Several Test Methods For PCBA

Home | Events | PCBA | About Us | News | Contact Us

Currently, the PCBA test methods for PCBA assembly circuit boards in the industry can be roughly divided into three parts: AOI, ICT/MDA, and FVT/FCT. In addition, some people use X-ray full-line inspection, but it is not common. The following is a general discussion of the capabilities of these three PCBA test methods.

AOI (Automated-Optical-Inspection)：

With the advancement and maturity of imaging technology, many SMT production lines have adopted AOI. This inspection method relies on image comparison, which requires a Golden Sample to be recorded for reference. The image of the Golden Sample is used to compare with that of other PCB boards, which helps to determine whether they are good or bad. AOI can identify various defects on the PCBA assembly circuit board such as missing parts, tombstones, incorrect parts, offsets, bridging, and empty soldering. However, it cannot identify the solderability of the solder directly below the part, such as BGA IC or QFN IC, and it also has difficulty in identifying false soldering and cold soldering. Additionally, if the characteristics of a part have changed or there is a slight appearance crack, AOI may not be able to identify it. Generally, AOI has a high error rate and requires experienced engineers to debug the machine for a period of time before it becomes stable. Therefore, when introducing new boards, more manpower is needed to re-judge whether the problematic boards created by AOI are really problematic.

ICT/MDA (In-Circuit-Test/Manufacturing-Defect-Analyzer)：

Traditional PCBA testing methods involve testing the electrical characteristics of all passive components through the PCBA test point. Advanced PCBA test machines can even run a program to perform some functional PCBA tests. If most of the functions can be completed through a program, you can cancel the subsequent FVT (functional PCBA test).

PCBA tests can detect missing parts, tombstones, faulty parts, bridging, and polarity reversal. They can also roughly measure the solderability problems of active parts (IC, BGA, QFN). However, these tests are not sufficient for detecting empty welding, false welding, or cold welding problems, as these types of solderability problems are intermittent. They may pass if they happen to be contacted during the PCBA test.

One disadvantage of PCBA testing is that there must be enough space on the circuit board to place the PCBA test points. If the fixture is improperly designed, it can damage electronic components on the circuit board, and even the traces within the circuit board, due to mechanical actions.

The more advanced the PCBA testing fixtures are, the more expensive they become, and some can cost as much as NT $1 million.

FVT/FCT (Function Verification Test)：

The traditional method of functional PCB testing (FCT/FVT) is usually done in conjunction with ICT or MDA testing. This is because functional PCB testing requires actual power to the circuit board, and if there is a short circuit in the circuit above some power supplies, it can cause damage to the board being tested. In severe cases, it may even result in burning of the circuit board, which can be a safety hazard. Additionally, functional PCB testing cannot determine whether the characteristics of the electronic components meet the original requirements, which means that the performance of the product cannot be measured. Moreover, general functional PCB tests cannot detect some bypass circuits, which need to be considered. The functional PCB test should be able to detect solderability, faulty parts, bridging, short circuits, and other issues of all parts, except for bypass circuits. However, empty, false, and cold soldering issues may not be detectable.