Flat no-leads package

Flat no-lead is a near chip scale plastic encapsulated package made with a planar copper lead frame substrate.

[1] Flat no-lead packages usually, but not always, include an exposed thermally conductive pad to improve heat transfer out of the IC (into the PCB).

In contrast, the air-cavity QFN is usually made up of three parts; a copper leadframe, plastic-moulded body (open, and not sealed), and either a ceramic or plastic lid.

This package offers a variety of benefits including reduced lead inductance, a small sized "near chip scale" footprint, thin profile and low weight.

It also uses perimeter I/O pads to ease PCB trace routing, and the exposed copper die-pad technology offers good thermal and electrical performance.

These features make the QFN an ideal choice for many new applications where size, weight, thermal and electrical performance are important.

A NSMD approach typically leads to more reliable joints, since the solder is able to bond to both the top and sides of the copper pad.

[8] Component packaging is often driven by the consumer electronics market with less consideration given to higher reliability industries such as automotive and aviation.

As a result there has been much experimental testing and finite element analysis across various QFN package variants to characterize their reliability and solder fatigue behavior.

[14][15][16][17][18][19][20] Serebreni et al.[21] proposed a semi-analytical model to assess the reliability QFN solder joints under thermal cycling.

[22] The dissipated strain energy density is then determined from these values and used to predict characteristic cycles to failure using a 2-parameter Weibull curve.

The die attach paddle is exposed on the bottom of the package surface to provide an efficient heat path when soldered directly to the circuit board.

A more recent design variation which allows for higher density connections is the dual row micro lead frame (DRMLF) package.