- By Susan Snyder
- May 12, 2005
- Microscan Systems
Perhaps every manufacturer's goal is to achieve six-sigma quality at the lowest cost possible. A work-in-progress tracking system works hard to achieve both goals. It ensures quality by providing process verification and early error detection. It lowers the cost of manufacturing by optimizing inventory, and increasing over-all yield.
Today it is no longer good enough for a manufacturer to track how many raw components are coming in the door and how many completed boards are going out. A manufacturer must also know the status of their work-in-process inventory as well. An automated complete "cradle to grave" component-level tracking system makes this possible.
While the overall concept of product tracking is not new, the automated tracking of products down to the individual component level has greater bottom-line impact. Many manufacturers have a system setup for tracking incoming inventory and how many boards are shipped out. Some even track how many boards have completed specific tests. However, a well-executed tracking system can do so much more than document the status of raw parts and finished product.
The most direct way to ensure complete quality control of the production process is a "cradle to grave" component traceability system where each part is permanently marked with a machine-readable code and verified at each stage in the manufacturing process. The amount of data generated from such a system can be used to optimize line performance, identify defects, increase first-pass yields and as a result, reduce the costs of manufacturing.
Matrix Codes Enable Component Traceability
Until recently, traditional 1D bar codes were the most common symbol used for part tracking. However, printed circuit boards are growing increasingly smaller and much more complex. Many boards no longer have enough real estate available to accommodate a bar code. For many manufacturers, 2D matrix codes such as Data Matrix and QR code are the only option.
Matrix codes have much more data capacity than a bar code within a dramatically smaller footprint. All a manufacturer needs is .1 inch of square space on a component and it can be marked with a 5 or 6 digit Data Matrix symbol. As a result, Data Matrix enables the traceability of components such as crystal oscillators or custom ASICs that in the past could not accommodate any type of machine-readable form of identification. Matrix codes can also be used to track small, complex printed circuit boards that cannot accommodate a bar code.
Data Matrix offers greater placement flexibility as well, since it can be formatted into either square or rectangular shapes. Additional characteristics include no orientation restrictions, virtually no contrast limitations, and the ability to accommodate a variety of marking methods. This makes the code extremely suitable for low contrast, permanent-mark applications such as laser etching directly onto the surface of a printed circuit board or the outer packaging of a crystal oscillator.
Technology Advancements Increase Ease of Use
While matrix codes offer many benefits over bar codes, they have one limitation. They can only be read by camera-based equipment. In the past this was a significant drawback. At the time Data Matrix was introduced, the only camera-based options available were high-end vision systems designed for much more complex tasks than simply decoding a symbol. Most vision systems required custom programming to accomplish a simple data capture application. Once installed, most required hours of training in order to operate them. If the type of symbol or contrast level changed, the system would need to be reconfigured before the next product run could start.
This caused a considerable amount of downtime, especially for fabrication facilities now dealing with a much higher mix of smaller product runs. Since one of the goals behind using a product tracking system is to optimize production while minimizing downtime and manufacturing errors, this was a problem. The benefits of using 2D symbols did not compensate for the extensive downtime and high total cost of ownership of the equipment required to read them.
Today there is an easier solution. The introduction of the new smart camera has all but revolutionized reading 2D symbols for product tracking applications. Simply put, smart cameras have the robust software functionality of a vision system but the ease of use and the price point of a laser bar code scanner. What used to take hours to accomplish with a vision system, has been simplified down to a button. The unit does all the rest. The entire set-up process takes less than 60 seconds.
New models offer many additional features that make them easier to use. Examples include a field of view indicator pattern and positive read indicators such as a green flash that informs the operator the smart camera is decoding the symbol. The data collected from the unit is translated into a simple text stream that can be sent directly into an existing database such as the database of an integrated AOI machine. There is no longer a need for extensive operator training, complicated set-up routines and custom software for each application.
Unlike laser scanners which can only read bar codes, smart cameras can read both bar codes and matrix codes. This makes them ideal for systems that use both code-types: bar codes on the printed circuit boards and Data Matrix on small components.
In addition to providing a much more user-friendly solution, smart cameras also offer an economical advantage as well. Since smart cameras average around $3,000, they are considerably less of a capital investment than vision systems, which average around $10,000 and up. In addition, vision systems also have a lot higher total cost of ownership than a smart camera because most still require custom programming and considerable training to operate.
Component Tracking System Model
The product tracking system begins at the point the symbol is applied to the unit being tracked. In the production of printed circuit boards, the code is often applied to the raw boards just before they enter the production cycle. Once the code is applied, the code is then read by a data capture device and validated for two things: to verify the readability of the code and to ensure the code contains the correct information for that board. Typically, the code contains critical part information such as the serial number, manufacturer's ID number, etc. After the code has been validated, the board is then transported to the first stage of production.
As the boards pass through the production cycle, the symbol on the board is read twice at each station. The first reading takes place before the next process begins for process control purposes. The information contained in the code might also be used to auto-calibrate the equipment for the appropriate procedure for that board-type.
Once the process has been completed at that station, the board is then read as it exits the station for process verification. This step documents that the procedure has been completed and provides a time stamp for the procedure. The time stamp can then be used for capacity planning and real-time forecasting. The information is also helpful for optimizing a line for the next product run.
While the codes on the raw boards are applied right before they enter production, components are often shipped to the assembly house already marked. These components are typically high-value parts that make tracking worthwhile, custom parts, or parts with low environmental tolerance. (At this point, it is often not cost effective to directly mark and individually track parts that carry a value in the sub-penny range.) Some production procedures rely on the code on the component to determine how the equipment should be auto-calibrated for the next step.
Optimizing Inventory By Increasing First Pass Yield
For facilities who participate in some sort of part tracking on the production line, the common practice is to read the code on the boards only 2 or 3 times: At the beginning of the line, again at the test station before the board is flipped for the second side, and then again at the very end once the board is completed.
While this documents how many boards have completed the production cycle and passed test and inspection, it does not provide enough information to prevent manufacturing errors or to aid failure analysis if a failure does occur. The operator still has to spend time debugging the board to detect the cause of the failure. Instead, verifying the boards at each stage of the production process provides full traceability of every element of the process and can prevent errors before they occur. If a defect does occur, then both a product and a process element are available for failure analysis.
For example, a data capture device is mounted inside a chip feeder to track and verify components. Before each component is loaded into a slot, the device reads and verifies the symbol marked on the reel containing the components. Another data capture device reads the bar code on the slot to verify that the reel of components will be loaded into the correct slot. Later in the process when the loaded components are needed, the symbol on the reel and the bar code on the slot are read again and verified before the component is fed to the pick-and-place machine.
This verification process ensures that the correct chip will be used before it is soldered onto the board. It also prevents reels from being loaded into the wrong feeders, which could result in multiple board failures. If the wrong reel was loaded into the machine, the error would be discovered before the components are actually soldered to the board, minimizing the impact of the error.
If the boards and components are not verified until the final testing stage, that same mistake would not be discovered until the board was nearly completed. Not only would the components have to be scrapped, but the entire board might have to be as well. Since the product has not been tracked through each stage of the process, it might be difficult to identify other defective boards. The entire lot of boards that passed through the same process might have to be pulled from the line, tested and possibly sent back for rework or scrapped – depending on the nature of the defect.
This is just one example of how a simple product tracking system can save a minimum of several thousands of dollars. A mistake discovered before it happens might only cost $10. The same mistake discovered during the final testing stage might cost a minimum of $10,000 in rework, downtime and the loss of entire lots of boards and components.
Aiding Failure Analysis
Product tracking provides additional benefits as well. The data generated by such a system can be critical for tracking down the root cause of process errors quickly and efficiently. The faster process errors can be identified and corrected, the faster production lines can be up and running, minimizing downtime and the total number of failures.
On a surface-mount production line, many different machines output all types of data on the production status of the boards. The data collection device is the only thing that links that data to a specific board's serial number and the components on that board. That link enables the complete manufacturing record of each product to be tracked and verified down to the component level, providing real-time process control. In real time, operators can track test results back to one specific board, not just a lot or batch number. The data can indicate the exact time a change in the process occurred, or which boards have the wrong component.
Generating Real Time Data
Detailed production records can also optimize inventory and other resources. As components and parts are used on the line, information can also be fed back to the stockroom and the purchasing department for real-time inventory control. If line A is down, the manager can see how much product is tied up on line A and when it is scheduled to ship. With detailed information from the line, the manager can then make good, educated decisions. Components with a high fall-out record can be identified on the line, on the shelf or in-transit and tracked back to a specific shipment and the responsible supplier.
The data is also critical for product repairs and upgrades in the future. It's important for limiting product recalls to only those products that are affected. Entire lots no longer have to be pulled, scrapped, or reworked because of insignificant data.
Doing More With Less
The benefits of 2D matrix codes and "cradle to grave" traceability have been recognized since Data Matrix was first developed more than a decade ago. But like most new concepts, the technology to read and mark matrix codes required time to develop and mature. Past data capture solutions made reading matrix codes a time-consuming, arduous task and expensive to implement.
However, the technology to read and mark matrix codes has matured. Today's smart cameras have reached plug-and-play status, and the generated data can easily be imported into existing databases. Depending on the type of mark desired, a new marking device may or may not even be needed. The thermal transfer printers already in use in many facilities also have the software capabilities to print Data Matrix codes. Others can easily be upgraded.
For permanent marks, the initial cost of a laser-etching machine has dropped considerably and is quickly offset when one considers it eliminates the need for consumables (labels and ink), improves mark quality, increases marking productivity, and offers lower long-term cost of ownership.
By utilizing accessories that can be easily integrated into existing systems, component tracking provides a low-cost solution for doing more with less
Perhaps every manufacturer's goal is to achieve six-sigma quality at the lowest cost possible. A work-in-progress tracking system works hard to achieve both goals. It ensures quality by providing process verification and early error detection. It lowers the cost of manufacturing by optimizing inventory, and increasing over-all yield.Click Here for More Information
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