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Directory of Functional Tests

Why do you need PCBA testing?

As one of the most important electronic products, the printed circuit board needs to go through a series of complex and tedious assembly processes to operate. For some complex electronic devices, there may be hundreds of components and thousands of solder joints on the PCBA board. While increased complexity allows for many new possibilities, it also increases the likelihood of failure. Electronic manufacturing technologies are always improving due to the gradual advancement of technology. As a result, devices and equipment are becoming progressively compact, with densification protruding. Furthermore, as components are reduced and Printed Circuit Boards are required to accommodate more electronic components in a smaller area on PCB results in greater density interconnections, resulting in the requirement for significantly higher product quality. To ensure that errors do not occur during these complex SMT and DIP assembly processes, it is especially important to test the PCBA, both before and after assembly. The purpose of PCB assembly testing is to detect PCB manufacturing failures, electronic component failures, soldering problems, and functional problems in time before mass production, in order to avoid damage to a company’s brand image. FS Tech has extensive testing capabilities to meet customer requirements. Expert testing team ensures defect-free, high quality and reliable products.

PCB Assembly Inspection Checklist

FS Tech utilizes advanced PCBA testing equipment to reduce incidents of failure and drive process improvement. Our comprehensive printed circuit board testing services include:

Visual Inspection

The purpose of PCBA Visual Inspection is to determine if the printed circuit board and PCB assembly  (PCBA) fulfill the customer’s requirements and related quality acceptance criteria using either the naked eye or optical equipment. Visual inspection is carried out throughout the design, production, and assembly stages. Visual inspection methods include: Manual Visual Inspection (MVI), Automatic Optical Inspection (AOI), Automatic X-ray Inspection (AXI).

Manual Visual Inspection(MVI)

Manual testing is an inspection method that relies on an experienced inspector to directly observe the circuit board with the naked eye or a magnifying glass. Manual visual inspection is the most basic type of PCB Assembly examination. To guarantee that all parameters were satisfied, the PCB will compare to the Gerber files. There are different types of issues based on the kind of board and the components on it.  As a result, visual inspection of PCB assembly is often just one of many testing steps in the production process.

A manual PCBA inspection can be done after the complete fabrication of PCBA is done, which might be beneficial. There is a thorough examination of PCBA for visual inspection. Mostly every manual visual inspection is carried out to check each and every aspect of PCBA in order to detect any defect that might present in PCBA. Normally PCB manual inspection checklist covers the following testing points:

  • Correctness, surface roughness, and thickness of PCB in PCBA.
  • Check PCB dimension according to requirements in PCBA.
  • Inspection of clearance and integrity of conductive paths on PCB.
  • Checking of solder bridging and open circuit.
  • Check for surface dents, scratches, or other defects.
  • Checking correct positioning and drilling of vias.
  • Checking other aspects like pad platting, toughness, dry-soldered, and coating quality.


  • Customers do not have to pay fees.
  • Exist throughout the production process.


  • Manual eye inspection is a low efficient and tiring method.
  • It has strong limitations and fails manual PCB Assembly visual inspection in more complex, denser PCBs.
  • In manual eye inspection there is a chance of human error and may cause defects in eyesight. The inspection effect depends on the inspector’s ability.
  • When visual inspection comes to PCB quality inspection then scratch, incorrect silkscreen, uneven solder paste and pads, and insufficient plating must have most of the attention, as all of these defects are mainly undetected by naked eyes visual inspection.
  • Some functional defects are hard to detect and data is not easy to collect.

Automatic Optical Inspection (AOI)

If an optical inspection machine carried out the visual inspection of PCBs in PCBA instead of manual  inspection then such inspection is known as Automated Optical Inspection (AOI) or automated visual inspection. AOI is a very advanced and precise technique that can identify a wide range of common faults in PCBs  and PCBAs. 

It is helpful in different phases during PCB fabrication. It is based on optical principles and comprehensively uses image analysis, vector imaging technology and automatic control technology to detect and deal with defects encountered in production. In order to improve the accuracy of detecting production mistakes, AOI employs high-resolution cameras and algorithms such as blob analysis, template matching, and object recognition. The program compares numerous photos of the PCB to a memory image of a golden board and flags any differences. Another way is to compare it to ideal design standards. AOI inspection is often used before and after reflow and before electrical testing to improve the yield of electrical handling or functional testing. At this time, the cost of correcting defects is much lower than the cost after final testing, generally more than ten times.

It is a faster technique as compared to a manual visual method and eliminates human mistakes. Just like manual visual inspection, this method can’t be used for such components which are placed out of line of sight or hidden underneath. This method  doesn’t help for some PCBAs with high electronic component concentration. 

Advantages of AOI System

  • Cost-effective: For customers, this testing service is included in the PCB assembly process, and customers do not need to pay for it. For factories, automatic optical inspection can save manpower and increase production efficiency.
  • Multiple inspection strategies: Provide comprehensive testing of bare boards, components, solder joints, solder paste printing, SMD quality and PCBA finished products.
  • Data collection capability: Collect inspection data in real time, and provide process analysis to enhance process capability.
  • Reliability: Fully automatic mechanical operation, avoiding the influence of human factors of manual visual inspection, can accurately find small and inconspicuous defects, and provide guarantee for large-scale orders.
  • Flexibility: The best part of AOI is that it can be applied and run at any stage of the process and as many times as needed.

Disadvantages of AOI Systems

  • Unable to detect circuit errors
  • The detection of invisible solder joints and double-sided soldered PCBs is powerless.
  • The detection effect of PCBA with high component density is poor.

Automatic X-Ray Inspection(AXI)

With the widespread use of SMT assembly technology (Surface Mount Technology), the complexity of PCB and PCBA also increased.  Mostly the aim is to mount more components in the smallest possible space on board and by doing so, it makes it difficult to carry on visual inspection either manually or automated. These challenges can be overcome by using x-ray inspection equipment. Automated X-ray inspection is primarily used to detect defects in ultra-fine pitch and ultra-high-density circuit boards, as well as circuit bridges, missing chips, misalignment, and other defects created during assembly. The inspection principle is to use the difference in X-ray absorption of different substances to inspect the part to be tested and find defects, for example, solder is made up of heavier material than components which means solder absorbs more x-rays and is more visible than components. Internal defects in IC chips can also be detected using tomography and is the only way to test the quality of ball grid array and solder ball bonding.

ICT Testing

There are several test methods, such as bed of needles tester and flying probe tester. Identify manufacturing defects with electrical performance testing and test analog-digital and mixed-signal components to ensure they meet specifications. The main advantages are low test cost per board, powerful digital and functional test capabilities, fast and thorough short and open circuit testing, programmable firmware, high defect coverage, and ease of programming. The main disadvantages are the need for test fixtures, programming and debugging time, expensive fixture manufacturing, and difficulty in use.

PCBA Functional Test (requires test modules)

Functional test is the earliest automatic test principle, which is a comprehensive test of circuit board functional modules using special test equipment in the middle and end of the production line to confirm the quality of the circuit board. Functional system testing is based on a specific board or a specific unit and can be done using a variety of equipment. There are final product tests, latest physical models and stack tests. PCBA functional testing generally does not provide in-depth data to improve the process, but requires special equipment and specially designed test procedures.

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