for example be silicon nanorods which are grown on the substrate and extend to a height of up to 500 nanometers if the substrate upper surface is relatively hydrophilic then the presence of the surface roughening nanoparticles serves to greatly increase the hydrophilic nature of the surface in what may be called hemi wicking conversely if the same surface is hydrophobic hemi wicking occurs nonetheless making the surface extremely hydrophobic generally a hydrophilic surface has a surface energy greater than or equal to 70 mn m a hydrophobic surface has a surface energy less than or equal to 20 mn m referring to fig1 a substrate 12 has an integrated circuit die 14 mounted thereon in a flip chip arrangement using solder balls 16 to electrically and mechanically connect the die 14 to the substrate 12 the substrate 12 may have interconnections which provide signals to the die 14 and transfer signals from the die 14 to external devices the upper surface of the substrate 12 may have peripheral regions 22 e g 22 a and 22 b which may be highly hydrophobic or hemi wicking conversely the regions 24 underneath the die and to a slight degree up from under the die may be very hydrophilic and hemi wicking thus the underfill material 20 once injected in the direction a for example using capillary forces moves away from the hydrophobic surfaces 22 a and 22 b and spreads on the.