PCB testing requires the use of the proper tools. Circuit boards generally consist of copper layers, and the substrate is the primary component. The copper layer is either flexible or ridged and carries electrical components.
We then laminate the copper layer onto the board. The type of PCBA determines the thickness of the layer. Copper traces are often covered in solder masks to prevent corrosion and shorts.
PCB testing systems help to verify the correct working condition of a circuit card assembly. These systems have two distinct functions: identification and fault isolation—the former aims to identify the failure modes and the latter to ensure the correct final assembly. The former enables the tester to identify the components that need improvement, while the latter focuses on the final performance of the board.
In-circuit testing is a highly accurate method of testing that identifies defective components. This is most effective when connecting multiple components to a single board. It also helps identify component alignment issues. It also allows for fast fault detection, and requires specialized equipment. Therefore, manufacturers should choose this method early in the manufacturing process.
Another way of testing ICs is by using the boundary-scan method. This method involves using PCBs with boundary-scan ports to access ICs. These interfaces can transfer data through shift register mode.
Testing Methods
There are various testing methods to determine the quality of a PCB. These include the in-circuit, flying probe, AOI, and functional testing. However, there are some things that you should know before using them.
For example, burn-in testing is not for all projects, but it can help you avoid embarrassing product launches and shorten the life of your product. However, it can also cause the board to be under more stress than it can handle. However, the limits can reduce if your board is free from defects.
In-circuit testing
In-circuit testing (ICT) is a highly reliable, automated test method that checks each circuit on a board. This method ensures that all component values are within specification and are free from human error. In addition, it can detect faults and short circuits and correct the orientation of components.
There are several common types of in-circuit testing. One test is called the peel test, which measures the strength needed to peel a lamination from a PCB. Another test is the solder float test. This test determines whether solder has penetrated the metal surface, thereby increasing the likelihood of a solid solder joint. Other common tests include solderability, surface mount simulation, and wetting balance analysis.
Another form of in-circuit testing is called burn-in. Burn-in testing uses a high-voltage power supply to simulate the operating conditions in a circuit board. This can detect hidden defects but can also damage PCB components. Therefore, burn-in testing should be helpful in combination with other tests.
Testing PCBs is essential because they can fail because of poor quality or design. In addition, failures in a printed circuit board can cost a company a lot of money. Therefore, whether your circuit board is manufactured in-house or outsourced, it is vital to check it carefully before assembling and shipping it to your customers.
Flying probe testing
The benefits of PCB flying probe testing are numerous. For starters, it is cheap and highly effective. Furthermore, it is suitable for prototypes and low-volume production. However, it is not suitable for high-volume production. Moreover, flying probe testers are not ideal for high-volume production.
Flying probe PCB testing involves applying power and electrical test signals to probe locations. The result of these measurements reveals whether the circuit piece has a fault or not. A deviation from the predicted results of the test will indicate that the unit does not meet the requirements. The flying probe test is more accurate than in-circuit testing and can test up to 99% of the PCBs.
Flying probe testing uses multiple probes to detect potential circuits. The probes are at different points on the PCB. This allows multiple measurements to operate simultaneously, reducing the time needed for each test.
However, it is essential to ensure that the PCB’s design includes a “non-tented” specification so that the probes do not touch the component legs.
Flying probe testing is less expensive than in-circuit testing. In addition, it only requires a small number of test probes to cover a board. Therefore, it is more suitable for small-scale production. However, this technique is not suitable for large-volume production.
AOI (Automated Optical Inspection)
AOI uses multiple cameras and microscopes to capture images of the PCB. Then, the software compares these images to the board’s schematic to detect differences. This process allows technicians to inspect each board closely, identifying any problems early. However, AOI is imperfect and may not cover all part types.
AOI can detect many defects that affect the performance of a PCB. Specifically, it can detect under and over-etching, solder gap, and excess solder. It can also detect component defects, such as missing components, incorrect component values, and improper placement or alignment.
AOI can also detect lifted lead deficiencies on printed circuit boards. Moreover, it can also identify and correct BGA shorts and open circuit connections.
AOI is a non-contact visual inspection for printed circuit boards. It can identify quality defects and catastrophic failures and is essential in manufacturing. AOI uses a camera to scan the device. It is the most accurate way to check a product for defects.
AOI systems can be at any stage of the manufacturing process. For example, they can be placed right before, during, or after reflow soldering, where most nonconformances occur. This way, we can correct any issues discovered during the inspection immediately. In addition, this way, more products won’t need to be rejected in the final inspection or circuit board testing methods.
Functional testing
If you consider hiring a functional test team, you’ve probably wondered how the process works. Functional testing involves examining the physical components of a PCB, including the signals it produces and the components that connect to it. A functional test also checks the fit and function of sub-components.
The functional testing process ensures that the final product will function as intended. This test may consist of an on/off power test or a detailed test that uses testing software. The ultimate goal of the testing process is to identify and correct any problems that may arise after the completion of a product.
Functional testing can ensure the proper operation of a PCB before shipping it to a customer. The process simulates the board’s operation by testing its digital and analog signals. It may also use specific software to detect circuitry problems. It may also include manual inspections to check different aspects of a PCB’s manufacturing process.
Inspection by humans
Many manufacturers rely on humans to inspect their finished products, but the process is not perfect. For example, the human eye requires heightened visual acuity and judgment to detect critical defects. Moreover, human inspectors may be prone to fatigue, miss small details, and make inconsistent determinations.
Human operators perform manual tasks in consumer goods, parts, food, and print markets. However, this reliance on manual labor can result in increased costs and downtime. Also, a high error rate can negatively impact product quality, hurting the company’s brand image.
An automated visual inspection system provides human decision support and can help manufacturers reduce manual inspection costs while ensuring the highest quality standards.
GM/LTS
GM/LTS pcb testing consists of various tests and processes. Typically, these tests can detect and eliminate internal CCA failures. They also include a MIL-STD-1553 interface test, memory, video, multiplexor, video sync, control relay, and analog discrete line tests.
In addition, a terminal computer executes a complete data pattern loop-back test and a self-test during the testing process. Both tests can identify problems early and allow you to replace defective parts with new ones.
One of the main advantages of a GM/LTS circuit card assembly test is the ability to identify and isolate faulty CCAs with high accuracy. In addition, this testing method also provides a standardized process for repairing GM/LTS circuit cards.
Burn-in
Burn-in testing is a critical part of the design and assembly process. The process involves pushing the maximum power levels through the electronic device over 48 to 168 hours. It is a highly intensive process often referred to as the infant mortality process.
The main benefit of burn-in testing is the elimination of premature failures from a product. It also helps reduce the risk of problems occurring in the field. The components must be exposed to high voltages, temperature extremes, and other high-stress conditions to conduct this test.
This allows for the elimination of components that are susceptible to premature failure due to excessive stress. In addition to eliminating the failures caused by early failures, burn-in testing can also help identify which components are vulnerable to failure.
Defects in Circuit Card Assembly Testing
Circuit boards are often prone to defects due to manufacturing errors. For example, thermal connections on PCBs can be faulty due to over-machining or poor molding. Replacing a faulty thermal can prevent other problems from arising. In addition, experienced manufacturers can identify faulty thermals and replace them before they cause problems.
Common defects in circuit board testing
Common PCB testing defects can affect a product’s performance and quality. In some cases, they can even lead to outright failures. In such cases, it is vital to have the PCB assembled adequately. There are several ways to ensure the quality of the final product. These include performing PCB testing before assembly and checking for any flaws. This way, you can ensure that your product meets your quality standards and is free from common PCB defects.
A common issue is incomplete soldering, or “tombstoning.” This defect occurs when a surface-mount component fails to make full contact with the solder. This can lead to an open or short circuit. In addition, bad soldering can result in unintentional contamination of the components. Unfortunately, these issues are often difficult to detect without performing functional circuit board testing methods.
Another way to check for PCBs is to use a flying probe tester (FPT). Flying probe machines are devices that use probes to make contact with the parts of a circuit board. These probes can be moved over different components of the board, making it possible to check whether each part is soldered correctly.
Inspection methods
One of the most common circuit-card testing methods is automated optical inspection (AOI). This process uses multiple cameras to take images of the assembled PCB. This process can replace the need for human visual inspection and provides a visual record of the entire assembly process. In addition, it can detect key faults, including misplacement, alignment, and dimensional errors.
Another common method is visual inspection, which involves inspecting the circuit boards with the naked eye. This method is relatively simple but has certain limitations. For example, the staff may miss a tiny defect or a component out of sight. In addition, visual inspection is not very effective when the board contains many small components.
The PCB inspection report is an essential part of circuit board documentation. The report should be accurate and easy to understand. The report must cover two stages: validation and review.
Detection of defects
PCB testing involves various processes to determine the quality of the completed product. The results of these tests can fine-tune the manufacturing process. The peel test, for example, measures the strength required to peel a PCB’s lamination. The solder float test measures the thermal stress imposed on a PCB. The solderability test measures how well the solder can adhere to the board’s surface. It ensures that the surface is sturdy, which increases the chances of a solid solder joint. Other circuit board testing methods include surface mount simulation and wetting balance analysis.
Another method of circuit board testing is automated optical inspection. This process involves the use of a microscope or multiple cameras. These tests not only verify the quality of the finished product but can also save time by reducing manual inspection. This method detects defects such as component misplacement, orientation, and polarity. It is also much more accurate than manual visual inspection and can easily integrate into the production line.
Cost of repairs
If your circuit board is faulty, there are a few ways to reduce the cost of repairs. First, make sure you know what is wrong. The more information you provide to a repair service, the easier it will be to repair. Knowing the problem and its cause can help you determine the best method for your situation.
Secondly, ensuring that the repair process goes as specified is essential. This includes appropriate preheating and rapid cooling. Unfortunately, many repair technicians overlook these fundamental steps and worsen the problem.
Summary
PCB Assembly Testing is a critical process that helps manufacturers detect manufacturing defects on their products. The process includes a variety of visual, functional, and electrical tests to determine whether a PCB is fit for use. Popular methods include automated optical inspection, X-ray imaging, and in-circuit testing. These circuit board testing methods is particularly beneficial for manufacturers who want to test their products before release.
The bed-of-nails test is excellent for measuring board integrity and identifying open and short circuits. This test requires a test fixture and design but can ensure product quality even in the case of minor defects. The downside of this method is that it cannot detect invisible solder joints or double-sided PCBs with a high component density.
Manual PCB assembly testing involves a person examining the circuit board. This inspection is the most basic form of PCB assembly testing. In this method, an experienced inspector compares the circuit board to its Gerber files, identifying issues that might otherwise go unnoticed. The issues we can find will depend on the board and component, but it is the most fundamental type of inspection.
Thermal testing is another essential PCB assembly testing technique. This test simulates the operating temperatures of a PCB. Changing the temperature of a PCB causes it to expand or contract in response to a load. The heat produced by the process is known as thermal shock, which can result in the circuit boards’ early failures.
