RFID tags and Data Matrix codes can help manufacturers error-proof assembly, track inventory and automate setup.

The Defense Department now requires all mission-critical parts, assemblies and equipment to be identified with both Data Matrix codes and radio frequency identification (RFID) tags. For many electronics assemblers, this mandate has brought these two technologies to the forefront. Any U.S. manufacturer that sells to the Defense Department must comply with this requirement. In the near future, the mandate could be applied to NATO countries, as well.

The mandate pertains to any contract issued by the government after January 2004. It applies to any part, assembly or product that costs more than $5,000, or is mission-critical, serially managed, or controlled inventory.

The mandate requires a unique tracking number to be marked directly on the item with a Data Matrix code that will last the life of the part. This code must include the identification number of the manufacturer, the identification number of the part type, and the serial number of the specific part. In addition, all pallets, containers and boxes for transporting the items must carry an RFID tag for tracking purposes.

The goal of the government is to track and trace anything it procures at anytime during the life of the part or product. This is true whether a part is used by itself or integrated into an assembly. Eliminating human-readable codes and manual data entry removes the potential for error.

Detailing Data Matrix

Data Matrix codes look like tiny checker boards, with light and dark cells. The 2D codes are typically applied with a laser, although dot-peening and ink-jet printing are also used.

Data Matrix codes can be marked directly on the product and offer several advantages over 1D bar codes. The most important advantage is that Data Matrix symbols encode information digitally in the form of on-off cells. In contrast, bar codes are read through analog measurements of the width of bars and spaces. Even low-contrast Data Matrix codes can be read effectively directly from the part; there's no need to print the code on a label or use a high-precision printing process. Data Matrix symbols are also scalable. They typically occupy one-tenth of the space of bar codes, while containing an equal or greater amount of information.

With small Data Matrix codes permanently marked on every circuit board and component prior to processing, a new level of control and traceability is possible. The codes can be used to identify very small components and very dense subassemblies that have no available space for labels.

The latest readers can decode Data Matrix symbols with very low contrast, almost to the level of "black on black." The codes can be read in any orientation, so they can be used with either fixed or handheld equipment. Most Data Matrix readers can also decode bar codes, making them backward compatible and easy to introduce to existing facilities.

Only a few years ago, Data Matrix readers were complicated, high-performance machine vision systems specifically adapted for that application.

Today, Data Matrix readers are as easy to use as plug-and-play bar code readers. In some ways, these devices are even more sophisticated than the original vision systems they replaced, but they require no more programming or setup than a conventional vision system. A built-in targeting system allows engineers to position the reader in the right spot and go directly to work. A PC or monitor is not needed for setup.

With advanced image processing, a large depth of field, and analysis algorithms, the reader can do its job even if the image is out of focus. As a result, the parts can shift without having to reposition the reader for reliable output. The reader automatically selects the right imaging parameters to get the best picture. The device can switch instantly from reading codes on bright, stainless steel parts to reading codes on black matte plastic.

Readers can be linked to shop-floor computer networks and accessed from remote locations, and some high-end models can save images of codes that they were unable to be read. As a result, engineers can diagnose a problem from anywhere in the world, without having to take a reader off-line. Modern readers have real-time operating systems that allow multiple tasks to be executed at different priority levels. Thus, an engineer can access saved images for remote troubleshooting, while the reader continues to read parts passing under it at high speeds.

Readers can also be used to verify the quality of codes marked directly on parts. All marking systems will produce codes of degrading quality over time. When they begin creating marks that are impossible to read, they will need maintenance.

Readers can be set up to monitor mark quality and signal when the marks start reaching below a specified level. Without stopping the line, a message can go out to an engineer well before any unreadable marks are produced, so maintenance can be performed the next time the line is down.

Understanding RFID

An RFID system consists of three main components: a transponder tag, an antenna and a transceiver. The tag contains a memory chip that stores information about the product to which it is attached. There are two kinds of tags: active and passive. Active tags are equipped with a battery and a transmitter, and are continuously powered. Passive tags are powered by radio frequency energy transferred from the receiver. Active tags have a greater communication range than passive tags. Like CDs, tags can be read-only or read-write.

The variety of RFID tags is endless. To create a tag, the chip and a tiny antenna are mounted to a base, which is then encapsulated with thermoplastic. The length of the tags ranges from 1/16 inch to more than 6 inches. Tags can be paper thin, often referred to as "smart labels," or they can be encased in materials that enable them to withstand the harshest temperatures, chemicals and environments for a lifetime. Some tags are reusable, and some can be handled just like surface-mount components, on tape and reel for automated assembly onto printed circuit boards. In fact, in the future, RFID tags may be integrated directly with some electronic components.

The tags transmit information to and from the transceiver via the antenna. A major advantage of this system is that the transceiver does not need to have a clear line of sight to the tag. Because each tag has a unique ID, there is no need to point the tag in the direction of the antenna, as needed with linear or 2D code readers. The tag could be hidden in a pile of other tags, but as long as it is within range of the antenna, it can be read and written to. If the product is moving, the tag on that specific box, pallet or assembly can be tracked and identified even if hundreds of similar items are moving at the same time.

Electronics Assembly Applications

Both RFID tags and Data Matrix codes can help streamline electronics assembly. Using a tactic borrowed from automotive manufacturing, high-memory RFID tags can be affixed to pallets carrying assemblies. Each tag holds all the information needed to assemble that particular product. Automated equipment at each station can read information from the tag as it moves down the line and perform whatever steps are necessary to assemble the product. No human input is required, since assembly information is programmed into the tags at the start of the process. At the same time, the tag can keep a detailed record of all the steps, costs and conditions related to the assembly of the product.

Marking Data Matrix codes directly on parts provides complete unit-level traceability. It is often impossible to put a label on some electronic components. Tiny 0201 chips or some ASIC devices are two good examples. Using direct part marking, traceability can go from the subassembly level down to each individual component. This makes it easy for assemblers to track changes in the design or track replacement components for quality control. In addition, Data Matrix symbols can encode a much wider range of information than just a serial number. Assemblers can use the additional information storage capacity to automate equipment setup and programming.

For contract manufacturers grappling with high-mix production, inventory control and process control can be a financial drain. Direct part marking and RFID are a valuable combination that reduces problems in these areas, offering "cradle-to-grave" traceability. If an assembly fails in the field, engineers can recover all product information from the pallet tag, traceable through all process steps to each individual component.

Direct part marking can also help prevent errors during assembly. Putting Data Matrix codes on each component greatly reduces the possibility that the wrong part or process will be used to assemble a product. The components and the board are always correctly matched, and setups can be read directly from the embedded codes.

New applications are continually arising for RFID. One area of growing concern in electronics assembly is product recycling. RFID tags can be placed inside computers so that when they are recycled, specific components can be easily identified without holding every part in front of a camera to read it.

In short, the two technologies are complimentary. Think of Data Matrix codes as permanent tattoos on part surfaces. They are designed to last for life. They can't be easily removed or scratched off. An RFID tag is like an ID bracelet. The Data Matrix codes contain part-specific data, while RFID tags track the movement of the finished assembly through the entire manufacturing process, the supply chain and use in the field.

RFID is used at the box and pallet level; direct part marking is used at the component, board and subassembly level. It would be difficult, if not impossible, to put an RFID tag on a very small electronic component. Likewise, it would also be difficult and expensive to track each and every part and subassembly with a line-of-sight reader.

Combined, Data Matrix and RFID create a total quality package. Eliminating both process and product defects represents a huge savings that any manufacturer can benefit from, not only those delivering products to the military.