A pillar-to-pillar flip-
chip assembly primarily comprises a substrate, a
chip disposed on the substrate, a plurality of first
copper pillars on the bonding pads of the
chip, a plurality of second
copper pillars on the bump pads of the substrate, and a
soldering material. A first height of the first
copper pillars protruding from the
active surface of the chip is the same as a second height of the second copper pillars from the
solder mask on the substrate. When the
soldering material electrically and mechanically connects the first copper pillars to the second copper pillars, a plurality of central points of the
soldering material are formed on an equal-dividing plane between the chip and the substrate to reduce the direct stresses exerted at the soldering material to avoid peeling or breaks from the bump pads. Moreover, each of conventional solder balls is replaced with two soldered copper pillars to meet the lead-free requirements with higher reliability and lower costs.