Inspection Industry Outlook – PCB Inspection Outlook 2005

Regardless of their labor rate, inspectors alone can t determine area-array solder-joint quality.

The use of smaller components, lead-free soldering, and greater PCB component density requires higher performance from automated PCB inspection systems. In separate ways, each of these factors has resulted in the need for higher resolution and accuracy from the inspection process.

Lead-free soldering affects X-ray inspection because of the altered mass absorption of the new solder alloys. Measurement of solder-paste volume by 3-D techniques now must account for slightly different fillet curvatures and a rougher surface finish. Higher temperatures are used, which means that board warping and component materials may become issues. In addition, new pad shapes have been proposed to assist automated determination of soldered-joint quality.

Smaller components such as 0201-size resistors really are minute. You need a 10- m pixel size to get the required magnification for accurate inspection. At least, this is the highest magnification one manufacturer offers via a zoom lens. Today, there's nothing smaller than a 0201, although one website mentioned the next step, 01005, which would be 4• smaller than a 0201.

Optical zoom or a higher pixel-count target must be used to provide high resolution. Both approaches are being pursued.

One way to achieve very high resolution, as described by George Blackwell, director of product marketing at Cognex, is by using line-scan cameras that also can reduce the peak power level needed to position the PCBs. Full-frame cameras require the board-positioning system to stop the PCB motion and allow time for settling before the board's image can be recorded. Stopping and starting takes much more power than a continuously moving conveyor such as used in a line-scan application.

And, both circuit and component densities are increasing, affecting throughput. There are many optical or X-ray images to capture and a huge number of computations to be performed on large, densely populated boards. The speed with which the actions can be accomplished largely determines the throughput.

Increased circuit density results from the trend to use more area-array packages in each assembly. Boris Mathiszik, vice president of sales at phoenix|x-ray Systems + Services, commented,  In the past, typical assemblies may have contained one to five area-array packages, but now designs frequently have 30 or 40. In addition, assemblies are becoming more complex. Double-sided reflow is more prevalent, often with mirrored BGAs. 

For boards populated on both sides, Mr. Mathiszik said that conventional 2-D X-ray inspection with top-down viewing might not be the best approach. Instead, at high magnification, oblique images of components are less likely to be affected by parts on the other side of the board.

Smaller components, lead-free soldering, and greater component density are the three main themes affecting PCB inspection, but they re not the only ones. Cost always restricts the technologies and performance available for an application. And, manufacturers continue to innovate, resulting in a wide range of inspection products with varying capabilities and benefits. It's not surprising then that few inspection processes have become completely standardized.

Implications for the Industry
With these trends forming the background to the inspection industry, we asked managers to describe their outlooks for 2005.

X-Ray
 We see nothing but increased opportunities for X-ray inspection, both in the product assembly and the nondestructive testing (NDT) markets,• said Lance Scott, president of FEINFOCUS/COMET North America.  All of the industry drivers are pointing to increased inspection needs. For instance, in electronics assembly,• he continued,  the move to smaller, denser assemblies has led to a greater use of area-array devices, which in turn, is dictating extensive use of X-ray inspection to identify faulty interconnects.

 Software controls have eliminated the need for an X-ray physicist to operate the tool and put high-resolution inspection in the hands of the manufacturing technician. For example, in the case of wafer-bump inspection,• he explained,  void detection requires analysis of multiple bumps. This means searching for slight variations in density, which often is outside the scope of manual inspection. 

According to Mr. Scott, wafer bumping is recognized as the largest challenge in semiconductor packaging because of the voids that often form beneath the bump surface. High-resolution X-ray inspection is the only technology capable of detecting and measuring these voids.

John Spofford, the vice president and general manager of Agilent Technologies•  Manufacturing Test Business, added that millions of units potentially could be affected by undetected failures in hidden joints.  As liability and risk move further back in the value chain, X-ray imaging will become a more important manufacturing tool. It's fixtureless and ready for lead-free processes,• he said.

Optical
Optical inspection deals with visible connections, and as components and their joints become smaller, generating the best possible image is more difficult. According to Alan L. Paris, the industrial microscopy marketing director at Leica Microsystems,  Advances in optical engineering software, manufacturing tools, and coating technology have improved optical performance in even the most basic inspection microscope. The price/performance ratio of today's optical microscopes is exceptional compared with levels only a decade ago. 

Software has been key to many recently introduced Leica tools such as 3-D analysis that can accurately measure solid-surface topography, surface areas, and volumes.  Only because of today's powerful PCs and digital imaging technology can the processing capacity and speed required for 3-D analysis move from research to the production floor,• Mr. Paris added.

Yet other innovations have extended what were physical limits to performance in the past. Here software has addressed such fundamental problems as small depth of focus through the application of multifocus algorithms for optical image stacking.

Also operating in the optical imaging space is JAI PULNiX. The company develops and manufactures smart cameras that include neural networks. Without requiring complex programming, the cameras take only microseconds to make image-related decisions that mimic human intelligence.

 Machine vision has a wide variety of applications spread across a range of fields,• explained Toshi Hori, the company's CTO.  In general, the industry is moving to higher resolutions and speeds, lower costs, and miniaturization of components. Applications that stand to substantially benefit from these trends include semiconductors, electronics, assembly and packaging, medicine, pharmaceuticals, military, and aerospace.

 More and more smart cameras will likely enter the market. New communications technologies such as gigabit Ethernet will reduce the need for large computers on factory floors,• he continued,  and make possible more network-based automation. We believe that most current trends'such as faster processors, smaller component size, and higher resolution will continue in the foreseeable future. 

Image Processing
Smart cameras are well suited for many applications and offer a very compact solution. On the other hand, several vendors agree that faster PCs have been key to today's improved pattern-recognition performance. And, for either conventional or smart cameras, lighting plays a critical role. Unless the item to be inspected is correctly lit, image-processing algorithms will not provide consistent performance.

National Instruments• Kyle Voosen, a vision/motion product engineer, explained how PCs have become faster.  The new PCI Express technology supports data transfer speeds up to 680 MB/s and higher speeds in the future. This provides a low-cost alternative to traditional approaches to high-speed inspection systems that generally were expensive. 

Modern pattern-matching algorithms require fast PCs because the algorithms are complex. However, he elaborated, in addition to matching objects, newer software also classifies them. This is very useful in large-mix manufacturing applications where you can quickly sort out parts regardless of the many possible combinations that may exist.

According to Francois Bertrand, vice president of sales and marketing at Matrox Imaging,  The fundamental science behind a number of techniques, such as geometric pattern recognition (GPR) and feature extraction, has been known for quite a while. However, the recent increase in PC processing power has made it practical to use compute-intensive algorithms in industrial inspection applications. The Matrox Geometric Model Finder tool,• he continued,  locates a model or multiple models by using geometric features instead of pixel-to-pixel correlation. 

Originally, normalized grayscale correlation (NGC) was the dominant pattern-matching method. As more complex requirements developed, companies turned to GPR. For example, the appearance of chemically and mechanically polished (CMP) wafers exhibits severe contrast changes, making NGC-based tools unsuitable. GPR tools can have a greater tolerance to lighting variations including specular reflection as well as module occlusion and variations in scale and angle.

Truly uniform lighting, noted Mr. Bertrand, was very difficult to provide, and advances in analysis algorithms have helped to relax previously stringent lighting requirements. For example, in addition to coping with shadows and reflections from objects in the vicinity of the inspection camera, GPR algorithms can identify features such as solder paste that become partially transparent under strong lighting conditions.

To give a good idea of the capabilities of modern feature-location software, Mr. Blackwell explained the different uses addressed by a few of the Cognex algorithms. PatMax• is the company's basic geometric pattern recognition tool. PatMax scene alignment (SA) provides partial-match alignment that eliminates the need for the entire pattern to be present in an image. PatFlexTM extends PatMax image processing to include the severe perspective changes and spatial distortion found in curved or warped surfaces such as flexible circuits.

 When an acquired image is unavailable or unsuitable for training,• he continued,  Synthetic PatMax can be used to generate reference models. This tool leverages the increased availability of electronic data and parts databases to automatically generate alignment targets from CAD data. Users can import CAD data, extract edges, or sketch freehand to create reference models without relying on image data. 

With regard to threats and opportunities for inspection companies in 2005, Mr. Blackwell cited the continuing shift of electronics manufacturing to China as a major concern. Because of the country's very low cost of labor, the decision to use AOI vs. manual inspection is based on criteria other than elimination of labor. In addition to throughput, these factors include the reliability, accuracy, robustness, and consistency of the inspection result.

 It used to be that the A in AOI was enough to justify the investment,• he continued.  As electronics manufacturing continues to move to China, that's no longer the case. It could take a while to saturate China's labor market. 

Continuing the optical-inspection and image-analysis themes, George Ayoub, president and CEO of Machine Vision Products, said,  AOI is mainly affected by advances in camera/electro-optical technologies and the computing power available to run robust algorithms in real time. Recent advances include faster large-format cameras, color-stable cameras, brighter and longer-life LEDs, and faster computers.• The company has introduced real-time color-processing algorithms and innovations that support concurrent 2-D/3-D solder-paste inspection.

 Although the future of AOI includes assembled PCB inspection,• Mr. Ayoub explained,  process control will be derived from AOI information to form a closed-loop feedback manufacturing solution. Doing so allows the entire process to be monitored and maximum efficiency achieved quickly. 

Process Inspection
View Engineering produces off-line optical measuring equipment used to calibrate screen printers, component placement systems, and glue-dispensing machines. Determining the deviations from nominal positions for all these operations helps eliminate a major source of surface-mount manufacturing errors.

Steven Rosso, the company's president, explained the benefits of a recently developed software product called Elements:  The software is dedicated to SMT electronics assembly applications such as stencils, PCBs, component-placement verification, solder-paste registration, and volume measurements. Using the CAD file of each application, an operator can identify the measurements of interest and assign tolerances for acceptable results before beginning the measurements.

 The program determines the optimal sequence of inspection for reduced cycle time and generates a comprehensive report including a histogram and scatter-plot analysis that clearly identifies the process trends. Because Elements eliminates programming,• he continued,  it allows quick changeover of parts on an SMT line, which typically is being used for high-mix and low-volume manufacturing. 

Mr. Rosso also discussed the relationship among inspection, outsourcing, and contract manufacture (EMS). As manufacturing continues to become concentrated in EMS companies, he believes the standardization of inspection should increase. Regardless of which EMS organization performs the work, the OEMs contracting for it will influence how their parts are inspected and measured.

Outsourcing to overseas companies involves a different competitive dynamic than what American inspection equipment vendors are used to, he explained. This could mean modification of equipment to meet local safety regulations, for example, or the transfer of technology to the local office to ensure adequate local support.

Summary
For most electronics manufacturing inspection applications, there are a number of proven solutions. Generally, that's true, but as little as a year ago, it wasn t necessarily the case. Timothy Ludy, product marketing manager at Data Translation, provided background details:

 A 25% increase in PC CPU speed per year has allowed our Vision Foundry product to take huge advances in the type of algorithms it uses. A 3.4-GHz Pentium 4 just about keeps pace with the faster applications,• he said,  and clearly one year ago, projects such as a high-speed, RGB color-print inspection system probably would have required DSP-assisted hardware. 

Of course, fast PCs are only one part, although an important part, of an inspection solution. Obtaining an optical or X-ray image and optimally applying the most relevant algorithms involve many other disciplines from optical design and material physics to complex mathematical modeling. And, in addition to technology, as View Engineering's Mr. Rosso pointed out, dealing with overseas contract manufacturers requires carefully tuned business skills.

Because his company provides both optical and X-ray imaging solutions, YESTech's CEO Don Miller has a slightly different view of the inspection industry.  The goal is to go beyond just improving defect detection to provide meaningful process-control information that supports yield improvement in a proactive manner. The key to this goal,• he concluded,  is to offer an efficient system at a price easily justifiable by our customers. 
 

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