Manufacturing defect

A manufacturing defect is a flaw built into a module at the factory. Wafer slicing, cell production, stringing and embedding the cells can all start cell cracks. Stringing and soldering carry the highest risk. Leftover stress from soldering causes the most common crack type, which starts at the end of the interconnect ribbon. Needles pressing on the wafer cause cross cracks. Laser cutting of half cells or third cells leaves small micro cracks at the cut edge. These may not show in the factory's final EL check, but they often grow into dendritic cracks during transport, installation and field operation. Cell interconnection failure is usually caused at the factory, for example by poor soldering, misplaced ribbons, a ribbon kink bent too hard, cells placed too close together or wrongly applied conductive glue. Thermomechanical stress or repeated wind load then makes it worse in the field. Glass breakage has been reported from a weak manufacturing process. Production is also listed as a possible origin of defective or detached junction boxes. In an EL image, a repeating crack pattern that is turned 180 degrees from one string to the next points to a stringer fault before lamination. Dendritic crack patterns point instead to heavy mechanical loads after lamination. Cracks made during production raise the risk that short cracks grow longer and wider in service under wind, snow and temperature changes. Cutting cells by thermal laser separation instead of laser ablation reduces cracking. An EL inspection when modules arrive on site can reveal cracks that were missed at the factory.

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• sentence 3: support check: partial - u31 supports micro cracks from laser ablation at the cut edge, missed in factory EL, growing into dendritic cracks, but says 'laser ablation' not generic laser cutting and 'frequently' rather than 'often'; fine, though the 'may not show in final EL' is only shown for the example. -->