Simplify test definition and shorten test throughput times by using an instrument that has universal adoption and inexpensive test automation software.
The latest design is finished. But before the R&D manager will sign the shipment release, he wants to see the design verification test results, and the test department manager won�t approve the release until he reviews the environmental characterization results.
Since no one in the test department knows the test methodology for the new devices, the designer will spend weeks writing a test program. Then the test engineers will tackle the long process of figuring out how to integrate that code into a test automation system and optimize it for the line. To accomplish this task efficiently, some serious collaboration between the departments is needed.
Today, developing good environmental test code requires weeks of work. And even when the test code is complete, to measure a design under varying environmental conditions such as temperature, humidity, and power supply normally requires much manual work on the part of the designer to:
� Capture a set of waveforms.
� Analyze them.
� Transfer the results to a spreadsheet.
� Change an environmental condition.
� Wait.
� Capture another set of waveforms.
� Analyze.
� Transfer the results to another spreadsheet file and then merge the new results with the previous results.
� Repeat these steps as required.
However, there are ways to streamline the environmental test process using simple tools and basic ideas that everyone can access.
Streamlining Test Development
More engineers are finding that their oscilloscope can become the centerpiece for testing time-domain devices, especially when used in combination with automation software. Developing the measurement methodology for your environmental test suite from within your oscilloscope�s PC can be performed quickly.
Oscilloscopes are almost always available. But because most engineers don�t use the same scope on a regular basis, a typical user is faced with relearning the user interface every time he switches scopes.
Adopting software automation and analysis tools that work on many scopes is highly preferable. That way, if the scope used to develop your environmental test is moved to another lab, you are not faced with rewriting code.
Although the differences have been made smaller via standards like GPIB and IVI drivers, scope manufacturers provide sufficient differentiation that measurement programs aren�t interchangeable. As long as product differentiation is based on software analysis features, this trend will continue.
Because most of the application software that comes from the scope manufacturers only operates in one or in a few product families, it is hard to standardize the test environment or the lab. So if the test system is based around an oscilloscope alone, the portability of test suites may become an issue.
Ten years ago, basic time-domain measurements were built into the scope, or if you wanted more complex measurements, they had to be custom written. Today, most of the scope manufacturers have developed many measurements that reside inside their scopes.
But the industry�s inventiveness has strongly outpaced the measurement capabilities in even the newest and most expensive of scopes, and few measurements ever get back into the previous models. Unfortunately, most of the important measurements cost extra, and you may need to purchase application software packages to get all the functions you require. Also, the turnaround time on new measurement development can be quite long�if ever.
Because of the increasing complexity of time-domain measurements, the algorithms usually are proprietary. For this reason, using algorithms from different scope companies always yields slight measurement inconsistencies and, in some cases, huge inconsistencies as large as �200% or more. A better alternative is external measurement software that uses the same measurement algorithms regardless of the scope�s manufacturer.
Some scopes can have only a few measurements open at one time. A better alternative is not to be limited by the number of the measurements that can be performed on the scope waveforms simultaneously.
Having the capability to take a single acquisition of data and make any number of measurements on it can greatly reduce test throughput time. If the user defines his measurement views so that all measurement results can be viewed in one window, this will greatly facilitate the collection of all of the measurements into one results archival process.
Software analysis applications that work inside the operating system of a scope or externally on a laptop connected to the scope are becoming popular. These tools add literally hundreds of new analysis and automation features, greater portability, automation enhancements, and custom measurements, and new capabilities become available in weeks, not months. Some application software tools now are available to download via web communities at no cost.
Everyone knows how to program via GPIB. It takes a long time, but it works. Automation tools can get you out of writing the waveform capture and analysis functions. These systems can be quite robust, but they also can require a significant amount of time to become effective. The best ones have a graphical user interface (GUI) to define the tests.
A number of test automation applications, such as Agilent�s VEE Pro and National Instruments� LabVIEW, help shield the test writer from these user interface and measurement algorithm inconsistencies. These tools are quite robust but don�t have the measurement algorithms needed to make the sophisticated time-domain measurements being called out in industry specifications.
A better approach than a GUI is a system that requires no programming. With no syntax to look up, your test development will be expedited.
Figure 1 contains a screen shot of the ASA M1 Oscilloscope Tools. It brings together time-domain analysis, ScriptBuilder automation, and oscilloscope independence into one platform that a test specifier can use to develop environmental tests quickly using a scope-like interface and without programming.
Sometimes more flexibility adds complexity. Most users prefer test automation systems that are as simple to operate as the scope. For example, you now can learn how to develop your environmental test on some automation systems with as little as 20 to 30 minutes of web training.
Ideally, defining a large number of oscilloscope measurement tests should be simple and fast, taking only minutes to define the entire test. The capability to record the status of all of the independent variables such as temperature, humidity, and voltage at run time reduces throughput time. Figure 2 shows a very simple example of how to bring all of the tests, measurements, dependent and independent variables, and notes needed for a simple environmental test report into one window.
Integrating Test Programs and Results
Test code should be developed so it not only can be transferred to any of the most popular real-time scopes, but also so it can be quickly transferred to your manufacturing test system. One of the most useful communications languages that help to facilitate this transfer is XML.
XML is easy-to-understand functional-based programming. Because some test automation tools automatically create XML command logs, it can be incorporated into larger test automation systems that already exist. Automation tools that require no programming and yet produce XML command logs are ideal.
Test engineers don�t have time to pick the brains of the designers and develop the test methodology themselves. Nor do they have time to teach their designers how to write code or to write code that integrates with their test automation system. The test engineer now can quickly integrate the results of the test runs into the test automation database infrastructure.
The test engineer also needs flexibility. Slightly modifying or redesigning XML files is easy even if an engineer is not intimately knowledgeable with the exact nature of the code. The test engineer should no longer have to worry that his test won�t work on all of his oscilloscopes. Using external automation software is one way to get away from using a scope-specific measurement.
Speeding Environmental Test Throughput
The test operator can use a number of methods to reduce the amount of time spent actually performing the environmental test regimen:
� Environmental tests must not be manual.
� The test program should have a common user interface. Teaching test operators to use different scope user interfaces is not the path to productivity on the line, especially as measurements get more complex.
Ideally, the test program should be able to turn on and run automatically, including changing of the variables. Robust test automation systems have done this for years, but even less expensive test automation software is moving in this direction.
� The test operator should be able to collect all of the measurement results of an unlimited number of environmental tests in one window.
The test operator wants to stay inside one application to perform the tests and collect the results of all measurements and all environmental conditions. This one application should be specifically tuned to the needs of the test operator. It should be easy to transition from each test condition, change the independent variable, capture and measure the waveform, and document the test results in the proper database.
� The test operator also must be able to easily save results of all of the environmental conditions to a spreadsheet.
� Parts fail and need to be debugged. An environmental test should not only perform quickly and accurately, but also give the operator insight into why some parts fail.
Team Productivity
The solution to long environmental test design cycles concerns more than just how one individual performs his job. The design engineer writes the measurement methodology. The test engineer integrates the test into the automation environment. By basing tests on oscilloscope-related test automation software, the operator is able to improve throughput time. In fact, one Bay Area semiconductor company using this tool was able to complete environmental test of devices in less than one minute, a task that previously took 35 minutes.
About the Author
Greg Walz is product manager at Amherst Systems Associates. Before joining ASA, he held various positions at Agilent Technologies and Hewlett-Packard: segment manager for the multi-industries business, sales and technical support manager for the 16500 logic analyzer products, co-creator of Design SuperCon, and product manager for the 54720-series of oscilloscopes, the 54120-series microwave oscilloscope, and TDR products. Mr. Walz received a B.S. in electrical engineering from Texas A&M University and an M.B.A. from the University of Colorado. Amherst Systems Associates, P.O. Box 24, Amherst, MA 01004, 413-596-5354, e-mail: [email protected]
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November 2006