Qualification of the Assembly Process of Flip-Chip BGA Packages ...

Texas Tech University, Nivetha Shivan, May 2012
This gives us an edge over Phase I, as we can also test the parts electrically to make sure
the new package has no impact on the electrical behavior of the die inside.
Phase II also introduces another variable, a change in the wafer fabrication technology
called Nitride Seal Mask (NSM).
3.1.2.1 Nitride Seal Mask concept [6]
When devices are stored in high humidity environments for an extended period of time,
there could be moisture absorption which could lead to die edge delamination. This
defect “die edge delamination” means there is a separation that has occurred in the edge
of the die (doped oxide layer) due to the moisture absorption. The oxides swells,
delaminates and this delamination propagates to internal active circuits and creates
separation in the metal contacts, causing the device to be inoperable.
In this NSM concept, an impermeable moisture barrier is formed around the perimeter of
the die by making use of the existing passivation layers. The existing passivation layers
are a thin layer of undoped oxide, above which there is a thicker layer of nitride. There is
also an opening in the passivation layer, to allow wire bonds to be connected to the metal
layer inside. Figure 3.7 explains the concept diagrammatically.
Figure 3.7: NSM Concept [6]
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