Western Digital EIDE Caviar hard drives are available in capacities to 13 Gbytes and have built-in detection and repair of problem areas on the drive. SPC software from Northwest Analytical keeps the quality at a peak.

One of the keys to maintaining quality in a manufacturing facility is the timely collection, distribution and statistical process control (SPC) analysis of test data on multiple production parameters at multiple workstations. Many people believe that automating this process has to involve expensive and elaborate software solutions, but this is not necessarily the case.

At Western Digital's thin film disk manufacturing facility in Santa Clara, CA (WDSC), we have created a highly successful automated system using a combination of custom programming and off-the-shelf software. We have implemented this system for a fraction of the cost of a fully customized commercial system.

Business needs

At WDSC our plant floor operators are the drivers of quality. One of the primary functions of the SPC system is to let them know immediately if a process goes out of control so that they can take appropriate action. Our process engineers and managers need the same SPC data for use in our Continuous Process Improvement (CPI) program.

The problem we faced was, how to cost-effectively collect and distribute this information to management in a timely manner while still having a reliable, easily maintained and operated real-time system for the plant floor. Our new system meets all of these goals and took only a relatively short time to install and implement.

System overview

Our SPC system uses standard Microsoft® Windows™-based PCs, a server, and a combination of off-the-shelf and custom software. The SPC charting and analysis functions are performed by Northwest Analytical's Quality Analyst software. I wrote the custom SPC interface using Microsoft's Visual Basic™.

At each workstation, a stand-alone module (SAM) automatically collects process data such as film layer thickness, magnetic parameters, and surface roughness. Each SAM is equipped with NWA Quality Analyst software, giving the operator the ability to analyze the process data. This integrated testing and reporting system gives operators the immediate SPC feedback they need to determine whether the process is in control.

To make the same information available to "external" customers such as engineers and managers, the SAMs also are networked with a remote server, to which they download their data every hour. External customers are provided with separate custom interfaces to the remote server so that routine observation of SPC charts is easy (Figures 1 and 2). Because Quality Analyst is available on one of our local LANs, these external users have the tools needed for the in-depth process analysis that's part of our Continuous Process Improvement program.

Figure 1

Typical operator (magnetic properties) screen with controls has access to production system information.

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Figure 2

Screen provides information on sputter processes, the application of metal films to the platter surface.

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And, because the process operator is the driver of quality, all of the data is retained locally at each SAM. Thus, if the server should malfunction, there will be no interruption of the plant floor SPC. We used stand-alone PCs at the operators' stations because we want each operator to be able to monitor a process whether or not the central server is working.

Yes, the SAMs are islands of automation, but if the server fails or the link between the PC and server is broken, the PC continues to collect data and continues to allow the operator to monitor the process. Later, when the server is back on line, the data can be uploaded to the server for engineering and management analysis.

Another feature of each SAM is an on-line Response Action Plan (RAP) sheet. These plans, which were developed by our process engineers, provide each operator with a step-by-step script that they use to react to an OOCE (Out Of Control Event) and return the process to a state of statistical control.

System configuration

The system is configured as shown in Figure 3. Each of the SAMs is interfaced with various standard test devices at critical process points using standard 3-wire RS-232C communications. A Terminate-and-Stay-Resident (TSR) program monitors the com port and captures any incoming data. My Visual Basic program then parses the data and saves it directly to the appropriate NWA Quality Analyst data file. Then, a dynamic Run File is created and the process parametrics are presented to the operator as a series of real-time SPC charts. This is the principal quality interface on the production floor and, as noted before, it places the process operator at the forefront of the quality effort.

Figure 3

System diagram of standalone I/O module.

If an out-of-control event (OOCE) does occur, the system immediately alerts the operator and automatically records the OOCE in an event log (Figure 4). These event logs not only serve to record all assignable causes, but also act as valuable repositories of process information. Our process engineering staff uses this information as the basis for our Continuous Process Improvement program.

Figure 4

Event list keeps operators and engineers up-to-date on process changes.

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Our new system is very easy for plant floor operators to use—in fact, they love it. The data is stored in space delimited ASCII text files (the NWA Quality Analyst default file structure). The charting functions are automated using the Quality Analyst Run File scripting utility. These Run Files are dynamically created and executed right after each measurement session. Run File creation is handled by a portion of my Visual Basic program. It's easy for the operators because all they have to do is enter an alphanumeric identifier code at the test device that describes the demographics of the sample (manufacturing system, product type, etc.) This identifier code is transmitted with the test data to the SPC Module, where a parsing routine allocates the data to the correct data file and generates the appropriate control charts.

An internal timer in Visual Basic code triggers transfer of all local data files to the external server once every hour. Thus, the data is locally retained and a copy is provided for analysis by "external" customers. The data is sent to the appropriate folder (directory) on the server and process engineers and managers can then download this data to their own PCs and analyze the data. At these PCs I have provided additional custom software interfaces so that the engineers and managers can easily use QA to identify the process problems and work to improve the process by reducing the variation—which is the whole purpose of SPC.

Real-time data for everyone

For process engineers and management, production data is accessible on a timely basis. In a worst-case scenario, they will be working with data that is an hour old. This currency and total integration allow them to identify problems promptly and routinely with testing devices or processes and make real improvements, reducing variation. For example, one of our engineers recently was able to significantly reduce variation in a process because he had complete process SPC visibility (Figure 5).

Figure 5

NWA Quality Analyst software keeps Western Digital products at peak quality.

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Our SPC system is regularly modified and upgraded to reflect changes in processes and procedures, but the key features remain intact. We have a system that provides cost-effective, real-time, on-line SPC for the people who drive our quality—the process operators.

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