Top-down vs. bottom-up: Two approaches to assembly integration

09/01/1999

Walter DeSouza, Michael Vinson
Kulicke & Soffa Industries Inc.

Full traceability of a finished IC through fabrication, assembly, packaging, and testing requires seamless integration of tracking data related to each process step. The legacy factory environment is such that some stages may be handled in-house while others may be outsourced.

A variety of MES and data collection systems are likely to be in place at the different factories. Some systems are commercial off-the-shelf packages, others in-house software. Moreover, systems coexisting in today's factories are likely to run on different platforms and to use different technologies, simply because they were developed at different times.

An architecture that can effectively support full traceability needs to allow for data collection from myriad incompatible systems and for its storage in an industry-standard database at a level above the equipment layer. This middle-layer data repository can then be used for queries, reports, and graphs that will aid in pinpointing process issues and equipment problems related to a specific situation.

An important characteristic of this architecture is the ability to ensure that all pertinent data are captured at the factory floor so they can be properly manipulated and stored in the reporting database in a consistent format, regardless of the source. For example, data being tracked will have date-time tags for proper identification and chronology.

In designing such an architecture, one might consider a top-down approach. This typically involves the design of layers, for example, higher-level systems with business functions such as enterprise resource planning (ERP), supervisory systems with process management functions such as recipe management, and control systems such as distributed control systems. Although these systems would have different functionalities, there would be a clean integration between layers as information flows up and down.

The top-down approach is recommended if there are no current systems in place and there is clear control over all manufacturing process aspects (i.e., all the resources producing product). If all manufacturing takes place within a single factory, and one has a clean slate or the power to replace all existing systems, then this is clearly the way to go.

Most legacy factories, however, do not satisfy any of these top-down design criteria. Consequently, the recommended approach is bottom-up, which maintains the existing data collection systems and creates an infrastructure that connects them to the middle-layer data repository. Part of this architecture is a set of tools that can communicate with the equipment and with data collection systems to standardize raw data and integrate various data streams, moving the resulting data to the reporting database. This flexible architecture enables in-house and subcontractor systems to continue to perform current functions while integrating and storing information required for process analysis and optimization. It uses open information technology standards that can be integrated to higher-level systems as required in the future.

The steps for the integration of such a system would be:

1. Connect all compatible equipment to a common data system through available tools.
2. Implement an automated material tracking system.
3. Include noncompatible equipment through a distributed data entry system.
4. Correlate data between machines and materials.
5. Prepare data for upper-level systems.

Such an approach allows the culture on the factory floor to change gradually and adapt to the least invasive data collection methods first. Once the benefits of the first step are realized, the more invasive procedures of steps 2 and 3 can be implemented, followed by steps 4 and 5. Upon completion, the bottom-up approach for integrating a legacy factory will provide benefits comparable to those that accrue from more costly top-down total automation.

Authors

Walter DeSouza is VP and CIO and Michael Vinson is director of the Factory Systems Group at Kulicke & Soffa Industries Inc., e-mail [email protected]; [email protected].