QFN packaging and process features

QFN is the most widely used BTC. At first it was only used for products with low reliability requirements but price sensitivity. Due to its excellent high-frequency performance, it is increasingly used in military electronics, network equipment, etc. The OFN package outline is shown in the figure.

The QFN package is very personalized. From the perspective of the layout of the solder joints, there are single-row (circle), double-row (circle), and irregular (irregular). There are also two major and three sub-classes in terms of the structure of the solder end.

1. QFN package features are as follows:

(1) Lead frame structure.

(2) The weld ends are flush with the bottom surface. "

(3) The standard of the center distance of the pins is commonly 0.65mm.0.50mm. 0.40mm. The center distance of the package structure and the soldering end is shown in the figure.

(4) There is a relatively large heat sink pad in the center.

2.Process characteristics

OFN is a packaging with relatively difficult assembly process, which is not only reflected in the pass rate, but also in the reliability and repair. The main soldering defects include:

(1) lead virtual soldering.

(2) Pin bridge.

(3) There are many solder joint voids, especially the heat sink pad in the center of the package bottom surface is most likely to generate voids.

(4) The inner layer of the package.

(5) The solder joint temperature cycle life is relatively short.

(6) The flux residue is not completely volatile, and the wet state is likely to cause leakage or even short-circuit breakdown.