ICT tester for printed circuit board assembly
Online testing is usually the first test production process, timely response to production conditions, conducive to process improvement and upgrading. ICT tested failed board, due to quasi-fault location, easy maintenance, and can greatly improve production efficiency and reduce maintenance costs. Because of the specific test items, is a modern large-scale production of important quality assurance test means.
Basic test methods
The use of operational amplifiers for testing. From the "A" point "virtual land" concept: ∵ Ix = Iref ∴ Rx = Vs / V0 * Rref Vs, Rref were excitation source, the instrument calculated resistance. Measurement of V0, the Rx can be calculated. If Rx is measured capacitance, inductance, then the AC signal source Vs, Rx for the impedance in the form, the same can be obtained C or L. 1.2 Isolation (Guarding) above the test method is for stand-alone device, but the actual devices on the circuit connected to each other, influence each other, so that Ix Min ref, the test must be isolated (Guarding). Isolation is a basic online testing technology. In the circuit, due to R1, R2 connection diversion, so that Ix Min ref, Rx = Vs / V0 * Rref equation does not hold. Test, as long as the G and F point with the potential, R2 is no current flow, there are still Ix = Iref, Rx equation unchanged. The G-point ground, due to the virtual point F, the two potentials are equal, you can achieve isolation. Practical reality, through an isolated operational amplifier of the G and F equipotential. ICT tester can provide a number of isolated points, to eliminate the impact of the external circuit to the test. 1.2 IC testing for digital IC, the use of Vector (vector) test. Test similar to the truth table vector measurement, the input excitation vector, measured output vector, by the logic functional tests to determine the actual quality of the device. Such as: non-door tests of analog IC test, according to the actual function of IC excitation voltage, current, measuring the corresponding output, as block testing.
With the development of modern manufacturing techniques, the use of ultra large scale integrated circuit, the device vector test program written often spend a lot of time, such as 80386 of the test program takes a skilled programmer nearly half a year. SMT assembly components of a large number of applications, the device pin open fault phenomena become more prominent. To this end the company's non-vector test technology, Teradyne introduced MultiScan; GenRad introduced Xpress non-vector testing technology. 2.1 DeltaScan simulation results testing techniques DeltaScan almost all digital devices to use the vast majority of mixed-signal pin and the pins have ESD protection diodes or parasitic, independent of the device under test pin for a simple DC current test. When a board's power supply is cut off, any two pins on the device equivalent circuit as shown in the figure. 1 plus one ground pin A negative voltage, current Ia flows through the pin A of the forward bias diode. A measurement of current flow through the pin Ia. A pin 2 to maintain the voltage at pin B plus a high negative voltage, the current Ib flowing through pin B of the forward biased diode. As from the pin A and pin B to ground the common substrate resistance within the current sharing, current Ia will be reduced. 3 A re-measurement of current flow through the pin Ia. When a voltage is applied to pin if B does not change when the Ia (delta), then there is a connection problem. DeltaScan integrated software on the device from the many possible pin on the test results to arrive at an accurate diagnosis. Signal pins, power and ground pins, the substrate are involved in DeltaScan test, which means that in addition to disengage the pin outside, DeltaScan device can also detect missing, insert anti-, wire torn off and other manufacturing fault. GenRad class type of test that Junction Xpress. The diode within the IC using the same features, but the test by measuring the spectral characteristics of the diode (second harmonic) to achieve. DeltaScan without additional fixtures hardware technology, a devaluation technology. 2.2 FrameScan capacitive coupling capacitive coupling detection test FrameScan pins disengaged. Each device has a capacitive probe above, a pin in the excitation signal, capacitive probes pick up the signal. Shown: 1 fixture on the multi-channel switch to select a device on board the capacitive probe. 2 Test the analog test board (ATB) test to each pin in turn issued a communication signal. 3 capacitive probe test pins on the collection and exchange of the buffer signal. 4 ATB measurement capacitive probe picked up the AC signal. If a pin and circuit board connection is correct, the signal will be measured; if the pin is disengaged, there will be no signal. GenRad class-based technology called Open Xpress. Principle is similar. This technique requires sensors and other hardware fixtures, test higher cost.