avenue, Tianzihu Town, Anji County, Huzhou City, Zhejiang Province, China
Phone: 86-571-26266266