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12 SMT Magazine • August 2015 paste deposit and the package solder bump. In these defects, the solder paste deposit coalesces properly with itself and typically wets to the PCB land. Displacement of each solder deposit (paste and bump) is a common feature of HiP defects. Non-wet open (NWO) defects are soldering defects characterized by a lack of wetting to a PCB land by a fully coalesced solder deposit on an area array package. In this defect, the solder paste and the package solder bump coalesce to- gether fully without wetting to the PCB land. A spherical or nearly spherical shape along the PCB side of the bump is a common feature of NWO defects. What Head-in-Pillow and Non-Wet Open are not It is important to discuss defects that can share some symptoms with HiP and NWO, in order to contrast against defects that require dif- ferent mitigation actions. One example of a de- by Jason Fullerton alpHa "If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will suc- cumb in every battle." —Sun Tzu, The Art of War What is Head-in-Pillow and Non-Wet Open? The most difficult aspect of any soldering de- fect on an area array package is the inability to observe the defect easily. It is important to un- derstand the characteristics of soldering defects in order to identify the proper action to take to mitigate the defects in a soldering process. Head-in-pillow (HiP) defects are soldering defects on area array packages characterized by a lack of coalescence between the solder The War on Soldering Defects under Area Array Packages: Head-in-Pillow and Non-Wet Open FeAture

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