Immersion Tin for QFN Packages to create a 3-D solder joint for reliability enhancement

The QFN (Quad-Flat No-leads) package is one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. The side edges of the standard QFN Package are not covered by solder, which results in the fact that the package is soldered only planar in 2 dimensions from the QFN bottom side onto the PCB as shown on fig. 1 a). The QFN where the side edge is covered by immersion tin will keep the side edged of a QFN solderable as shown in fig. 1 b). This allows the package to be soldered in 3 dimensions onto the PCB providing a stronger solder joint and a better reliability. The suggested paper describes a new process to cover the side edges of the package with immersion tin after the QFN package singulation step. The exposed lead frame edges are covered by immersion tin. No exposed copper is visible and delivers a 3 dimensional solder joint with better reliability and protection for the soldered package.