Dual sided bus bar designs actually require higher precision, given the cell can base thickness and direct proximity of the cell chemistry.
Cross sections are laborious but still the most established method for detailed weld examination. F&K also utilises SAM Scanning acoustic microscopy, EDX Energy-dispersive X-ray spectroscopy.
Pull tests are used to asses the welds strength. “Buttoning out” refers to the welded material remain after the TAB material itself fails first.