Wafer Level Chip Scale Packaging is a redistributing of the bond pads on a die. Customers may use this interconnect method when the application requires the smallest form factor possible. WLCSP is gaining popularity in the technology forum, medical R&D facilities and commercial marketplace. It allows for size and weight advantages as well as reduction in costs once the production cycle is met.

While the name implies that the device would come in a package it is actually the bare die itself modified to add solder balls or "bumps" that are then used as the direct connection to the package carrier or substrate. The die are inverted and placed bump side down on the substrate, hence the name for the process, "flip chip". The electrical connection between the die and substrate is then made using an ultrasonic process to flow (melt) the solder, causing the die to adhere to the substrate. It is common to then add an electrically-insulating underfill to maintain the connection and protect it from any un-due stressors.

To learn more about WLCSP and the design requirements for using this interconnect method please refer to the technical papers section in the resource center.