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Move to PC-Based SMD Placement Vision Simplifies Hardware and Reduces Cost
Cognex Corporation Posted 07/05/2012
Universal Instruments Corporation (UIC) is a global electronics productivity specialist, providing innovative automated electronics assembly equipment, integrated systems solutions, and process expertise to manufacturers in every sector of the global electronics industry. Universal’s solutions can be found in both original equipment manufacturers’ (OEMs) and contract electronics manufacturers’ (CEMs) facilities, with a global installed base of over 100,000 machines.
At the core of the company’s product portfolio are its Genesis and Advantis® surface mount platforms, delivering high-speed and high-accuracy component placement to populate printed circuit boards (PCBs). For many years, Universal integrated a VME-based vision system to inspect and center components and ensure accurate placement on the PCB. The company has recently migrated from a VME- to a PC-based platform architecture, and selected Cognex’s SMD4 placement guidance package due to its algorithm performance, support for industry-standard cameras and experienced engineering support team.
“Since moving to a PC-based platform, we have monitored the performance of the new machines in the field and found it to be significantly improved,” said Damon Ashman, Vision Manager for Universal Instruments. The new vision platform has allowed us to simplify our hardware requirements while adding capability. Moving forward, it will enable us to provide more value to our customers by delivering a wide range of new functionality.”
Universal’s surface mount platforms offer placement capabilities ranging from the smallest passive components to the largest ball grid array (BGA) packages. They employ a single, dual, or quad-gantry positioning system driven by the company’s patented linear motors. These motors use Variable Reluctance Motor (VRM) technology to deliver high positional repeatability and high-speed component placement. One of three types of placement heads – 30-spindle rotary Lightning®, 7-spindle InLine7, or 4-spindle InLine4 – rides on the gantry and picks components from various fixed feeder locations.
SMD placement is challenging vision application
SMD placement is one of the most challenging vision applications because it requires high levels of speed and accuracy as well as the ability to handle many different component types and sizes. The role of vision begins when a camera attached to the placement head determines the position of components in a waffle pack, tape or other source so they can be picked. Each time the placement head picks up a component, it rapidly passes it over another camera. The vision system acquires the image from the camera and inspects the part. If leads or balls – extremely small component features – are missing, damaged or out of tolerance, then the part is rejected. If the leads and balls are good, the vision system determines their location. Another camera system attached to the carriage captures images of the fiducials and placement sites on each PCB to locate the board position. The machine software then uses the known position of the component on the pick nozzle and the board to position the component within a tolerance ranging from 10 to 50 microns.
“Our previous generation of vision systems provided excellent performance but the integration costs and complexity of the previous VME-based vision hardware were excessive,” Ashman said. “Our goal was to maintain the performance of the vision system while consolidating its functions into the PC that already exists in our machine.” Universal decided to continue using its existing product line of camera systems, including integrated optics and lighting, that it has developed specially for this application. The company then set about selecting a supplier of software algorithms and vision tools to determine the location of the component leads and balls, and the PCB from the camera images.
Selecting a vision package
Universal Instruments’ engineers evaluated the leading vision tools designed for SMD placement applications. They measured the performance of each vendor’s algorithms against a library of component images that they had collected over the years. They compared the speed, positional accuracy and inspection accuracy of each algorithm. They also considered each vendor’s ability to support off-the-shelf cameras, its roadmap for developing and improving its technology, and its total cost of ownership.
“We selected Cognex because its algorithm performance was outstanding and because the company presented a compelling vision for the future of its product,” Ashman said. “In addition, Cognex has an extensive engineering team that is fully committed to supporting their vision products.” At the time the decision was made, Cognex had recently ported its vision process software to the PC platform. Since then, Cognex has also provided networking support for inexpensive industry-standard cameras using the IEEE 1394 FireWire® bus.
At the core of the SMD4 toolset is Cognex’s PatMax® geometric image analysis technique for accurately locating devices and device features despite wide variations in device appearance or image contrast. This is useful in situations, for example, where surface reflections or nozzles show up in the image, creating a visually confusing scene. PatMax is able to tolerate the confusing scene and locate the device reliably. PatMax also helps SMD4 to accurately locate fiducials that have been degraded by oxidation, hot air solder leveling (HASL), and other PCB manufacturing processes. This helps increase PCB alignment yield while reducing production downtime and the need for operator intervention.
Three levels of vision development tools
The SMD4 package provides an open, PC-based software development architecture for building SMD placement guidance applications. It includes calibration tools, nozzle location tools, graphical diagnostics, and device description data structures. In addition it offers with direct access to three different levels of software tools. The first is a library of high-level software tools for locating and inspecting chips, leaded devices, BGAs, chip scale package (CSP) devices, and flip chips. These tools, based on Cognex’s proven solutions, automatically locate the device, determine the precise X, Y, and theta location of each device and then examine the device for missing or damaged leads, solder balls, or bumps.
The second is a library of flexible, mid-level software tools for locating and inspecting device features such as leads, device bodies and ball patterns. These tools can be easily grouped together in user-defined sequences and are ideal for those who wish to create custom device inspections to help optimize the speed and placement accuracy of their particular mounter. Finally, Cognex offers an extensive library of low-level, general-purpose image processing and analysis tools. With these tools, users can write their own device inspections from scratch or add other functions to their SMD application such as post-placement inspection or PCB identification.
The implementation process
During the implementation process, the SMD4 platform was integrated with Universal Instruments’ vision code, library code, graphical user interface and servo control technology. The basic interaction between the platform and machine begins with Universal Instruments’ control software directing the SMD4 platform to acquire an image. In the case of a BGA, the SMD4 platform captures an image from the camera and processes it to determine whether all balls are in place and positioned within tolerances on the device and the distance by which the balls are off of the center of the vacuum tool. The SMD4 platform then provides the information back to the control software.
Ashman added that the new PC-based architecture will expedite the introduction of new devices. “For example, instead of having to spend time manually entering parameters into the system in order to create device descriptions, Cognex tools enables users to simply present a device to the vision camera and the system will automatically learn the device geometry,” he said. “This improves the accuracy of device descriptions and speeds up the process of creating and testing descriptions – especially in situations where new devices are frequently introduced or where uniquely shaped devices need to be described.”
The SMD4 placement guidance package has now been integrated into Universal’s Genesis Series 2 and Advantis 3™ surface mount platforms and the results have been excellent, with the machines performing very well. The Cognex SMD4 Placement Guidance Package has clearly provided a distinct advantage in terms of the speed, accuracy and flexibility required for SMD placement.