Wiki

QFN Package: Everything You Need to Know

In the electronics domain, QFN is one of the most popular semiconductor packages today. These packages are applicable for various applications. Today, we will learn more about the QFN package, including its types, ways to solder the QFN, and more.

What is the QFN Package?

QFN stands for Quad Flat No-Lead package. QFN is the semiconductor that physically and electrically connects the integrated circuit (IC) to the PCB. It uses surface mount technology(SMT)for this process. Unlike traditional packages, this QFN is rectangular, square, no-lead, no-leg thin. While it has an electrical connection at the bottom of the package, it is mounted directly on the PCB surface. Due to its small size, low cost, lightweight, and lead-free Compliance coupled with excellent electrical and thermal performance, this package is ideal for any application where size, weight, and performance are critical.
 
These features of QFN make it the choice for applications with high performance and space constraints. Standard Properties of QFN Packages include:
Height
It should have a standard height of 0.85 mm, ranging from 0.35 mm to 2.10 mm.
Halogen-and lead-free
It should be halogen—and lead—free. To understand QFN’s lead-free properties, check out RoHS compliance.
Compliance
It should follow the RoHS, REACH, and ELV compliance.

Types of QFN Package

FC’s QFN packages are versatile and can be adapted to electronic devices. Some of the major QFN package types include:

Wire Bond QFN

It uses traditional wire bonding to connect the die to the package or lead frame. It is a cost-effective QFN type with suitable consumer electronics, medical devices, and automotive applications.

Flip-Chip QFN

It uses a flip chip to connect the die to the lead frame. The flip chip QFN offers better electrical performance than wire bond QFN. This is because the shorter connection paths enhance thermal dissipation. It has applications in high-performance computing, RF, microwave, and other mobile devices.

Punched QFN

In this type, the QFN package is formed by punching the lead frame from a continuous strip of material. It is used for high-volume and cost-sensitive applications. It produces the package with precise dimensions and is often combined with wire bonding.

Sawn QFN

This method involves sawing a large molded panel into each QFN package. It allows for varied package sizes and helps with flexible designs. Due to the sawing process, it offers high precision and a clean edge. It has applications in custom electronics, small to medical production, and industrial applications.

Advantages and Functions of QFN Package

After understanding QFN encapsulation and its types, we can discuss its advantages and functions. 

Advantages

Firstly, we have discussed some of the major advantages of QFN chip are as follows:
  1. QFN packages are small and save space on circuit boards.
  2. They dissipate heat effectively due to their exposed thermal pad.
  3. QFNs offer good electrical performance with short paths.
  4. They’re sturdy and less prone to damage.
  5. QFNs are easy to handle and suitable for automated assembly.
  6. They maintain good signal quality, which is important for high-speed circuits.

Functions

Then, the most important functions of QFN chip are as follows:
  1. QFNs protect semiconductor chips from environmental damage.
  2. They facilitate electrical connections between chips and PCBs.
  3. QFNs help in dispersing heat generated by chips.
  4. They contain various components for signal processing.
  5. QFNs integrate multiple functions into one package.
  6. They come in various sizes and configurations for different needs.

Components of the QFN Package

The central part of the QFN chip includes:

  • Lead frame: The lead frame is the major part of the QFN package. The metal frame provides mechanical and electrical support and determines the IC’s overall performance.
  • Die: Silicon dies to perform electronic functions.
  • Bonding Wire: A tiny wire connects the die to the lead frame.
  • Exposed Pad: The central pad on the bottom of the package improves thermal dissipation.
  • Compound: Compound is a protective material (usually plastic) that covers and protects the die and wires.

How To Solder A QFN Package?

Surface mount technology involves placing and soldering components directly on the PCB surface. The QFN package is commonly used in SMT due to its small size and excellent electrical performance.
To solder the QFN package, you have to consider the following steps:

Step One: Prepare the PCB

First, the PCB should be cleaned. You can use isopropyl alcohol to clean the PCB pads.

Step Two: Apply Solder Paste

Using a stencil, apply a thin, even layer of solder paste to the PCB pads. Ensure the stencil is properly aligned with the PCB pads for accurate deposition. Ensures, the optimal solder paste coverage of 60-85% on the thermal pad.

Step Three: Position the QFN

Then, align the QFN component with the pads on the PCB.

Step Four: Place the QFN Component

Use the machine to pick and place the QFN components accurately on the PCB pads. Try to use the pick-and-place machine with an accuracy of ± 0.05 mm.
 
You can use the manual method, using tweezers to pick up the QFN component. The exposed pad in the center should be directly over the corresponding pad in the PCB, and then you can gently place the component.

Step Five: Preheat the PCB

Preheat the PCB using a reflow oven or hot plate.
  • Hot Air Rework Station: Evenly heat the QFN until the solder paste reflows.
  • Reflow Oven: Use the appropriate reflow profile to melt the solder paste.
  • Hot Plate: Heat until the solder paste reflows.
The thermocouple monitors the top surface temperature of the QFN package throughout the process. It ensures that the peak package temperature does not exceed the standard value.

Step Seven: Manual Soldering

  •   Secure two opposite corners with a fine-tipped soldering iron.
  •   Solder the Pads: Carefully solder each pad using flux to prevent bridging.

Step Eight: Inspection and Testing

  • AOI and X-ray: Automated optical and X-ray inspections detect soldering defects, such as bridging, open joints, and voids.
  • Functional Testing: Verify the functionality of the assembled board to ensure all components are correctly soldered and operational.

QFN Package Process Considerations

Although the QFN package is a highly applicable, simple, and cost-effective package. It still has its limitations:

Wire Bonding

Gold wire bonds have been used as the default material for many years. Although they are still available, they are gradually being replaced by copper. This is because copper wire bonding is low-cost and has good electrical conductivity. However, copper wire requires more effort to bond wires to pads.

Chip Mounting

Epoxy can be used to secure the core to the lead frame pad. Two main types are used, conductive and non-conductive, depending on the system’s electrical requirements; conductive materials have better thermal conductivity.

Soldering Issues

Since the pad spacing of QFN packages is very narrow, this introduces a soldering issue called solder bridging. In addition, since QFN packages do not contain lead, there can be challenges when preparing these packages for disassembly.

Compatibility Issues

QFN packages can be affected by changes in component or board size. The absence of lead in QFN packages causes this to happen. As a result, they become vulnerable whenever they experience some nominal CM or OEM practice.

Difference Between QFN and QPF

Once you know about QFN, then let’s compare it to QPF:

Feature
QFN (Quad Flat No-lead)
QFP (Quad Flat Package)
Package Design
Flat package with no leads extending from sides
Flat package with leads extending from all four sides
Size
More compact and space-saving
Generally larger due to extending leads
Thermal Performance
Excellent due to exposed die pad
Moderate, depends on lead frame design
Electrical Performance
Lower inductance and resistance
Higher inductance due to longer lead paths
Assembly
Surface mount technology (SMT)
Surface mount technology (SMT)
Mounting
Mounted directly onto PCB with solder paste
Mounted on PCB with leads soldered to pads
Manufacturing Cost
Generally lower due to simpler design
Higher due to the complex lead structure
Reliability
High reliability, robust mounting
Moderate lead bending can be an issue
Applications
High-performance, space-constrained applications
General-purpose, moderate-performance applications
Inspection
Optical and X-ray inspection
Easier visual inspection due to visible leads
Common Uses
Mobile devices, automotive, and medical devices
Consumer electronics, industrial control systems
Assembly Complexity
Requires precise alignment for reflow soldering
Easier alignment due to visible leads

Application Of QFN Package

With the rapid development of modern science and technology, electronic products are becoming smaller, more portable, and multifunctional. While continuing to develop advanced packaging technology, FC also continues to promote the advancement of traditional packaging technology to meet the increasingly diversified application needs.

Due to space constraints, the small size, lightweight, and good thermal performance of the QFN package make it an ideal choice for mobile devices, such as smartphones, tablet PCs, and other products.

In the field of communications equipment, such as wireless routers, base stations, and other products, the QFN chip package is a form of high integration and easy-to-realize thermal management, so that it can meet the needs of high performance and high reliability.

In automotive electronics, such as car navigation, car entertainment, and other products, the QFN chip package forms shock resistance and high-temperature performance, so it is suitable for complex car environments.

QFN chip package form is also widely used in industrial control, medical equipment, aerospace, and other fields

Conclusion

QFN package is an excellent choice for connecting the IC to the PCB. Its compact and lead-free design makes it ideal for many high-performance and space-saving applications. The package is cost-effective, works well with automated assembly methods, and is environmentally friendly.
QFN provides a reliable and efficient solution for improving electric device performance and miniaturization through effective thermal and electrical performance.

FAQs

Yes, QFN is suitable for high-frequency applications. The QFN chip has a low parasitic effect and good signal integrity. However, proper design consideration is required to minimize distortion.

QFN packages come in various configurations, including standard QEN, think-QFN, dural row QFN, and custom variants with various pads, package sizes, and arrangements.
Common challenges include the suitable deposition of solder paste, precise component location, prevention of solder bridging or inadequate soldering, control of heat concerns, and potential flaws such as voids or solder ball development.

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *