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Electronics manufacturers today are faced with many new challenges, including new regulations like lead-free solder, RoHS, and specialized package types such as high-power devices and devices with high pin-counts. Together, with the trend of miniaturization, many packages now have solder joints hidden beneath the body. To ensure product quality and for process monitoring reasons, the manufacturers need tools that ensure reliability and cost efficiency. Naturally, manufacturers often balk at investing in such “nonproductive”equipment. Due to the hidden solder joints, traditional optical inspection tools are not able to inspect all the connections on a modern PCB. For many years, x-ray systems found their way onto the production floor to aid manufacturers in process monitoring and quality assurance. These usually were quite expensive, fast, fully automatic systems using specialized hardware components. With today’s technological evolution, automated x-ray systems became more affordable and available to a larger number of electronics manufacturers. But what requirements must be fulfilled by such systems? From an economical viewpoint, there are return on investment (ROI) and cost of ownership factors to consider. Process engineering may prefer system resolution, required footprint, system availability, reliability, system throughput, and size and weight of the samples thesystem can handle. Nobody’s perfect. There are many things that could go wrong in a production environment, from material-related problems to human error. Let’s discuss some implicationsand reference it on an x-ray inspection system. Cost of ownership
ROI often seems non-existent when test equipment is seen as non-productive. This may be true at first glance. But depending where a test is performed, substandard products are identified and will be eliminated in the next process. This will avoid costs generated by continuing to manufacture a piece when the fault is caught earlier in the process. Now, isn’t such “cost-avoidance” a kind of productivity? Monitoring production costs before and after the implementation of the x-ray inspection will show the costs saved by that measure. This number, in turn, allowscalculating an ROI period. When talking about cost of ownership, the savings are not just answered in the amount of capital spent to keep the equipment in, let’s say, operational state. The ability to upgrade the system to cover future inspection tasks is also a considerable factor. Such upgrades may be software evolutions, stronger x-ray sources or newer detector technologies. Eventually, as with most technology, obsolescence will require a new system but being able to keep the equipment up-to-date can stretch the need ofinvesting in new equipment for a much longer period. Operational costs can be improved if a system is chosen that minimizes the amount of time to perform preventive maintenance or service tasks. Easy access to system critical components is as essential as having a system with a small number of parts that need special care. Another factor for operational cost is the software of such equipment. How easy it is to operate and program goes along with the qualification required for operators and programmers. Short programming times are enhanced by the ability to import CAD data to generate inspection programs. A CAD file on the other hand typically does not contain all the information of the complexity and routing of layers underneath a solder joint. Product-dependent modifications are absolutely necessary to adapt inspectioncriterion to local conditions. Availability, dependability, traceability
System availability is a key demand to achieve the planned inspection volume in the given time frame. A system must be designed to allow 24/7 operation. Every system component must be carefully selected. That might include such simple things like “X-Ray On” light bulbs. Many countries may require an x-ray system to stop generating x-rays if the X-Ray On light is defective. The use of maintenance-free x-ray sources is also a considerablemeasure to ensure system availability up time. How dependable are the results of the inspection? What is the false-call rate? What is the repeatability of inspection results? Questions like this find their answer in the almost all components of an x-ray system, from the stability of the x-ray tube itself and the stability of the detector, to the mechanical system around the x-y table and the z-axis to the stability of the image processing tools. Every variation will impact the reliability of the inspection results. Such systems need to provide tools to ensure the dependability of their results. Equipment manufacturers need to provide tools and measures to calibrate and verify the performanceof such systems. Product traceability is mandatory. All inspection efforts are worthless if the results of a particular product cannot be linked to that physical product. A system must be able to allow handling product identifiers that are usually barcodes. It is possible that in the near future RFID tags will replace barcodes. Some production environments even require multiple barcode readers to identify every part in a multi-up tray. At the verify/repair station where problems found are to be corrected, any mismatch between theinspection results and the product can be catastrophic. Let’s communicate
“Not-Aus aktiviert!” What? Globalization has differenteffects. Systems are sold worldwide and operators comefrom various countries. A system must be able to supportlocal languages. Time wasted to browse through foreigndictionaries to understand messages like the one abovedefinitely decreases equipment productivity. A system integrated in a production line must be able to communicate with the environment around it even if it is as “simple” as interpreting SMEMA signals correctly. As operation systems and computer platforms are standardized, the capability to integrate into the factory network may seem trivial but, nevertheless, this interface is essential. It may be used just to transfer new or modified inspection programs to the system. Another form of communication is required if a manufacturer wants to implement product marking systems. Test equipment must be able to provide power and other measures of communication for such requirements as well. Hurry up, time is money
Usually there is some buffering around productioncritical equipment such as the assembly machines of the reflow oven. Being behind a bunch of chip shooters can be hard for a single inspection system. Manufacturers usually try to split the workload over more equipment to overcome bottlenecks of the inspection process. This is another challenge for an inspection system. It must be able to provide inspection results in a form where it can be understood by other systems around or it may be necessary to import such data from upstream equipment. On the programming side, inspection routines must be adjustable to various conditions. Programmed components must be able to be ignored at one day or inspected on another day. It must be able to assign such “skip-flags” remotely while the system is performing other inspection tasks or at the system in case other equipment becomes momentarily unavailable for any reason. From the operation viewpoint, an automated system should only require a minimum of operator interactions. The systems must be able to run fully unattended, enabling operators to manage multiple systems simultaneously. Some systems are advertised with features like an enormous magnification range, which in an in-line environment doesn’t really make sense and is unnecessary. High magnification goes hand-in-hand with small field of views and the field of views per second are a measure for the throughput of any system. For the inspection of even double-sided PCBs, tubes with a maximal energy of 130 kV are usually more than needed. On the lower end, to be able to penetrate solder balls of FBGAs, systems with tubes below 90 kV are hardly suited for the inspection of such components. Some of these features belong in a laboratory environment as on the production floor. There may be a more productive way to invest money. Safety first
Operators may initially be hesitant to work with x-ray systems. In the early days, as x-rays became commercially available, they were used for many tasks that today we would not even think about. The nature of x-rays as invisible and “untouchable” means we do not feel anything if we are getting irradiated and the fact they are dangerous if applied uncontrolled. But their ability to penetrate material to reveal its internal structure offers valuable applications in numerous fields. As with many other things in life, it’s a matter of quantity. There is natural and cosmic radiation around us all the time and some of it even has positive effects. Whatever concerns an operator might have, today’s x-ray systems are safe. The regulatory agencies of the USA and many other countries around the world have raised limits and regulations that an equipment manufacturer must fulfill and maintain. Some companies do only what is required but some do even more to further reduce the risk of uncontrolled radiation. Robert Meller X-ray image of high mag BGA X-ray image of off axis BGA BGA Analysis X-ray image of a CSP Robert Meller is Product Manager of X-Ray Systems at VJ Electronix Inc. | 
