Understanding the Situation PCB assembly inspection and testing options With the advancement of technology and the increasing complexity of PCBA, careful consideration must be given to the testing and inspection options for these boards. PCBs are critical components expected to function properly in various environments. Appropriate testing procedures and inspection measures are necessary to maintain product quality and reliability. Benefits of PCB Inspection and Testing Having a reliable contract manufacturer is a key step in successfully building circuit boards. The company takes pride in delivering high-quality products to its customers. This is achieved through years of repetitive PCB assembly and manufacturing processes. We pay close attention to preventive measures and pre-construction steps rather than discovering issues later and fixing defects through rework. Our experienced and commonly used inspection and testing methods include: Visual inspection Automated optical inspection X-ray inspection First article inspection Online testing Functional testing Aging testing PCBs come in various shapes, sizes, and quality requirements. They can be rigid or flexible, single-sided or double-sided, multi-layered, and so on. The industry also uses three "classes" to classify PCBs and PCBA. They are Level 1, Level 2, and Level 3, with Level 3 being the most quality-sensitive and requiring special attention. Printed Circuit Board Assembly As the class requirements increase, the complexity of inspection and testing methods also increases. PCB manufacturing and assembly require a unique set of inspection and testing methods to manufacture circuit boards according to specifications. Visual Inspection The basic form of inspection is visual inspection. This is done by having technicians inspect the circuit board with gold plating, material lists, and prints. Then, specialists check for various errors such as wrong components, missing components, solder bridges, solder leakage, tombstone defects, etc. Equipment that can be used includes magnifying glasses, high-magnification microscopes, and, of course, good lighting devices. Since this method heavily relies on the operator, it can be time-consuming for large and complex circuit boards. This is mainly done afterward, but it is important to visually inspect the circuit board throughout the manufacturing process to validate procedures and programs. After SMT placement, inspection can identify issues such as missing or misaligned components and solder paste problems. The company provides high-power lighting sources and glare-free illumination for our operators to thoroughly examine the PCBA under inspection. Each lens has an adjustable high-magnification lens to minimize eye fatigue.

Automated Optical Inspection (AOI)  

Automated Optical Inspection (AOI) uses high-resolution cameras and software to capture manufacturing errors. The software essentially compares multiple images of the inspected circuit board with a "golden" board image stored in its memory and marks any differences.

These machines can be placed on the entire SMT production line. Inspection after the reflow soldering stage can identify soldering defects such as dry joints, solder bridges, insufficient wetting, tombstone defects, and more. Operators can then make finer adjustments to preceding stages based on the machine's feedback to minimize defects.

Although AOI technology has made significant progress, it still has some weaknesses. On one hand, AOI is not adept at through-hole components. It can capture many through-hole errors, such as component errors or absence, but height variations, shadow projections, and hidden components may limit AOI's effectiveness. Programming also takes some time, adding extra overhead.

X-ray Inspection X-ray inspection is required for components with hidden leads. Beneath the BGA, there are arranged pins that cannot be visually inspected after soldering. X-ray is used to inspect whether all leads are correctly soldered.

First Article Inspection To validate procedures and components, OEMs often require a first article inspection of the product. The company's fixed asset investment plans differ. Some require the CM to verify the completion of FAI in written documentation, while others request the actual article for approval. It is crucial to communicate with the CM to check all the necessary checkboxes, no matter what you deem necessary.

Online and Functional Testing Online Testing: This testing form requires a custom fixture, commonly known as a bed of nails. Typically, several spring-loaded metal probes are assembled in an array on an insulated bed. If ICT testing is considered a critical form of testing, it is usually planned during the design stage, as it requires the designer to place test pads in critical locations on the PCB's bottom layer copper traces.

The test instrument places the assembled PCB onto the probes to electrically connect it to the test pads. Sometimes it is done manually or built-in within the fixture. The test then checks various parameters, such as resistance, capacitance, and inductance between specified probes, and marks any deviations from established standards.

Functional Testing: This method can vary significantly. It essentially simulates on-site equipment. The test procedure is created by the OEM and handed over to the CM for execution. It typically involves a power supply and multiple inputs to ensure the circuit board functions as expected.

Aging Testing Aging testing simulates real-life conditions. PCB components are subjected to elevated temperatures for 24 hours and held for a specified period. After cooling, the board should not exhibit any expected performance issues. This can be validated through functional testing or ICT.

Our Inspection and Testing We provide inspection and testing methods here based on customer requirements. Whether your PCB requires multiple forms of testing or a few, our experienced team is here to assist you. We provide detailed explanations and share a guide to PCB assembly inspection and testing options, testing procedures, and inspection measures to maintain product quality and reliability in the PCB manufacturing process.