Increased device complexity and the quest for quality have prompted component suppliers to continually improve process control and the thoroughness of end-product test. As a result, the devices they deliver now are virtually faultless. This has brought the electronics industry one step closer to fulfilling the old adage “as soon as all components and manufacturing processes are defect free, board test will become unnecessary.”
Relying on defect-free components is the major reason many companies now designate manufacturing defect analyzers (MDAs) or manufacturing process testers (MPTs) as the preferred PCB manufacturing test tools. Also, the increased UUT complexity has made traditional in-circuit or functional tests too time-consuming and expensive to implement for many products.
Today’s test paradigm is: concentrate on finding and preventing manufacturing defects and perform powered in-circuit or functional board test only under exceptional circumstances. While this practice is appropriate for most production test operations, it does not necessarily apply to all products or nonmanufacturing situations.
Maintenance depots, for instance, cannot economically stock the many MDA test fixtures needed for the variety of products they service. They will continue to rely on limited functional testing. Similarly, PCBs that are deliverable end items, such as PC-motherboards or data acquisition boards, will still require a full final functional test.
But instead of relying on large, full-featured, multipurpose functional ATE, the trend now is to use application-targeted testers. These test systems may be configured from a set of modules, be VXI-based or PC-based, or consist of an MDA outfitted with supplemental functional test facilities.
Today’s board test systems have MDA and MPT capabilities that pinpoint physical defects, as opposed to electrical performance defects. And functional test now is better served by a wider range of modular systems that addresses the application at hand and, therefore, is more economical. Common to almost all of these systems is the ubiquitous PC, serving as the controller, test-result-processor, and human interface.
MDA/MPT Capabilities
MDAs always have provided continuity test and analog component measurement capabilities. While these facilities were well-suited for locating defects on PCBs employing through-hole mounting, they became inadequate with the advent of surface-mount technology (SMT). The reason—most through-hole defects are shorts, which could easily be found with a continuity test, while most SMT defects are opens.
To find opens, the PCBs had to be powered up, test vectors applied, and responses evaluated. This situation changed drastically when Hewlett-Packard introduced the TestJet technology, a capacitive physical-defect-based open-circuit technology that detects open circuits without applying test vectors.1
Other companies quickly developed equivalent methodologies and introduced more physical-defect-targeted fault-isolation techniques. GenRad, for instance, offers Junction Xpress™ for detecting opens on ICs and Opens Xpress™ for detecting opens on surface-mount connectors
Similarly, Teradyne developed DeltaScan™ vectorless test for high coverage of VLSI device opens and FrameScan Plus™ for finding connector opens.2 Other companies, such as CheckSum and Testronics, provide vectorless test capabilities based on HP TestJet licensing arrangements. Scorpion uses a transistor-model-based vectorless test technique called ChipScan.3
While these techniques provide programming and equipment cost savings, they require dedicated fixtures (as was the case for in-circuit testing) and reasonable physical access. For some components, especially ICs in ball grid array packages, this access is not available.
Boundary Scan to the Rescue
Many designers have recognized the limited-access problem and include boundary scan circuits in their ICs. “Boundary scan helps test dense PCBs that would be difficult or impossible to accommodate using traditional bed-of-nail fixtures,” commented Roger Richards, marketing manager at Corelis. “Boundary scan test is an attractive solution in the production environment. The availability of inexpensive automatic test-program generation tools and the absence of fixturing requirements make the test process economical.
“When components, such as edge connectors or other digital interfaces, are not visible from the boundary scan chain, they can be accessed through our family of SCANIO modules,” Mr. Richards continued. “Automatic cluster test-vector generation software also is available to handle hybrid boards and extend the capability of boundary scan testing beyond the scan chain.”
ASSET InterTech also offers an IEEE 1149.1 boundary scan diagnostic system that pinpoints manufacturing defects. And scan test facilities can be added to many MDA and functional test systems. For example, the CheckSum TR-8-BST offers integrated MDA/BST facilities.
MDAs Are Upgradable
Most of today’s MDAs are offered in a basic configuration, which is more than adequate to support unpowered test of the majority of PCBs. But to avoid future obsolescence, or accommodate units which require additional facilities, almost all are upgradable.
For instance, “To maximize the economic return of the test system over time, our Z1803 systems can be field upgraded to meet most test-strategy requirements,” said Craig Pynn, marketing manager at Teradyne’s Assembly Test Division. “Upgrades provide the required level of digital backdrive, pattern testing, flash memory programming, and comprehensive digital functional testing.”
Functional Test Capabilities
Full-featured functional ATE accommodates a variety of UUT types, speeds up changeover from one UUT type to another, and therefore is economical for testing a variety of PCBs produced in small lots. But, functional ATE targeted at specific applications can provide substantial cost savings since they do not contain unneeded features. They are most appropriate when high quantities of a few UUT types are to be tested, when all UUTs belong to one class, or when test volume is so low that full-featured functional ATE is not cost-effective.
Targeted facilities may range from an inexpensive basic source/measure and control unit to a fully automated modular system containing application-specific stimuli. An example of the former system is the Y-tek FT-100 Programmable Functional Tester which is programmable, contains digital and analog I/O lines, furnishes power to the UUT, collects data, and controls additional instrumentation.
Many of today’s UUTs contain microcontrollers or microprocessors. Testing these types of UUTs requires a system that offers many high-speed digital I/O lines with memory behind each pin, and, in some cases, emulation facilities. A typical unit that includes both stimulus/response and emulation capabilities is the VXI-based Talon SR192. It can be equipped with only the number of daughter boards needed for your test application.
Some test-system suppliers have adopted a modular approach so you can configure a system containing only the facilities you need. Besides potential cost savings, the advantages include the use of standard models that will play together under the furnished operating system and the vendor’s full responsibility for overall ATE functionality and performance.
Such modular systems may provide MDA, in-circuit, or functional test capabilities, or combinations of these. “The Series 3900 is a modular combinational tester that supports MDA and in-circuit tests, and provides power-up testing, various emulation approaches, and edge-connector testing,” said Michael Fettes of Wayne Kerr. “It performs analog functional tests to 450 MHz and digital tests to 50 MHz, and accommodates a range of units including PCBs, hybrids, and complete assemblies.”
Functional modular test systems also may be configured by using a freestanding or an embedded PC and VXI modules or PC plug-in boards. Geotest, for instance, offers ATE using PC-based plug-in boards for analog, digital, and mixed-signal testing. Boards range from simple ADCs, DACs, and static and dynamic digital I/O units to a ROM emulator.
“Most of our PC-based ATE are targeted for testing boards with on-board microprocessors and high-speed digital circuitry where you test the UUT at the bus or the microprocessor’s speed,” said Hadi Shavarini, sales and marketing manger of Geotest. “To accomplish this, you need RAM-backed digital I/O, emulation capability, and other high-speed instruments. Couple these facilities with a simple switch matrix, a DMM and other measurement components, and an ATE operating environment and you have a complete mixed-signal tester.
“With today’s high-speed PC-based instruments, engineers test UUTs at their bus speed,” Mr. Shavarini added. “For example, our digital I/O boards run digital vectors at up to 50 MHz, providing full test rate at the UUT’s required speed.”
Software Issues
Physical layout information and basic component data are required to generate UUT fixtures and test programs for MDAs. Most MDA suppliers furnish automatic fixture-design and program-generation tools that extract the needed information from PCB layout information contained in CAD files and from component definition lists. Alternatively, position information may be manually entered and electrical data obtained by letting the system self-learn the component behavior from a known-good board.
While automatic data extraction for fixture design purposes usually is without problems, this is not always true for test-program generation without human intervention. “The price of ‘automation’ is almost always marginal fault coverage, because only the simplest circuit configurations and component types are handled effectively,” warned Mr. Pynn. “Even worse, when only one or two known-good board samples are used in the self-learn programming process, test limits may be skewed, leading to problems in test repeatability during high-volume production.
“In fact, manufacturers of advanced SMT/VLSI boards still need a suite of programming tools that produces high fault coverage and test stability in the shortest overall time. They need to know exactly what’s being tested and how. A parametric analysis tool, such as the Z1803’s ProcessWatch software, serves this function and provides the information to set limits and to arrive at optimum tests quickly,” Mr. Pynn concluded.
Scan test-specific automatic test-program generators provide a simple method for developing test vectors to verify the infrastructure and interconnections of nets between boundary scan devices. “Netlist information in computer-aided engineering independent formats and component information in the form of Boundary Scan Description Language files give the information needed to achieve complete test coverage for bridging and stuck-at faults on the UUT,” said Mr. Richards. “Also, test data in Summit Designs’ industry-standard TSSI-format consisting of Signal Definition Files and Signal Level Files may be converted into test files.”
Test programs for multipurpose functional ATE are most readily generated using the software environment provided with the ATE. But for modular, VXI, and other PC-based test systems, more options exist.
National Instruments’ LabVIEW and LabWindows/CVI or Hewlett-Packard’s HP-VEE instrumentation development software often is used in conjunction with test- execution programs to generate Windows-based targeted test-software environments. Also, ATEasy from Geotest provides a Windows-based test environment that includes program-development tools, driver and test-program editors, and a run-time test executive.
Because ATEasy is based on the Windows open system architecture, its drivers and test routines connect to the test executive via targeted dynamic linked libraries (DLL) command sets, according to Mr. Shavarini. As a result, the DLLs become generic test program components that can be used and reused in a variety of ATE systems. Test engineers also can expand or customize test-program features by using DLL and dynamic data exchange facilities.
Regardless of the type of test-program environment, Mr. Shavarini suggests that ATE software used in today’s production environment not only should contain all tools needed to develop, debug, and execute test programs, but also:
Allow easy access to shop-floor control utilities, including quality-control functions, and where applicable, the company’s computer-integrated manufacturing environment.
Provide easier maintenance, modifications, or updates; and include built-in security options and multiple protection levels with minimum software changes.
References
1. “New Technique Reduces Test Development Time for SMT Opens,” EE-Evaluation Engineering, February 1993, pp. 62-71.
2. Pynn, C. T., “Vectorless Test Boosts Fault Coverage and Cuts Cycle Time,” EE-Evaluation Engineering, August 1995, pp. 37-41.
3. “MDA Uses Novel Technique to Perform ICT,” EE-Evaluation Engineering, August 1994, p. 124.
Low-Cost Board ATE
MDA/In-Circuit Test Systems
Are Modular, Upgradable
The HP 3272 and 3273 Board Test Systems target applications requiring high-fault-coverage test on boards with up to 1,296 nodes. The HP 3272 includes TestJet and six-wire analog in-circuit technology for diagnosing analog-device failures. The HP 3273 adds powered in-circuit test performance, a six megapattern vector rate, and a library of more than 8,000 devices for digital fault diagnosis. The systems are modular and upgradable. Starting at $50,000. Hewlett-Packard, (800) 452-4844.
Electrical Inspection System
Suited for High-Volume Testing
The Viper System electrically inspects all classes of manufacturing process defects on PCBs. It supports up to 3,200 pins, and is available in two configurations: ergonomically optimized for sit-down operation or in-line automated in conformance with SMEMA standards. Diagnostics are achieved with the TEST Xpress™ Analog Toolsuite, Junction Xpress™, Opens Xpress™, Orient Xpress™, and Cap Xpress™. Other features include automated program development and debug, and the InPro Inspection Process Control Suite. Starting at $40,000. GenRad, 800-4-GENRAD.
JTAG Controller Features
Network Connectivity
The Net-1149.1™ Boundary Scan Controller provides an intelligent interface between scan-development, production, and test processes and any PC or workstation that includes TCP/IP protocol and Ethernet networking support. Net-1149.1 features four independent IEEE 1149.1 test access ports with programmable JTAG clock rates to 35 MHz, a memory-behind-the-pin architecture, and 16 I/O lines for remote control/sense. UUT responses are stored in 4 MB (expandable to 16 MB) of dual-port memory and can be uploaded to the host for further analysis. $5,950. Corelis, (562) 926-6727.
MDA/Boundary Scan ATE
Offers Integrated Diagnostics
The Model TR-8-BST ATE integrates boundary scan test facilities with manufacturing defects analysis (MDA) capabilities. As an MDA, it tests and diagnoses shorts and opens, diodes, and FETs and measures resistors, capacitors, complex impedances, and transistor beta. In the boundary scan mode, it powers up the UUT and performs vector tests to assure that scannable circuits are performing properly. The TR-8-BST provides the hardware and integrated environment to execute vector files created by UUT designers. $9,995. CheckSum, (360) 435-5510.
Diagnostic System Pinpoints
Manufacturing Defects
The 2.1 release of the ASSET® IEEE 1149.1 boundary scan diagnostic system pinpoints defects in manufacturing. Parallel-to-serial vector translation helps reuse test vectors developed during design. Standard boundary scan data formats, such as BSDL, HSDL, and SVF, are supported. Customized production-oriented interfaces can be generated using the company’s Scan Function Library, National Instruments’ LabWindows/CVI or HP VEE. A full 32-bit implementation makes the 2.1 release faster than previous versions. It runs on PCs or VXI-based systems under Windows 95. From $8,495. ASSET InterTech, (214) 437-2800.
Software and Test Modules
Improve ATE Performance
Software upgrades and new test modules enhance the operation of Wayne Kerr’s 3900 Series ATE. The new software, Version 1.5, simplifies test-routine development and accommodates improved reporting and datalogging schemes. The new modules are part of the family of VXI-compatible test instruments and encompass a range of signal and measurement functions. The 3900 Series performs functional and combinational testing of complex PCBs and assemblies that contain both analog and digital signals. Call company for price. Wayne Kerr, (617) 938-8390.
SCPI-Compatible Module Tests
Digital Boards, Systems
The message-based SR192 VXI Module features a stimulus-response architecture and dual bus emulation. It uses a motherboard/daughter board structure accommodating up to 12 16-channel I/O modules, two timing modules, and one voltage/clock module. I/O modules are TTL compatible, CMOS compatible, or programmable to ±15 V with 25-mV resolution. Several SR192s can be synchronized, yielding test systems with up to 1,152 I/O channels. Signals can be clocked to 50 MHz. Serendipity software provides fault-dictionary, guided-probe, and UUT display facilities. Call company for price. Talon Instruments, (909) 599-0690.
Functional Tester Exercises
Analog and Digital Circuits
The FT-100 Programmable Functional Tester checks digital and analog circuits and assemblies. All tester functions are controllable and accessible via a simple programming language. It may be programmed through the RS-232 communications port or via its IBM-compatible disk drive. The tester offers 40 digital input lines, 40 digital output lines, 8 analog input lines, 7 analog output lines, and 3 fixed and 1 variable power supply voltages for the UUT. An extension module increases I/O up to 880/880 lines. $3,900. Y-tek, (800) 707-YTEK.
MDA/ICT Offers Selectable
Test Facilities, Configurations
The Scorpion® Super MDA/ICT Board Test System features multiple MDA functions and expands to a full in-circuit test system. It includes ChipScan, a patented vectorless IC test technology, the BodeBox, and a four-quadrant power amplifier stimulus and measurement system. The BodeBox is an in-circuit network analyzer which isolates low-value resistors, capacitors, and inductors which may be part of complex serial and parallel circuits. Automatic discharge and active guarding are provided. Tests are performed at speeds of up to 1,000/s. A combinational Super MDA/ICT with 512 Super MDA pins and 64 bidirectional asynchronous function test pins is less than $100,000. ITA, (714) 583-1553.
System Provides MDA Benefits
And High Fault Coverage
The Z1803 Test System combines the cost and cycle-time benefits of MDAs with the high fault coverage and upgradability of manufacturing process testers. It features power-off analog in-circuit test, DeltaScan™ vectorless test for high coverage of VLSI device opens, and FrameScan Plus™ and CapScan™ vectorless test for finding connector opens and reversed electrolytic capacitors. The Z1803 offers up to 2,048 nonmultiplexed pins, a PC-based run-time operating and programming environment, and the Momentum™ programming environment for direct CAD-to-tester data transfer. Under $50,000. Teradyne, (510) 932-6900.
Preconfigured ATE Available
In PC Instrument Chassis
A series of preconfigured instrumentation systems uses standard PC boards housed in the GTXI PC Instrument System Chassis. The chassis features extra shielding, buffering, front-loading of PC cards, built-in cable ways, and a hinged front panel. Configurations encompass digital test, mixed-signal test, waveform analysis, and analog test systems for applications such as digital comparison testing, emulation, pattern generation, vector capture, and signal analysis. Test software includes ATEasy for PC Instrumentation. Call company for price. Geotest, (800) 330-9774.
Open Architecture
Assures Configurability
The 405 Series Test Systems include the 405A Benchtop MDA with a GenRad 2270-Style Receiver, the 405B Modular MDA and Assembly Test System with UUT ribbon-cable connections, and the 405C Combinational MDA System. Analog and digital stimulus and measurement cards, in-circuit test modules, and source and sense resources can be configured to provide any required MDA and digital test-point combination. With the six-wire matrix cards, any node can be software-defined as source, sense, return, or guard. Automatic program generation and autoguard facilitate programming. From $15,000. Testronics, (972) 542-3111.
Copyright 1997 Nelson Publishing Inc.
June 1997