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62 SMT Magazine • August 2014 ondrej Simecek is a technical specialist, global marketing, at Test research inc. (Tri). 3D AXI inspection uses slices through the PTH joint to determine if the required amount of solder is present at the solder joint. QFN Package Inspection QFN is a leadless package where electrical contact is made by soldering the pads on the bottom of the package rather than on the pe- rimeter. In most cases, this type of package can- not be inspected using optical inspection (AOI) and has to rely on X-ray imaging. Most common QFN defects involve voiding and non-wetting of leads around the package pe- rimeter. The large ground pads on the bottom of QFN packages can be a frequent source of void- ing defects, and as a result the entire package may begin to float on the liquid solder and fail to form proper solder joints around the perimeter. AXI systems search for large discontinuities in the solder pad area to locate voids and cal- culate if the proportion of voiding is above the tolerable limit. Conclusion Selection of an AXI system is a complex pro- cess which depends on many variables, includ- ing customer's manufacturing process, inspect- ed product complexity, production volume, required inspection coverage and cost, among many others. It is important for manufacturers to choose inspection solutions providers that can offer an extensive portfolio of AOI solu- tions suitable for various environments, from small desktop products to high performance in- tegrated in-line systems capable of inspecting even very large and complex boards while con- nected to a high volume production line. sMt Figure 17: large ground pads on QFn packages often exhibit voiding, which may cause reliability problems with outer solder joints. INtRODuCtION tO INLINE aXI tEChNOLOgy continues aRTIClE