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QFN Package Thermal Resistance Supports High Power Applications

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • QFN packages are used in the semiconductor industry because of their small size, affordable price, electrical characteristics, and thermal performance. 

  • At the chip level, thermal energy is produced by heat generation at the transistor function, and thermal energy is produced due to the chip circuit's resistive layers.

  • The exposed thermal pad decreases the thermal resistance of QFN packages. 

 QFN package

QFN packages are used in the semiconductor industry because of their small size, affordable price, electrical characteristics, and thermal performance

QFN packages have gained popularity in the semiconductor industry due to their small size, affordable price, good electrical characteristics, and excellent thermal performance. High thermal performance is possible with QFN packages. The QFN package thermal resistance value is dependent on ambient temperature, type of PCB board used, number of layers in the PCB, etc. The QFN package thermal resistance is low and offers an exceptionally good thermal path to the board.

We will explore QFN packages and their thermal performance in this article.

Semiconductor IC Thermal Management 

The thermal environment of a chip is important, as it influences performance and reliability. For all the ICs available on the market, there is a maximum junction temperature specified in the datasheet for safe operation. Whenever the junction temperature goes beyond the upper limit, it affects the reliability and performance of the IC.

The packaging used in an IC is of paramount importance for efficient heat transport from the IC to the board or ambient. At the chip level, the thermal energy is produced in two ways:

  1. Heat generation at the transistor function.

  2. Thermal energy produced due to the chip circuit's resistive layers.

To maintain the chip's life, the maximum temperature needs to be kept below the prescribed value given in the datasheet. IC packaging influences how the heat travels from the transistor junctions or resistive layers to the ambient. The thermal resistance of the package is significant, as a low value indicates faster thermal energy transport.

Let’s look at how  QFN packages establish thermal management.

QFN Packages

Quad flat no-lead (QFN) packages are popular due to their low cost, small size, good electrical performance, and heat dissipation capabilities. The thermal performance of QFN packages is the main reason they are used in automotive systems, industrial power applications, and consumer electronics. The lead frame-based package is extensively used in high-speed and high-frequency applications. The exposed paddle in QFN packages makes it suitable for high power systems.

QFN Package Thermal Resistance

Thermal resistance is a measure of how effective the IC package is at dissipating heat. Generally, thermal resistance is the rise in temperature for 1 Watt of power dissipation in the IC. The unit of thermal resistance is °C/W. In data sheets, the ‘'  symbol is used to denote thermal resistance.

QFN packages are designed with an exposed paddle. This exposed thermal pad at the bottom of the package is soldered directly to the PCB. This type of connection establishes a thermal path for heat transfer from the die to the board. The exposed thermal pad decreases the thermal resistance of the QFN package. The thermal pad acts as a built-in heat sink for the IC, carrying the majority of the thermal energy generated and dissipating it to the PCB.

QFN Package Variants

Due to their extraordinary thermal performance, QFN packages are used in telecommunications, portable consumer products, and automotive electronics. As the demand for QFN packages increased, different variants were released in the market. A few of them are:

  1. Micro lead frame (MLF) packages

  2. Leadless plastic chip carrier packages

  3. Quad leadless packages

All these belong to the QFN packaging family and exhibit the same thermal performance. The need for miniaturization and fast performance encouraged the development of other variants. Let’s take a closer look at high power quad flat no-lead (HQFN) packages.

High Power Quad Flat No-Lead IC Packages for High-Power Applications

The thermal performance of ICs influence the performance, life, and reliability of the entire system. With miniaturization, the thermal performance of ICs face challenges, as the area for heat dissipation is drastically reduced.

One packaging style that supports miniaturization and thermal performance is the high-power QFN package. High power QFN packages are designed for large-scale power dissipation. Even though HQFN packages are based on lead frame designs (just like basic QFN packages), they can dissipate heat from both sides. The availability of two surfaces for heat dissipation enhances the thermal resistance of HQFN packages. These packages incorporate a silicon lid attached to the die to spread heat.

Cadence tools support the simulation of the thermal performance of various IC packages. Cadence software offers simulation tools that can assist in the thermal evaluation of integrated circuits.  Leading electronics providers rely on Cadence products to optimize power, space, and energy needs for a wide variety of market applications. If you’re looking to learn more about our innovative solutions, talk to our team of experts or subscribe to our YouTube channel.