The Use of Steady State Thermal Analysis on Power Semiconductor Devices

Key Takeaways

• Gain an understanding of the purpose of Steady State Thermal Analysis.
• Learn how these types of analyses provide insight into a device’s performance.
• Gain an understanding of the steps involved in performing this type of analysis.

A computer’s CPU is created from semiconductor materials

In the field of electronics, specifically in the area of PCBA, thermal conditions are critical to a device's lifecycle, performance, and functionality. Environmental conditions often influence a designer's approach to the layout of their components on a PCB.

With such an emphasis on thermal conditions in the field of electronics, it is only logical that specific types of thermal analysis are warranted. One such form of analysis is called Steady State Thermal Analysis, which is what we are going to focus on. 

What is a Steady State?

In the field of Physics, a steady state is a stable condition that does not change over time or one in which change in one direction is balanced continuously by a change in another. In Chemistry, a steady state is a situation where all state variables are constant despite ongoing processes that attempt to change them.

The field or area in question may change, but the definition of a steady state remains constant. What also remains constant is the adverse effects of thermal conditions (i.e., high temperatures) on semiconductor devices.

The need for miniaturization exacerbates these conditions since it involves mounting power semiconductors at small distances, thus utilizing the same heatsink.

What are Power Semiconductor Devices?

When a semiconductor device is in use as a rectifier or a switch in power electronics applications it is called a power semiconductor device. A typical example of a power semiconductor device would be a switch-mode power supply. We call a device of this nature a power device, or a power IC, if utilized in an integrated circuit.

Typically, a power semiconductor device is in use in commutation mode, and thus its design optimizes this particular type of use. We find power semiconductor devices in systems that provide power ranging from tens of milliwatts to as much as a gigawatt. This includes devices like audio amplifiers in a typical pair of Bluetooth headphones as well as in HVDC (high-voltage direct current) transmission lines.

Note: Commutation is the process of turning off a conducting thyristor. In general, there are two types of commutation: voltage-based and current-based. There are also three methods of achieving commutation: natural, forced, and dynamic.

Soldering iron of a robotic system

Steady State Thermal Analysis

We define a Steady State Thermal Analysis as an analysis of changes in which the properties of a substance are at a constant temperature. An analysis of this nature is vitally essential to accessing proper operating parameters of power semiconductor devices.

In the area of electronics, semiconductor devices can be adversely affected when the junction temperature reaches a high enough value, which can cause melting and thermal runaway.

A steady state thermal analysis is the final step of a transient thermal analysis. Furthermore, a steady state thermal analysis is essential in determining the heat flow rates, temperatures, heat fluxes, as well as thermal gradients in devices under the supply of constant heat. Steady state thermal analysis utilizes heat sources such as radiation, convection, and continuous temperature boundaries. In summary, this type of analysis provides a linear graph when drawn as a function of time.

The Negative Effects of Heat on Semiconductor Devices

The advancement of semiconductor technology is synonymous with the continuous miniaturization of nearly all electronic devices. The only real exception is smartphones, which demand a premium for similar models only a few inches larger.

However, regardless of the size parameters of the device, mitigation of excessive heat is still a top priority. With regards to semiconductors, this is especially true and is evident in the maximum junction temperatures specified by their manufacturers. These parameters provide the temperature thresholds that govern acceptable operating conditions.

This demonstrates the importance of measuring the operating temperature of power semiconductor devices, including applications such as thyristors, power MOSFET, IGBTs, and power diodes.

The Purpose of a Steady State Thermal Analysis

The overall purpose of a steady state thermal analysis is to calculate the thermic response to heat loads depending on the applied convection conditions, the specified temperatures, or both. A steady state thermal analysis presumes a steady state for all boundary conditions and thermal loads. However, a steady state analysis does not assess these changes over time.

In other words, a steady state thermal analysis analyzes the effects heat will have on the performance of a particular product. It studies the effects these changes in temperature will exert on a material's properties. Understanding these results allows a company to predict product performance behavior, increase product lifecycle, and improve upon their designs. This also enables a company to manufacture products that are more robust and resistive to the effects of high temperatures.

Thermal analysis, which is a branch of materials science, provides a deep understanding of the ways to reduce the thermal-related risk of temperature to a system and its components. In the area of PCBA, excessive thermal stresses are one of the significant issues affecting performance, functionality, and lifecycle. Therefore, proper thermal assessment is a requirement to determine temperature gradient, temperature distribution, and heat flow or exchange between the device and its environment.

The importance of mitigating heat through better design and component choices is paramount in the area of PCBA. With the effects of heat impacting design, performance, functionality, and life cycles of PCBAs, steady state thermal analysis is a vital assessment. The insight it provides companies enables them to manufacture better products that are better suited for their intended environment. This, in turn, reduces costs and increases the lifecycle of products.

Using a multimeter to assess power semiconductor measurements

Thankfully, with our PCB Design and Analysis overview page, you’ll be sure to have your designers and production teams working together towards implementing the use of Steady State Thermal Analysis to assess your company’s product performance under extreme thermic conditions. 

Designing a robust PCBA starts with using the right tools. PCB Design and analysis tools from Cadence, have the capabilities you would expect to be able to produce the best product possible. This makes it easy to identify and mitigate any issues for your  thermally sensitive designs right from the beginning. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.