Quad-flat-no-lead (QFN) packages are popular in circuits due to their small size, light weight, and thin profile.
A larger portion of the QFN package gets soldered to the PCB and enhances the mechanical strength.
QFN packages are otherwise known as chip-scale packages, as the lead can be contacted and seen even after assembly.
Quad-flat-no-lead (QFN) packages are popular in circuits due to their small size, light weight, and thin profile
Depending on the circuit requirements, engineers choose between leaded chip packages and non-leaded chip packages. Quad-flat-no-lead (QFN) packages are popular in circuits due to their small size, light weight, and thin profile. But, you might still be at the stage where you are wondering, “What is a QFN package?” Here is what you should know about them, including their challenges and advantages.
But, before we jump in, let’s go over the difference between leaded and non-leaded chip packages.
Leaded and Non-Leaded Chip Packages
Circuits are realized using ICs of different packaging styles. The packaging styles are chosen by considering weight, size, thermal dissipation, vibration impact, application area, etc. Leaded and non-leaded packages are both used in printed circuit boards, and there are advantages and disadvantages to both. Let’s focus on leadless packages here.
Leadless packages are IC packages without any projecting terminals. When it comes to the mass manufacturing of electronic circuits, leadless packages are advantageous over leaded packages. As the electrical contact points of leadless packages are beneath the package, they save space. And, the mechanical structural integrity of leadless packages is excellent; the package sticks to the PCB under most environmental conditions. A large portion of the QFN package is soldered to the PCB and enhances the mechanical strength. The contact area to package ratio of leadless packages is high, holding the IC package onto the PCB.
Besides reduced weight and space, and mechanical strength, other advantages of leadless chip packages include:
- Reduced lead inductance, which is a missing feature in most leaded packages.
- Better electrical conductivity due to reduction in lead resistance.
- Low thermal resistance, which improves the thermal performance of the IC.
- Easy handling and placement.
Okay, now we can jump into your question about what a QFN package is.
What Is a QFN Package, Really?
QFN packages are globally used IC packages. They offer low cost, small size, excellent thermal performance, and better electrical performance compared to leaded packages. QFN packages are free from extension pins. Instead of physically projecting terminals for establishing electrical contacts, QFN packages are surrounded by electrode contacts in their perimeters. As there are no leads, their mounting area is less than leaded packages. The height of a QFN package is also less. However, there is a considerable reduction in the number of electrode contacts when it comes to QFNs.
QFN Package Constructional Features
The QFN package is linear, with either a square or rectangular shape. At the center of the QFN package bottom, there is a large exposed pad. The heat conduction is improved with the presence of the exposed pad. The heat dissipation through the exposed pad introduces a direct heat dissipation channel in the package. Generally, the heat dissipation pad is directly soldered on the circuit board. Heat dissipation vias are also used to divert the excess power consumption to the copper ground plane.
QFN packages are otherwise known as chip-scale packages, as the lead can be contacted and seen even after assembly. QFNs either have multiple pin rows or single pin rows. Electrical connections are established using the conductive pads around the perimeter of the package. As the internal pin and pad get shorted for electrical connections, the wiring resistance and self-inductance get reduced considerably in the QFN package.
Types of QFN Packages
Based on the die-to-package connectivity, QFN packages are classified as:
- Wire bond QFNs - In wire bond QFNs, wire bonding is used for connecting the die to the package.
- Flip-chip QFNs - In flip-chip QFNs, flip-chip technology is used for connecting the die to the package.
- Punched QFNs - Molded into a single mold cavity setup. The punch tool is used to split the molded cavity.
- Sawn QFNs - The mold array process (MAP) is used. The MAP process involves cutting a massive box set into smaller parts. The sawn QFN packages are sorted by sawing bulk packaging into single units.
Flip-chip QFN packages are extensively used in RF and wireless applications. The electrical performance of flip-chip QFNs is better compared to their wire bond counterparts. However, the cost of manufacturing flip-chip QFNs is greater.
Now that you know what a QFN package is, you should know there are some disadvantages to them: oxidation problems, missing clearance of soldering pencils to reflow pads, and floatation problems are all things to look out for.
Cadence’s suite of PCB design and analysis tools can help you design QFN packages for various applications such as dc-dc conversion, signal processing, etc. 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.
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