Method for forming bumps on a substrate

摘要

Solder bumps are formed on a substrate, such as a semiconductor die (28) or wafer, using a screen printing and reflow operation. Solder paste (18) is screened into openings (14) of a stencil (10). The paste is reflowed within the stencil to produce a solder preform (22). The stencil and solder preforms are then aligned over the substrate to be bumped so that the preform aligns with a metal pad (30) on the substrate. The solder preforms are again reflowed, and the solder within the openings of the stencil is drawn onto the metal pad. To facilitate the transfer of the solder from the stencil to the metal pad, a second stencil (12) can be used to form a protrusion (27) on the solder preform. The protrusion contacts the metal pad during the transfer reflow operation to facilitate removing the solder from the stencil.