With electronic products becoming more complex, detecting faults in electronic circuit boards is an ever-increasing challenge. Today’s boards are smaller and more dense, and providing access to test the circuits is more difficult with every new product design.
Finding a fault at one step in the test process usually costs 10 times as much as finding the same fault at the previous step in the process. Or said another way, finding a fault at functional test costs 10 times as much as finding it at in-circuit test, and an in-circuit test station should reduce functional testing and debugging costs substantially.
But this logic could prove faulty. It is based on the assumptions that the in-circuit test station can increase fault coverage sufficiently to justify its cost, and the station has access to the board’s nodes through a bed-of-nails fixture.
Unfortunately for many of today’s boards, bed-of-nails access remains an unattainable luxury. Many boards include components on the traditional solder side, which complicates the access even more. In addition, the use of flip chips, ball-grid arrays, and other devices whose nodes reside underneath the component defies conventional access through a bed-of-nails fixture.
Forcing design engineers to provide test pads for in-circuit test gets a mixed reception at best. Nodes occupy precious real estate and could add to propagation delays and other performance-degrading problems. Sometimes, fault reports from an in-circuit tester are invalid because of the complexity of the assembly.1
Typical Operating Characteristics
Responding to these challenges, board ATE manufacturers have developed systems for an almost limitless assortment of circuit boards and a wide range of test applications. Modern test systems are built with an open architecture, using industry-standard buses and widely accepted software. The intent is to make them easy to program and simple to upgrade.
The days of the big one-size-fits-all board test system are over. “We see at least two distinct families of board testers,” explained T. J. Wilkinson, sales manager of Digalog Systems. “First, there is the need for test systems to span a range of product technologies capable of being reconfigured or upgraded easily and painlessly to meet unforeseen test requirements. Second, users are asking for a more economical approach for those cases where the test system is likely to be dedicated to a particular product family.”
Since automatic detection and identification of faults are the basic purposes of a board tester, fault coverage is high on the list of requirements. Paul Groome, product marketing manager of board test systems at GenRad, confirmed this:
“Customers need the highest fault-coverage test programs. This includes automatic translation of CAD data to the test system, generation of algorithmic models, and full boundary scan testing including virtual nail tests. Also, they need unpowered capacitive and harmonics tests, circuit-based test generation, and support for programming and testing flash components,” he said.
Kamran Firooz, manager of the manufacturing test division of Agilent Technologies, continued the same theme. “Consider fault coverage when determining the best board test strategy. Pick the system with the most cost-effective fault coverage for the types of faults you expect to find in your boards. Possibly the strategy will be different for different types of boards,” he said.
Mr. Firooz moved from strategy to the subject of upgrades. “Because of the rapidly expanding product technology, test engineers need assurance that new features and test capabilities can be added easily and at a reasonable price,” he continued. “This will extend the useful life of the system and lower overall test costs dramatically.”
There can be a big difference between the system purchase price and the overall test costs, so as an astute test engineer, you must look at other factors. Some of them—throughput rate, up-time, maintainability, logistic support, ease of programming, adaptability, expandability, and commitment of the vendor to be there when needed—were outlined by Mr. Wilkinson of Digalog Systems. Over the expected lifetime of a test station, these factors can outweigh the original purchase price.
Standards
With standard architectures available, customers want the ability to reuse test elements and code. Robert Fogarty, a product manager at Teradyne, noted that customers “…demand open, standards-based systems that are modular, upgradeable, and easily adapted to suit different test strategies and board technologies. Testers based on proprietary architecture are a thing of the past.”
Mr. Fogarty pointed to a specific standard. “The Interchangeable Virtual Instrument (IVI) Foundation, formed in 1998, defines standard interfaces for programming test instruments. This impacts both hardware and software developers because it provides a path for graceful replacement of obsolete test hardware or software and gives the overall system a long and useful life,” he explained.
Kevin Leduc, product marketing manager at Racal Instruments, agreed. “IVI will have a big impact on board test-station design,” he said. “When a user can take one instrument out of the station and replace it with another, even from a different supplier, without changing any software, it will be much easier to keep a test platform at optimum efficiency.”
Mr. Fogarty looked at yet other standards elements—interface buses and software. “The optimum board test system is flexible because it is built with such industry standards as the VXI bus and VXIplug&play software. It can be expanded easily as test requirements change. It is efficient because it has a common architecture. The test environment has lower operating costs because of common training, maintenance, spares, and documentation. Reusable code reduces software development costs. Open hardware and software architectures are scalable and can be configured for a wide range of tests,” he concluded.
Reference
1. Scheiber, S. F., Economically Justifying Functional Test, Quale Press, 1999.
Board ATE
Small-Footprint Tester
The 3070 Series 3 Board Tester supports unpowered, in-circuit, or combinational testing in a compact size and form factor. Using mathematical algorithms to characterize boards, it automatically tests analog clusters, often with diagnostics down to the component level. It is compatible with IEEE 1149.1 and troubleshoots the development process from design through test. It also verifies digital termination components without adding test points or probes. On-board flash programming is supported. The automated board handling fixture accommodates high-speed throughput. 3073: starts at $132k. Agilent Technologies, (970) 679-3512.
Flexible System
The Series 2040 Test System operates in one of three modes. For analog in-circuit test, the programs are generated from CAD inputs and check for shorts, opens, orientation of components, and proper resistance and capacitance. The analog functional test mode provides stimulus, response, and switching. Digital functional operation uses digital I/O with internal or external clocking and triggering and tests simple logic or complex bus-based products. The digital and analog functional modes can be synchronized to accomplish mixed-signal testing. $40k to $150k. Digalog Systems, (262) 797-8000.
In-Circuit Test System
The GR Test Station has up to 7,680 driver/sensor pins in combination with analog, digital, and frequency/time instruments. It performs in-circuit, functional digital, functional analog, or mixed-signal testing. Either multiplexed or nonmultiplexed pin cards are acceptable, and upgrades can be made with minimal interruption of testing. Setup can be by CAD transfer, graphical user interface, or menu response. The maximum clock rate is 20 MHz, and data rates are up to 5 MHz. Starts at $150k. GenRad, (978) 589-7000.
Compact System
The Portable Aurora™ Century Test System is built around the PXI technology and interfaces to several types of instrument modules. It has 192 individually programmable digital I/O lines at rates to 20 MHz. The optional analog subsystem operates up to 200 kHz. Digital and analog functions can be operated independently or synchronously. Each subsystem uses an on-board 4k FIFO buffer for burst-mode tests. Windows-based software has a graphical user interface for entry of setup data. Starts at $95k. ManTech Test Systems, (703) 633-1300.
Custom Systems
All the FREEDOM® Series systems are custom-designed. The systems use conventional test instruments from LeCroy, Tektronix, Agilent Technologies, and other suppliers and can be built around VXI, IEEE 488, RS-232-C, or PC control architectures. Software choices include LabVIEW, Visual C/C++, and HP VEE. The first test program for any FREEDOM Series application is written by Racal Instruments as part of the system installation. Contact company for prices. Racal Instruments, (800) 722-2528.
Functional Test Platform
The Spectrum 9000-Series Functional Test Platform with the M9-Series Digital Test Instrument outputs digital, analog, or mixed synchronous stimuli for board testing applications. Analog frequencies to 50 MHz are generated, and signals to 200 MHz can be monitored in the standard system. Instrument setups are loaded by CAD transfer, graphical user interface, or VXIplug&play drivers. A suite of VXI instruments and switches is integrated into the system. Starts at $145k. Teradyne, (925) 932-9000.
Copyright 2000 Nelson Publishing Inc.
February 2000