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PC-Based Vision Lowers The Cost Of Electronics Manufacturing And Inspection

by Stephen Albanese, Matrox Imaging

Vision is used at many stages in electronics manufacturing, from alignment of a semiconductor wafer for die slicing, to inspection of a fully populated PCB. The demand to improve and increase yields has driven the demand for new vision technology used in automated optical inspection (AOI) units, surface mount technology (SMT) equipment and other machines. Now, with the advent of lower cost, higher performance, off-the-shelf vision hardware, developers who exploit this enabling technology have an edge in delivering new machines to the market or retrofitting older units more quickly and cost effectively.

Industry standards such as the PCI bus, Windows NT and powerful DSPs like the Texas Instruments TMS320C80 (C80) have brought with them many new higher performance, lower cost vision products. Matrox is one of the vendors that has recently delivered a new image processor based entirely on this technology. Matrox Genesis was designed from the ground up for today's demanding applications, with built-in scalability so developers can map out a migration path for increasing performance in the future.

Electronics manufacturing and inspection requires vision technology that can handle many requirements. Some include:

interfacing to different camera types i.e. analog or digital

on-board, real-time processing

display with non-destructive overlay of text and graphics for system set up and process monitoring

Until recently, most vision systems for electronics relied on expensive VME or proprietary vision hardware to process the huge number of pixels involved. If PC-based technology was already being used, multiple boards were required. Now, a developer can choose an off-the-shelf image processor with flexible acquisition, real-time processing, and high resolution display on a single PCI board. And since it is based on Windows NT, a host of software development tools such as Microsoft Visual C/C++ and Visual Basic are available for rapid application development and deployment of systems.

An interface to all video devices

Given the wide range of cameras used, imaging hardware targeted at electronics manufacturing and inspection should interface to a range of input devices. For PCB component presence/absence inspection, this device may be a CCIR camera with asynchronous reset control for synchronizing to external events. Inspecting a highly populated PCB might require a high resolution camera to capture an image with enough detail (one million pixels or more). For PCB panel inspection, a digital camera may be used to capture images with less noise and more accuracy than analog cameras.

In order to meet these acquisition demands, the Matrox Genesis main board's mezzanine grab module is fully programmable. It interfaces to virtually all analog, digital, monochrome, and color area and line scan video devices.

Matrox Genesis PCI image processor main board pictured with grab module and companion processor board.

Real-time processing and scalable power

Some applications may require tremendous processing power. For example, when manufacturing a PCB panel, PCB artwork may be compared to the original CAD design using a pixel-to-pixel comparison process. Later, during mass production, the panels may be inspected for defects such as damaged or missing traces and pads. As many as millions of pixels per square inch may need to be processed in real time, necessitating the power of a dedicated processor.

This kind of demanding processing requires a powerful solution like Matrox Genesis. A C80 DSP combined with Matrox's neighborhood operations accelerator (NOA) ASIC and up to 64 MB of speedy synchronous DRAM (SDRAM) make up the processing core, or node.

A common processing operation, morphology, may be used during inspection of a PCB panel for defects such as pinholes. Genesis executes a morphological 3x3 erosion operation in as little as 1.8 ms on a 512 x 512 x 8 bit image. While a main board has the power to solve a variety of demanding real-time applications, some may require additional speed. Performance of a main board can be augmented by adding companion processor boards, each integrating one or two processing nodes. Up to six processor boards can be used with the main board for a total of 13 processing nodes and the power to execute over 100 billion operations per second.

However much processing power a board delivers, real-time online applications can be hampered by I/O bottlenecks. Matrox Genesis sustains high throughput I/O by using a custom video interface ASIC (VIA), as well as dedicated high speed buses for performing transfers on and off board.

Advanced integrated display with overlay

Display requirements may vary with applications, but real-time display of processed images and interactive operator intervention is likely. Another requirement might be having a large desktop to place multiple windows, to work efficiently. Graphics such as rectangles and cross hairs that are used to mark ROIs and edges may need to be written over a live video window for such tasks as alignment of components.

The integrated display on the Genesis main board is managed by a second VIA and incorporates the Matrox MGA 2064W graphics engine, up to 8 MB of WRAM, and a 220 MHz RAM DAC for resolutions up to 1600 x 1200 @85 Hz. This provides a large desktop. As well, dual frame buffers, one for the image and one for the overlay, allow the desktop and other graphics to be nondestructively superimposed over the live video window.

Advanced integrated display with overlay

BGA inspection is but one example of the applications being solved with PC-based vision systems.

Applications and off-the-shelf software

In component inspection, a BGA package may be checked for missing or deformed balls using blob analysis operations. Gauging functions can be used to measure ball pitch. Vision is also used to properly position components before soldering. At various stages of production, vision may be used to see if solder work meets specifications and to detect presence/absence of components.

PCI frame-grabbers and image processors are used for wafer alignment and inspection.

In semiconductor manufacturing, vision technology guides robot pick and place machines. For wafer slicing, various preprocessing vision algorithms are first used to remove noise and enhance images. Pattern matching and recognition algorithms are used to locate fiducials for guidance and handling of the wafer.

Developers use the Matrox Imaging Library to quickly create reusable application code

Closing words

This new wave of off-the-shelf PC vision hardware and software offers great promise to developer's willing to exploit it. The rewards are faster time-to-market with lower cost systems that are upgradeable and easily maintained; good for both developers and electronics industry customers alike.

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