| 摘要 |
A method and system for preventing undercutting of the solder bump in a C4 package by forming a barrier of resist that effectively widens the footprint of the solder bump. The BLM is then etched to the perimeter edge of the barrier rather than the solder bump, thereby precluding any undercutting of the solder bump by the BLM. The barrier may formed by using a half-tone mask that fully exposes the immediately surrounding regions to define a sidewall enclosing the C4 cavity. The barrier may also be formed by applying a second resist prior to, or after, plating the solder and then patterning to inhibit etching directly adjacent to the C4 cavity. The barrier may additionally be formed by overfilling solder into the C4 cavity so that it spreads laterally over the sidewall portion of the resist layer. The resist is then etched anisotropically to leave the barrier. In another embodiment, a taper is introduced into the profile of the C4 cavity by reflowing the resist by an annealing step. The resist is then etched anisotropically to leave the barrier surrounding the C4 solder. |
