When testing a component or an electronic gadget, it is usual to hold two probes to the test points. Probes are metal prods insulated except for the tips touching the test points on one end and connected by flying leads on the other to an instrument. The instrument could be a voltmeter, an ammeter, an ohmmeter or a combination called the multi-meter. Such an arrangement is good for testing individual components or a printed circuit board. However, in a manufacturing scenario, where boards are produced in hundreds or thousands, humans cannot match the speed and special testing machines are used.
Such testing machines use a set of flying probe test systems for testing, trimming or alignment of components on a printed circuit board or a gadget. Most of these machines are computerized test beds with high speed, unprecedented positioning accuracy and extensive test coverage. They remove the requirement for a bed-of-nails testing fixture and provide a wide variety of test facilities contributing to validation of low-volume production and of the R&D department.
The typical configuration of a flying probe test system consists of four standard moving probes installed diagonally to the board under test. Advanced machines may also have two optional Z-mechanisms for holding another pair of moving probes that can move up and down vertically.
The vertical Z-axis probes enable access to test points that the standard moving probes find difficult to reach. In addition, the Z-axis probes can make proper contact with locations at different heights. With such flexibility, flying probe test systems can directly contact through-holes and heads of connector pins. To prevent slippages and false contacts, the probe tip may be of the dagger or inverse cone head type, all resulting in increased test coverage.
The testing machines are highly accurate measurement systems that include several 4-quadrant sources and measurement systems. Almost invariably, these are embedded with AC programmable generators that can also be used as function generators. Therefore, the testers are capable of applying measuring signals that are best suited to specific electronic components.
The measurement system associated with the flying probes usually features high-resolution ADC/DACs, which help to make precise tests and measure the dynamic characteristics of the circuit.
To enable accurate and repeatable measurements, these testers possess an XY table or stage made of highly polished native granite. Modern flying probe test systems boast of superfast movement of probes with positioning accuracies better than conventional models by at least 25%.
The super-fast movement is the result of using state-of-the-art high power and fast-moving drive motor systems controlled by new control software speeding up the test by 30-50% over conventional models. With the addition of three bottom probe units, combination tests can be performed more efficiently, further cutting down test times.
Modern flying probe test systems come with vision test systems offering simple AOI functions. Detection of missing, wrongly oriented or positioned components is made simple with the use of megapixel color digital cameras, backed by ring illuminations with high-intensity white LEDs. This combination is helpful in reading not only barcodes and 2D codes, but in color identification tests, OCR functioning and modifying contact points as well while debugging testing programs.
