A surface-mount package with terminals exposed around the perimeter of its underside and no leads projecting from the sides. The central thermal pad on the bottom can be soldered to the board, making it small with good heat dissipation.
Japanese name: QFN
QFN (quad flat no-lead package) appears in 2 practice questions across 2 topics, including Packaging and assembly, How to read datasheets.
Field: Packaging and assembly
QFN stands for quad flat no-lead and is a type of lead-frame package. The die is mounted on a die pad, wire-bonded to the surrounding leads and covered with mold compound, but the leads do not project from the sides; they are exposed as terminals along the four edges of the package's underside. The die pad is usually exposed at the center of the underside too, and is called the exposed pad or thermal pad. Terminal pitches of about 0.4 to 0.65 mm are common. Most QFNs are made by molding many units at once on a lead-frame strip and separating them with a dicing saw. Versions with terminals on only two sides are called DFN or SON.
Because the leads sit under the package and are short, their inductance and resistance are small, which suits RF circuits handling high frequencies and fast-switching power ICs. The central thermal pad is soldered to a pad on the printed circuit board, and multiple thermal vias beneath it carry heat to inner-layer or back-side copper, so thermal resistance can be lower than for a leaded package of the same size. The thermal pad is often tied to ground and doubles as an electrical connection. Its small footprint and low profile make QFN common in compact devices such as smartphones.
Since the terminals are on the underside, most of each solder joint is hidden, so inspection relies mainly on X-ray. Where joints must be confirmed by optical inspection, as in automotive use, wettable-flank versions are used, processed so that solder also wets the sides of the terminals. Too much solder on the thermal pad can float the package and cause poor perimeter joints, while too little hurts heat dissipation, so the stencil opening is split into a grid to control solder volume and voids. Because the solder layer is thin, joint fatigue under temperature cycling also needs attention in large packages.
Letters such as V, W and U in front of QFN mainly denote thickness classes; VQFN is a very thin QFN, meaning a low-profile part with a mounted height of roughly 1 mm or less. Class boundaries and naming differ between manufacturers, so dimensions should be checked on each package drawing. QFP brings gull-wing leads out from four sides, making joints easy to inspect but taking more board area. BGA arranges solder balls in a grid across the whole underside and can provide many more terminals. Because QFN can place terminals only around the perimeter, it is used especially for ICs with relatively few pins.
Answer: B. A small package with no protruding leads, with electrodes on the four edges of its bottom
A QFN has no leads protruding from its sides; electrodes are exposed around the perimeter of the bottom. The short leads give low inductance and allow small, thin packages. A large thermal pad in the center is soldered to the board, and heat escapes through board vias, giving good thermal performance. The hidden joints make visual inspection difficult, however. Long leads on four sides describe a QFP, and a ball array describes a BGA.
Answer: C. Provide a land on the board, solder the pad, connect it to the specified potential (often GND) and conduct heat away through thermal vias
The exposed pad is the underside of the die pad, on which the chip is mounted, exposed outside the package; it is the main path for heat into the board. The datasheet θJA value is typically measured with this pad soldered to the board and connected to inner-layer planes through thermal vias, and leaving it unsoldered greatly degrades heat dissipation. The recommended land pattern may also show the stencil aperture divided into segments to adjust the solder volume and prevent voids and component lifting. Follow the datasheet for the potential to connect it to.
Quad flat no-lead: a flat package with terminals on four sides that has no leads projecting from its sides. The terminals are exposed on the package's underside.
VQFN is the name for a thin (very thin) QFN; the structure is the same. Thickness classes and naming vary by manufacturer, so check dimensions on the package drawing.
It is the exposed die pad that carries the die. Soldered to the printed circuit board, it becomes a heat path through thermal vias, and in many cases it is also connected to ground, serving as an electrical connection.
A QFN has no leads protruding from its sides; electrodes are exposed around the perimeter of the bottom.
Which correctly describes a feature of QFN (Quad Flat No-le…As an Amazon Associate I earn from qualifying purchases.
Interconnect via QFP (quad flat package) BGA Exposed pad Backgrinding CSP (chip-scale package) Dicing Die bonding Flip chip Lead frame