What Are QFN (Quad Flat No-Lead) Packages

As electronic devices become smaller and more compact, there is an increasing demand for smaller and more efficient components. The QFN chip package is one such component. QFN packages are popular surface-mount technology packages due to their small size, excellent thermal and electrical performance, and ease of assembly. They are widely used in various electronic applications, such as mobile devices, automotive electronics, and industrial control systems. 

In this blog, you will get information about the features and benefits of QFN packages and their various types and applications in various industries. Whether you’re a hobbyist in electronics or a professional engineer, this article will give you a thorough understanding of QFN packages and their role in modern electronics.

What does QFN stand for?

The QFN packaging stands for quad flat no-lead. It physically and electrically connects integrated circuits with printed circuit boards. Through holes are not necessary because of surface mount technology, which connects ICs to the printed circuit board’s surface. 

The printed circuit boards benefit from moderate heat dissipation in this small leadless package. Heat transfer can be facilitated. Flip-chip technology is sometimes used instead of wiring to connect the die and the frame, especially when electrical performance is critical.

Inside a QFN package

The QFN chip or package has a die surrounded by a lead frame. However, the lead frame comprises copper alloy and a matte coating. The die and frame are connected to each other using wire bonding. Gold or copper is used as a wired bonding. 

The flip chip technology works better than a conventional chip. The metalized terminal pad is situated on the bottom surface. These pads are there, along with the four edges of the bottom surface. It also provides electrical interconnection to the printed circuit board. 

The exposed pad is located at the bottom of the package. It provides an efficient heat path to the printed circuit board. The QFN packaging is soldered to the PCB at the exposed pad. The die attached to the epoxy component is utilized to fix the exposed pad die. Below are some properties of the standard QFN component:

• 0.35 mm to 2.1 maximum seated height
• Halogen free and lead-free
• REACH, RoHS, and ELV compliance
• Terminal plating of Sn and Ni-Pd-Au

Thin QFN (TQFN), micro-lead frame (MLF), and more commonly used QFN components or packaging variants. 

Advantages of the QFN package

There are uncountable semiconductor packaging technologies available on the market. But the packaging of QFN components has become the top choice for semiconductor packaging due to its advantages. Below are the top benefits that you can avail yourself of with the QFN component:

• The low cost of the packages, which lowers the overall cost of production and paves the way for the manufacturer to offer affordable electronic products, is one of the most significant benefits of quad-flat no-lead packaging.
• Quad flat no-lead packages are lightweight and easy to handle. Both advantages are significant today, with a growing emphasis on producing lightweight electronic goods.
• QFN packages have outstanding electrical and thermal performance and are ideal for heat dissipation applications.
• The small form factor of QFN packages reduces the complexity of the circuitry, making it easier for developers and designers to work on them.
• A bond wire that connects the die and frame is short.
• The lead inducement of these packaging is low.

Different types of QFN packages

There are several types of QFN packages available in the quad-flat-no-lead packaging market today, which are used depending on the needs of the circuitry and the electronic goods being manufactured. Below are the types of QFN packages:

•  Sawn QFN packaging

Punch QFN packages are the core packages molded in a single cavity format. It is separated with the help of a punch tool. Punched quad-flat-no-lead packaging is designed in such a way that it works perfectly for low-volume products.

•  Sawn QFN

Sawn quad-flat-no-lead packaging or QQFN is created by cutting many packages using mold array processing. The package was developed to create individual-sawn QFN packages. These packages are mainly used in high-volume production.

What are the different types of QFN package terminal pads?

The terminal pads are different from each other based on shape, design, and dimension. Below are the different types of terminal pads:

•  Completely exposed terminal ends

This type of terminal end is fully exposed to the package’s edge and side.

•  Pull-back terminal end

This terminal end is pulled back from the package edge. After the reflow soldering process, solder is not added.

•  Side wettable flank

This type of terminal end is an altered form of the fully exposed terminal end. It enables solder wetting for the creation of solder fillets. The inspection of solder failure with AOI becomes more accessible with the help of soldier fillets. This eliminates the need for inspection via X-ray machines.

How to solder a QFN onto a PCB?

Soldering is a necessary step in the QFN assembly process. The parts are mounted after screening for solder paste during the assembly process. Reflow soldering is used to connect the QFN pieces once they have been mounted.

When the PCB is placed under the reflow oven, the temperature will make certain areas of the board heat faster than the rest. The large copper area and heavier components will take longer to heat.

The QFN top surface temperature is monitored with the help of a thermocouple throughout the process. This ensures the peak package body temperature does not exceed the standard values.

How are the solder joints on QFNs checked?

The QFN components’ solder joints are formed beneath the package. Optical and X-ray inspections are used to inspect the QFN solder joint.

Differences between QFP and QFN

Quad flat package, also known as QFP, is a surface mount integrated circuit package, like QFN. The lead, unlike QFN, is extended out in an L-shape. It provides an excellent foot for the package during the PCB assembly process.

The QFP package is available in different numbers of pins, ranging from 8 pins per side to 70 pins per side—the usual pin space range is 0.4mm to 1mm. Thin QFP, very thin QFP, and more are the variants of QFP.

The main distinction between the two is that QFP packages have leads (also known as pins) extending from the bottom of the package and connecting the package to a printed circuit board (PCB). In contrast, QFN packages do not have leads and are connected to the PCB using surface mount technology.

What is an LQFP64 package?

LQFP64 is a low-profile QFP that comes with 64 pins. It provides the same advantages as QFP. But LQFP64 has a thinner body thickness of 1.4mm, distinguishing it from QFN. They also have a standard lead-frame footprint of 2 mm.

Conclusion 

QFN packages are a popular and versatile component in modern electronics due to their small size, excellent thermal and electrical performance, and ease of assembly. They provide a cost-effective solution for high-density PCB layouts and are widely used in various applications, including mobile devices, automotive electronics, and industrial control systems. As the demand for smaller and more efficient electronic devices grows, QFN packages will undoubtedly play an essential role in meeting these demands.