No matter what kind of printed circuit boards you’re building or what type of device they’re being used for, your PCBs need to function correctly. These boards are key to the performance of many products, and malfunctions can have serious consequences.
Inspecting PCBs throughout the design, manufacturing and assembly processes is crucial to assuring that your product meets quality standards and operates as expected. Today, PCBs are complex. While this complexity makes room for lots of new capabilities, it also creates more chances for failures. As PCBs have gotten more advanced, so have the inspection techniques and technologies used to ensure their quality.
You can choose from various methods of PCB inspection. The right technique to use depends on the PCB type, the current step in the production process and the faults for which you want to test. Creating an adequate inspection and testing plan is crucial for ensuring a high-quality product.
Here’s an overview of various tips and techniques for PCB assembly inspection.
Why Do PCBs Need to Be Inspected?
Inspection is a critical step in any PCB production process. It can help you to catch defects so that you can correct them and improve your overall operation.
Inspecting your PCBs can uncover any defects that may have occurred during manufacturing or assembly. It can also help to reveal any design flaws that may exist. Checking PCBs after each phase of the process enables you to catch flaws before moving on to the next stage, which can save you from wasting further time and money on a defective product. It can also help you catch one-off defects that affect one or several PCBs. This process helps to ensure consistent quality among your boards and final products.
Without a proper PCB inspection procedure in place, flawed boards may make it into the hands of customers. If a customer receives a faulty product, your company may lose money through warranty payments or returns. The customer will also lose some of the trust they had in your company, and your reputation will suffer. This situation can result in missed opportunities if that customer takes their business elsewhere.
In a worst-case scenario, a defective PCB can cause injury or death if it’s used in a product such as a medical device or an automotive component. Such a disaster can lead to severe reputation damage and expensive litigation.
Inspection of your PCBs can also help you improve your overall PCB production process. If you notice a particular defect frequently, you can take action to correct that flaw at the process level. In this way, PCB inspection can contribute to the continuous improvement of your business.
Printed Circuit Board Assembly Inspection Methods
What is PCB inspection? In order to make sure that PCBs are performing as intended, manufacturers must verify all components are assembled correctly. This is done with a range of techniques including simple manual inspections to automated tests that use advanced PCB inspection equipment.
Manual visual inspections are a great starting point. For simpler units, they may be all that’s needed. At Electronic Manufacturing Services Group, we perform a manual visual inspection under magnification of every board we produce to ensure we meet all customer expectations. We also offer other inspection services that involve the use of advanced equipment. This equipment can speed up the inspection process and may be necessary for more complex board types, such as multi-layer boards and those with high numbers of components.
Manual Visual Inspection
The simplest form of PCB inspection is manual visual inspection (MVI). To perform this type of test, a worker looks over the board either with the naked eye or through magnification. They’ll compare the board to the design documents to ensure that all specifications were met. They’ll also look for common defaults. The type of defects they look for vary depending on the kind of board they’re checking and the components on it.
It can be useful to perform an MVI after nearly every step in the PCB production process, including assembly. EMSG conducts an MVI under magnification of every board we produce. You may also wish to follow MVI with a more advanced, comprehensive examination.
Inspection staff members inspect nearly every aspect of a board and look for various common defects on each of them. A typical visual PCB inspection checklist might include the following:
- Ensure that the board’s thickness is correct, and check for surface roughness and warpage.
- Check the dimensions of the assembly match the specification, and pay particular attention to dimensions related to electric connectors.
- Inspect the integrity and clearness of conductive patterns, and check for solder bridging, open circuits, burrs and voids.
- Check the surface quality, then look for the existence of pits, dents, scratches, pinholes and other defects on printing traces and pads.
- Verify that all vias are in the correct positions. Make sure they aren’t missed or inaccurately punched, that their diameter matches design specifications and that there are no voids or nodules.
- Inspect the firmness, roughness and brightness of pad plating, and check for any bulge defects.
- Assess coating quality. Check the color of plating flux and whether it is even, firm and in the correct position.
MVI has several advantages over other types of inspection. Due to its simplicity, it’s low-cost. You do not need any specialized equipment except potentially for magnification. You can also conduct these inspections very quickly, and it’s easy to add them on to the end of any procedure.
The only thing you need in order to perform this type of inspection is staff members who know what to look for. If you have the necessary expertise, this technique can be beneficial. It’s crucial, however, that staff has access to the design specifications and knows what defects to watch for.
The capabilities of this inspection method are limited. It doesn’t allow you to inspect components that aren’t within workers’ line of sight. Hidden solder joints, for instance, can’t be checked via this method. Staff may also miss some defects, especially small ones. It’s especially challenging to inspect complex boards with many small components using this method.
Automated Optical Inspection
You can also use a PCB inspection machine to conduct a visual inspection. This method is called automated optical inspection (AOI).
An AOI system conducts an inspection using several light sources and one or more still or video cameras. The light sources light up the board from various angles. The cameras then take still images or video of the board, compiling them to create a complete picture of the unit. The system then compares the images it captures with information about what the board should look like taken from design specifications or an approved completed unit.
Both two-dimensional and three-dimensional AOI equipment is available. 2D AOI machines use colored lighting from multiple angles and side-angle cameras to inspect components for which height is a factor. 3D AOI equipment is newer and can quickly and accurately measure component height.
An AOI can find many of the same defects that an MVI can, including nodules, scratches, open circuits, solder thinning, missing components and more. At EMSG, we sometimes use AOI, especially for more complex boards and higher-volume production runs. Our MIRTEC MV-3L AOI system can reveal lead-level defects for components as small as 16-mil pitch. It can accurately detect bridging, insufficient solder, reversed polarity and damaged parts.
AOI is a well-established, accurate technology and can detect many well-known faults in PCBs. It’s useful at many stages of the PCB production process. It’s also faster than MVI and eliminates the possibility of human error. Like MVI, it can’t be used to inspect components that are out of the line of sight, such as connections that are hidden underneath ball grid arrays (BGAs) and other types of packaging. It might also not be effective for PCBs that have a high concentration of components because some of them may be hidden or shadowed.
Automatic Laser Test Measurement
Another option for PCB inspection is automatic laser test (ALT) measurement. You can use ALT to measure the dimensions of solder joints and solder joint deposition as well as the reflectivity of various components.
An ALT system uses lasers to scan PCB assemblies and take measurements. As the light reflects from the board’s components, the system uses the position of the light to determine their height. It also measures the intensity of the reflected beam to determine the component’s reflectivity. The system can then compare these measurements to design specifications or to a board that has been approved as accurate to identify any defects.
Using an ALT system is ideal for determining the quantity and position of solder paste deposition, and it provides information about the alignment, viscosity, cleanliness and other attributes of solder paste printing. The ALT method provides detailed information, and you can conduct a measurement extremely quickly. These types of measurements are typically accurate but can suffer from interference or shielding.
With the rise of surface mount technology, PCBs have become more complex. Boards can now be more densely populated, feature smaller components and include chip packages such as BGAs and chip scale packages (CSPs) through which you cannot see hidden solder connections. These features present challenges for visual inspections such as MVI and AOI.
To overcome these challenges, you can use x-ray inspection equipment. Materials absorb x-rays according to their atomic weight. Heavier elements absorb more, while lighter ones absorb less, enabling you to distinguish between materials. Solder is made of heavy elements such as tin, silver and lead, while most other components on a PCB are made from lighter elements such as aluminum, copper, carbon and silicon. As a result, solder is easy to see during x-ray inspection, while most other components, including the substrate, leads and silicon integrated circuits, are hardly visible.
Rather than being reflected like light, x-rays travel through an object, forming an image of it. This process allows you to see through chip packages and other components to inspect the solder connections beneath them. X-ray inspections will also let you see inside solder joints to reveal bubbles that you couldn’t see using AOI.
X-Ray systems can also see the heels of solder joints, which are masked by leads during AOI. Also, with x-ray inspection, there are no shadows to get in the way. For this reason, x-ray inspection works well for densely populated boards. You can conduct manual x-ray inspection using x-ray inspection equipment, or you can conduct automated x-ray inspections (AXI) using an automated x-ray system.
X-ray inspection is ideal for more complex boards and offers some capabilities that other inspection methods do not, such as the ability to see through chip packages. It also works well for inspecting densely packed PCBs and allows for a more detailed inspection of solder joints. The technology is a bit newer and more complex, and it can be more expensive. It might only make sense to invest in x-ray inspection equipment if you have a high volume of densely populated boards with BGAs, CSPs and other such packages.
If the design of your PCB requires a unique form of inspection, EMSG can offer specialized inspection services to meet your needs. Our in-house team of experts knows the importance of quality control and we will work with you to make sure your PCB assembly meets all expectations of performance. We would love to work with you to determine if our PCB X-Ray inspection service is the right process for your product.
Working With EMSG
At EMSG, we understand how important the performance of your PCBs is as well as how crucial proper inspection is to ensuring adequate performance. We’re experts in how to implement quality inspection of PCBs. Our team will work with you to determine the ideal printed circuit board inspection criteria and method to use for your project while maintaining acceptable cycle times.
We perform a visual inspection under magnification of every unit we produce and can also provide other inspection services depending on each project’s requirements. We may use AOI to inspect your PCBs optically. If your boards require testing, we can conduct in-circuit testing using the Genrad 2287A as well as functional testing using our in-house designed test equipment or test equipment that you supply. We also offer board-level and complete box build assemblies. We specialize in short-run productions of 50,000 units or less, which allows us more flexibility to adapt to the needs of our customers’ projects.
Our York, PA, production facility features world-class assembly, inspection and testing equipment to help provide quality products. Our ISO 9001:2015-registered quality management system (QMS) also helps us to ensure that our inspection services are performed in accordance with best practices and that our equipment is properly maintained and calibrated. We strive to continually improve our operations, so when you work with us, you can expect quality, reliability, accountability and transparency.
Over the years, we’ve worked with companies across many industries, including the consumer products, telecommunications, automotive and heavy machinery manufacturing sectors. We have developed an extensive printed circuit board inspection checklist to ensure quality and dependability. We’re registered with the Food and Drug Administration (FDA) to provide sanitary manufacturing and testing services to medical device and food companies.
We offer PCB inspection services as a standalone solution and as part of our turnkey box build or contract manufacturing services. We’d love to work with you to determine the best inspection process for your needs and provide you with the high-quality services your project requires. The first step in this process is a consultation, during which our engineers will take the time to understand your requirements and provide you with a quote detailing how we can help you achieve your goals.