Method for planting solder balls on encapsulated mother board of semiconductor assemblies

Disclosed is a method for coupling a plurality of solder balls on an encapsulated chip substrate. A vacuum plate including a solid plate and an elastic plate disposed on the solid plate is provided. The solid plate has a plurality of holes. And, the elastic plate has a plurality of patterned openings, each corresponding to a hole of the solid plate. The patterned openings may not be coupled to each other, but the patterned openings are each connected with the corresponding hole of the solid plate. Each of the patterned openings has a plurality of channels extending from a center. The patterned opening is concentric with the corresponding hole of the solid plate. An encapsulated substrate is fixed to the vacuum plate through vacuuming process. A plurality of metal pads are stamped on the encapsulated substrate. Through the flux spots, the solder balls are temporarily fixed at right positions before a reflowing process.