Visible burn marks

Burn marks show up as burnt, blackened areas on a module that can be seen with the naked eye. Near a burn mark the polymeric encapsulant may bubble or melt, the glass may break, or the backsheet may have a hole in it. Burn marks on the backsheet may not be visible from the front. If you cannot reach the back of the module, check it with an IR camera. IR inspection may miss a burn mark if the spot is no longer heating. Burn marks are found by visual inspection and infrared thermography, and electroluminescence imaging is listed as a possible extra method. Burn marks can appear on the backsheet from heating along a busbar, or on the front with discoloured encapsulant from overheating along the metal interconnections. Reported causes include open-circuited or defective bypass diodes combined with current mismatch from shading or cracked cells, and interconnect failures in the junction box. Other reported causes are poor soldering of the bussing ribbon, which can also break the glass, and intrinsic shunting caused by a manufacturing error.