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The impulse flashover voltage (FOV) in air across a short gap between foil conductors on a printed wiring board was studied to obtain fundamental and remarkable characteristics that will be useful in the design of wiring on the board. Two types of conductor configuration on the test boards were studied. The studied gap distance (d) ranged from 20 mum to 1200 mum. The board thicknesses (t) and the foil thickness (s) were changed from 60 mum to 800 mum and from 6 mum to 18 mum, respectively. The following results were obtained in the two types of the conductor configuration. FOVs for the boards in the studied range are independent of the foil thickness. FOV is almost un-influenced by the board thickness in the gap distance range shorter than 30 mum or 50 mum. In the gap distance longer than this range, FOV characteristics strictly depend on the board thickness; FOV for t=60 mum steeply increases with an increase in the gap distance, and FOV for t=800 mum gradually increases with an increase in the gap distance. These experimental results were discussed basing upon the calculation results of electric field around the HV foil conductor edge.