Packaging requirements and solutions for CMOS imaging sensors

Digital imaging is a new, rapidly developing market segment for integrated circuits. If this technology is to be used as broadly as other IC products, these products must provide performance at low cost. The CMOS image sensor plays a central role in meeting this goal, as it facilitates the manufacture of sensors in high volume and at cost low enough to meet the aggressive product goals. In addition, CMOS-based technology permits integration of a wide range of camera system functions that are not easily integrated into conventional CCD devices. Image sensors place additional demands on packaging technology, beyond those encountered for conventional ICs. These include: 1) an optical quality window, 2) precision mechanical alignment of the die and 3) protection of imaging attributes of the die from environmental and manufacturing effects. A variety of solutions meet the requirements for packaging the relatively small volumes of CCD image sensors manufactured to date. However, the cost/performance requirements of a broad-based digital imaging market impose a new set of manufacturing requirements. As part of our development of the CMOS sensors, we chose a commercially available package(1), the Windowed-QFP, as the basis for the CMOS sensor package. A pre-molded epoxy cavity package provides moisture protection similar to that attained for ceramic packages. Control of tip and tilt components of the die/package alignment and the tolerance stackup between the die and the lens enables a simple alignment of the lens system. The ceramic/glass lid maintains the moisture protection, while providing superior thermomechanical performance. This packaging technology provides customers a substantial advantage in board assembly with a mass reflow capable package that is unique in the industry.