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WLP changes are now evolutionary
October 8, 2007
After looking at the presentations of the recent Int Wafer Level Packaging conference in San Jose last month it is clear that changes in bumping and WLP have become evolutionary vs the revolutionary changes that were occurring 10-15 years ago.
David Hays of Amkor addressed what he called “the changing landscape of WLCSP”. The landscape changes that he mentions such as such as die size increases (to > 6 mm ) and pitch (to 0.4 mm) are normal evolutionary changes. Some of his historical facts about the materials that were initially used are highly flawed and I will deal with them in a future blog.
Asymtek detailed the potential use of jetting ( think ink jetting) for the dispense of underfill. An interesting concept but I didn’t see any discussion of filled materials which are used to address the CTE mismatch between the solder and the epoxy. Anything that lowers the cost of underfill (still needed to insure passing the drop test) is a good thing.
DEK printing detailed the evolutionary move of WLP towards 0.2 mm solder balls on 0.3 mm pitch by vacuum transfer or stencil printing. Their experiments indeed show that automated 0.2 mm ball placement is possible with a yield of > 99.99% with very little change in current technology (more evolution).
Autotech reported on a study of SAC (Sn/Ag/Cu ) Pb free solder balls with Ni(P)/Au vs Ni(P)/Pd/Au UBM’s. The reliability of the solder joints were characterized by ball shear testing after multiple reflows. Differences in ball shear strength are related to morphology differences due to the presence of the Pd. Nice materials science work.
Micron presented data on their studies of Cu pillars capped with Ni/Au or Sn . Such Cu pillar technology, first described by Fujitsu in their “Super CSP” 14 years ago, has become very popular due to its capability for increased packaging density. Electro-plated Cu-pillar bumps compared to spherical solder bumps show a finer pitch (less than 100μm) and improved standoff (70-90μm). Tessera also discussed their similar μPILR technology which reportedly can be built on 0.2 mm pitch (micropilars shown below)
Tessera’s μPILR's
Posted by Philip Garrou on October 8, 2007 | Comments (0)
