Abstract: A vapor phase processing system includes a vessel providing a processing chamber in which a two-phase treatment fluid bath is present. A conveyor for moving flat circuit boards on horizontal pallets down into, through and up out of the vapor phase of this treatment fluid includes two pairs of parallel rails. A first pair of rails supports a front end portion of each pallet and a second pair of rails supports a rear end portion thereof. Downward sections of each pair are parallel with downward sections of the other pair; and upward sections of each pair are parallel with upward sections of the other pair. These mutually parallel sections are spaced apart by the distance between the front and rear pallet supports. This results in the pallets and the circuit boards on them remaining horizontal while passing through the processing chamber.