Critical Inspection & Quality Assurance of PCBs

Visual inspections focus on identifying physical imperfections in the PCB. However, just because these imperfections are visual doesn’t mean it’s an aesthetic inspection. Rather, these defects reveal clues about the functionality of the board in its final product.

Physical attributes like thickness, roughness, dimensions, dents, scratches, holes, pitch, and positioning are evaluated with visual inspection. Technicians can use microscopes or vision inspection systems to inspect dimensional aspects.

Electrical inspections assess the circuits, solder joints, and functionality of a PCB. These inspections involve tests that simulate future tasks for the PCB to ensure that it behaves as expected within a larger component.

MVI involves a technician inspecting a PCB with their naked eye or a magnifying glass. During the viewing, the technician manually compares a PCB’s joints and circuits with a design image.

An AOI system is automated PCB inspection equipment that uses high-definition cameras and diversified lighting options. The lighting is shone from different angles, brightnesses, and colors for a clear view of the PCB.

The camera, lighting, and integrated software work together to automate the visual inspection process. Instead of manual comparisons, the AOI automatically uses the design image to identify defects like missing components, misalignment, or solder joint issues.

This automated approach is crucial for finding issues that may be overlooked by manual inspection because of the limited optics. AOI equipment pinpoints surface, dimensional, and placement defects.

Automated Laser Test (ALT) equipment uses lasers for visual inspection. The laser scans the PCB and the laser is reflected. The ALT system then analyzes the reflection position and uses that to measure the PCB height and alignment.

X-ray inspection uses X-rays to look beyond the first layer. The X-rays inspect solder, delamination, and voids in a PCB.

Since the solder is made of heavy metals and the substrate is light silicons, the X-ray waves are absorbed only by the solder. The solder absorbing the rays allows for an internal look at a PCB.

A multisensor measurement system is an inspection device that combines optics, a touch probe, and a laser. These systems are used for PCB inspection because of the three-way expertise of combining the benefits of ALT and AOI with a probe. With these capabilities, multisensor systems are ideal for inspecting dimensions.

The design, circuit, and layer complexity of your PCB all play a role in your approach. Single-sided PCBs will not require as detailed examination as dual or multi-layer. Therefore MVI may be an appropriate approach for single-sided PCBs.

Multi-layer PCB inspection requires internal inspection that can’t be achieved with the naked eye or just a microscope. Because of the complexity, multi-layer PCBs are compatible with X-ray, AOI, ALT, or multisensor measurement systems.

Reviewing your production volume and its alignment with automated versus manual systems is crucial for your approach. Large PCB production volumes benefit from AOI, ALT, and multisensor measurement systems because of the complete automation. Smaller PCB production volumes may not require the same investment into an advanced machine.

Although it's tempting to choose the novelty of an X-ray machine, the newer technology comes at a high cost. Likewise, MVI is more budget-friendly but will not offer the same level of precision or expertise.

When choosing your approach and weighing options against a budget, consider multi-sensor measurement systems. Multisensor measurement systems combine ALT and AOI methodologies into one machine.

Considering industry tolerances is necessary for your inspection approach. Even if your PCBs are single-layered or simple, strict tolerance industries like medical devices or EVs will need an advanced system.