Difference: Connectivity (2 vs. 3)

Revision 32012-07-13 - ThomasMcMullen

Line: 1 to 1
The connective task has two main areas of work, TSV and flip-chip bonding development.

Flip-chip bonding at STFC-RAL

 STFC/RAL are developing a fine pitched Indium flip-chip process. The samples first have a under bump metal (UBM) layer deposited upon them where the bump is to be grown. The UBM used to date is Ti/W, Ni, Au. The Ti/W is an adhesion layer to the Aluminium pad of the device. The nickel is the solderable metal layer and the Au is an oxidation barrier. The indium is deposited in a theraml reactor at RAL. The Indium is heated under vacuum and condenses on the sample that is held at a lower temperature. The samples can then be flip-chipped bonded. The flip-chip process is to work at room temperature or slightly elevated temperatures.

There is some worry that the Indium bumps require more pressure to form a bump than should be the case. One suggestion for this high pressure is that the gold used in the UBM is moving into the Indium and forming an Indium/Gold alloy which requires more force to deform. A SEM/FIB/EDX study of an Indium bump formed on a silicon substrate was performed in Glasgow to try and test the hypothesis that the gold had moved into the Indium. The report is found here:

The report's conclusion is that teh gold does indeed appear to have migrated into the Indium bump.
The report's conclusion is that the gold does indeed appear to have migrated into the Indium bump.


Details of the TSV activity are given on the next page.

  -- RichardBates - 2011-06-09
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