The Quad Flat No Leads package, or QFN, is a very small square-shaped or rectangular surface-mount plastic package with no leads.  It is basically a quad flat package, except for the absence of leads protruding from its sides. Metal pads or lands around the periphery of the bottom of the QFN package serve as electrical connection points to the outside world. Because the QFN has no leads and has shorter bond wire lengths, it exhibits less inductance than leaded packages and therefore provides a higher electrical performance. The QFN package also includes an exposed thermal pad at the package bottom to facilitate heat dissipation from the die.

The QFN package has two common types:  the 'plastic-molded QFN' and the 'air-cavity QFN'.  Of these two, the plastic-molded QFN is less expensive because of a simpler body structure consisting of just a lead frame encapsulated by plastic.  The air-cavity QFN, on the other hand, has a cavity inside the package body and requires a third part: a ceramic or plastic lid to seal the package.  The air-cavity QFN, however, allows device operation at much higher frequencies: 20-25 GHz vs. the 2-3 GHz possible with the plastic-molded QFN. 

The QFN package may also be classified according to its assembly process: either as cavity-molded punch-singulated QFN or as array-molded saw-singulated QFN. 

The body sizes of typical QFN's range from 3 mm. square to 12 mm. square.  The standard QFN pad pitch (distance between pads) is 0.5 mm. 

Table 1. Properties of Some Examples of QFN's