For mold inserts fabricated using precision machining for example in brass or stainless steel), the
following design restraints are valid in addition to the ones given above:
a) Minimum feature size
The minimum feature size for sunk features (i.e. features where the mold insert material has to be
removed; see Fig. 410) is 50 μm. For features in the range between 50 and 100 μm, the aspect ratio is
limited to 1.5.
b) Minimum radius of curvature
At intersecting features (e.g. channel crossings), a radius of curvature of 40 μm occurs as standard.
Smaller radii down to 10 μm are available upon request and depend on the aspect ratio of the
c) Feature heights
Different height steps as well as slopes of up to 45°–90° (depending on absolute feature size) are
d) Surface roughness
Mechanical machining results in a surface roughness of the order of 0.5–1 μm RMS. The features can be
polished if protruding (e.g. channel floors in the polymer part which are ridges in the mold insert; see Fig.
410), to create an optical finish (roughness < 50 nm RMS).