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

Texas Tech University, Nivetha Shivan, May 2012
There is a need to incorporate the additional step in the wafer fabrication technology
called NSM which goes around the perimeter of a die with totally different geometry,
extra metal stacks and a thicker Aluminium layer.
There is a requirement of changing this packaging technology to Flip chip due to the
following reasons.
Flip Chip allows the I/O signals to be distributed over the whole die area rather than
being concentrated only to the periphery of the die. This feature provides the advantage
of designing the die with power and ground distributions. As a result of which there is
improved signal integrity. This is particularly helpful when the device requires
performing at high speed [8].
As there is more routable area owing to the I/O signals being distributed over the entire
die, the package can be used for devices with higher pin counts as compared to the other
types of package which has limitations on the number of pin counts.
Since the assembly interconnect technology has transitioned from the traditional wire-
bonding technique to Flip-chip, there is quite a need to qualify the new package type. The
goal of this project is to qualify the new package type for an existing product (pre-
engineering qualification). Engineering qualification is when the new package type will
be qualified for the new product.
The various failure mechanisms that could result as a consequence of changing the
package type:
� Die crack
� Substrate pop corn crack
� Electrical Continuity failures due to underfill delaminations or an open bump
In this project, we use acoustic microscopy and cross-sectioning for examining these
failures in the Flip Chip devices. This project is a team effort which consists of product
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