No more heat margin for the product? How a knowledge of semiconductors is key to making accurate predictions

Hello, everyone. I’m Urase, manager for a technical department.

Today, I would like to talk about thermal analysis (simulation), dealing in my division.

With the reduction in the size of products in recent years has led to more and more serious thermal problems, we receive an increasing number of inquiries about thermal analysis from our customers. There are various types of inquiries, but in this blog, I will briefly explain a thermal resistance of semiconductors, which is essential for thermal analysis.

Thermal resistance of a semiconductor is often listed in the semiconductor specifications (data sheets) provided by the semiconductor supplier, so you need to find out how it is defined. However, the items for thermal resistance listed in the data sheet vary for each semiconductor supplier, and I feel that the first hurdle is to understand what these thermal resistances represent. (This is where many customers get confused.)

<Typical thermal resistances and their equations>

θja = (Junction Temp. – Ambient Temp. ) / Power
θjc = (Junction Temp. – Case Temp.    ) / Power
θjb = (Junction Temp. – Board Temp.   ) / Power
ψjt = (Junction Temp. – Top case Temp.) / Power

Thermal resistance can be calculated by dividing a temperature difference between two points by a power consumption, as shown in the formula, and by measuring one of the temperature out of two points, you can derive another point temperature by using this formula.
As you can see from the equation, it’s easy to understand because it consists of simple expressions, so you won’t feel the difficulty.

However, there is a tricky point to be considered here. It is significant change in thermal resistance depending on the defined environment*1 (PCB size, external heat sink, etc.). That means the thermal resistance defined by a semiconductor supplier might not suitable for thermal prediction of a product under design.

*1 Thermal resistance specified by semiconductor suppliers is often defined in accordance with JEDEC standards.

In order to perform thermal simulations utilizing thermal resistances defined by a semiconductor supplier, it is necessary to fit the thermal resistance in the environment defined by the semiconductor supplier, and then deploy the optimized thermal resistance to the thermal simulation model under design.

You might wonder, “That’s pretty bothersome!”, hearing I have explained so far.

We are well experienced in thermal analysis (simulation) considering both customer’s operating environment and optimization of a thermal resistance defined by a semiconductor supplier. So if that’s what you’re looking for, please feel free to contact us.

Click here for more details on thermal analysis (simulation)

Click here for an explanation of analysis (simulation) in general.


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