Automatic test equipmentAutomated test equipment (ATE) is computer-controlled test and measurement equipment that allows for testing with minimal human interaction. The tested devices are referred to as a device under test (DUT). The advantages of this kind of testing include reducing testing time, repeatability, and cost efficiency in high volume. The chief disadvantages are the upfront costs for programming and setup.

Automated test equipment can test printed circuit boards, interconnections, and verifications. They are commonly used in wireless communication and radar. Simple ATEs include volt-ohm meters that measure resistance and voltages in PCs; complex ATE systems have several mechanisms that automatically run high-level electronic diagnostics.

 

ATE is used to quickly confirm whether a DUT works and to find defects. When the first out-of-tolerance value is detected, the testing stops and the device fails.

 

Semiconductor Testing

 

For ATEs that test semiconductors, the architecture consists of a master controller (a computer) that synchronizes one or more sources and capture instruments, such as an industrial PC or mass interconnect. The DUT is physically connected to the ATE by a machine called a handler, or prober, and through a customized Interface Test Adapter (ITA) that adapts the ATE's resources to the DUT.

 

When testing packaged parts or directly on the silicon wafer, a handler is used to place the device on a customized interface board and silicon wafers are tested directly with high precision probes.

 

Test Types

 

Logic Testing

 

Logic test systems are designed to test microprocessors, gate arrays, ASICs and other logic devices.

  • Linear or mixed signal equipment tests components such as analog-to-digital converters (ADCs), digital-to-analog converters (DACs), comparators, track-and-hold amplifiers, and video products. These components incorporate features such as, audio interfaces, signal processing functions, and high-speed transceivers.
  • Passive component ATEs test passive components including capacitors, resistors, inductors, etc. Typically, testing is done by the application of a test current.
  • Discrete ATEs test active components including transistors, diodes, MOSFETs, regulators, TRIACS, Zeners, SCRs, and JFETs.

 

Printed Circuit Board Testing

 

Printed circuit board testers include manufacturing defect analyzers, in-circuit testers, and functional analyzers.

  • Automated Test EquipmentManufacturing defect analyzers (MDAs) detect manufacturing defects, such as shorts and missing components, but can't test digital ICs as they test with the DUT powered down (cold). As a result, they assume the ICs are functional. MDAs are much less expensive than other test options and are also referred to as analog circuit testers.
  • In-circuit analyzers test components that are part of a board assembly. The components under test are "in a circuit." The DUT is powered up (hot). In-circuit testers are very powerful but are limited due to the high density of tracks and components in most current designs. The pins for contact must be placed very accurately in order to make good contact. They are also referred to as digital circuit testers or ICT.
  • A functional test simulates an operating environment and tests a board against its functional specification. Functional automatic test equipment (FATE) unpopular due to the equipment not being able to keep up with the increasing speed of boards. This causes a lag between the board under test and the manufacturing process. There are several types of functional test equipment and they may also be referred to as emulators.

Interconnection and Verification Testing

 

Test types for interconnection and verification include cable and harness testers and bare-board testers.

  • Cable and harness testers are used to detect opens (missing connections), shorts (open connections) and miswires (wrong pins) on cable harnesses, distribution panels, wiring looms, flexible circuits, and membrane switch panels with commonly-used connector configurations. Other tests performed by automated test equipment include resistance and hipot tests.

  • Bare board automated test equipment is used to detect the completeness of a PCB circuit before assembly and wave solder.

Configurations

 

In a bed-of-nails configuration, each circuit net on the board is connected to the tester, typically with one nail per net.  The pins are aligned to make contact with test points on a printed circuit board. They are also connected to a measuring unit by wires. When the DUT is pressed against the BON,  contact is made simultaneously with hundreds or thousands of individual test points. BONs typically require a vacuum or air source to ensure hold-down force is provided.

 

The flying probe system uses a low number of moving probes rather than the high number of fixed probes in the BON. Test times may be slower due to probe movements, but the method has compensating benefits. In practice, a flying probe can provide close to 100% test coverage on a board with thousands of nets of passive components and hundreds of digital devices. It is best used with assembled boards for new product introduction.

 

Flying Probe Testing

Video Credit: Nexlogic PCB Design

 

Optical inspection methods include scanning probe microscopes that reveal surface defects. Optical inspections do not need test fixtures and requires no electrical sources or measurements. Automatic optical inspection is helpful when placed at the end of a line producing soldered boards. Here it can quickly  locate production problems such as solder defects and incorrect component orientation. The set up time can be tedious but once set the system can process boards efficiently, making it ideal for high volume processing. Automated x-ray inspection is similar to optical inspection. It can look through IC packages to examine solder joints.

 

DEFECT TYPEAOIAXIICT
      Soldering defects      
            Open circuits Y Y Y
            Solder bridges Y Y Y
            Solder shorts Y Y Y
            Insufficient solder Y (not heel of joint) Y N
            Solder void N Y N
            Excess solder Y Y N
            Solder quality N Y N
      Component defects      
            Lifted lead Y Y Y
            Missing component Y Y Y
            Misaligned or misplaced component Y Y Y
            Incorrect component value N N Y
            Faulty component N N Y
      BGA and CSP defects      
            BGA shorts N Y Y
            BGA open circuit connections N Y Y

Comparison of the major defect detection capabilities of AOI, AXI, and ICT

Chart Credit:  Radio Electronics

 

Features

 

Common features for automated test equipment include boundary-scan capabilities, temperature control, and support of STDF (standard test data format).

 

Standards

 

Automated test equipment must adhere to several national and international standards. The U.S. Air Force publishes standardized policy for ATLAS high order language (HOL) for automatic test equipment as well as a policy for modular ATE. British Defense Standards have specifications for automatic test equipment and a general purpose ATE date requirements.

 

 

 

Images

 

RITA | BK Precision | SPEA

 

Resources

 

Overview of Various Bed of Nails Test Fixture Features and Designs

 

Automatic Test Equipment (ATE)

 

Automatic test equipment ATE

 

Electronics Test and Measurement

 

Practical Guides for Building a Test System

 

 


Related Products & Services

  • Data Loggers and Data Recorders

    Data loggers and data recorders acquire digital data from sensors and other signals. They are primarily used to store data for subsequent downloads to a host PC, but may also include real-time features such as monitors and alarms.

  • Fuel Cell and Solar Test Equipment

    Battery, fuel cell and solar test equipment consists of specialized test stations, stands or systems, monitors and component modules for performance or endurance testing.

  • Laser Beam Analyzers

    Laser beam analyzers are used to determine the quality of a laser beam.

  • Spectrum Analyzers and Signal Analyzers

    Spectrum analyzers and signal analyzers display raw, unprocessed signal information such as voltage, power, period, wave shape, sidebands, and frequency. They can provide the user with a clear and precise window into the frequency spectrum.

  • Thermocouple Simulators and RTD Simulators

    Thermocouple simulators and resistance temperature detector (RTD) simulators provide precise standard values of resistance or voltage for simulation and calibration.