PCB X-ray Inspection
Most quality products that are available in the market today are because of quality inspection. The quality inspection eliminates the unnecessary cost, time wastages, and failures. It also improves an organization’s reputation and client’s trust. Hence, partnering with a reliable PCB manufacturer with High-quality standards of X-ray inspection is vital. This is what UNI X-RAY offers.
An understanding of quality control with excellence is at the core of our services at UNI X-RAY. We have full-service solutions for inspection and testing with our X-ray inspection station with image identifiers, an x-ray source comprising digital controls, and an X-Y table for fine-tuning. UNI X-RAY cuts across various industries to make available industry-standard PCB test at your demand.
UNI X-Ray delivers inspection as a standard service with PCB manufacturing and a reputation for providing consistent quality. UNI X-RAY can supply all your PCB manufacturing needs.
Defects detection type
- shorts caused by solder bridging between the balls,
- tilted BGAs,
- BGA voiding,
- insufficient/excess solder,
- BGA missing balls,
- BGA poor wetting
- BGA misalignments.
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Why Global Clients Choose Us?
18 Years of Expertise
We have over 18 years of experience that specializes in X-ray Technology.
Excellent Image Quality
Uni X-ray produces X-ray machines that offer excellent and ultra-sharp image qualities.
High Degree of Safety
Our X-ray machine is one of the safest choices you can make because it ensures maximum safety.
Uni X-ray produces machines that have an easy mode of operation.
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About PCB X-ray Inspection You Should Know
For the last few years, area array packages or devices such as QFNs, BGAs, CSPs, and flip chips are extensively used in all sectors like industrial, aerospace, military industry, communication, etc., where solder joints will get hidden under the package. Hence it will not be possible for traditional inspection devices to inspect PCB devices with more accuracy. Additionally, the appearance of surface mount technology (SMT) that helps in making both leads and packages become smaller. Components like PCBs have got more density with their hidden solder joints and buried holes.
Hence, the already prevailing traditional inspection methods such as optical inspection is not enough. This is where X-ray machines play a vital role to inspect the manufactured components in detail.
X-ray inspection technology is otherwise called as automated X-ray inspection. This technology can find unseen features in any target object. Starting from the medical sector to aerospace manufacture, X-ray inspection is widely used to detect manufacturing errors. Compared to other inspection methods, X-ray can effectively penetrate into the inner packages, and inspect the quality of those hidden solder joints.
When it comes to PCB inspection, X-ray test is vastly carried out during the PCB assembly process to test the quality of PCBs. This is one of the major steps carried out by the PCB manufacturers to assure its quality. It can quickly and accurately detect the hidden defects without causing any damage to the target object.
Hence with the rapid increase in miniaturization of semiconductor components, it’s better to consider an X-ray inspection system.
Before understanding the importance of an X-ray test in PCB inspection, you first need to know how X-ray inspection works.
All X-ray inspection devices are composed of three basic features:
- X-ray tube to generate X-ray photons
- Operation platform to move the given sample in varied directions so that it can be inspected from all angles and magnitudes.
- A detector located on the other side of the sample to catch and collect X-ray photons and convert them into an image.
X-ray imaging test works with the help of X-ray photons, which are passed through the target material kept on the operation platform. The resultant rays will be collected on the other side through a detector, which results in an image formation. Based on the differential absorption principle, the X-ray photons pass through the target object in a differential manner depending on its physical properties, such as density, atomic weight, and thickness.
Usually, heavier objects absorb more X-rays, so that they can develop into an image, whereas lighter objects are more transparent. Since different objects has unique characteristics, different amounts of X-ray photons are collected on the other end of the target object, to form a final image.
Since the components in a PCB consist of heavier elements, it is easier to view their internal parts on an X-ray image.
The attributes such as an increase in density, size reduction, and intense complexity of PCBs and their components have made it nearly impossible for traditional inspection methods to detect intricate defects thoroughly. The traditional inspection methods such as optical, ultrasonic, and thermal imaging methods are relatively not effective in inspecting the components especially PCBs. This is where an X-ray inspection test can take detailed images, compared to other tests.
- The X-ray beam can penetrate every layer of PCB to check the inner layers and packaging. Hence, it can accurately inspect the solder joints of complex PCB assemblies.
- X-ray inspection in PCBs helps you to take the final call in terms of the quality as well as measurement criteria.
- PCB X-ray test helps you to inspect solder voids and anomalies like non-wetting solder balls, and take measurements.
- Other applications of these X-ray test include the determination of the hole in solder joints without performing any destructive test like cross sectioning.
X-ray inspection tests can study the wetting features of solder on pads beneath a component as well as the characteristics that remain hidden due to the high density of the printed circuit board (PCB).
PCB X-ray machine can be used to inspect the following components:
- Electrical and electronic components for lifted ball bonds, broken wedge bonds die attach, and wire sweep
- Populated and unpopulated PCBs
- Find surface mount defects such as solder joint porosity, misalignments, as well as bridging
- Non-lead solders
- A detailed study of vias through multi-layer alignment and hole plating
- CSPs and BGAs
The below listed seven parts are required to build a basic PCB X-ray machine:
- X-ray tube to produce X-rays
- Vacuum System where the X-ray tube should be operated
- Loading table or sample operating table to place the sample and move them during testing
- High Voltage Generator to produce high voltage 90-130 KV and power to the entire system
- Overhead power line
- Lead room having two layers of stainless-steel plate + 6 to 8 mm of the lead plate (Feinfocus) to prevent X-ray discharge
- Detector to determine the intensity of X-rays and produce black and white signal through the computer.
The major parameters of a PCB X-ray inspection machine include:
- Geometric magnification, with the optical magnification
- The total magnification that can enlarge the photo digitally via the computer, followed by an in-depth observation.
- Anti-collision design
- The more the shafts, the better will be the precision
- 360-degree plane rotation
- Sample holder
- Radiation protection to prevent leakage
- As per the international standards, the permissible level of radiation leakage will be less than 1µSv/hr.
X-ray inspection systems for PCBs, BGAs, and CSPs are divided into two categories. The inspection systems may be 2D or 3D, which may be operated either online or offline. Let us go through them in detail:
- 2D X-ray inspection system:
It shows the two-dimensional images from both sides of the PCB at the same time, thereby delivering a clear picture of the board’s components. This mechanism is similar to the traditional medical X-ray, which was used to view the bone fractures. These 2D systems can be operated either online or offline.
- 3D X-ray inspection system:
It creates the three-dimensional image of a PCB by forming a series of 2D cross-sections. This mechanism is similar to the CT scan used in the medical industry. This system also works using the laminography method, where it combines the cross-sections and eliminates the images from other sections to build up a specific area precisely. The CT method of the 3D system can only work offline due to its complex algorithms. But the laminography method can be used both online and offline.
- Online X-ray inspection system:
Several X-ray devices are used online for data collection and comparison. Most of these devices are put after the reflow oven. Hence, it will be easier to process enormous quantities of complex PCBs, based on the additional cost and safety elements. However, the online operations will slow down the efficiency of the X-ray machine, thereby consuming more time and expenses. It is the slowest part of the assembly line, where the ability of the fabrication line becomes low.
- Offline X-ray inspection system:
All types of X-ray devices can be operated offline to achieve panel inspection and sampling inspection. This operation type is comparatively quick to run. It is possible to inspect PCBs conveniently at any stage in the assembly line. Hence, it is less cost-effective with higher productivity.
Selecting the perfect system for your operation must be done carefully. Opting for a 2D or 3D system with online or offline abilities usually depends on the measure of the target product inspected, the expected quality of the inspection, as well as the quantity of time required to complete the inspection process.
The X-ray inspection system with CT function is usually operated offline due to the requirement of more 2D images and complicated algorithms. Hence, this CT X-ray inspection system is used only in the less significant professional research areas. Other 2D and 3D systems were instructed with the best image at the least time in order to cut the cost of the inspection.
There are three types of X-ray tubes listed below:
- Open X-ray tube (open tube)
- Need regular maintenance
- Possess longer life with long-lasting performance over time
- Can self-calibrate
- Filaments and targets are the consumables
- X-rays will be transmitted through the target
- Conventional enclosed radiographic tube (closed tube)
- Not so expensive
- No need maintenance
- The life span of the tube life will be about 5000 hours. After that, the tube should be replaced
- As the tube ages, its focus will increase followed by the blurring of the image
- Here, tubes are the consumables
- X-rays are emitted by refraction
- New type closed tube (marketed as “NT” ray tube)
- Not so expensive
- The life span of the tube life will be about 5000 hours. After that, the tube should be replaced with the new one.
- As the tube ages, its focus will increase followed by the blurring of the image
- Here, tubes are the consumables for users. Filaments should be changed for manufacturers.
- X-rays get emitted by the transmission
The following are the parameters considered for the X-ray tube:
- Voltage in KV
- Tube current and tube power
- Target current and target power
- Relationship between tube power and target power
- Target current measurement
- Focus port size
- Spatial resolution
- Focal size VS geometric shading
- Feature resolution
- Detail detectability of the system
The detector is the major part of the PCB X-ray inspection system. It converts invisible X-rays into visible light. Hence, it is possible to view the images easily through the naked eye. By sensing the intensity of the X-ray beam passing through the object, the detector produces varied black and white values (gray levels) on the image. That is why if the detector gets damaged, its replacement costs will be tremendous.
So, let us have a fair idea of how to select the right X-ray detector:
- Before choosing the detector, check for the best brand by searching via the internet.
- Check the flat detector of modern technology that can intensify the image.
- Try to select the amorphous silicon flat-panel detector.
- Do not opt for CMOS flat-panel digital detector.
One should pay attention to the following specifications while selecting a fluorescent tube for the X-ray machine:
- X-ray tube type:
Opt for the open tube or closed tube type, which is correlated with the resolution and life expectancy of the inspection devices. The more the resolution, the more will be the view of intricate and delicate details. If you inspect the target at a large scale, then it’s not an issue to choose the device with a relatively low resolution. As far as CSPs and BGAs are concerned, the resolution of 2μm or smaller is needed.
- Target type:
The target type plays a vital role in influencing the distance between the sample and the X-ray tube focus. This type will eventually influence the magnifying level of inspection devices. Hence, the target type should be reflective or penetrating.
- X-ray voltage and power.
The penetrating ability of the X-ray tube is always proportional to the voltage. Hence when the voltage is large, it is easier to inspect the objects with higher density and thickness. If the inspected target is single-sided boards, select the devices with low voltage. Similarly, if the inspected target is multi-layer boards, select the high voltage. At a certain voltage level, the image definition is proportional to the X-ray tube power.
- Parameters of X-ray tube such as spatial resolution, target current, detail detectability, and focus port size
- Geometric magnification
Below is the list of attributes to be checked on PCB:
- Any break in the solder joint
- Any short circuit
In the case of LED, BGA, SMT, and IC chip, we check:
- Internal deformation
- if the gold wire is normal
- Empty welding
- Bubble and other defects
The spatial resolution is defined as the ability to spatially differentiate the structure of objects. In case if the user is checking an object for any spatial defect, there will be a change in the adjacent position within the object. This is considered as a defect between two lines. Since each line has a geometric shadow (vignette) while viewing under the X-ray beam, you can find the defects where the geometric shadows (vignettes) of two adjacent lines overlap exactly.
For example, consider that there is a BGA crack between the tin ball and the pad. The pad is geometrically shaded in X-rays, whereas the BGA ball is geometrically shaded in X-rays. Hence when the geometric shadows of the BGA ball overlap exactly with the geometric shadows of the pad, the crack cannot be seen.
The major purpose of the X-ray inspection system is to detect the defects by localizing and magnifying objects. The greater the geometric magnification, the greater will be the ability to inspect the minute defects in a target object. For example, a 5µm defect with a geometric magnification of less than 1000X is not visible in the X-ray image. Geometric magnification is also called as optical magnification.
To understand the geometric shadows intuitively, follow the below steps:
- Place a finger in front of the projector
- View the shadow of that finger on the wall
- At the same time, you view an imaginary shadow next to a shadow. That’s called the geometric shadow.
- The finger image magnification is defined as the distance from the wall to the projector divided by the distance from the finger to the projector.
Calculation of the geometric magnification of a system:
Maximum geometrical magnification of the system = (maximum distance of the detector + maximum distance of the ray tube) / Minimum object distance (the nearest distance of the ray tube to the object i.e. FOD) (0.25mm for FEINFOCUS)
The minimum FOD will be the target heat sink thickness.
- The greater the focal size of the X-ray machine, the greater will be the geometric shadow of the object followed by the blurredness of the image.
- The smaller the focus, the smaller will be the geometric shadow of the object followed by the sharpness of the image.
The maintenance tips are categorized day-wise, monthly, bi-annually, and annually. Let us go through each of them in detail:
1 Daily check items
1.1. Check whether the safety induction switch found at the back door of the X-ray machine is working properly.
Method: Close both front and back doors to see whether the contact indicator of the relay is ignited. If the contact indicator light on the relays KA2(front door) and KA3(back door) is on, the safety induction switch is effective. If the indicator light is not on, the safety induction switch is considered as unacceptable.
1.2. Check whether the X-ray machine rotation axis and four-axis movement are working properly.
Method: Once when the total power is turned on, click on the software, and shake the joystick on the comfort to see whether the motion of X-axis and Y-axis is normal. Click both up and down buttons of the X-ray tube and the image detector on the software interface to check if the two axes are moving properly.
1.3. Verify if the motion axis of the X-ray machine sensors is working appropriately.
Method: This test is done to control the movement of each axis to the position of the equivalent limit sensor. When the indicator light of the sensor is switched on, the movement will halt. Check whether the computer is booting properly.
2 Monthly check items
2.1. Inspection of the X-ray machine movement mechanism
- Check whether the movement of each axis is normal and pay attention to the exact method of daily inspection items.
- Check whether the movement of each axis is smooth.
- Check whether the moving parts of the screw nut along with the work platform above the screw are not loose
- Check whether the X-axis and Y-axis of the screw is smooth. If there is any rust formation, apply grease in each of the screws. Check the movement after this lubrication.
2.2. Inspection of the emergency stop switch working condition
- Press the emergency stop button manually to check if the X-ray machine is down.
3 Biannual check items
3.1. X-ray machine power detection
Method: First, open the back door. Check whether 24VDC and 5VDC power supplies are working properly.
3.2. Equipment guide rail on the lubricating oil for its clean appearance
Method: First, turn off the device as well as disconnect the power supply. Open the back door, lubricate each screw rod with grease, and run it over and over to lubricate while cleaning the portions of the inner wall. In the end, open the side door and wipe it with a clean cloth.
4 Annual maintenance
4.1. Check for the signs of damage on the inner side and the outer side of the machine, if any.
4.2. Check the observation window glass to find if there is any scratch.
4.3. Check the rotation pattern of the X-ray light tube, platform movement axis, as well as the detector.
4.4. Check all the fans and clean the filter properly with cotton.
5 Check X-ray image quality
Description of the problem
Analysis of the problem
The computer has a starting problem
· Loose computer power connectors
· Presence of virus can cause a system failure
· Reinsert your computer’s power plug
· Reinstall the entire system
Automatic reboot after power-up
Presence of the virus in the computer
Perform system restoration
X/Y/Z axis motors are not running properly
· Issues with the power
supply to the drive
· Loose B joints
· Drive anomalies
· Replace the power supply
· Use fasteners
· Use replacement Drive
Jarring of the rail
during the movement
· Loose couplings
· Linear guide and roller screw without any lubrication for a longer duration due to dryness
· Check couplings and tighten them.
· Lubricate the linear guides and roller screws using grease
Inadequate power supply
Change the power supply
The following parameters should be taken into consideration while choosing the right PCB X-ray machine.
- Image Quality
If you are planning to buy a good camera, obviously the one with a higher pixel rate, say 24MP (megapixel), is better than the one with say 15MP, right? If this is the case for photography, choosing the best qualitative X-ray machine can be even more complicated. A lot of physics along with clever software is involved. The factors that can affect image quality in the PCB X-ray machine may include voltage, power, spot size, the field of view, the proximity of the X-ray source to the target object, as well as the detector resolution. Consider voltage as an example; a higher voltage (say 160kV) system will have greater X-ray penetration ability, compared to the lower voltage one (say 130kV). The higher voltage can unfavorably affect the image contrast and henceforth the ‘quality’. In that case, how can you determine the quality? The best practical solution is to pick several typical sample assemblies and create the X-ray system. Determining the quality of an image can be a subjective opinion. The good news is that you can very well find the systems targeted at PCB assemblies that can deliver image quality ranging from very good to excellent. Perhaps, this is connected more with the inspection set up rather than the technical competence of its components.
- How many ‘D’s?
The letter ‘D’ stands for dimensions. There are three kinds of dimensions:
- 2D (two-dimensional) to provide a straight top-down view
- 2.5D (2.5-dimensional) to allow top-down as well as angled or tilted views
- 3D (three-dimensional) assembly re-construction using techniques like laminography or computed tomography (CT)
Remember the more details you view, the slower the examination is. That is why complex CT scans take hours to complete.
If you would like to check any missing solder balls or shorts between them, then 2D can be fine. Nevertheless, tilting will help in getting a better view if there are any components concealing the target area of interest. Hence, 3D will be used for an extensive detailed qualitative study of the target object.
- Ease of use
Several X-ray systems allow a grade of automated inspection, like pass/fail’ criteria through programming sequences of inspections. This strategy helps to operate easily with repetitive inspection, thereby allowing an ‘in line’ process if needed. Hence you need relevant skills to set it up and perform ad-hoc inspections. Nowadays in the recent X-ray machines, it is easier to interpret the final images easily with the help of varied colors. Though modern X-ray systems are easy to use, the inspector, at times, need to understand the application of all the settings like voltage and contrast settings. Not only that, but the inspector should also be able to interpret the findings which require the knowledge of PCB assembly.
Remember that the Health & Safety Executive (HSE) must be notified in advance before using an X-ray machine. There will be obligations for creating instructions, procedures for use, and involving radiation protection supervisors with advisors. The machine suppliers should provide timely advice, and perform an annual qualitative check on the system.
It is a well-known fact that there are varied types of the X-ray tube. ‘Open tube’ types are comparatively quick, inexpensive, and easy to replace. Perhaps, you need to spend a few pounds and a couple of hours. But the tube should be replaced every 200-300 hours or so of use. In the case of ‘Closed tube’ types, they can last for many years. But they are relatively more expensive, where you will spend thousands of pounds. Hence the selection of the best one depends on how much you will be using the system.
Select the X-ray detectors with standard or High Definition flat panels. The flow of X-rays leads to the degradation of detectors over time, say around 20% after ten years. Hence, it is recommended to replace every 8 to 12 years when the machine is in use.
Never forget to check for the common system failure modes, since the similar component parts can be assembled in varied ways. Remember to replace power supplies, cables, or connectors in time.
We have the right combination of the technical knowledge with qualified service expertise to provide proper maintenance service on our every X-ray system. If you have any query about our products or services, you can immediately contact us via online chat, phone, or email, so that our professional team will solve them at once.
- Professional Service Team
Uni-Xray has a team of well-experienced engineers to provide timely services for every customer, including consulting services, custom design, equipment qualification, safety inspection service, and so on.
- Training & Maintenance Services
Uni X-ray offers an exceptional range of after-sales services, such as online video instructions and installation guides for our customers to ensure that their new or existing equipment is in safe and good operating mode, with a long life cycle. Additionally, we provide prompt safety inspection with regular maintenance service as per the personalized needs of our customers. These services are also available for X-ray machines delivered by other suppliers.
- Customized Services
Once when you share the application details to our team, we will recommend the best X-ray inspection solution for you. At times, a customized solution will be the best, where we’ll work with you to suggest the right X-ray machine that will meet all your requirements. Hence, you can contact our sales and support team to discuss our services at any time as per your convenience.
- Pre-installationservices including free installation instructions with the online video tutorials
- Warranty services
- Online support via call or chat at your own convenience
- User training
- Creation of customer profiles including personal details, product purchase date, product receipt date, and customer feedback. This service provides a timely one-stop service to solve all the customer’s worries.
Hope you have found this detailed blog post more informative that helps you to understand all the focus areas in detail before investing in industrial X-ray inspection equipment.
Does your equipment emit excessive radiation? What methods do you use to ensure radiation safety?
For the Safety Radiation, the Chinese and international standards are both <1uSn / h. but the Radiation from our equipment is much smaller than this standard.
Our radiation control methods are:
- Sheet metal factory test;
- Radiation Test before debugging;
- Radiation Test after debugging.
What is the warranty period for your equipment? After the warranty period, how do you guarantee?
The equipment warranties period is one year. During the warranty period, repairs and possible parts and component changes are free.
What does your warranty cover?
The warranty covers defects in machines. It does not cover damages issues caused by damage due to handling, shipment, storage, accident, impact, abuse, or misuse.
We have bought your equipment. How can we get started? What kind of training do you offer?
We offer three training methods:
- The customer (or agent) sends their engineers to our company for on-site training.
- If our staff goes to the customer’s site for training, the customer will pay for the hotel and air ticket fee and also a training fee.
- Video remote training: The machines are equipped with instruction manuals, and machine operation training is done using videos. After the training, a certificate of completion of training is
What is the image quality of your device? How do you ensure high-quality images?
The customer provides samples and takes pictures for a report. Images taken are subject to customer approval.
The operating software is in Chinese and English (switchable) with a human-computer interaction screen, easy to use.
What is the delivery time for your equipment?
- Off-line equipment are shipped out within 20 days after payment confirmation.
- Online standard equipment will be issued within 45 days after receiving the payment.
- Non-standard customized order within 90 days after we receive payment, depending on the customization.
This can be done according to the needs of customers. ocean freight costs are cheap and long, while air freights are expensive but take a shorter time.
You can contact us by filling the form on the right, and we will get in touch with you within 12 hours.