Work-in-progress (WIP) tracking has been used in the semiconductor industry for years, in both wafer processing and final assembly and packaging. In addition to generating a record of the manufacturing history of every component, product tracking also provides optimal control over the entire fabrication process. Manufacturers gain real-time feedback from every stage in the process. The information generated from the product tracking system can then be used for a variety of functions, such as providing a safeguard against manufacturing errors. For example, in integrated circuit manufacturing, if every wafer is positively identified before each step, a wafer would be rejected by the PLC before it was inserted into the wrong furnace, avoiding a very costly production error.

Positive identification is used to automatically call the appropriate equipment setup for the next procedure. This eliminates human interaction and further reduces the chance for manufacturing errors. The same procedure is used for test and inspection. Identifying a unit before and after each test stage provides verification that the component passed inspection. This information is extremely valuable for warranty repairs and product recalls.

Since product tracking provides real-time data from the production floor, the information can also be used to monitor WIP inventory levels. One large manufacturer uses their product tracking system to aid them with product forecasting. By monitoring the results of each test, the manufacturer can react immediately as necessary. If the manufacturer experiences a large percentage of fall-out, the manufacturer can then decide whether or not to schedule production overtime or re-allocate resources to compensate for the scrapped product.

2D SYMBOLS MAXIMIZE WAFER REAL ESTATE

Over the last several years, linear bar codes such as the BC-412 developed by IBM have worked fine for several applications. However, new options are needed for wafer production today.

Circuit designs are growing increasing smaller while wafer diameters are growing increasingly larger in an effort to drive down the costs of production. As a result, real estate on wafers has become even more valuable. Soon bar codes will no longer be a viable option for product tracking applications. Tiny matrix codes are now much more attractive than ever before.

Two dimensional matrix codes such as Data Matrix have several benefits over traditional linear codes. Matrix codes have a much higher data capacity and a dramatically smaller footprint. All a manufacturer needs is .1 inch square space on a wafer, and they can mark it with a 5 or 6 digit Data Matrix symbol. This enables the trace ability of components that in the past could not accommodate any type of machine-readable form of identification. The symbology allows for an increase in placement flexibility over other codes because it can be formatted into either square or rectangular shapes.

Matrix codes offer additional benefits as well. They have no orientation restrictions and very few contrast limitations. They can be applied in a variety of methods and have a robust form of error correction. Since matrix codes can also be applied to the wafer in the same method as a bar code, typically by photo-etch, manufacturers do not need to invest in additional marking equipment to apply the symbol.

Two-dimensional matrix codes are also easier to read than the BC-412 bar code. Due to the high degree of specular reflection from the wafer surface, traditional bar code scanners often struggle reading BC-412 and usually require some degree of custom software. Since two-dimensional codes are read by camera-based equipment instead of laser-based equipment, there are more methods available to help minimize the impact of specular reflection, allowing for a higher read rate. As a result, matrix codes enable a more reliable tracking system. Until recently, the drawback for using the two-dimensional symbols has been the limited number of products capable of reading them.

PAST PRODUCTS FOR READING 2D SYMBOLS TOO COMPLEX

Many factors have contributed to the slow adoption rate of matrix codes in wafer processing and electronics manufacturing. Standards and specifications for the symbols, such as Data Matrix have been slow to be developed due to the symbol’s complexity and sheer versatility. For the same reasons, education on how to use the symbol has been slow to develop as well. However, perhaps the most significant factor has been the limited number of products capable of reading the symbol. Most have either been light on performance, or overly complex and too expensive for the task they needed to accomplish.

Since Matrix symbols cannot be read with a laser, traditional bar code scanners cannot decode the symbol. Matrix symbols can only be decoded by camera-based equipment. 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 a higher mix of smaller product runs. Since one of the goals behind using a product tracking system is to optimise production and minimize downtime and manufacturing errors, this was a problem. Most manufacturers did not want to trade in their plug-and-play bar code scanners for a complex vision system that creates new bottlenecks in the production process. The real estate gained by using 2D symbols did not compensate for the extensive downtime and high total cost of ownership of the equipment required to read them.

NEW SMART CAMERAS SIMPLIFY TRACKING

Today there is an easier solution. The introduction of the new smart camera has all but revolutionized reading 2D symbols in dynamic applications. A fixed-position reader that functions like a laser bar code scanner, the smart camera combines the separate components of a vision system into one fully integrated unit. 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 scanner.

The first smart camera emerged on the scene in 1997 when Microscan introduced its Quadrusä , the first fully integrated reader to combine the light source, processing platform and camera all in one compact unit. Now a few years and several patents later, Microscan has developed another smart camera, Quadrus EZ™ that picks up in performance and ease of use where the first one left off. What used to take hours to accomplish with a vision system, has been simplified down to the touch of a button. Line operators no longer need to use a monitor or a PC to reconfigure the reader during line changeovers. Quadrus EZ™ is as simple to use as a bar code scanner.

During a changeover, only two steps are required to setup Quadrus EZ™. Using the field of view indicator pattern, the operator can easily align the reader to the symbol. Next, the operator only needs to push the "EZ" button on the back of the unit. The reader automatically calibrates on the symbol. Once the green light flashes, the operator knows the reader has positively decoded the symbol and is ready for use. The entire process takes less than 60 seconds. No operator training or computers are needed.

In the past, most solutions required the user to perform ladder logic programming for the PLC to provide control based on the decoded information provided by the tracking system. Since Quadrus EZ™ is designed specifically for product tracking with bar codes and two-dimensional codes, no custom programming is needed. All control features are embedded inside the product. All the user needs to do is enable them and the product is ready for use.

TRANSITIONING FROM BAR CODES TO 2D SYMBOLS

The transition from linear bar codes to 2D codes doesn’t usually happen quickly. Most often, facilities use both codes for an indefinite period of time. While the larger wafers with new, more complex circuit stencils might be marked with Data Matrix, the older wafers typically remain marked with BC-412 bar codes until they are phased out.

Quadrus EZ™ makes the transition period a lot smoother. Since Quadrus EZ™ can read both code types with the same unit with the same settings, two separate readers – one for each code type – are not needed. This makes processing the data from 2 separate codes a lot simpler. As an additional benefit, no downtime is accrued by using one reader. Quadrus EZ can read both codes interchangeably without requiring reconfiguration in between product runs.

In the face of the current economic climate, increasing production efficiency has become even more critical. Since many do not have the resources to invest in new equipment, production efficiency will have to be achieved through other means. Instead of adding more production lines, existing lines will have to operate more efficiently. Maximizing machine uptime while reducing the risk of costly production errors and rework will be the means to success. A solid product tracking system utilizing smart cameras helps accomplish exactly that. By using space efficient Data Matrix codes, wafer real estate will be maximized in the process.