Surface-mount IC packages can be utilized on a PCB in a variety of ways. For the QFN harvesting service, the QFN bundles are by far the most common option. QFN stands for Quad Flat No-lead package in electronics. Despite its small size and minimal heat dissipation, this package is lead-free. QFN packages, like all other IC packages, connect the embedded system to the circuit board by way of the silicon plate.
Overview of the QFN Package
QFN packages are widely used in semiconductors due to their inexpensive cost, compact size, and superior electrical and thermal performance. QFN packages link silicon dies to printed circuit boards using surface-mount technology, much like any other semiconductor package.
After assembly, QFN, also known as CSP, is a lead frame-based packaging that allows for visual and physical interaction with the leads. QFN packages commonly employ copper lead frames for die assembly and PCB connections. Multiple rows of pins are possible in the QFN packaging. Either punching or sawing may create the single-row construction.
Reduced lead inductance owing to suitably short bond wires, low weight; thin profile; and a “near chip-scale” footprint are some of the advantages of QFN. It is ideal for new applications that require greater performance in terms of size, weight, and thermal conductivity.
Advantages of QFN packages
- No-lead quad-flat packaging is light, compact, and easy to handle.
- They come in a range of sizes, including a tiny footprint with a sleek profile.
- Bond wires must be reasonably short to connect the die and frame.
- Inductance in the lead is relatively low.
- These parts are ideal for applications needing effective heat dissipation.
- A wide range of options is available at a reasonable price point.
Flip Chip QFN vs. Wire Bond QFN
In addition to wire bonding, several packaging companies also provide a flip-chip QFN form of die-to-package connection. Flip-chip QFNs are commonly employed in RF and wireless applications because of their superior electrical performance. When a flip-chip QFN is assembled, bumping is required in addition to the usual assembly procedures, which raises the cost of Flip Chip QFN.
QFN: Punched vs. Sawn
When a single mold cavity is utilized to produce a package, a punch tool is used to separate it. Thus, just one package may be made using this method.
These packing components are made with the use of molds. This strategy aims to dismantle a large number of packages. The sawn-type packages can be separated into individual ones using a final saw approach.
Detailed Overview of the QFN LeadFrame
Leadframe is a copper frame surrounding the die and contains all of the packaging pads and the exposed pad in every QFN package. LeadFrames are generally 0.3-0.4 mm thick copper sheets with a matte tin covering.
The sheet is exposed to a photochemical etching solution to get rid of the extra space. The next step is to cut the edged sheets into thin strips. Wire bonding occurs on the inner leads, while the QFN package leads are attached to the outside leads.
The leadframe strips go through a stamping procedure throughout the assembling process. The assembling procedure can begin once the stamping phase is complete. Die pads are connected to the leadframe pads through wire bonding, and optional downbonds from the die to the uncovered pad for grounding can also be added.
Thermal Properties of QFNs
Due to the low thermal resistance of the QFN package exposed pad, it is advised that the exposed pad be soldered to a wide conductive surface, such as the GND plane. Approximately 70% of the heat generated by the package is dissipated along this channel. Metal planes can boost heat transfer through the exposed pad by 90%.
Electrical Properties of QFN
An effective technique for transferring heat from the die to the PCB is using a thermal pad or exposed thermal pad. QFN is a particularly cost-effective option for thermal efficiency with the exposed pad. QFNs can withstand up to 2W-3W without the need for external cooling.
These packages go by a variety of names depending on the manufacturer, such as MLF, FL, and can include pads on only two sides or four sides, as is more common.
- Wire Bonding
For a long time, gold wire bindings were the norm. Copper is taking their place, although they are still accessible. Lower cost and improved conductivity are two advantages of copper wire bonding.
However, bonding copper wires to a pad requires more significant force. Several semiconductor foundries provide IO pad cells with copper bonding in mind to accommodate thicker pads.
- Die Attach
Leadframe pads are held in place by this epoxy. Electrically conductive materials tend to have superior thermal conductivity than non-conductive ones, although there are two primary varieties to choose from: conductive and non-conductive.
The small size and good heat dissipation of QFN IC packages make them desirable. QFNs can be employed in a wide range of applications. As a result, there is a high demand for QFN surface-mount packages.