Double-Sided MOSFET Cooling Package Offers Improved Reliability

Thermal performance in PCBs is a key metric in determining power electronics' overall compliance, reliability, and ruggedity. At the component level, thermal management is greatly influenced by the device's packaging, with packages integrating different heat-sinking methods and techniques. The challenges of PCB design and PCB reworking for thermal management vary among device packages.

Recently, Alpha & Omega Semiconductor Limited (AOS) unveiled a lineup of power MOSFETs offering better thermal management owing to their unique package design. The product aims to solve the challenges facing thermal management.

 

AOS power MOSFET with cooling package. Image used courtesy of Alpha & Omega

 

Cooling Mechanism in DFN MOSFET Packages 

Switching devices in power electronics dissipate heat through their exposed contacts, either directly attached to the PCB or the heat sink. 

Dual Flat No-Lead (DFN) packages are known for their compact form factor, which enables higher power density. These packages feature a flat, leadless design that minimizes parasitic effects, enhancing high-frequency performance and thermal management in electronic circuits. The lack of leads in DFN allows a shorter distance for heat dissipation to the PCB substrate, and hence, better thermal performance is ensured compared to packages with leads. 

 

AONA66916 DFN 5x6 top and bottom views. Image used courtesy of Alpha & Omega

 

For the PCB designer, the bottom contact cooling mechanism necessitates considering thermal performance during the PCB design phase. For example, one PCB consideration for efficient thermal management is incorporating thermal vias. Moreover, the PCB substrate must exhibit low thermal resistance and enhanced thermal conductivity to ensure lateral heat distribution. 

Bottom-sided cooling may also be more susceptible to environmental factors, such as tiny dust particles or contaminants left on PCB, which could degrade heat dissipation capability over time.

 

The AONA66916 MOSFET

AOS recently unveiled the AONA66916 MOSFET, a 100V N-Channel device based on the company’s AlphaSGT technology.

The most notable feature of the AONA66916 is the introduction of a new form of DFN 5x6 package offering cooling surfaces on both the top and bottom sides. A top contact with a large surface area maximizes contact with the device’s heat sink, allowing for better thermal dissipation and performance. The modified package has a low top-side thermal resistance of 0.5°C/W, compared to 0.58°C/W on the AONS66917T, which features a standard DFN 5x6 package.

 

The power dissipation versus case temperature of the top-side versus dual-sided MOSFETs. Image used courtesy of Alpha & Omega

 

While this difference seems minor, for the same junction temperature (175oC), the double-sided cooling package MOSFET can dissipate 35 W more than the single-sided bottom-cooling package. 

Beyond thermal dissipation, other noteworthy specifications of the device include a continuous drain current of 197 A @ 100 V and an RDS(on) of less than 3.4 milliohms at a VGS of 10 V. According to the company, the device is ideal for applications including DC/DC converters, telecom, and solar.

 

The Way Forward for the Electronic Design Process

AOS’s package design is a notable innovation aiming to make the electronic design process more efficient, reliable, and flexible. By enabling greater thermal dissipation, the device package can help ensure greater reliability and performance of a power system without the fear of de-rating. For this reason, the DFN 5x6 double-sided cooling package has the potential to become viable in mission-critical applications requiring rugged electronics products like military appliances and space missions-related equipment.