Tuesday, June 19, 2018
Publication Date: 12/1/2007
Archive >  December 2007 Issue >  Special Feature: Test and Measurement > 

Flexible or Dedicated AOI: Making the Decision
Landrex Optima 7200 platform, designed for post-place defect detection and measurement, and optimized for flexibility.

In the search to find what kind of AOI system was really needed by our customers, we had to consider two opposing viewpoints: provide AOI for fixed locations in the assembly process, or provide AOI systems with maximum flexibility, so they can be moved around. But the question had to be answered by our customers. Did they want flexible machines? Did anyone ever move their machines around from one place in the line to another? We decided to divorce ourselves temporarily from what the market was asking for and to perform a study. The goal of the study was to determine whether dedicated machines or flexible machines could best meet customers' inspection needs at each place in the line.

We did extensive investigations on what type of technology, both hardware and software, was required to meet the rigorous requirements for inspection at each point in the line: post-paste, post-place, and post-reflow. We analyzed each problem from a purely scientific perspective. We gathered the requirements for each place in the line, analyzed the inspection task with respect to the material properties at each place in the line, looked at different image capture configurations, reviewed a suite of image analysis tools as well as our own proprietary techniques.

The conclusions: To meet low false fail rates, to keep up with or exceed the speed of the line, and to perform the inspection tasks required — each place in the line needed very different hardware and image analysis.

Reaching Conclusions
  • Post-paste requires a three-dimensional imaging system to determine the brick size and height and brick shape. Solder paste, however, has some beneficial properties that aid 3D inspection. The bricks themselves have a diffuse property, meaning that when you shine light on them they shine light back in a number of different directions. In addition, their rectangular shape makes them amenable to many different types of 3D image processing.
  • We found that for post-place inspection, color, more than any other attribute helped us to determine part from board. Thus, a combination of white light, color cameras, and complex image analysis allowed us to create a post-place and measurement system that could both leverage the color of the boards and components and adapt to their constantly changing appearance.
  • Post-reflow inspection was an entirely different problem. The joints themselves are specular and, therefore, can cause problems for many different imaging systems. The specular nature of the joints means that when one shines light on them, they reflect the light back in the direction that is determined by the angle of the surface. So it became necessary to create a flexible angled lighting system that allows shining light from any number of angles. The lighting system also allowed us to specify lights that are directional or uniform across the angle of light. We further augmented this system with angular cameras so that we get an extended view of the joint. Since the system is looking at "white" specular surfaces, we outfitted the system with blazing fast monochrome cameras.
    From the scientific perspective, the best thing we could do to meet our customers' needs was to develop and sell individual boxes. However, we need to dig a little deeper into the story to really discover the truth. One has to keep in mind that in 1998, most people wanted post-reflow systems. The concept of incorporating pre-reflow systems was being considered or adopted by only a select few of the manufacturers. Thus, if the customers were demanding only one type of system, it made perfect sense to sell them a specialized box that fit into the most popular place in the line. In 2003, things had become dramatically different. The adoption of pre-reflow technology was taking off. In addition, customers wanted a line-wide management system, meaning that the output of these machines needed to talk to a central system or even each other. Some customers even went a step further and asked the AOI machines to feed back information directly to the manufacturing equipment.

    With the desire to have a machine at every point in the line, there also comes the hard reality of budget constraints. Most manufacturers weren't able or willing to equip their lines with AOI at every inspection point. That was when the concept emerged that they could capture some of the line-wide management ability by asking for a flexible machine that could be moved around as needed. Thus, we had two opposing forces at work. Budget demanded flexibility. Science suggested that specialized machines were necessary. Was there a happy medium?

    We began to investigate how we could both meet the customers' needs for flexible machines while also providing the high level of inspection quality. We saw many of our competitors providing the same image capture platform and analysis software for deployment at any point in the line. We wondered if we should follow suit. However, we were greatly concerned that by doing so, we might compromise our inspection and measurement results at all places in the line, thus, providing a "partial solution" to everything and a "full solution" to nothing.

    How Flex Is Used
    Now fast forward to 2006: Our marketing manager did a study of how people really use "flexible" machines. He found that most customers have a primary place in line for the machine that they are buying — usually post-place or post-reflow. However, their fear of being boxed in to one location should some new need arise was significant. Based on this information, we decided to take a hybrid approach to flexibility. We developed new software for each machine which is based on our understanding of how the brain can adapt to variations in imaging conditions. The software was optimized for each hardware configuration in order to allow it to adapt to other inspection problems, thus, allowing us to make each machine more flexible. We added 2D paste inspection and are developing post-reflow inspection for the post-place system that takes advantage of our color image and our proprietary color processing algorithms. We augmented the post-reflow machine with post-paste and post-place capabilities that takes advantage of our flexible lighting. Thus, with a given machine hardware and expanded software, we provide a high level of performance a variety of places in the line, with an especially fine-tuned capability for a specific inspection location. We found that this was just the right combination to meet our customers' need for excellence and flexibility.

    It turns out, therefore, that both of our national sales managers with opposite points of view were correct. It took our scientists to determine the happy medium that we should provide machines that are specialists at what they do with the capability to extend themselves without degrading performance. We dub these machines "flexible specialists" and have incorporated this idea into our line of Landrex Optima — inspection and measurement systems.

    For more information, contact: Landrex, 309 Laurelwood Rd., Suite 22, Santa Clara, CA 95054. 408-567-9801; fax: 408-567-9760. Web:

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