X-ray PCB Inspection and its classifications

Testing of PCB X-RAY

Area array packs, such as BGAs and QFNs, flip chips, and CSPs, have been popular recently in a variety of industries, including industrial control, communication, military industry, and aerospace, with solder joints hidden beneath the packages. Because of this, typical inspection instruments are unable to perform flawlessly in PCB inspection Furthermore, because PCBs have a greater density, with solder joints hidden and holes buried or blind, traditional test methods such as optical, ultrasonic, and thermal imaging are inadequate since the introduction of surface mount technology (SMT), which makes both packages and leads smaller.

Furthermore, with the rising downsizing of semiconductor component packages, the tendency of both present and future component miniaturization cannot be overlooked when considering X-ray inspection systems. X-ray is capable of entering into inner packaging and examining the quality of solder junctions, which is not possible with conventional testing. This is why it has been picked up.

X-ray examination, commonly known as automatic x-ray checking, is a technique for detecting hidden characteristics within a target object. X-ray examination is a commonly utilized approach to identify manufacturing mistakes, from the medical industry to aerospace manufacturing.

It's very common in PCB inspection because x-rays provide a great technique to check PCB quality and discover hidden problems without damaging the board. We'll go over what x-ray inspection is, how it works, and what the benefits are in this tutorial so you can figure out how to use PCB x-ray examination for your company's needs.

Why Are X-Ray Machines Becoming More Common in the Electronics Manufacturing Industry?

Over the last several decades, electronics manufacturing has become extremely advanced, with electronics in the industrial, communication, army, and aerospace industries progressing in ways that make inspection much more challenging. The following are some of the most prominent trends that have a detrimental impact on inspection:

1.  Placing of Parts: 

To reduce space and maximize functionality, equipment is becoming smaller and more stacked. As a result, many solder joints and components in electronics are being shifted to interior layers, either between PCB layers or hidden within the finished device.

2.  Size of parts:

 The downsizing of circuit board components is becoming more common. PCB components are projected to follow this trend as the requirement for more dense boards grows.

3.  Surface mount technology:

 Surface mount technology reduces the size of leads and packages, resulting in higher density PCBs with more parts buried between layers. Traditional inspection methods have become practically impossible to discover flaws thoroughly because of the increasing density, decreasing size, and more complex positioning of PCBs and their components. Due to the density of current PCBs, optical, ultrasonic, and thermal imaging methods are inadequate.

X-ray inspection, on the other hand, can acquire detailed images that these other technologies cannot. Because X-ray can penetrate PCB layers to inspect interior layers and packaging, it is more suitable for inspecting solder joints on complicated PCB assemblies. As a result, PCB examination using x-ray technology is becoming more common.

Working on X-Ray testing

To comprehend what x-ray PCB inspection entails, you must first comprehend how x-ray examination operates. All x-ray inspection devices have three basic characteristics:

1. X-ray tube: 

This tube is capable of producing x-ray photons.

2.   Platform: 

The operating platform allows the sample to be inspected from multiple angles and magnitudes by moving it in different directions.

3.  Detector: 

On the other side of the sample, the detector captures and gathers x-ray photons before converting them to an image.

X-ray imaging uses photons of x-rays that travel through a material and are captured on the opposite side. The physical qualities of materials, such as atomic weight, density, and thickness, affect how x-ray photons flow through them. Heavy elements absorb more x-ray photons and are thus easier to photograph, whereas lighter elements are more transparent. Because various materials act differently, photons collect in varying amounts on the other side of the object, resulting in a picture. A PCB's components are often made up of heavier elements, making them visible on an x-ray scan.

X-Ray Machine characteristics

PCB x-ray inspection systems can be classified into two groups. Systems can be 2D or 3D, and they can be operated locally or remotely. These are described in greater depth below:

1. Two-Dimensional system: 

A 2D x-ray system shows 2D images from both sides of the PCB at the same time, forming an image of the board's elements. This is comparable to how an x-ray is used to examine bone fractures in the traditional sense. Both online and offline operations are possible with 2D Systems.

2.  Three-Dimensional system: 

A 3D x-ray system can build up a sequence of 2D cross-sections to create 3D images of a PCB. In the medical field, this is analogous to how a CT scan works. The laminography approach, which combines cross-sections to build up a particular region or area, is also used in 3D x-rays. Due to the complicated techniques utilized, the CT approach can only be performed offline, but the laminography method can be performed both online and offline.

3. Operations that are done online:

 Certain x-ray machines are utilized online for data collection and comparison. This makes processing huge batches of complex PCBs much easier. However, having online capabilities slows down the x-ray machine, increasing costs and reducing capacity.

4.  Operations that are done offline: 

All x-ray devices can be used to perform panel and sampling inspections while not connected to the internet. Offline tools are often quick to use, however they are less cost-effective as item volumes increase. The number of goods checked the desired audit quality, and the amount of time available to complete the inspection process will all influence which system is best for your operation. Choosing a 2D or 3D system with online or offline capabilities will depend on the quantity of product inspected, the desired inspection quality, and the sum of time available to complete the inspection.

Benefits of QAQC

Metal appears black in x-ray images of PCBs, whereas other materials like glass, plastic, and ceramics seem translucent. Metal parts are easily visible as a result of this. This, when combined with magnifying capabilities, allows inspectors to see various metallic elements on a board during x-ray inspection of PCBs. Inspectors will be able to see numerous qualities of a printed circuit and discover a variety of potential issues using the x-ray, including:

1. Solder bridges

 On circuit boards, solder bridges are a prevalent issue. This happens when solder joints are too close together or when a connection is made where none should be. Solder issues are often obscured by neighboring components, making optical inspections difficult to detect, but x-rays reveal them quickly.

2.  Solder voids

 Solder voids are formed when gas or flux is trapped during soldering, usually as a result of solder paste contamination with water. These voids impair heat conductivity at the solder connection, resulting in physical faults as well as decreased reliability. Because X-ray is one of the only methods for detecting solder voids, it is critical to use it frequently to assure product and process quality.

3. Pin-hole fills

Circuit boards with insufficient pin-hole fill for through-hole connectors are a common

problem. These flaws can be detected utilizing X-ray equipment, which can also be used to quantify the amount of fill missing using coordinate measurements.

A ball grid array (BGA) inspection is one example of how x-ray is employed. A BGA is a surface mount device that makes connections with an array of metal spheres composed of solder. This device is widely used because it allows for high-density connections without complicating PCB design.

However, the problem with BGAs is that the connections are done on the backside of the chip. This property, combined with the density of the solder balls, makes soldering and de-soldering more difficult and increases the chances of generating solder bridges. BGA chip solder junctions are additionally challenging to check due to their position. By seeing through the gadget to see the solder joints underneath, an X-ray streamlines the inspection.

X-ray machines may be used to discover these issues and more thanks to magnification and the ability to vary the viewing angle. Even better, because, unlike medical imaging, operators do not have to worry about radiation dose during operation and can use the equipment for as long as they need it, all of these issues may be found during a single examination.

Conclusion

X-ray inspection technology, also known as Automated X-ray Inspection (AXI), is a technique that uses X-rays to inspect concealed aspects of target items or products. X-ray inspection is now widely employed in a variety of fields, including medicine, industrial control, and aerospace. In terms of PCB inspection, X-ray is widely utilized in the PCB assembly process to assess PCB quality, which is one of the most critical processes for quality-conscious PCB producers.