1. Field of the Invention
This invention relates to optical systems. More specifically, this invention relates to optical systems utilized in automatic inspection equipment.
While the present invention is described herein with reference to an illustrative embodiment for a particular application, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope of the present invention.
2. Description of the Related Art
For many applications, the speed and efficiency associated with optical, and other noncontact, measurement and inspection systems has afforded substantial reductions in manufacturing costs. In printed circuit board fabrication, for example, optical systems, such as the Opti III made by Hughes Aircraft Company, verify the dimensions between metal and substrate with heretofore acceptable resolution.
These conventional systems typically scan a spot beam across a board under test. Where the spot illuminates metal, e.g. copper, the reflected light is detected at one amplitude and where the spot illuminates the board, a second amplitude is detected. The detected signals are compared to a threshold to make the desired measurement. The tolerance of the measurement is the diameter of the spot. That is, the measurement is often inaccurate when the spot straddles both copper and board.
Accordingly, efforts to improve the performance of these systems have focused on reducing the diameter of the spot. However, this approach has been found to be problematic. One reason results from the higher costs associated with generating smaller spots. That is, smaller spots require larger, more expensive lenses and associated optical equipment.
A more significant limitation derives from the added processing requirements. To utilize a spot having a diameter 1/n times smaller than that of a conventional spot, where n is a number, necessitates an increase in the load on the processor by a factor of n.sup.2. This is due to the need to process n times as many spots in the inscan direction and n times as many spots in the crossscan direction. Thus, with this approach, a doubling in resolution requires a four fold increase in processing speed and power. There are also comparable associated increases in other key components and parameters such as memory, bandwidth, power, number of detectors, and system noise.
There is therefore a need in the art for a an improved inspection system or a technique by which the performance of conventional measuring systems may be improved without forcing added burdens on tee associated optical and processing systems.