PCB Tech - What is ICT? The role of ICT testing in PCBA testing

During ICT testing, test probes are used to contact test points on the PCBA board, which can detect short circuit, open circuit, SMT patch and component welding and other faults. It can quantitatively measure resistance, capacitance, inductance, crystal oscillator and other devices, perform functional test on diodes, triodes, optical couplings, transformers, relays, operational amplifiers, power modules, etc., and perform functional tests on small and medium-sized integrated circuits, such as all 74 series, Memory type, common drive type, exchange type and other ICs.

What is ICT? ICT (In-Circuit Test System), commonly used in Chinese as in-circuit tester, is mainly used for PCBA testing (PCBA testing). "Online" here is a literal translation of "In-Circuit", which mainly refers to components on the line. Online testing is a testing technology that does not disconnect the circuit and does not remove the component pins. "Online" reflects that ICT focuses on detecting circuit board assembly problems by testing the components on the circuit or the open and short circuit status.

Which PCB components can be measured with the basic functions of ICT?

Open, short circuit, resistance, capacitance, inductance, diode, IC protection diode test, etc.

Why use ICT?

According to the statistical data of the PCB assembly industry, assembly defects are mainly reflected in circuit board welding open circuit, short circuit, offset, missing parts, etc., accounting for more than 90%, as shown in the figure below, so the principle of online testing technology application is to be able to quickly detect faults Components or assembly defects, and can accurately locate defects and defect classification.

Can ICT be regarded as a multimeter?

ICT can be regarded as an automated advanced multimeter, and because it has the function of circuit isolation (Guarding), it can accurately measure the actual value of each component in the circuit.

What are the functional differences between ICT and general electricity meters?

An electric meter is used to measure a single part. In addition to measuring a single part, ICT can also measure parts on a real board through a needle bed. It's just that there are many loops on the real board, it is easy to split the signal source and divide the voltage, so it is often necessary to add the "Guarding" function to make the measurement accurate.

What is the relationship between ICT and AOI?

ICT is mainly carried out through electrical measurement methods, while AOI is carried out through optical image processing technology. Both have their own strengths and complement each other. In terms of process arrangement, AOI first, then ICT.

The role of ICT testing in PCBA testing

1. ICT has a wide range of use, high measurement accuracy, and clear instructions for detected problems. It is a standard test method. It is very easy for workers with average electronic skills to deal with problematic PCBA. The use of ICT can greatly improve production efficiency and reduce production costs.

2. ICT Test is mainly to detect the open circuit, short circuit, and welding of all parts of the PCBA through the test probe contacting the test points of the PCB layout. It can be divided into open circuit test, short circuit test, resistance test, capacitance test, diode test, and triode test., Field effect tube test, IC pin test (testjet` connect check BasicScan Bist) and other general and special components such as missing installation, wrong installation, parameter value deviation, solder joint welding, circuit board open and short circuit and other faults, and Which component is the fault or at which point the open or short circuit is located is accurately told to the user through the printer or screen display.

3. Functional testing of TTL, OP RELAY and other functional devices, and IC programming.

Some methods of ICT testing are:

1. Analog device test

Use operational amplifiers for testing. The concept of "virtual land" from point "A" is:

∵Ix = Iref

∴Rx = Vs/ V0*Rref

Vs and Rref are the excitation signal source and the calculated resistance of the instrument respectively. Measure V0, then Rx can be calculated. If Rx to be measured is capacitance or inductance, then Vs is an AC signal source, and Rx is in impedance form, and C or L can also be obtained.

2. Vector test

For digital IC, Vector (vector) test is used. The vector test is similar to the truth table measurement, in which the input vector is stimulated, the output vector is measured, and the quality of the device is judged through the actual logic function test. Such as: NAND test

For the test of analog IC, the voltage and current can be excited according to the actual function of the IC, and the corresponding output can be measured as a function block test.

3. Non-vector testing

With the development of modern manufacturing technology and the use of very large-scale integrated circuits, it often takes a lot of time to write vector test programs for devices. For example, the 80386 test program takes a skilled programmer nearly half a year. The large number of applications of SMT devices has made the fault phenomenon of device pin open circuit more prominent. To this end, each company's non-vector testing technology, Teradyne launched MultiScan; GenRad introduced Xpress non-vector testing technology.

ICT testing is at the back end of the production process. The first process of PCBA testing can detect problems in the PCBA board production process in time, which helps to improve the process and increase the efficiency of production.