Flip Chip and Wafer Level Packaging - Past, Present and Future

Flip chip packaging was developed nearly 50 years ago by IBM for the purposes of improved reliability and automated semiconductor assembly. For the first 35 years the use of flip chip technology was limited to a few large IDMs and automotive companies. Beginning fifteen years ago, companies providing flip chip bumping services were established. The primary reason for adoption of flip chip in the 1990s was to enable higher I/O count chips and to improve the power and ground distribution through the use of area array interconnects. Beginning in the early 2000s high speed serial links and other I/O with fast edge rates required the use of flip chip interconnects to improve signal propagation. In the future a greater percentage of devices will utilize flip chip interconnects as these chip requirements continue to drive increased demand. Future challenges include the requirements for better power and ground distribution, finer pitch interconnects and higher I/O count devices while protecting the every more fragile inter layer dielectrics (ILDs) present on the device. Wafer Level Package (WLP) technology was developed approximately fifteen years ago to address form factor requirements in mobile products. Today WLPs play an ever increasing role in both mobile and other applications. An understanding of the market drivers, technology limitations, and variety of WLP structures used will be reviewed from both a historical perspective and current implementation. The breadth of products that are currently packaged with WLPs will also be reviewed. The principal challenges for WLPs both today and historically has been to provide adequate thermal cycle reliability and drop test capability for ever increasing device sizes and ball counts. Future market requirements for WLP technology will likely require new structures that can be cost effectively produced.