Abstract: Articles such as substantially flat, electronic chips (10) are positioned in an array with surfaces (11) to be treated facing upward along a succession of specially selected tiers. Such tiers may preferably be horizontal rows (20-24) of top rims (19) of vertical suction tubes (18). A leading row (20) of such top rims (19) is at a first elevation and each succeeding row is parallel to, elevated above and offset horizontally from a preceding row in stepwise fashion. At least one nozzle (40) is provided for propelling a stream (52) of a treating medium upon and at an angle "H" to the surfaces (11) to be treated. Angle "H" is selected so the medium and any dislodged matter is deflected from the respective surfaces (11) without contacting other such surfaces (11) of chips (10) positioned for treatment in the array.