Inspection is a critical part of the PCB assembly process. Without it, electronics manufacturers would never know for sure whether the PCB—and therefore the device—would work properly. This could lead to a massive loss in sales, customers, and a big hit to reputation. Depending on the device, the result could even be harmful or deadly. To prevent such disastrous outcomes, PCB manufacturers incorporate various inspections throughout the design, fabrication, and assembly process.

Because PCBs have grown in complexity over the years, so too have inspections. As a result, professionals in the circuit board manufacturing industry can choose from a variety of inspection methods best suited to examine the board in question.

Before we dive into our inside look into inspection methods and techniques in PCBA, or printed circuit board assembly, let’s talk a bit more about why PCB inspections are so important.

The Importance of PCB Inspection

As stated above, if a PCB isn’t inspected, its performance is a gamble. The component could perform well, or it could fail to function from the get-go. PCBs need to be inspected multiple times throughout the production process to:

• Catch defects early, whether it be a short circuit or improperly placed electrical component.
• Uncover design flaws that went unnoticed during the design stage.

Once these defects or design flaws are discovered, technicians can take action to correct them, as well as note any potential mistakes to prevent them in the future.

The Benefits of PCB Inspections

In addition to a well-crafted circuit board, the benefits of PCB inspections are:

• Cost-savings. This benefit is threefold:
  • By inspecting circuit boards throughout production, technicians can halt the process to catch flaws. As a result, manufacturers avoid wasting precious time and money fabricating a useless product.
  • Customers will not demand warranty payments or institute returns for a quality PCB.
  • A quality circuit board will likely not cause injury or death as a faulty PCB would, sparing the company from expensive litigation.
• Consistent quality. PCB inspections ensure that all circuit boards are created with the same level of quality, no matter their function or complexity.
• Improve manufacturing processes. If a defect or design flaw pops up again and again, it could be a sign that something needs to be adjusted in the production process. Once the culprit is uncovered, processes could be changed to prevent that flaw or defect from appearing in the future.

Different PCB Inspection Techniques

There are a variety of different inspection methods that take place in the printed circuit board assembly process. These techniques include:

• Manual visual inspections
• Automated optical inspections
• Automatic laser tests
• X-ray inspections

Let’s take an inside look into the inspection methods and techniques in PCBA.

Manual Visual Inspections

Many times, PCB inspections use this method to start. During a manual visual inspection, a trained technician examines the circuit board with their eye or a magnifier. The technician will have a copy of the design documents with which to compare the board. This will help them determine whether all specifications are met and if there are any defects. They will also:

• Check for warpage
• Ensure that the board’s thickness and dimensions are correct
• Look for open circuits, burrs, solder bridging, pits, dents, pinholes, and scratches
• Inspect plating flux

When compared with other inspection methods, MVIs are simple, affordable, and quick to complete. The only caveats are:

• Having a technician with the expertise needed to perform the inspections properly
• Inability to inspect what the technician cannot see (ex. Hidden solder joints, minuscule defects)

Automated Optical Inspections

This inspection method is similar to MVIs with the exception of using a PCB inspection machine rather than a human being to analyze the circuit board. The machine uses light to illuminate the board, followed by cameras that take pictures or videos of the PCB. Special software then compares the footage with design specifications or a preapproved finished product. AOIs are best used for more complicated or high-risk circuit boards, as they can better detect flaws, defects, and damage.

Automatic Laser Tests

Automatic Laser Test systems use lasers to inspect a PCB and take measurements. These measurements include height, solder joint dimensions, solder joint deposition, and reflectivity. The collected measurements are then compared to design specifications or a preapproved completed circuit board. Any inaccuracies, flaws, or defects will be uncovered during the comparison process.

X-Ray Inspections

To better scrutinize complex circuit boards, manufacturers prefer to use X-ray technology. These inspections allow technicians to analyze smaller and more numerous components and chip packages, which often feature hidden solder connections. Technicians are also able to see bubbles in the solder work that wouldn’t otherwise be spotted. There are two types of X-ray inspections:

• X-Ray Fluoroscopic System: This inspection method uses a beam of x-rays to analyze solder work and uncover defects such as cracks, bridging, and misalignment.
• X-Ray Lamination System: This method allows technicians to inspect different sections of PTH and BGA solder joints.

How Is the Inspection Method Determined?

With so many different types of inspection methods available, technicians must match each PCB with the right technique. To do this, workers consider three factors:

• Defects: The particular defect(s) that the manufacturer or client is most interested in uncovering.
• Cost: Some techniques are more affordable and more expensive than others.
• Speed: Some techniques are quicker to perform than others. In applications that require high production volumes, automated techniques are best.

Manual visual inspections are ideal for simpler PCBs and clients who are on a tight budget. Automatic optical inspections, X-ray inspections, and laser tests are helpful for higher-risk PCBs, such as PCBs for medical, manufacturing, and automotive applications. X-ray inspections are also helpful for circuit boards featuring densely populated electrical components.

Other aspects to consider when determining an inspection method are:

• Analyzing solder paste volume
• Uncovering solder defects
• Determining component positioning
• Discovering warpage
• Finding short circuits
• Checking polarity

One thing to keep in mind is that manufacturers don’t always use one single inspection technique. Many times, they use numerous inspections throughout the production process. In one stage, a technician may use the manual visual method, while in another they may utilize an X-ray lamination system.