Foldable 3D Wafer Level SSL Package Using Flexible Interconnect

Abstract

Solid State Lighting (SSL) is on track to replace conventional incandescent and fluorescent sources for general lighting. Even though it offers many benefits, the high initial device costs are still a major hindrance for many consumers. Packaging can account for up to half of the total device price, offering high potential for cost reduction. In this thesis, novel silicon wafer level packaging (WLP) concept and development platform are presented. The proposed packaging platform consists of silicon chips connected with neutral bending plane based flexible interconnect. Each chip contains an etched reflector cavity with wire bonded LED. The polyimide encapsulated flexible interconnects offer the benefit of folding the package into a 3D geometric shape. The space around the reflector cavity could be used to integrate active components and the backside { for passive components of the SSL driver circuit. The design, fabrication and characterization of the package is presented. A novel method to interconnect the front and backside of the chips is also incorporated into the process flow. After fabrication, packages are completed by adding LEDs, applying phosphor color conversion and release from substrate, followed by characterization of electrical, mechanical, thermal and optical performance. The developed packaging platform offers potential for future functional expansion by means of heterogeneous integration, possibly leading to a smart WLP package for SSL.