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How to Use X-ray for PCB Inspection?

In this blog post, you’ll read:X-ray test is used to detect the sample that cannot be detected by the appearance of the position. X-ray penetrates the material of different densities due to the change in its light intensity. The resulting contrast effect can form an image to show the internal structure of the object to be measured.

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During the manufacturing process, PCB failures can be very frustrating. This becomes even more frustrating when it is hard to detect what defect is causing these failures. Finding the right inspection machines will help reduce the time it takes to identify and rectify defects thus reducing the frustration caused by the defect.

X-ray PCB inspection is one of the methods that you can efficiently inspect your PCBs for defects. The x-ray’s ability to look for defects even where they are hidden below other layers makes it the most effective way to inspect PCBs for defects. In this article, we will share how the x-ray inspection works, what benefits it will bring to your manufacturing processes, and how to select the best machine for your type of operation.

 

Why X-ray Inspection are Becoming Popular in Electronics Manufacturing

 

X-ray inspection is becoming popular among manufacturers as it can address defects arising due to innovations in electronic manufacturing. This coupled with the fact that it provides for faster inspection with fewer damages to other components means that more manufacturers are preferring it to other inspection methods. Innovations such as smaller PCB components mean that manufacturers can mount more of these components on the PCB. With more components on the board, traditional inspection means will likely miss defects such as poor soldering and missing components as these may not be visible on the surface. X-ray inspection allows you to have a better view of all components of the PCB, even those that would be hidden to other methods such as visual inspection.

On the other hand, the major defects on PCBs would be very hard to detect visually. These defects include misaligned or missing components and excess soldering or poor soldering resulting in solder bridging. Most of these defects are minute and would require invasive methods to confirm and this could lead to damage to other components of the PCB.

 

Advantages of Using X-ray Inspection Equipment

 

Using x-ray inspection provides visibility to the internal composition of solid or compact materials. The process can be applied in the pre-production, production, and post-production of electronic components. In pre-production, x-ray inspection is useful in selecting good-quality material to be used during production. Ensuring that only good-quality materials used in the final product will save you money in the long run. This is because there will be fewer defects in the finished product and therefore fewer returns.

During the production process, x-ray inspection ensures that only good-quality products are released to consumers. X-ray inspection systems can detect faults in densely populated boards. Using x-ray inspection ensures that there are no shadows in the way, and this means that all the components of the board are inspected. The x-ray system is important in the inspection of solder joints, especially where the joints are masked by other components.

 

The role of printed circuit board (PCB) is to provide electrical connections for electronic components. The advantages of PCB include reduction of assembly and wiring errors, automation improvement, and production of labor rates. Depending on the number of circuit board layers, it can be divided into single-sided, double-sided, four-layer, six-layer, and other multilayer circuit boards.

 

Seven Inspection Methods in PCB Manufacturing

To ensure the production quality of PCB boards, there are seven inspection methods during the production process. Each inspection method targets different PCB board defects. Let us go through these methods one by one.

 

① Manual Visual Inspection

This is the oldest visual traditional method to determine the failure of the circuit board using magnifying glass or calibrated microscope. Here, you can predict when the correction is required. The advantage of this method is the low cost. The disadvantages include high long-term costs, human subjective errors, difficulty in data collection, and discontinuous defect detection.

pcb x ray inspection

 

② Online Test

This electrical method detects manufacturing defects and tests analog, digital, and mixed-signal components using a needle bed tester and flying probe tester. The major advantage of this method includes low test cost of each board, fast and thorough short and open test, programming firmware, strong digital and functional test capabilities, high defect coverage, and easy programming. The disadvantages include the need to assess fixtures, programming and debugging time, the cost of making fixtures, and the difficulty of using them.

 

pcb x ray inspection

 

③ PCB Board Function Test

This method tests the functional modules of the circuit board at the middle stage and the end of the production line using special test equipment to confirm the quality of the circuit board. There are two types of functional testing namely the latest solid model and stack testing. This method does not provide in-depth data such as foot-level and component-level diagnostics for process improvement and requires specialized equipment with a well-designed test process. Since it is difficult to write functional test programs, it’s not suitable for most circuit board production lines.

PCB board function test

 

④ Automatic Optical Inspection

This method confirms manufacturing defects using a combination of image analysis, computer, and automatic control technologies. This test is done before the electrical testing to improve the pass rate of electrical processing or functional testing. Hence, the cost of correcting defects is much lower than the cost of the final test.

x ray circuit board

 

⑤ Laser Detection System

 This latest method uses a laser beam to scan the printed board, collects all measurement data, and compares the actual measurement value with a preset pass limit value. Since this method works on light boards, it is also considered for assembly board testing at speeds sufficient for mass production lines. Its major advantages include fast output, no fixtures and visual unobstructed access. The disadvantages include high initial costs and maintenance issues.

x ray circuit board

 

⑥ Size Detection

This method measures hole size, length and width, position and other dimensions accurately using two-dimensional image measurement since PCB is small, thin, and soft.

 

⑦ Automatic X-ray Inspection

This method is used to detect defects such as ultra-fine pitch and ultra-high-density circuit boards and bridging, chip loss, and misalignment during the assembly process using high-definition X-rays (PCB X-ray machine). Using tomography technology, it can also detect IC chip internal defects. This is the only method to evaluate the soldering quality of ball grid arrays and shaded solder balls. Its major advantages include no fixture costs.

 

Automatic X-ray inspection

 

Hence, it’s mandatory to ensure the quality of PCB by inspecting them during the production process. Right inspection at the right time can maximize efficiency.

 

How PCB X-ray Inspection Works?

To be able to appreciate the importance and benefits of x-ray inspection, it is important that you first understand how PCB x-ray inspection works. Materials tend to absorb X-rays in proportion to their atomic weight, thickness, atomic number, and density. X-ray board inspection is possible due to this unique characteristic of X-ray. Heavier elements on the board will absorb more X-ray and are therefore easily imaged, while lighter materials absorb lower amounts of X-ray and appear lighter on the X-ray image.

All X-ray Inspection machines are made of the following basic components:

  • X-ray tube. This tube generates X-ray photons.
  • Sample operation platform. The platform moves around with the sample so that it can be inspected from different angles.
  • A detector. The detector collects the x-ray photons after they have gone through the sample and transforms them into an image.

During x-ray circuit inspection, the image developed is checked for defects by comparing the result to the expected standard. 

 

Benefits for Quality Control and Superior Quality

X-ray inspection can help identify defects on complex boards and offer more insights compared with other inspection methods. This is because an X-ray can go through chip packages and see any interior defects. The inspection process produces images that can be magnified for closer inspection which allows for the detection of even the most minute defects.

Incorporating an inspection step during the pre-production process can save you money as only good products that have passed the inspection process will be mass-produced. Regular testing during the production process can also help identify process gaps that need to be improved for a better final product. Some benefits of having a good quality control process are discussed below:

  • Quality Assurance. The inspection ensures that only good quality components and equipments are delivered to the consumers. This inspection guarantees the premium product quality. 
  • Consumer Protection. Some defects on electronic components and devices can cause damages that affect the consumers. The defects can cause damages such as fire and injuries to the users.
  • Recall Prevention. Inspection of the PCB for boards will help reduce the number of machines that are sent back due to faulty components. This also helps protect the brand as it is associated with good quality machines with few recalls and manufacturer faults.
  • Regulatory Compliance. Many regulators will inspect samples provided by manufacturers to test for any defects on the product. The test is done during the production process, which ensures that none of your products are flagged by regulatory bodies as faulty. 

 

Can You List the Major PCB Defects?

The inspection process is critical in any manufacturing process. Early detection of defects can help you save money by reducing faulty components and customer returns. Some of these defects that can cost you significant amounts in returns and repairs are the following:

 

– Soldering Defects

One of the main soldering defects is solder bridging, this occurs due to the inability to separate solder on two or more leads before the solder solidifies. Solder bridging can be because of several factors including, closely spaced pins, poor fluxing, the high number of components on the board among others. This can be especially hard to notice where the board is densely populated. Left unchecked this will result in damage to the entire board.

Another common soldering defect on the board is open solder joints. This mostly occurs due to the separation of the PCB pad and the component lead. However, it can also occur due to lack or inconsistency in the solder paste application.

Performing a solder x-ray can help identify the presence of any defects caused by either open solder joints or solder bridging. Early detection of either of these defects can help come up with better soldering processes to reduce defects. 

 

– Missing Components

Several factors can lead to missed components on the board. These include vibrations on conveyor systems, poor places solder and bent leads. Components can also be misaligned and therefore placed in the wrong position on the board. This mostly occurs during the reflow process as the components flow with the molten solder and settle on the wrong position when it solidifies.

To avoid component shift during PCB manufacturing, it is advisable to maintain the correct humidity levels and temperature during the soldering process. It is also important to reduce the number of movements during the reflow process.

The X-ray inspection process can help identify both missing and misaligned components. The image produced can be compared with that of a complete board to identify any gaps and make corrections. 

 

– Wire Breaks

It is hard to pinpoint the location of a broken wire on the board especially where the board is densely populated. A broken wire will cause the board not to work and this can be the major headache to the manufacturer. X-ray inspection is used to identify the exact location of the broken wire, and this can help identify the cause of the break. Identification of the cause of break can help you adjust the manufacturing process, ensuring that new boards do not have the same defect. 

 

– BGA & CSP Defects

The ball grid array is a surface mount component that uses different metal balls to make a connection on the board. The BGA is popular as it enables high-density connections on the board without having to complicate the layout of the PCB.

The BGA makes connections on the underside of a BGA chip, which increases the likelihood of making solder bridges. The locations of the chips make it extremely difficult to inspect and make corrections. BGA X-ray inspections make it possible to inspect these types of connections and make the necessary adjustments.

The Chip Scale Packages (CSP) are designed to optimize the space on the PCB while keeping manufacturing cost low. 

 

Factors to Consider when Choosing PCB X-ray Machine

Acquiring a PCB X-ray machine can be challenging, especially when doing it for the first time. To be able to get the machine that works for you, it is important to consider the following factors: 

 

– Performance of Core Components

X-ray inspection machines are designed to work on different materials ranging from metals to foods. It is therefore important to choose a machine that is designed for the task that you want to use it for.

An X-ray machine designed to inspect PCBs should be able to penetrate different types of material including solder, flux, and the metallic components of the board. It is therefore important to ensure that the x-ray machine is designed for pcb inspection.

The main components will determine how many angles the sample can be inspected from. It is therefore important to ensure that the component can turn to allow for inspection of the sample on all sides. The main component also determines the quality of the image that is produced after your board is inspected on the x-ray machine. A high-resolution image is important as it is easier for you to inspect any defects. 

 

– Safety of the Machine

X-ray inspection machines produce X-ray photons that are harmful to you if exposed to high doses and over a long period. It is important to check that the device that you acquire is of the highest quality and safety standards. The machine that you select should be able to produce X-rays that are direct to the item that needs to be inspected without the rays leaving the machine.                                                                                                                                 

The x-ray machine should also be correctly calibrated to avoid using more or less power than what is required. This can cause damage to the sample being tested or produce incorrect results.

 

– Legality of Software

The X-ray inspection machine comes installed with software that allows for user interactions. The software allows for the user to make changes to how they want the inspection done. This includes determining how many angles the sample is tested, how many D’s the image is returned, and what type of material is being inspected. It is therefore important to ensure that when acquiring an X-ray inspection equipment, the software installed is of good quality and legally installed on the equipment.

 

–  Performance of Software

The performance of the software on the x-ray inspection device can be the difference between a good and bad user experience. Software that is working correctly will take in the users’ requirements and have the machine work on them thus providing the expected result. On the other hand, software that is not working correctly might lead to the misinterpretation of user commands leading to the machine performing the wrong tests. Good software can also be used to automate repetitive processes thus helping you to save time. 

 

– User-friendliness of Software

A good device should come installed with software that is easy to use. Hard-to-use software will mean that users take more time figuring out how the x-ray machine works as opposed to using it to do the necessary tests. 

 

– Price of the PCB X-ray Machine 

The technology behind X-ray inspection equipment is still relatively new. This coupled with the expensive software and component parts used to make the device can result in them being highly-priced. The technology is however proven to be important in the manufacturing process and it is, therefore, an important device to have.

Before deciding on which machine to buy, it is important to have a checklist of all features that you need the device to have. This allows you to compare prices across machines that have similar features. The price must tend to be higher for machines that have more features and uses. 

 

– Warranty and Support 

 

The X-ray inspection equipment requires expert knowledge to repair. It is therefore important that you ensure that the device you acquire is covered by the manufacturer under warranty and that they can also provide spares and service of the devices after the device is out of warranty.

 

Conclusion

Inspection is an integral part of producing good quality products for the end-users. Having X-ray PCB inspection devices will help ensure that your electronic devices are of high quality and safe to use. The inspection device can be the difference between a company being associated with poor or good quality products. It is therefore important to invest in a good quality device that will help improve your inspection process.