13 Popular PCB Test Methods in PCB Manufacturing

PCB is available in various electronic devices, including mobile phones, complex machines, computers, etc. If there are any defects or problems in the PCB, it could fail the entire system and cause inconvenience. Thus, manufacturers must reinvest equipment, time, and resources to repair the faults. Therefore, PCB test methods have become one of the important parts of the PCB manufacturing process. It can help early detection of problems, help in dealing with them quickly, and ensure high-quality PCBs. 

This article will provide some of the basic PCB testing methods in the manufacturing industry.  

What is PCB Testing?

PCB testing is the process of detecting a small fraction of errors of defects other than the structural defects in the circuit board to ensure that the PCB operates as required. PCB testing helps the designer to verify the correct working of the circuit. The manufacturer carried out the PCB testing after the complete assembly of the PCB. Even after completing the design, various factors affect the PCB, and there could be multiple defects, including solder and components joints. This could result in poor functionality of the board. Thus, PCB test methods are a crucial part of manufacturing the process that allows faster fault detection. 

We can also say that it is a versatile tool for examining and verifying a board for usage in real-time. There are many PCB test methods, and each testing method has its advantages and disadvantages. Thus, selecting the best way for PCB test methods is a daunting task.

Benefits of PCB Testing

Finding defects

PCB testing helps in finding bugs or defects in the circuit board. The PCB problem can be functional or manufactural. PCB testing can help to find many kinds of detects on PCB design and layout so that the designers can fix the problem accordingly.

Saves Times

Early detection of PCB defects and bugs can save time in reworking the system. The designers can find the problems during the manufacturing or prototyping steps. Complete testing helps the designer easily discover the cause of the issues. This will help for a faster production time of the PCB products. 

Reduce Costs

PCB test methods eliminate waste by using small quantity assemblies to test the products. Designers can avoid the mass production of defective PCBs by performing comprehensive testing early in the design process. This step contributes significantly to lower production costs. 

Improved Safety

PCB is common in almost every electronics. Their defects can result in a significant problem for the company resulting in accidents like injuries, fire, etc. Pre-manufacturing ensures that the worker and equipment are not damaged during production.

Reduced Return Rate

With PCB testing, there is less chance of returning products that don't meet the standards or are defective. This lowers the costs of refunding customers and dealing with defective merchandise. Furthermore, lowering returns can improve customer satisfaction and company reputation.

What does PCB Testing Check?

The major purpose of PCB test methods is to check if the PCB follows the standard performance of the circuit board. The PCB test methods should consist of the following checks:

• Copper Plating: PCB has copper foil attached to the PCB board that helps in conductivity. Designers need to check the quality of copper for a detailed analysis of elongation and tensile strength. 
• Lamination: The longevity of PCB depends on the lamination quality of PCB. The peeling of laminates can affect the functionality of the board. Thus, the lamination test checks the resistance of laminates to peel by heat or force.
• Solderability: The PCB's solderability ensures the components' stability on the board. Thus, solderability testing is prioritized while testing PCB to prevent soldering defects later. 
• Electrical Testing: Conductivity is a crucial thing in any PCB. Thus, the measurement of leakage of current in any PCB is essential. 
• Environment Testing: This is the performance test for PCB to operate in harsh environments. The weight comparison is made by placing PCB in a wet environment, and PCB with a significant weight change is rejected. 

Popular PCB Testing Methods

Visual Inspection

It is part of the manual testing method that requires experienced skills who checks for defects like weld and other visible defects with their naked eyes. It is more applicable for the PCB's visual inspections, placement of compliments, and solder mask application that could lead to the failure of the circuit board. This is considered one of the simplest, most important, and basic PCB inspection methods. 

Advantages

• It is easy to set up and one of the cheapest options.
• It can detect major solder defects.

Disadvantages

• It is time-consuming, inconsistent, and labor-intensive work.
• It could have many human errors and mainly depends on technician skills.
• It can only inspect the visible solder joints.

Application

This method applies to simple designs that have larger components.

Flying Probe Testing

Flying Probe Testing is less expensive than in-circuit testing, which is also a form of in-circuit testing. This test uses an element with a smaller pitch to make contact with that of the test point, like SMD pins. The flying probe method tests the pads and tests for detecting the PCB unit. 

Flying probe testing involves applying electrical and power test signals in the probe's location. The result of this test shows if the circuit board has a fault. The deviation from the expected result shows that the circuit didn't meet the requirements. The flying probe test is the most accurate test that can provide the test with up to 99% of accuracy. The flying probe test can check for defects like an open and short circuit, capacitance and impedance control problems, and inductance and diode problems. 

Advantage

• This method is cheaper and faster to implement. 
• It provides wider test coverage where the component pads and vias are used as the testing points.
• It saves space and doesn't require adding the testing points.

Disadvantage

• It is not an effective method for large-scale testing.
• It can't evaluate the defects like improper solder ratio and voids.

Application

Flying probe testing is applicable to prototypes, small or medium boards with a higher density of components. 

Automated Optical Inspection (AOI)

AOI takes high-resolution images of the PCB using single or two cameras. The captured image is collected with the images of the template board of the tested design or the images of boards stored in a database. In addition to providing quality assurance, an AOI machine can provide in-situ production process adjustments and work directly at the end of the production line. As long as the components are discernible, AOI will uncover all the errors that manual visual Inspection might miss and will be more accurate and consistent than manual visual Inspection.

Advantages

• It can help to identify major solder defects.
• It is more accurate and consistent testing than a manual inspection method.
• You can directly implement this process in the production line for defect identification in the early phase.

Disadvantage

• AOI can only detect surface defects, and it is hard to cover them 100%. 
• The programming and the setup for the template matching require redoing with every change in design.
• Database matching is not accurate and mainly depends on the database's quality. 

Application

It is applicable for testing mature products in high quantities.

Automated X-ray Inspection (AXI)

With AXI testing technology, x-rays are used, which makes it unique among other inspection methods. A solder joint can be visualized in 2D or 3D using X-rays that penetrate the PCB and component body. It hides joints and is a perfect candidate for ball grid arrays (BGA) and other underside pads with hidden joints. Other optical inspection techniques cannot detect solder voids, but AXI can.

In the production process, AXI can provide engineers with early detection of defects so they can adjust their processes to eliminate the problem. As a result, fewer boards require expensive repairs. If you are working with small batches or prototyping, it may be sufficient to inspect only the chip components with hidden pads by x-ray.

Advantages

• It can have the highest defect detection rates.
• It mainly emphasized solder joint quality instead of connections only.

Disadvantages

• It is considered a time-consuming and cost-expensive process.
• It requires well-trained and experienced operators. 

Application

AXI testing is used for high-volume production and boards with chip components. 

In-Circuit Testing (ICT)

In-circuit testing is considered a highly reliable and automated test that can help check each circuit in PCB. It is also the popular type of PCB test methods for high-quantity components. This automated fault testing system covers the fault of 90%. This testing method is also known as a bed of nails test as it powers up and activates each circuit in PCB. 

This test can check for open and short circuits, solder defects, improper orientation, or placement of the transistor and diode. 

Advantages

• It can cover the fault on the board up to 98%.
• It is one of the efficient and quick testing methods for mass-produced boards.

Disadvantages

• It is not suitable for small-batch boards or prototypes. 
• It cannot detect some defects like excess solder.
• The designers should add the test points to the board as it can only access the test points.

Application

It is applicable for testing mature products in high quantities.

Burn-In Testing

PCB burn-in test is a process in which circuit boards are subjected to a period of high temperature and voltage stress to accelerate the aging process and detect latent defects. This process is typically used on newly manufactured boards to detect any defects before they are shipped to the customer. The test is used to identify any weak components or solder joints that may fail prematurely. Burn-in testing also helps to identify any issues with the design that may not be immediately apparent.

Advantage

• Increased reliability: Burn-in testing helps to identify any weak or faulty components or connections that may cause the product to fail prematurely. This helps to ensure that the product is more reliable and longer lasting.
• Reduced costs: By identifying and replacing any defective components before they are shipped to the customer, burn-in testing helps to reduce the costs associated with product returns and warranty claims.
• Improved quality: By ensuring that all components are functioning properly, burn-in testing helps to ensure that the product is of a higher quality. This helps to improve customer satisfaction and loyalty.

Disadvantage

• Cost: Burn-in testing is an expensive process and requires additional time and resources to complete.
• Damage: Burn-in testing can cause damage to components and connections, resulting in reduced reliability.
• Stress: Burn-in testing can place a lot of stress on components and connections, leading to premature wear and tear.

Application

This testing is useful for equipment that operates in extreme environments where there shouldn't be any chance of failure. E.g., medical devices.

Functional Testing

The final quality control procedure during production is functional testing. The device under test (DUT) is checked to ensure it functions as intended. An on-off power test can be as simple as a power cycle or as complex as a comprehensive protocol and testing program, depending on the complexity of the design.

Thanks to this flexibility, functional testing is flexible enough to be used in place of more costly testing procedures. You can test functionality more directly than other testing methods since it simulates the operating environment. In contrast to burn-in testing, functional testing may be harder to determine the cause of any defects, and it may not catch early failures of boards.

Using a complete 100% functional test on every board produced for small-batch manufacturing is becoming increasingly common. 

Advantages

• This is one of the most flexible testing processes and is highly customizable. It can test almost all types of PCB.
• It provides a cheaper and more convenient solution than a testing method requiring special devices. 

Disadvantages

• It requires trained manpower to isolate the defect causes.
• The board can fail even after passing the testing under the condition of stress.

Application

This testing is ideal for small-quantity board manufacturing. 

Time Domain Reflectometry Test (TDR)

Time Domain Reflectometry (TDR) is a testing method used to determine the electrical characteristics of a printed circuit board (PCB). It is used to measure the impedance, capacitance and inductance of the components on the PCB. TDR works by sending an electrical pulse along a trace on the PCB and then measuring the time it takes for the pulse to travel along the trace and reflect back. By analyzing the reflected pulse, it is possible to determine the electrical characteristics of the trace and the components on the PCB.

Resistivity of the Solvent Extract Test (ROSE)

The resistivity of the solvent extract test in PCBs is usually measured in ohm-cm (Ω·cm). This test is used to measure the amount of ionic contamination present in the PCB. The test requires a sample of the PCB material to be extracted in an organic solvent, usually a mixture of acetone and isopropyl alcohol. The resistivity of the extract is then measured with an instrument such as a digital multimeter or a special test fixture. The higher the resistivity, the lower the ionic contamination present in the PCB.

PCB boards tested using Rose Testing ensure they are free of significant surface debris. PCB board contains surface debris, which usually comes from manufacturing processes or excess conductive material. Thus, ROSE provides an ionic cleanliness test that determines the presence of ions in the circuit board. This iconic debris includes chlorine, fluorine, sodium, and bromine. These ions can cause chemical reactions in the circuit board and cause system failures. 

Sensitive industries such as the military and medical measure ionic cleanliness and track using ROSE testing, the industry standard for measuring and monitoring ionic cleanliness.

Boundary Scan Test

It is a common method to test interconnections between components on a PCB using a boundary scan. Batteries are inserted into leads connecting the die to external pins to test the functionality of the board.

Detection of the board without reaching all nodes is the biggest difference with this way of testing. PCBs with multiple layers and high densities, becoming increasingly common in recent years, require this quality for evaluation.

This method has many applications, including testing at the system level, testing memory, programming flash, and emulating the central processing unit (CPU).

Aging Test

A condition-strengthening test on products' aging involves simulating various factors involved in the actual use conditions of the products. Testing in a specific environment aims to determine whether a product is reliable and stable. The product must be placed at a specific temperature and humidity level based on the design requirements, simulated continuously for 72 hours to 7 days, recorded the performance data and reversed for improvement to ensure its performance meets market requirements. Electrical performance tests are usually referred to as aging tests. Salt spray test, vibration test, drop test, and vibration test are all similar tests.

GM/LTS

GM/LTS PCB test methods consists of various processes and tests. This test can help to detect and remove internal CCA failures, including memory, video sync, multiplexer, control relay, and analog discrete line tests. 

In addition, during testing, terminal computers run complete loopback tests and self-tests. You can detect defective parts early and replace them with new ones with either test. GM/LTS circuit card assembly tests effectively identify and isolate faulty CCAs. With this testing method, it can repair GM/LTS circuit cards.

Laser Detection

In terms of PCB test methods, this is the newest development. It uses laser beams to collect the measured data and thus compares the measured data with the preset limit. The bare board verified this technology and was finally considered for the assembly board testing. This test best suits the mass production line, where it provides the advantage of faster output results with no defects and unobstructed vision. Besides, its drawback includes high initial cost and higher maintenance and use problems. 

Common Defects in PCB

Manufacturing errors often lead to defects on circuit boards. For instance, poor molding or over-machining can cause a faulty thermal connection on a PCB. In addition to preventing other problems, replacing a faulty thermal can also prolong its life. A manufacturer with experience can also identify and return faulty thermals before issues arise.

PCB testing defects can affect the quality and performance of the circuit board. Occasionally, they even result in outright failures. PCB assembly is vital in such cases. Manufacturers can ensure a final product in several ways. Testing PCBs and checking them for flaws are some of these steps. By doing so, your product will meet quality standards, and there won't be common PCB defects. 

Incomplete soldering is a common problem. When an IC fails to make full contact with the solder, it refers to a surface-mount defect. Short circuits or open circuits can result from this. Unintentional contamination of components can also result from poor soldering. Functional circuit board testing methods are often necessary to detect these issues. A flying probe tester can also check the PCB. A flying probe machine is an apparatus that uses probes to contact circuit board parts. It is possible to check whether each part on the board is fully soldered by moving these probes over it or not.

Conclusion

PCB testing is a necessary procedure that helps the manufacturer to detect PCB defects in the very early phase. The process is manual, automated, and semi-automated. These methods help the manufacturers to test the product before their release in the market. Thus, based on your requirements and the nature of your PCB, you can test your PCB board and check for any defects. 

If your PCB has any defects and seems faulty, then there are some ways to reduce the repair cost. Initially, it would be best if you had an accurate idea about the problem in your PCB. After then, based on that information, you can provide your board to your manufacturing company which could determine the best way to solve your circuit.

NextPCB provides you the all PCB-related services including manufacturing and testing of your PCB. We provide you with the best quality PCB work. Please feel free to contact us at any time.