Self-arrangement of solder balls by using the surface wettability difference

This letter describes a simple and efficient method of the solder ball placement for electronic packaging. For self-arranging solder balls by using the surface wettability difference, the substrate surface was patterned into the hydrophilic Au solder ball land array with the hydrophobic Teflon passivation layer. Water droplets were formed only on the solder ball lands after dipping the patterned substrate into water. Then, the solder balls were placed on each of the wetted solder ball lands. After soldering two plates with 3 × 3, 4 × 4, and 5 × 5 arrayed solder balls, their average shear strengths were as high as 195, 220, and 251 MPa, respectively.