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VOLUME -22 NUMBER 10
Publication Date: 10/1/2007
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October 2007 Issue
Special Feature: PCB and Assembly
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Changing In-Circuit Testing to Meet Design Changes
Lineup of test platforms to meet a variety of test needs.
By Olaf Rohrbacher, Digitaltest GmbH
In the course of electronics manufacturing, printed circuit boards are exposed to a process of continual change. There are several reasons for such changes. The layout of a PC board might have to be modified to enhance its performance or to add new features. Also, manufacturers tend increasingly to terminate the production of certain devices — making design modifications unavoidable.
Due to these constant design changes, the manufacturing process must be adapted repeatedly to the new PC board versions. In production planning, it is vital to know how long this conversion process will take. For the In-Circuit Test (ICT) process, test engineers should provide information on how long it will take to convert the fixture and to tailor the test program.
In order to estimate the extent of the modifications to the board and how much they will affect the fixture and the test program, test engineers require detailed information. However, it is often the case that not enough information is available. When test engineers ask about the extent of changes, they are often told, for instance: "Not much...", "Only a few values..." or "Nothing of real importance...". Such information is not very helpful. Only rough estimates — often based on experience — can be made. So-called engineering change orders can be used as a basis for analyzing the overhead for implementing the modifications. However, the change orders often fill entire file folders, with extra documentation including mechanical items such as labels, cables, screws, sheet metal and other device changes.
Finding the relevant information for ICT by scanning all this documentation becomes a time-consuming process. A good solution to quickly estimate the overhead for the required modifications should to use CAD data and parts lists from the various development stages along with a software tool that can compare this data and generate meaningful reports. C-LINK is a CAD/CAM software that produces all of the data required to insert parts on and test PC boards. The fixture design in C-LINK can contain all mechanical components, in addition to nail positions, channel numbers, and diameters and head shapes.
C-LINK Saves Functions
Hence, C-LINK allows engineers to design fixtures with positioning pins, press-down elements, spacers, transfer pins, OpensCheck plates for ICs and plugs and much more. Whenever a new version of a PC board becomes available, the CAD file is simply imported into C-LINK and the Redesign function is called. A detailed report is generated on the spot with an easily understood table listing all tester pins which can no longer be used, such as if the test pad was moved in the design. This is a standard function of many CAD/CAM solutions, but C-LINK offers more than that. All mechanical components of the old fixture are checked and used in the automatically generated test job, if possible. As an example, a message is generated if a device is moved and collides with a press-down element. Often, the CAD data itself makes it difficult to devise useful comparisons. Every year, CAD software companies issue 2 to 3 releases. If a new CAD release has been installed between two versions of a PC board, then differences in origin, factor or units can occur.
This situation becomes even worse if different CAD systems were used, for instance because development projects were outsourced or old CAD systems were abandoned. Many CAD/CAM solutions fail in such circumstances. C-LINK not only deals with such problems — it even supports tolerances. If a test pad, for example, is moved a few hundredths of a millimeter (by the layout system designer or by rounding the export/import interfaces), then using tolerances will produce a smarter report where this tester pin is still transferred.
After the Redesign report, nails can be placed on those networks which are not yet or no longer bonded. This takes account of the existing adaptation and the nails which had to be removed. The output of drilling data merely adds the new tester pins to the CNC files. These delta files can be used to redrill and wire the existing fixture. If too many modifications are required, C-LINK can of course output all of the drilling and wiring data. The Redesign feature of C-LINK generates a report, to verify if the new board version can be tested on an existing fixture. This report can be returned to the CAD engineer. He, in turn, can revise the layout — so that all nails and mechanical elements in the fixture can remain unchanged.
If the original fixture was not designed in C-LINK, it can still be re-created in C-LINK. This is done simply via text import. For instance, a wiring list of the fixture is often entirely sufficient.
What modifications on the PC board influence the test program? This information can be obtained quickly in C-LINK, based on the parts list for the new PC board. This parts list can be imported with the freely configurable BOM converter tool. The devices of the new PC board are compared with the item numbers of the parts list. The Compare Boards function in C-LINK then generates a comprehensive report in tabular form. This report shows all differences between insertion and network list. The format is HTML, enabling rapid navigation via hyperlinks. If there are differences in the insertion, then measurement values must be tailored. If devices have been added, then they must be entered in the test program. If devices have been removed, then the test steps can be commented out or deleted. If devices in the new version of the module are now connected to other networks, then these devices are tested via other test channels.
When the network list is modified, then guarding points and other parameters must often be changed. The Compare Boards function provides valuable services for quickly stating the required modification overhead in the test program. This report is also used to add the modifications to the testing program.
C-LINK complies with the market needs. With its enhanced range of comprehensive tools C-LINK enables the user to introduce new products within the shortest possible time.
For more information contact: Digitaltest, Inc., 5046 Commercial Circle, Suite C, Concord, CA 94520
925-603-8650 fax: 925-603-8651 Web:
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