E-NEWSLETTER l Flex and Rigid-Flex

May 2023

President's Message, May 2023

This month we’re keeping things cool with Thermal Management PCBs. The main goal in thermal management is to control the of heat in electronics, especially in printed circuits boards.

As we travel the world going to trade shows, doing lunch and learns, and conducting webinars, people often ask for in-depth explanation regarding the need for thermal management PCBs.

Here are some of the most important reasons to utilize thermal management PCBs:

1. High thermal conductivity: Allows the PCB to efficiently transfer heat away from components and dissipate it into the surrounding environment.
2. Effective heat dissipation: Dissipates the heat generation by the components quickly and efficiently.
3. Thermal Stability: Allows the PCB to maintain its thermal stability under varying operating conditions.
4. Low thermal resistance: Should be kept as low as possible to minimize the temperature rise of the components.
5. Optimal component placement: Ensures that heat is effectively dissipated and does not accumulate in certain areas of the PCB.

At ASC we have spent years focusing on and developing our expertise when it comes to thermal

management as it is our passion and our obligation to our customers to stay on top of all the latest technology.

Enjoy the newsletter and as always, thank you for your business.

Sincerely,

Anaya Vardya

President and CEO

American Standard Circuits

Our Latest 77 Second Webinars

View our latest 77 second videos. This month we focus on Embedded Coin Design Considerations.

Thermal Properties Explained

A thorough understanding of a number of different thermal properties is needed to be able to design the appropriate thermal solution to a design.

Thermal Conductivity

• Measurement of the ability of a substance to conduct heat, Measured in W/mK.
• A material property, meaning that it does not change when the dimensions of the material change, as long as it is made up uniformly.
• For example: the thermal conductivity of a cm 3 of gold is exactly the same as the thermal conductivity of a 100m 3 of gold.
• Generally obtained in the industry using one of two tests, either the D-5470 test, or the E-1461 standard ASTM tests.
• The D-5470 test measures the thermal impedance in Ccm 2 /W (Celsius, centimeters squared per Watt) of the sample and gets a value of the thermal conductivity through the relation:

Thermal Conductivity = Thermal Diffusivity * Specific Heat Capacity * Density

Thermal Impedance

• This is the opposite of thermal conductivity. It is a measurement of the ability of a material to oppose the flow of heat, so from a PCB point of view, we want this value to be low. The lower the thermal impedance, the quicker heat flows through the PCB and to the heat sink where it is dissipated.
• Its value is dependent on the thermal conductivity of the material and its thickness; in other words, this is not a material property, but is an object property, as changing the thickness of the material will change this value. Saying that, changing the area of the material will not change this value (as long as the thickness stays constant).
• For example: the thermal impedance of a sheet of laminate is the same as the thermal impedance of a cut piece of the laminate, say a cm 2 of it. Whereas the thermal impedance of a sheet of gold of 1mm thickness is different to the thermal impedance of a sheet of 2mm thickness.
• This is generally obtained using the D-5470 test mentioned above and relates to the thermal conductivity via the relation:

Thermal Impedance = Thickness / Thermal Conductivity

Thermal Resistance:

• Thermal resistance (measured in Kelvin / Watt) is basically the same as the thermal impedance. The difference is that it takes into account the area of the sample as well as the thickness and conductivity.
• Changing either the thickness or the area of the material will change the associated value of the thermal resistance.



Thermal Resistance = Thickness / (Thermal Conductivity * Sample Area)

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