Challenges in Developing Thin Profile, Smaller Flip Chip Bump Pitch FCBGA Packaging

The influence of substrate copper density distribution, substrate bump coplanarity, stiffener attach process, and substrate clamping by magnetic boat during die attach were evaluated. The substrate warpage behavior throughout the package assembly process was characterized using shadow moiré. Balanced substrate copper density distribution, pre-stiffener substrate before flip chip bump reflow, and substrate clamping during reflow reduced flip chip solder bridging fall-out. The decrease in solder bridging was due to the lower substrate warpage seen during die attach. In particular, solder bridging fall-out was well-correlated to die attach area warpage. Substrate with and without clamping during reflow has met the package reliability requirement.