Under-Bump Metallization

Advafab has developed an optimal under-bump metallisation structure for the flip chip bonding of the semiconductor dies, to gain the best possible wetting for solder alloys.


UBM – Solid Base for Soldering

AdvaFab deliver thin film Under-Bump Metallization (UBM) pads on sensor wafers. The role of the UBM is to:

  1. Provide good and reliable surface finishing for soldering
  2. Act as diffusion barrier against the components of the solder alloy
  3. Provide good adhesion to the wafer.

The AdvaFab-deposited UBM pads are compatible with InSn, SnPb, AgSn and other typical solder alloys. The UBM pads have been designed to allow flip chip bonding of multiple dies on the chips and rework of some chips.


  • UBM process is available for AdvaFab fabricated Si sensor wafers (stand-alone and SOI wafers) and for third-party manufactured wafers. The process is available for thin stand-alone thin wafers with thickness starting from 100 um. The thin-wafer UBM process uses temporarily bonded carrier wafers to support the fragile wafers during the processing. The process is available for individual and mid-sized production volumes up to thousand wafers per year.

    Besides the thin film UBM pads, electrodeposited UBM pas also be offered for 500 um thick or thicker sensor wafers. It is important that the wafer edge has been ground to increase the robustness of the wafers. The typical electrodeposited UBM pads are Ni/Au or Cu.



Simplified description of lift-off process

  • image-1144

    Sputtered thin-film UBM pads are made of noble metals that wet solder well and act as efficient diffusion barrier against the elements in the solder alloy.

  • image-1213

    Electrodeposited Ni/Au UBM pads.

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