In-Depth Analysis of the Soldering Quality of QFN Packages (Part 1)

QFN (Quad Flat Noleads, Quad Flat Noleads) seems to have a more and more common trend in IC packaging in the electronic industry today. The advantage of QFN is that it is small in size, comparable to CSP (Chip Scale Package) packaging, and its cost is also low. Relatively cheap, the IC production process yield is quite high, and it can also provide better coplanarity and heat dissipation capabilities for high-speed and power management circuits.

In addition, the QFN package does not have to lead out pins from four sides, so the electrical steam performance is better than the leaded package. Traditional packaged ICs such as SO, which have multiple pins must be drawn from the side. Although the QFN package has so many advantages in electric steam and use, it has brought a lot of soldering quality impact to the circuit board assembly plant. Because of the leadless design of the QFN, it is generally difficult to find the solder joints of its appearance. Judge whether its solderability is good.

Although there are still solder feet on the side of the QFN package, some IC packaging companies just cut the lead-frame (lead frame) to expose the cut surface, and do not apply electroplating, so basically the side of QFN It is not easy to eat tin, and the cut surface is easy to oxidize after storage for a period of time, which will cause the difficulty of tin on the side.

1. QFN eat tin standard       In fact, in the IPC-A-610D (PQFN) specification, it is not clearly defined that the side of the QFN must have a smooth arc-shaped curve. That is to say, the welding of QFN can actually ignore the welding condition of the side, just make sure that the bottom of the QFN solder leg and the heat sink position on the bottom are really tin-eating parts. The tin-eating at the bottom of the QFN can actually be imagined as BGA, so it is recommended to refer to the IPC-A-610D, Section 8.2.12 Plastic BGA standard. As for the tin-eating of the middle ground pad, it may depend on the design of each company. .