Automated Test Equipment
Automated test equipment (ATE) is computer controlled test and measurement equipment, arranged in such a way as to be able to test a unit with minimal human interaction. The advantage of this kind of test is that they are repeatable and cost efficient in high volume. The chief disadvantages are the upfront costs; programming and setup.
Automated test equipment can test components, printed circuit boards, and interconnections and verifications. Test types for components include logic, memory, linear or mixed signal, passive components and active components. Logic test systems are designed for handling the testing of microprocessors, gate arrays, ASICs and other logic devices. Memory testers are automated test equipment for the testing of SDRAM, DDR-SDRAM SIMMs and DIMMs. Linear or mixed signal equipment is used for the testing of 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 automated test equipment tests active components including transistors, diodes, MOSFETs, Regulators, Triacs, Zeners, SCRs, and JFETs.
Printed circuit board testers include manufacturing defect analyzers, in-circuit testers, and functional analyzers. Manufacturing defect analyzers (MDAs) detect manufacturing defects, such as shorts and missing components, but they can’t test digital ICs as they test with the UUT (unit under test) powered down (cold). As a result, they assume the ICs are good. MDAs 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 UUT is powered up (hot). They are also referred to as digital circuit testers. A functional test simulates an operating environment and tests a board against its functional specification. They may also be referred to as emulators.
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 for automated test equipment include bed-of-nails (BON), flying probe, and optical. In a bed-of-nails configuration each circuit net on the board is connected to the tester, typically with one nail per net. BONs typically require a vacuum or air source. 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. Optical inspection methods include scanning probe microscopes to reveal surface defects. Optical inspections do not need test fixtures and requires no electrical sources or measurements. Common features for automated test equipment include boundary-scan capabilities, temperature control, and support of STDF, Standard Test Data Format.