MATERIALS INTERACTION IN PB-SN/NI-P/AL AND PB-SN/NI-B/AL SOLDER BUMPS ON CHIPS

Electroless deposits Ni-P and Ni-B were investigated for their feasibility as a diffusion barrier between solder and Al pad. Solder was selectively deposited on the aluminum pad by dipping. With the aid of scanning Auger microscopy (SAM) and X-ray diffraction (XRD), it was found that Ni3Sn4 is the only phase formed between the electroless Ni-P or Ni-B deposit and the solder after heat treatment. The phosphorus content of the electroless Ni-P deposit did not tend to affect the barrier performance of the deposit. However, the electroless Ni-B deposit is effective as a diffusion barrier only when the boron content is less than 3 wt.%. The tin of the solder can penetrate the electroless Ni-B layer at higher boron contents.