Printed circuit boards flow from the bare board state through screen printing, component population, automated optical inspection, and finally through the soldering oven. Each of the above steps adds value to the board. According to PCB Trace Technologies Inc, it is necessary to establish traceability of the quality data to repair or replace an electronic device in the event of failure.
Board manufacturing may continue for months or years. During this time, the manufacturer may have changed parts or the design of the board. In most cases, boards typically have individual serial numbers for facilitating repairs and modifications. Technicians need this traceability for installing the correct parts.
Designers and manufacturers typically have various schemes for adding the identifying the part or serial number on a PCB circuit board. Here are some of them:
- The part number on a PCB may identify the built-up circuit board. Sometimes there are two numbers visible—One for identifying the bare circuit board, and the other for the complete assembly. This is usually the circuit card assembly number and is distinct from the number representing the bare board. Most often, the serial number of the assembly appears next to the circuit card assembly number. This may be handwritten or stamped with ink. Typically, the serial number is short, in hexadecimal or alphanumeric numbers.
- Some manufacturers etch the part number onto a large copper land or a broad wiring trace. It may include the manufacturer’s logo, a patent number, and a circuit card assembly number, along with a serial number. It may be possible to identify the serial number with the inclusion of an SN or an S/N before the number. Some manufacturers may affix a small sticker bearing the serial number near the circuit card assembly number. Some manufacturers use bar codes in place of numbers for both part number and serial number. Others may use RFID chips.
- Manufacturers may typically store the serial number information in a memory chip on the board. To read this information, it is necessary to use a serial data communication program. Most professional repair facilities will have the means of extracting such information from boards. Automated test equipment typically use a subroutine for fetching the serial number, which helps in the identification of the circuit card assembly. This method of information storage may also contain the modification and repair history of the board assembly. It is necessary for serial data communication programs to use simple queries to access this information.
Tips and Warnings
It may be necessary to use proper magnification to read the serial numbers on printed circuit boards. In old boards, the print or ink may be smudged, which may make it difficult to distinguish the numbers like 0, 3, and 8.
Barcodes for Serial Numbers
Barcodes typically encode information about when and where a board was made, its flux density, solder temperature, component numbers, and test data. It is necessary to track this information properly using automatic identification to ensure that the assembly of the PCB has followed proper steps and procedures, and that all the necessary components are present. Barcodes are becoming more sophisticated and can store more information than before with the help of automatic identification systems.
Modern barcode readers may use Hotbars and PowerGrid barcode reading algorithms. They can reliably identify 1D and 2D barcodes that manufacturers print or stamp on labels, or laser-etch directly on the board surface. As this does not involve manual reading, the board can move at the greatest potential between machines and processes.
Machine vision systems often use OCR or optical character recognition and OCV or optical character verification for identifying boards and high-value components along with their serial numbers. These systems may also contain information that the original barcode label does not incorporate.
Disadvantages with Barcodes
With electronic manufacturers facing tough competition, they are reducing costs and increasing revenue by improving their production efficiency, improving their quality, and finally outsourcing. To assemble many products requires flexible manufacturing processes, improved accuracy and better lead times. For mitigating manufacturing liability, manufacturers must limit the scope of product recalls, and comply more with regulations.
The main problem with tracking printed circuit boards using barcodes is it requires a line of sight arrangement between the label and the reader. This limits the amount of information that the system can encode. Even with 2D barcodes, there can be significant trade-offs that include the cost of readers and their inherent accuracy. Moreover, most high-density boards typically lack real-estate for placing a single barcode. On the other hand, multiple barcodes many prove difficult for a single barcode reader.
RFID Chip Technology for Serial Numbers
For tracking and traceability of printed circuit boards, manufacturers are using the RFID chip technology. The RFID chip holds the manufacturing and product information directly on the PCB. This may include the board’s serial number, model number, manufacturing processes involved, and other individual product information.
It is possible to securely access or update the information on the RFID chip at any point during the manufacturing, shipping, or repair processes the board undergoes. This is an off-the-shelf solution providing automated real-time visibility of the board. Moreover, the system maintains a complete electronic pedigree for tracking and traceability of parts or work-in-progress.
The RFID system offers a real-time dashboard, various alerts, and reports for the management on the shop floor. It is possible to mount the RFID tag or chip onto the PCB as a standard SMT component. There is no need for a physical connection to the RFID chip for programming it with the manufacturing pedigree information. Likewise, it is possible to access critical data rapidly from the chip without a connection.
Benefits of RFID Chip Technology
There are several benefits of the RFID chip technology:
- Automatic traceability of the work-in-progress
- Real-time alerts for anticipating and addressing production issues
- Ready assessment of delivery capabilities for new orders
- Quick isolation of defective components
- The product has integrated authenticity
- Quick reconciliation between shipping and receiving
- Easy connection between supply chain and manufacturing visibility
Conclusion
Continual improvement of board development quality in PCB assembly is typically through a succession of design, build, test iterations. The ability to make improvements at key steps makes this possible by identifying the previous progression through the process. This requires traceability as an integral part of the PCB assembly risk management. According to PCB Trace Technologies Inc, the objective is to optimize the build process of the board for improving the quality.
