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12 SMT Magazine • July 2014 Clearly there is a great deal of nuance in the detection and identification of solder related de- fects; numerous books have been written over the last few decades that both characterize and suggest methods for eliminating or mitigating them (the devil is also "in the details" as anoth- er aphorism attests). It is not within the scope of this brief commentary to provide detail on all of the various types of solder related defects which can extend from the macro to the micro but for the benefit of the reader the following figure is offered providing representative ex- amples of a number of the defects described above. The "Devil's" Impact on the PCB The importance of managing the soldering process is clear, but making a good solder joint is also just part of the story and there are a number of defects that can be generated within a printed circuit assembly because of the soldering process, including: a) Corner Cracking: A crack that forms at the interface between the whole and the land that sur- rounds. It is normally the result of the Z-axis expansion of the PCB during the thermal excursions such as soldering. b) Barrel Cracking: Another phenomenon associated with the soldering process; it is similar in some ways to a corner crack except that it is manifest near the center of the hole. c) Post Separation: A separa- tion of the plating in the through hole from an innerlayer connection d) Hole-Wall Pull Away: Hole-wall pull away is manifest as a bulge in a plated through hole, which reduces its diameter. e) Resin Recession: Roughly, the opposite of hole-wall pull away wherein a small gap is formed be- tween the plated hole wall and a resin rich area of a plated through-hole f) Delamination: A separation of the lay- ers of a multilayer circuit. It is normally seen in cases where the glass transition temperature of the resins used in the multilayer structure is exceeded. g) Pad Cratering: Another phenomenon unseen before the introduction of lead-free sol- ELECTRoniC inTERConnECTionS ElECTRoNIC ASSEMBly WITH SolDER continues figure 1: Representative images of some of the solder related defect found on printed circuit assemblies. Top row – left to right: head in pillow, graping, misregistration short and over- heated flux. Second row, left to right: tombstoning, insufficient solder with open, popcorning. Third row, left to right: dewet- ting, blowhole, shorting between adjacent leads. fourth row, left to right: cracked solder joints, voids, excessive solder. Bot- tom row, left to right: cracked component, tin whisker, open (lifted lead).