  We investigate the capillary filling of three dimensional micro-channels with
surfaces patterned by posts of square cross section. We show that pinning on
the edges of the posts suppresses, and can halt, capillary filling. We stress
the importance of the channel walls in controlling whether filling can occur.
In particular for channels higher than the distance between adjacent posts,
filling occurs for contact angles less than a threshold angle \sim 55 deg.,
independent of the height of the channel.
