Forming solder filet on leadframe edges of a QFN with immersion tin

Abstract

The QFN package is one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. The standard QFN Package soldered on a PCB is shown on fig. 1 a). The side edges of th. QFN are not covered by solder, which results in the fact that the package is soldered only planar in: dimensions from the QFN bottom side onto the PCB as shown on fig. 1 b). The QFN were the side edge is covered by immersion tin will keep the side edged of a QFN solderable. This allows the package to be soldered in 3 dimensions onto the PCB providing a stronger solder joint and; 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 three dimensional solder joint with better reliability and protection for the soldered package.