PCB X-ray Inspection: The Importance of X-ray Inspection in PCBA

PCB X-ray inspection is one of the breakthroughs in manufacturing. It allows designers and engineers to detect defects. The defects could be in several parts of their components like BGA, soldering, and CSP defects.

X-ray inspection is a process for raw and advanced PCBs. Manufacturers combine x-ray inspection with functional testing. This process gives an accurate result with peace of mind during manufacturing.

During the mass production of various prototypes and complex boards, x-ray inspection comes in. With this technology, manufacturers can supply PCB components of high integrity to clients.

What is PCB X-ray Inspection?

We also call it Automated X-ray inspection (AXI). These are special rays with powerful electromagnetic waves and extremely short wavelengths. The wavelength is way shorter than that of visible light, less than 10 nanometers.

What makes x-ray find application in an industrial setting is the high penetrating power. An X-ray can penetrate a substance that visible light cannot detect.

Some of the properties of X-rays are:

• Ionization

• Penetration

• Heat

• Refraction

• Fluorescence, etc.

The penetrating effect of X-ray makes it useful in PCB manufacturing. With the penetrating effect, manufacturers can use it to detect faults and other hidden features in target objects. Today, many applications like medical, aerospace, industrial control, quality assurance check, etc. use X-rays.

PCB manufacturers today use x-ray for inspection. They use it to access the quality of PCBs – a crucial step towards quality PCB manufacturing.

In electronics manufacturing, we have seen a wider use of CSP, QFN, flip chips, etc. Designers made these parts with smaller inductance, better cooling capacity, and reduced surface area to meet design needs. Even though this met some design needs, there is the problem of inspection. The naked eye can neither judge the soldering quality nor detect faults in the design.

The high penetrating power of the x-ray solves this issue. Under high pressure, X-ray emits light that can penetrate the test subject. This reveals an image with various thickness and density. The image quality helps explain the quality of the joint.

How Does PCB X-ray Inspection Work?

Many industrial processes use an x-ray to inspect the internal layout of the PCB and other components. It helps determine the efficiency and identify faults in the design. This happens during the initial manufacturing stage and testing.

During testing or inspection, the designer positions the component between the X-ray machine and the detection component. The penetrating power of x-rays depends on some factors like:

• The energy of the x-ray

• The density of the material

• The material’s nuclear charge

Before the inspection, an X-ray machine can be set such that it considers the above factors. As a result, the detection component will give out a visual element of the filmed component. The film can either be a modern digital media or a traditional radiographic film.

The modern digital media could be direct digital arrays or phosphor screens.

We prefer modern digital media due to many advantages like:

• Impressive resolution

• High flexibility

• High contrast

• Saves time and conserves resources

Many X-ray systems have a fixture that allows user to hold and manipulate the subject. This allows the engineer to access the subject from a different angle. As the X-rays journey through the test subject, the rays will reduce in quality and intensity. This is due to the varying density in the test subject. The effect of this is various shades of light and dark areas on the detection surface.

This explains why a crack or crevice present in a solder ball will show up easily in an x-ray. Its visibility is because the solder has a greater density compared to air present in the crevice. As a result, the reduced density weakens the intensity of the x-rays. You will see the solder ball as the light area on the X-ray result since the density weakens significantly. The crevice will also show up as a dark crack where the x-rays' density was reduced experienced a little reduction.

Uses of X-ray Inspection in PCBA

Thanks to an improvement in technology, many industries use automated x-ray inspection. There are manufacturing processes where safety is paramount. As a result, there must be thorough checks of all parts that they produce.

These apply industries in the detection of impurities (glass, metal, sand) in processed foods. It also helps optimize processing and boost yields. For instance, food industries use it to determine the size and the perfect place for better slicing patterns for holes in the cheese.

When manufacturers want to produce an item in mass, X-ray inspection also applies. In the manufacturing of electronics, for instance, X-ray inspection can help detect defects early. As a result, manufacturers will not use a defective part in mass production. This leads to significant cost savings. It also saves companies from a soiled reputation that could arise from mass-producing faulty outputs.

In summary, here are the benefits

• Manufacturers get feedback on their products as early as possible. This allows them to know if the materials are compromised. They can also detect if the integrity of process parameters gets compromised.

• Designers will not have to build on defective parts. As a result, they get to save unnecessary costs.

Techniques in X-Ray Inspection

There are two primary techniques used for the X-ray inspection system for CSPs and BGAs. These are the 2D (two dimensional) system and 3D (three dimensional) system.

2D Transmission X-ray:

This process generates x-rays at a single point. The x-rays then pass through the PCBA. This process triggers an image on the electronic detector. You will get the image in a digital format on a computer after it completes the analysis.

Designers use this technique for single-sided boards and assemblies where accuracy is of utmost importance. The medical field uses this principle where an X-ray to inspect the condition of a fractured bone. Similarly, the 2 D x-ray system displays the entire component's 2D image from both sides of the PCB.

3D X-ray Transmission:

Engineers use 3D X-ray transmission for complex double-sided PCBs. 3D X-ray inspection needs two essential components: the detector and the X-ray source. The detector undergoes a 180-degree circular movement.

The idea of a 3D X-ray transmission is to generate images of various cross-sections. It does this by reconstructing series of 2D images. The X-ray focuses on a single feature at once. It blurs the components of other features like soldering joints. As a result, 3D X-ray transmission allows you to dwell on a specific component of interest at a time.

X-Ray Inspection: How It Works

The test sample absorbs the X-ray coming from the automated X-ray tube. There is a detector on another side of the machine. As a result, the detector provides the optical image from the camera. It also transfers the X-ray to visible light.

The test subject has various density, atomic weight, and composition. As a result, the degree of the absorption of the rays differs significantly. This will reflect a unique image on the receiver. Thus, places with higher density will reveal a clear shadow image. This happens because the absorption of the X-ray is stronger at this point.

The designer can increase or decrease the image's size. This depends on the distance of the X-ray tube to the image.

Application of X-ray Inspection

The use of X-ray inspection is to detect various faults and defects in the manufacturing of PCB. Here are some flaws PCBs help take care of the following:

• Soldering Defects: With X-ray inspection, manufacturers can detect countless soldering problems. Examples are solder bridges, open circuits, excess solder, cold soldering, poor soldering, insufficient soldering, solder shorts, solder voids, etc. They can even access the soldering quality.

• Component Defects: X-ray inspection also helps check component defects like lifted leads, faulty components, misplaced components, and missing components.

• CSP and BGA defects: The complexity of various BGA components and CSP components makes them invisible to the naked eyes. With advanced X-ray inspection, designers can detect defects like open circuit connections, soldering bumps, and BGA connections.

Conclusion

The introduction of X-ray checking in PCB is a breakthrough. It helps detect faults early in the manufacturing process. This saves the company in many ways. It also guarantees the integrity of every manufactured component.

In conclusion, here is a comprehensive guide to PCB X-ray inspection and its application in the manufacturing industry.