Quad-Flat No-Lead (QFN) packages are very popular and widely used nowadays in the semiconductor industry.  Its primary advantages compared to leaded packages (SOICS, SSOPs, QFPs, etc.) are its small size and greatly enhanced thermal capability, which transforms into more power handling. Let's repeat it, more power in a small size, which fits into the present script of today's electronic gadgets and products: keep it small.  At Bluewater Systems, QFNs are always present in every moderate to complex board design.  There are a lot of advantages with this package compared to leaded packages, but it is not the advantages that cause this blog to be written.  It is something about the way they are presented in the data sheet and the way that they are typically called out for a given number of pins (e.g. QFN32 or 32-pin QFN). Normally, a device's data sheet contains the "features" list which includes the device's package in the very first page, such as, "6x6 32-leadless QFN or 4x4 16-leadless QFN".  But here's the catch, QFN doesn't always imply equal number of pads on all four sides making it square in form. It can also be rectangular, which means two sides have a lesser number of pads than the other two.  QFN16 could mean 4x4 pads on all sides (image on the left) or 2x6 pads (6 pads on the longer side and 2 on the shorter side, image on the right) and so on. Fig1a. 4X4 QFN16Fig1b. 2X6 QFN16 In PCB design, it is always a standard procedure to check the mechanical dimensions of the package to map a correct footprint, even with conventional lead packages. Usually, a package's mechanical details are put on the last few pages in a data sheet.  Worse, some data sheets don't even provide the mechanical details of the package (though this is rare for devices in a QFN package) based on experience. It is sometimes hidden in the manufacturers website. However, in large complex boards, there may be multiple devices in QFN packages with the same number of pads but different pad configurations (square or rectangular in form) which could be prone to human error by interchanging footprints at the pre-layout stage.  So, extra car must be taken when dealing with QFNs. At Bluewater Systems, as part of its evolving quality procedures, a special footprint naming convention for QFNs has been adopted. It must include a QFNs pitch, pad configuration (number of pads in two adjacent sides) and package size. It's quite a lengthy naming than the conventional footprint naming before QFNs were popular, but it is effective in eliminating errors.