It is becoming increasingly important that camera modules provide cars with the power of "human eyesight". Sensor manufacturers, camera integrators and automotive developers are working under great pressure to achieve or even surpass the resolution, field of view, color perception and dynamics of the human eye with camera modules. At the same time, the transfer of human "sight" to camera modules also means a transfer of responsibility for the safety of the vehicle's passengers and other traffic participants to technology.
Lawmakers are currently working on creating the legal framework for autonomous driving. This means de facto that camera modules will be developing into car systems relevant to safety in the coming years. In addition to the demands on quality, the camera modules must be able to be mass-produced economically for car manufacturers. This places very high demands on the production lines of such modules.
A Fully Automated Solution
A fully automated production line for camera modules start with the PCB assembly and includes the fully automated incoming test of critical components, the cleaning and activation of component surfaces, the application of adhesives, the active alignment and UV attachment, the curing in the oven, the subsequent assembly of the housing parts and ultimately the final quality test and calibration of the camera parameters.
An important feature of camera module production is that the produced camera module is not passive during "assembly." The activated sensor of the component itself is used to mutually align optics and sensors in sub-micrometer and arc-second resolution.
A multi-axis system is used to align either the optics or the sensor in real-time based on test-image data in up to 6 degrees of freedom.
High precisions are achieved by using collimators to project test patterns onto the camera module. These patterns are used at several points in the image to simultaneously compute the image contrast and determine the best image plane location.
The Production Process
Measurement parameters are collected during the entire production process.
This begins with the tests of the individual parts (sensors, optics) before they are assembled and continues to the ejection of defective parts. Tests then follow after the assembly for process monitoring and finally, an end-of-line test for ensuring consistent quality and/or for calibrating the camera parameters.
The following parameters are recorded for this:
● The optical properties (e.g. distortion, focal length, relative illumination, image quality, MTF)
● The optomechanical properties (e.g. alignment of the optics to the sensor, focussing, angle of view, roll angle)
● The optoelectrical properties (e.g. linearity, signal-to-noise behavior, dynamic range, color reproduction)
One or another of the parameters is required, depending on the application in the automobile. For example, the calibration of the distortion and relative illumination is important for the wide-angle rearview cameras, while, in contrast, the uniform MTF and the mutual alignment of the cameras take center stage for the stereo cameras used to record distance information.
In the manufacturing process, the measuring technology must be selected in a way that enables reproducible, absolutely comparable measurement results.
Camera modules in the car (with the exception of the rearview camera) do not produce any images in the actual sense, but rather data and key figures for the onboard electronics.
A major challenge is translating requirements on driver assistance systems such as "the double-line street marking must be reliably distinguished from the dashed line street marking in all lighting situations and for all conceivable curve radii" into measurement parameters such as MTF (modulation transfer function), OECF (optical-electronic conversion function), distortion, etc.
These system requirements on the measurement parameters must not only be carried down to the camera module but also broken down into the parameters of the individual parts. The measuring technology must be able to continuously measure the different components along the entire supplier chain.
