  Evaporation-driven particle self-assembly can be used to generate
three-dimensional microstructures. We present a new method to create these
colloidal microstructures, in which we can control the amount of particles and
their packing fraction. To this end, we evaporate colloidal dispersion droplets
on a special type of superhydrophobic micro-structured surface, on which the
droplet re- mains in Cassie-Baxter state during the entire evaporative process.
The remainders of the droplet consist of a massive spherical cluster of the
microspheres, with diameters ranging from a few tens up to several hundreds of
microns. We present scaling arguments to show how the final particle packing
fraction of these balls depends on the dynamics of the droplet evaporation.
