Technology trends in the manufacturing and packaging of Wafer Level Cameras

For many years digital cameras have been integrated into mobile phones. In the beginning the camera phone was just another gimmick with limited value to the end user. Today, imaging is considered as a core feature by the user and major mobile phone manufacturers and most mobile phones are equipped with two cameras, a primary Mega-Pixel (MPx1) camera for photography and a secondary CIF or VGA camera for video calls. Far more than a billion mobile phone cameras were sold in 2009, and the numbers are still increasing rapidly. The increasing demand for more functions and features coming along with cost reduction plays a significant role in today's product design and manufacturing technologies of mobile phones and pushes the industry to continuously improve the performance and the manufacturing technologies. Wafer Level Cameras (WLC) is supposed to be the technology of choice to address these requirements. This application currently drives many equipment and process innovations that will become key for cost effective 3D and MEMS packaging later on. Within the manufacturing process of wafer level cameras one can identify two complementary technologies. One is the wafer-level packaging of image sensors and the other is the wafer-level manufacturing of camera objectives. Both the sensor device and the objectives will be finally assembled on wafer level by a wafer bonding process. However, today's reality is the wafer level manufacturing of the optical module and the chip-level assembly of optical module and image sensor chip. Wafer level optics (WLO), part of the wafer-level manufacturing of cameras, is a novel technology that is designed to meet the demand for smaller form factors of the optical system and cost reduction in the next generation of camera phones. The optical components are fabricated by UV replicating the optics through a stamp material into a polymer layer, coated on a glass wafer. Another key challenge in the manufacturing is the alignment in the wafer bonding process step. Replicated lens wafers are aligned and adhesively bonded at the wafer level using a UV curing process in order to achieve excellent alignment results. Finally the bonded Opto Wafers are subsequently diced to form individual camera modules. This paper explores the latest fabrication techniques used in the Wafer Level Camera manufacturing process (WLC) to support >3MPxl systems and describes main challenges and available solutions. The paper presents latest lithography results of TSV formation, the replication of micro lenses (Fig. 2) and the wafer level packaging of microlens wafers (Opto Wafers) via UV bonding are depicted as well. Finally new UV curable materials for microlens replication and for Wafer Level Packaging of Opto Wafers (lens stacking) are presented.