Assembling Lenses to CCDs for Camera Modules
Compact camera modules consist of a focal plane array detector and an imaging optic, the lens. Other than for pure cameras the lens of such a camera-on-a-chip module is permanently fixed to the image sensor. Due to this fact there is no chance for adjustments after fabrication. Nevertheless this type of cameras have been designed for specific tasks which usually put high demands on the imaging power of such systems.
Such dedicated cameras usually are manufactured in high volume and within contain low cost components. Consequently these components show a larger spread in specifications than acceptable for passiv assembly by design dimensions. During the production process of those monolithic modules attaching the lens to the sensor therefore becomes an extremely critical step. Each pair of sensor and lens has to be aligned to each other individually.
Basically the aligment of the two components can be done in two ways. When using the passive approach the optical properties such as the optical axes of both the sensor chip and the lens as well as the focal point and the center of the chip are determined using external metrology. When being actively assembled the image sensor itself is used to generate a feedback signal for the motion system of the bonder by looking at a target (physical or virtual). Both methods demonstrate their advantages in different fields. Depending on the dedicated performance of the camera or its mechanical layout the one or the other alignment philosophy may be the most suitable.
ficonTEC builds solutions for both philosophies making ficonTEC one of the key supplier of equipment for automated camera module asssemply. If the design of the camera requires additional components, e.g. for thermal expansion compensation the assembly process of the camera module becomes even more complex and so becomes the machine concept.
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