The pressure dependence of the breakdown of nitrogen gas by a microwave field in microgaps down to 13 μm has been measured. Fits to a phenomenological function suggest that microwave breakdown in small gaps requires a higher collision frequency, νc. If the effective electric field on an electron in a microgap is interpreted as Eeff=Eoνc2/(νc2+ω2) and then as the gap size is reduced, we find that the collision frequency needed to produce a minimum breakdown electric field shifts from νc = ω for large gaps to νc = 2ω for small gaps.