What condition must not occur regarding the surface damage of laminate fibers?

The correct answer highlights the importance of preserving the integrity of laminate fibers in electronic assemblies. The condition that must not occur is the presence of any damage that cuts into these fibers. Laminate fibers are crucial for providing the necessary structural integrity and electrical isolation in printed circuit boards (PCBs). When damage penetrates into the fibers themselves, it can compromise the mechanical strength and the overall performance of the board, potentially leading to failures during operation or manufacturing processes. This kind of damage can create pathways for moisture or chemicals, which can further degrade the performance of the PCB over time.

In contrast, while surface discoloration, minor scratches, and dirt accumulation may alter the aesthetic appearance of the laminate, they do not necessarily affect the underlying structural or functional properties as severely as damage to the fibers. That said, it's still essential to manage these aesthetic issues to ensure that they do not escalate into more significant problems affecting the assembly's reliability.