When flux is applied, it adheres to the areas surrounding the holes in the board.
The applied flux is vaporized by heat emitted during the flow soldering process. If
this vaporized flux penetrates into the product, the metal terminals will halogenize, and an insulating
layer (oxide layer) will be generated at the point of contact between the metal terminals and the
vibration plate.
As a result, a continuity fault (open circuit) may occur, preventing sound from being emitted.
Fig. 1 When flux is applied
Fig. 2 During flow soldering