BGA packages have become more and more popular for both the packaging of microprocessor devices and for the assembly of Multi Chip Modules. This is due to the advantages the Ball Grid Array offers concerning high leadcount combined with large pitches, process-able with standard SMT equipment. For encapsulation of BGA packages mostly epoxy resins are used either as Glob Top or as Molding Compound. For cost effective encapsulation of large numbers of BGA packages the Transfer Mold Process offers various advantages. The process is fully automated with short process times and the glass transition temperature Tg of the Molding Compound is very high (>200°C) compared to Glob Top encapsulants (～160°C) offering higher reliability at elevated temperatures. But BGA packages challenge both, material suppliers and packagers as this package type is an asymmetric one and thus very sensitive to encapsulation material properties. Properties to consider are on the one hand reduced encapsulation material shrinkage after molding to provide low warpage. And on the other hand optimized adhesion of Molding Compound to the various materials present inside a BGA to avoid delaminations that might cause electrical failures. Fraunhofer IZM and Toshiba Chemical have designed test vehicles to investigate different BGA molding compounds concerning adhesion to substrate with various types of solder resist after molding and also after reliability testing of the packages. Results of these investigations will be reported and additionally investigations regarding humidity sensitivity (according to JEDEC Std. 020) of the encapsulated BGA and the relationship between adhesive strength of EMC to Solder Mask and humidity uptake of the package will be described.
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