1. Field of the Invention
The present invention relates to a method for assembling a camera module for a vehicle.
2. Description of Related Art
Camera modules are being increasingly used these days in vehicles, for example for use in night vision systems or as lane departure warning (LDW) systems. Particular demands in terms of robustness are made on such cameras with regard to their installation in the vehicle, given the vibrations that unavoidably occur during operation.
Two fundamentally different approaches are known for the assembly of camera modules for vehicles: An imager module is used which encompasses an image sensor chip, a basic housing, and a lens, the lens being produced and tested as an independent module. Imaging modules of this kind can be attached to the circuit board, for example by thermal joining, e.g., using soldering methods, or by way of a cable end having a plug. The circuit board, completed in this fashion, is then installed into the housing, which must have a corresponding receptacle for the lens. A disadvantage of this procedure is the fact that imager modules having chip and lens dimensions suitable for motor vehicle applications cannot be reliably produced using common soldering methods (e.g., reflow methods). Because of the high heat capacity, poor solder connection points can form, or the optics can be damaged. On the other hand, the plug contacts known as alternative solutions are not fault-free over the long term in vehicles. A further problem that has emerged here is sealing of the entire camera module in the context of a circuit board plus imager module configuration, since mechanical stresses acting on the imager module often occur; this can result in subsequent damage.
A further assembly concept is based on configuration of the circuit board with an independently packaged image sensor; this typically involves a ceramic housing having a glass cover. The sensitive pixel array can thereby be sufficiently protected from particles. Such housings can moreover be processed using reflow processes. The lens can be focused either in a lens holder mounted on the circuit board, or in the housing shell of the camera module. This approach, however, exhibits a very long tolerance chain because of the larger number of individual components requiring installation; after assembly this can result, in the least favorable case, in inaccurately operating camera modules due to addition of the greatest tolerances.
Published German patent document DE 10 2004 001 698 discloses an optical module. According to this approach, an optical module encompasses an image acquisition device made up of optical and electronic components, the components of the image acquisition device being disposed together on a carrier plate. The components of the image acquisition device are disposed on a first principal surface of the carrier plate, an optical system associated with the image acquisition device being disposed on a second principal surface of the carrier plate. The carrier plate and the optical system are embedded in a sealing compound. The optical module encompasses a holding element for securing the optical module to a vehicle part or the like. The holding element is sealed to the optical module, and the optical module encompasses a shield against electromagnetic interference radiation. According to this approach, the shield can also be embedded in the sealing compound. The shield is preferably embodied as a net or lattice embedded in the sealing compound, or can be made up of particles embedded in the sealing compound.