BY ROBERT FOY AND DAN FRITSCHEN
Total factory automation in test, assembly, and packaging (TAP) facilities has changed very little over the last decade. Today, however, TAP factory owners and managers are hearing the wake-up call their counterparts in the semiconductor fabrication world answered long ago: automate or fall behind.
Manual Processing
As much as half of all processing during assembly, testing, and packaging phases is purely manual. Far from the paperless manufacturing in most modern fabs, “paper” abounds within TAP facilities. Operators rely on paper “travelers” that move with each batch or “lot” of material through the factory. These travelers document the lot number and processing information crucial to identifying the correct actions to perform. Lots to be processed are manually located, and the paper travelers are consulted for process steps, recipes, and tool setups. An operator then manually sets up the tool and enters the lot ID, recipe, and other data into the tool controller computer. The tool controller generates data on the production run and may automatically send the data to a centralized process database, but more than likely the tool controller stores this data locally and the operator must manually record this data onto yet more paper. Once a processing step is finished, the operator manually unloads the material and transports it to the next process step — typically using a wheeled cart. Reliance on manual operations adds to processing costs, reduces tool productivity, and increases the frequency of costly mistakes. Delays in production of a tool, while waiting for an operator to select the recipe and identify the right lot to process, can be costly.
Low-tech Mistakes, High-dollar Results
Mistakes can result in expensive deductions from a company's balance sheet. Further exacerbating the problem of how to reduce the likelihood of errors within TAP, is a growing shift in the balance of the contribution to component cost originating from the fab and TAP sides of the semiconductor industry. Corporate accountants and managers define component cost as the raw cost per chip, or component, that the company invested in building each product it sells.
Traditionally, the split of component cost contribution between fab and TAP factories is heavily weighted toward the fab. Continuing advances in efficiency through automation and hyper-volume manufacturing methods, like the advent of 300-mm in fabs, have resulted in a continual slide of the cost scale toward TAP. Simultaneously, TAP has seen its world grow more complex and costly through a plethora of packaging, speed, and platform options (PDA, laptop, desktop, server, etc.); all that must be considered and managed. To make matters worse, zero-inventory goals, and near just-in-time demand-based manufacturing required by the discount build-to-order PC market, continue to increase the importance of optimized manufacturing in TAP facilities.
Trouble with Little Automation
So, where is automation in TAP today? Automation systems exist, but often have little to do with managing and directing processes on the factory floor — instead, they focus on work in progress (WIP), or inventory management, product nomenclature and specification management, and order management. Automation is absent, or at best spotty, in critical areas closer to the actual work of the factory, such as automatic station control and recipe management, process tool event and utilization tracking, real-time collection of data or control of the process, and automated material handling.
Without automation that has an on-line interface to the tool, and the benefit of accessing in-process data directly from the tool, new software can only hope to replace pen and paper with keyboard data-entry time. While data capture may be more complete and only marginally more accurate than with paper, the real question automation designers must ask is whether efficiency is improved by simple automation of paper processes. In many cases, cycle time can increase because of a loss in flexibility resulting from rigid and voluminous data entry demanded from software systems.
What sort of automation suit will the best-dressed TAP factory of the future be wearing? As costs of process tools and the factories that house them rise, expect the maximization of tool utilization to be paramount. Improving tool utilization can be realized by attacking two primary goals: ensuring tools stay busy all the time, and eliminating as many breakdowns as possible. Some strategies toward this end include:
- CFM and AMHS technologies that transport product from station to station throughout the factory and ensure that no tool “waits”.
- Implementing automated identification of lot ID speeds the loading of WIP into the tool, eliminating the tool production delays of an operator manually entering the ID. Using automated WIP ID and tracking technologies enables operators to locate and deliver more quickly WIP to tools.
- Connection of the tool to an on-line station controller to speed tool setup, recipe selection, and data collection eliminates the tool's down time waiting for an operator. CFM and auto ID integration further close the loop between actual tool operations and the loading and balancing of work.
- e-Diagnostics data allow equipment maintenance engineers to shorten time required to determine corrective action, and even predict and proactively make repairs before costly downtime of the tool occurs.
Today's automation improvements by advanced TAP facilities include:
- Using advanced batch and dispatch systems based in WIP tracking & location systems, tied into planning systems, to allow tighter management of inventory and more optimal scheduling of work in the factory.
- Elimination of non-value-added steps through automation to reduce the overall start to finish product cycle time. Examples include using CFM and WIP tracking technologies to eliminate loading or unloading of materials from transport carts, or eliminating off-line metrology steps through on-line tool automation and station control.
- By optimizing the dispatching and batching of work into the factory process time, variations and unnecessary tool setups or changeovers are reduced.
- By tying maintenance schedules to actual run cycles or equipment performance and diagnostic data, unnecessary scheduled tool maintenance is eliminated.
Technology Enablers
Key technologies will help bring these solutions to reality, including:
- Advanced Equipment Integration. It's hard to imagine any of this technology working without the free and available flow of data, the lifeblood of automation. Advanced equipment integration means having process tools that can “talk” to the factory and its systems, without needing a human to translate the conversation. On-line, network-accessible communications with equipment using the latest SEMI standards and protocols are key. Equipment makers and semiconductor manufacturing customers are using the object-based equipment models (OBEM), common equipment models (CEM), and diagnostic data acquisition (DDA) standards as a way to work together toward automation solutions. OBEM and CEM promise an object-oriented method to manage the configuration and data contained within process tools and to present it to the factory automation systems through an open standard. Tools compliant with the CEM standard can be more “plug-and-play” with factory systems, and offer factory engineers the opportunity to link or rollup tools into a larger object model — automating a series of tools that work together to complete a single process step.
Multi-client, simultaneous access to the equipment from many points in the factory will be offered by leading commercial vendors of the SEMI standards. Retrofit updates of legacy tools will be possible, so that older factories can take advantage of software systems based on new standards.
This focus on advanced equipment integration means data trapped inside today's process equipment will become available throughout a factory network, spawning faster implementation of critical technologies such as station control, data collection, SPC and CFM, to name a few (Figure 1).
 Figure 1. Technology enablers, such as advanced equipment integration, allow access to process equipment data. |
- Auto ID and Tracking. Improvement in production cycle time and equipment productivity, as well as reduction of overall WIP levels, can be accomplished by enabling the automated identification of the WIP. In a TAP facility, WIP is transported in a variety of carriers at the beginning of the process, to carriers and reels at the end of the process. RF tagging technology offers the flexibility to accommodate this range of applications (Figure 2). Due to recent advances in RF technology, RF tags and readers are now available that offer low-cost tags (under $1) for most common ID applications. High-temperature tags (up to 220°C) for oven applications and long-range tags (100 m) are available for tracking a large number of items from a single reader as they move between processing steps at the facility.
RF system advantages outnumber traditional barcode systems in reliability, flexibility, and durability. Modern tags offer low maintenance through “passive” designs, requiring no power source other than the reader's communication signal itself.
 Figure 2. RF tags offer the flexibility, reliability, and durability necessary to accommodate a wide range of applications. |
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Conclusion
Through automation implementation, TAP facilities can achieve improved cycle time and equipment productivity, while reducing human-caused errors.
ROBERT FOY, director of Professional Services and Strategic Accounts, and DAN FRITSCHEN, director of Product Management, may be contacted at Asyst Technologies Inc., 48761 Kato Road, Fremont, CA 94538; (510) 661-5000.