Why is a PCB visual inspection important?

Consumers and businesses expect their Printed Circuit Boards (PCBs) to perform well. Whether the PCB will be used in a smart TV, the safety systems in an automobile, or avionics in an aircraft, PCBs across industries need to be operational.

This is why PCB inspection is critical at all stages development in every industry. PCBs should be inspected after design and first build all the way to the manufacturing and assembly process. Inspection after the design stage ensures that the PCB works well and is ready for production. Inspection after manufacturing and assembly stages helps identify flaws in the processes, preventing further production of inoperable PCBs. Overall, thorough inspection saves future headaches and costs.

PCB Inspection

After assembly at any stage of the process, PCBs are often visually inspected. Visual inspection can happen in three different ways. PCBs can be inspected manually or automatically.

Manual PCB Inspection

Manual inspections are the backbone of the inspection process, often serving as the final check before packaging the PCB for storage or shipping. While multi-layered or more complicated PCBs typically require further testing, simple, single-layered PCBs may not require testing beyond manual inspection.

  • An inspector typically views a PCB under good light or a light microscope during a manual inspection. The process includes cross-checking the PCB against the design specification. After that, the PCB is checked for defects like poor soldering or missing parts. Some common things to check for during a manual inspection include:
    • Making sure the PCB has the correct dimensions. The dimension check should include the components on the PCB. Are they in the correct place? Are they the correct size? Does their placement near electrical connectors appear right?
    • Checking the surface of the PCB for pitting and any warps. A deeper analysis of the pitting, warps, scratches, pinholes, etc., is usually completed when imperfections are found.
    • Check the quality of the coating and make sure the plating flux is firm, even, and in the right position.
    • The PCB should also be checked for the clearness and integrity of the conductive patterns. The integrity of the solder bridging should also be checked to make sure there are no open circuits, voids, or burs.
    • Vias should also be checked for their existence, size, and positioning.
    • Check the pad plating for bulge defects, roughness, and brightness.

Manual inspections are advantageous for their low cost. As mentioned above, you need very little equipment to carry one out; the critical part is having an inspector that knows what to look for. On the other hand, this type of inspection might not be enough for a PCB that contains layered components that cannot be seen with a microscope or good light.

Automated PCB Inspection

An automated inspection involves an inspecting system designed to inspect PCBs. The system is usually comprised of a computer, a PCB reader, different types of light, and a camera. The system takes photos of the PCB in question, compiles them, and then compares them to a set of rules or specifications.

Automated inspections can be faster than manual ones; they also remove the chance of human error. They also can perform 2D and 3D types of inspection. Automatic inspection equipment is well-established and reliable but costs quite a bit more than a few handheld lights and tabletop magnifiers.

One alternative light source includes lasers. These units are typically separate from common automatic inspection systems. A laser-powered system accurately assesses PCBs by measuring the reflected beam’s intensity. This type of system works well for understanding the PCBs solder deposition, alignment, clarity, viscosity, and more. The only drawback to laser inspection is that the system needs to be calibrated for each PCB to prevent errors from interference or shielding and can be time-consuming.

Automated x-ray inspection is best for more complex and layered PCBs. Because x-rays are absorbed in proportion to atomic weight, lighter components appear less dense, and multiple layers can be inspected simultaneously. X-rays are the only way to properly inspect Ball Grid Array (BGA) components where all the leads are under the component.

Additionally, x-ray analysis is not complicated by light diffraction or shadows, reducing errors introduced by light-based automated systems. However, x-ray analysis is fairly new and expensive.

Which Inspection Method is Right For my PCBs?

Many PCB designers and manufacturers start with manual inspections. Once they reach a capacity or complete level that requires automation, they might choose to go in that direction. Inspection services are also available for a second opinion or assistance with a new PCB or manufacturing method.

Where to Find Your Inspection Supplies:

You can find manual inspection supplies at TestEquity. TestEquity is known for carrying top-of-the-line inspection products including microscopes from Unitron, Scienscope, and OC White, as well as magnifiers from Aven, Daylight, and Vision Luxo. TestEquity also carries Optica and Dino-Light portable lights, and Daylight and OC White task lamps. What’s more, TestEquity’s knowledgeable technicians are available to answer questions about all your PCB inspection needs and offer their brand-agnostic expertise. Visit TestEquity today.