Select the correct Units
and scaling factors 
:
DXF files are unitless —
a distance of e.g. 10 units may correspond to 10 microns, 10 inches,
or even 10 meters. It is therefore very important that you specify the
meaning of the DXF units. Select microns
if you want a distance of 1 to represent 1 micron in the DXF file. This
does not limit your drawing's resolution to one micron because DXF supports
fractional units.
.