Printed Circuit Board Assembly is a process by which all the electrical components of the circuit board are brought together by soldering and installation to make it functional. It is a complex procedure, as even a slight defect in the assembly would affect the performance. So, to ensure the quality of the PCB and to omit any manufacturing defect, in-circuit testing is performed.

In-circuit testing (ICT) is a fully automated test used to find defects in different parts of PCB, such as resistors, capacitors, transistors, and checks for shorts and opens. ICT helps to ensure that each component is placed accordingly and is of the required value.

Components of ICT

ICT is also known as the bed of nails test. There are different types of in-circuit tests available for different PCBs. However, the basic elements required are the same for all In-Circuit testers. These include software, an In-circuit tester, and a fixture.

Software is written, which provides details of the test to be performed. It is different for each board type and gives information about the pass and fail criteria. The In-circuit tester consists of several driver sensor points that are connected to the connectors on the system.

A Fixture is also a part of the in-circuit tester. It is developed specifically for each type of circuit board. It connects the driver sensor points to the points present on the board using the bed of nails.

These three elements form the major component of any In-Circuit test. Fixture and software are specific to the board or assembly, while the users can use the same tester for multiple board types.

Advantages of ICT

In-circuit testing is not a time-consuming method, unlike other PCB testing methods, as it takes a few minutes to test the PCB. It is relatively easy to perform. ICT is considered to be very reliable in detecting any flaws or defects, as it is considered to have good fault coverage. In addition to that, the detected faults can also help in improving the quality of the circuit boards and deliver what the consumer needs. Microchips and printed circuit boards are used in most gadgets, for example, cell phones, television, and computers. Thus, ICT helps to make them functional and non-defective.

Disadvantages of ICT

As a specific fixture is created for each board and mechanically assembled examinations are used, it becomes expensive to manufacture. The probes require cleaning to prevent the test from failing, also done mechanically, which makes it more costly.

Proper contact is required, between the pins and the board, for accurate results. With the advent of smaller gadgets and tools, the need for smaller Printed Circuit Boards has increased. The decreasing size of the PCB makes it difficult to ensure proper connection between the connectors and the board. Therefore, it might lead to inappropriate results.

In-Circuit Test for PCB Assemblies Steps:

After the production of electronic products is completed, we need to take multiple processes to test whether the products meet the quality requirements, such as ICT test, AOI visual test, laboratory limit test, FT function test, etc.

This part mainly introduces the knowledge about ICT testing of PCB, so Let us introduce the process steps of the In-Circuit Test for PCB Assemblies.

Steps:

1) After the SMT component mount is completed, the first test is the ICT test, which can effectively prevent quality problems caused by SMT during mass PCB manufacturing. The first step of the ICT test is to test the short circuit and open circuit on the PCB. The test instrument will prompt an error if there is a short circuit or open circuit outside the design.

2) If there is no open circuit or short circuit problem in the circuit board, the second step is to test the components on the PCB. The system will test the inductance, resistance, capacitance, diode, triode and other independent components. Diode and triode tests are mainly forward and reverse conduction tests to determine whether the direction is wrong.

3) Of course, due to the limitations of PCB board size and test pin distribution points of the test system, not all independent components on the circuit board can be tested, so next step, we need to carry out the modular test, that is, test the local circuits on the circuit cloth as a whole to ensure that there is no problem locally.

4) The above tests are done when the circuit board is not powered on, also known as the unpowered test. We also need to test the PCB with power on. The test system can automatically power on the PCB power port.

5) After the PCB is powered on, we will conduct the triode switching characteristic test, high and low-level test of the chip input and output ports, and voltage test at important voltage points.

6) If there is no problem in the above tests, the test system will write a program to the master chip on the PCB of the product. Of course, this step is not required for all products, and it needs to be determined according to the product function.

7) After the product can work normally, it is also necessary to test some components, such as angle sensor test, large capacitance-voltage test, etc., because these tests can only be tested when the product is actually running.

8) After the product passes the test, if there is no problem, the test system will perform the power test, excluding the large capacitance of the product. If there is no problem, it will prompt that the test has passed successfully.

The above is the whole ICT test process of PCB. The ICT test process is complex and fine. We need to operate strictly according to the regulations to ensure the high quality of the PCB circuit board.

Conclusion:

An in-circuit test is a major tool used to assess the Printed Circuit Board for any defects. It is one of the reliable methods that provide the consumer with a flawless board to function effectively. It examines for any manufacturing faults, as it tests each board component individually in a short period.

Even a minor flaw may affect the function of the board drastically. So any defect that is found is replaced before the delivery of the circuit to the consumer. It helps to ensure that the circuit is built as per the specifications required and fulfils its purpose. Despite the high cost of designing and maintaining ICT, it is considered a powerful and accurate tool to measure the parameters of the circuit board.