QFN is an acronym for the Quad Flat No-Lead package and is one of the most popular semiconductors used worldwide. There are four main reasons why.
- Low cost
- Small form factor
- Good thermal performance
- Impeccable electrical performance
Like other semiconductor packages, QFN’s function is to connect (both electrically and physically) silicon dies to a printed circuit board (PCB) via surface-mount technology.
QFN is a lead framed package, also known as chip-scale package or CSP, that has the ability to contact and view leads after assembly.
A QFN package typically uses a copper lead frame for PCB interconnection and a die assembly.
Single vs. Multiple Rows QFN
A QFN can have a single or multiple rows of pins; the single row structure forms either by a saw singulation or a punch singulation process.
Both of the processes mentioned above divide a large array of packages such as an 18” X 24” sheet into individual packages.
On the other hand, the multiple rows QFN relies on the etching process to realize the required number of pins and rows, which are then singulated using a saw.
At the bottom of the QFN package, there is an exposed thermal pad that you can solder directly to the PCB system for optimal heat transfer from the silicon die.
Benefits of Choosing the QFN
Some key benefits of using QFN are as follows:
- Decrease lead inductance by using optimally short bonded wires
- It is lightweight
- Small size and thin profile, i.e., “near chip-scale” footprint
- Having an exposed copper die is perfect for several applications with better performance needs
- It uses a standard surface-mount flow and equipment for PCB assembly
- It has no lead associated coplanarity issues
Not many, but there are certain downsides to adopting QFN packages, including:
- Possible floatation of the DFN packages on the molten solder pool found under the thermal pad
- An exposed chip contact pad may face oxidation problems
However, you can mitigate these issues by controlling the re-flow process better and using plated QFN packages (tin), which reduces the oxidization issues.
QFN Thermal Characteristics
A QFN package has an exposed pad that offers low heat resistance allowing it to transfer to your PCB. Therefore, it is highly suitable for soldering the exposed pad to large conductive surfaces like the GND plane.
QFN also allows adequate physical and electrical connection between the IC and the PCB.
QFN Electrical Characteristics
An exposed or thermal pad is an efficient means of drawing heat from a die to a PCB. QFN is thermally efficient, whereas the exposed pad is a cost-effective solution. QFN can handle anything between 2W – 3W without needing forced air cooling.
Other Names of QFN
Different manufacturers name these packages differently, such as Micro Lead Frames (MLF), and Flat no Lead (FL). Both of them are available with pads on two, as well as four sides.
Other names include Micro-Leadframe Package Dual (MLPD), Micro-Leadframe Package Micro (MLPM), and Micro-Leadframe Package Quad (MLPQ).
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