The last thing customers want to see is that after the PCB assembly is completed, or even after the product is assembled, they find that there is a problem with the PCB, causing huge losses. Even though the design of the PCB is perfect, the entire manufacturing process is complex and affected by many factors. There may be hundreds of components and thousands of solder joints on a circuit board, and a PCB can also exhibit poor functionality without adequate verification. Baineng Cloud understands this, so we believe that testing printed circuit boards (PCBs) is very important, because testing can help identify problems at an early stage, increase yield and reduce costs, and improve overall quality and safety. Since each testing method has its advantages and disadvantages, it can be difficult to determine the best testing method for your situation and budget.
Benefits of PCB Testing:
1.Bugs found:The main benefit of PCB testing is that it effectively identifies problems in the PCB. Whether the issue is functional, manufacturable, or otherwise, PCB testing can uncover issues in PCB design and layout so that designers can adjust accordingly.
2.Cost Reduction:By using prototypes and small-scale assemblies to test products, PCB testing prevents waste from producing defective products. By completing thorough testing early in the design process, designers can prevent defective PCBs from being mass-produced, ensuring that designs are as defect-free as possible before they are put into production. This step helps to significantly reduce production costs.
3.Save time:In the long run, PCB testing at an early stage helps save time and allows designers to identify major issues during the prototyping phase. Complete testing allows designers to quickly and easily identify the source of problems and make adjustments, allowing production to resume faster and reduce product lead times.
4.Reduced return rates:When a company conducts PCB testing, it can effectively reduce the chances of selling defective products or products that do not meet performance standards. This reduces the costs associated with refunding customers and disposing of defective goods. In addition, fewer returned products can increase customer satisfaction and improve the company's reputation.
5.Improved security:Since printed circuit boards are often used in basic electronic technology, their failure can cause significant problems for a company's productivity or an organization's ability to provide essential services. Defective printed circuit boards may lead to accidents such as accidents, and in severe cases, may cause injuries to nearby workers. Pre-manufacturing testing also ensures that machines and workers are not damaged or injured during production due to improper design.
While it is not necessary to thoroughly test all types of PCBs, especially those that are technically mature. But most new and custom PCB designs require robust, frequent testing during the design process. Baineng Cloud Board provides customers with high-quality and reliable PCBs by establishing PCB testing procedures that suit their needs.
PCB test content
The purpose of PCB testing and inspection is to check whether the PCB meets the performance of a standard printed circuit board. Ensure that all PCB manufacturing processes are functioning properly according to project specifications without any defects.
A PCB is made up of different elements, components, and each element affects the overall performance of the electronic circuit. These components are analyzed in detail to ensure PCB quality. The test to be performed should include the following checks.
Pressing. The quality of the lamination is critical to the longevity of the PCB. Peeling laminates can directly cause problems with board functionality. Typically, lamination tests are used to test the resistance of a laminate to spalling under force or heat.
Bore wall quality:Bore walls are often analyzed in an environment with cycles and rapid temperature changes to understand how they react to thermal effects. Ensure that the hole walls do not crack or delaminate when the PCB is put into use.
Electroplated copper:Copper foil on a printed circuit board is attached to the circuit board to provide electrical conductivity. The quality of the copper is tested, and the tensile strength and elongation are analyzed in detail.
Cleanliness:The cleanliness of a printed circuit board is a measure of the board's ability to withstand environmental factors such as weathering, corrosion, and humidity.
Solderability:Materials are tested for solderability to ensure that components can be securely attached to the circuit board and to prevent soldering defects in the final product.
Electrical Testing:Electrical conductivity is critical to any PCB, as is the ability to measure the PCB's minimum leakage current. Please refer to the detailed electrical test content and method"Gain a comprehensive understanding of PCB electronic testing"。
Cleanliness:Cleanliness of printed circuit boards is a test of the board's ability to resist environmental factors such as corrosion and moisture.
Environmental Testing:This is a test of the performance and quality changes of the PCB when operating in a wet environment. Weight comparison is usually done before and after putting the PCB in a humid environment, and if the weight changes significantly, it is considered a scrap product.
The 8 most common PCB testing methods
1.Visual inspection
Visual inspection is a part of visual inspection, which is a manual method of testing that requires an experienced inspector to use a magnifying glass or microscope to inspect weld defects and other defects that are visible to the naked eye. Visual inspection is suitable for visual inspection of circuit boards, and seemingly poor solder mask application, component orientation, or scratch stains can all cause the board to fail.
Pros:
* Inexpensive and simple to operate – no test fixtures or complex setups required.
Most of the major welding defects can be identified.
Cons:
Subject to human error. This may depend on the technician's skills.
Only visible solder joints can be inspected, hidden solder joints cannot be evaluated.
2.Automated Optical Inspection (AOI).
AOI inspection can find faults or defects in PCBs at an early stage of development. AOI uses a single (2D) or two (3D) cameras to capture high-resolution images of the PCB, which are compared by the program to a detailed schematic or a database of good and bad board images to detect defects. AOI is often used as the first step in quality assurance. Ensure that problems are detected early and production is stopped as soon as possible.
Different types of defects can be detected, and if the board is in some way inconsistent with the schematic, it is marked on the board for inspection by a technician.
Don't rely solely on automated optical inspection. AOIs should be used in conjunction with other tests. Some of the combinations that Baineng Cloud Board suggests to offer are:
AOI and flying probes.
AOI and ** Testing (ICT).
AOI and functional testing.
Pros:
Most of the major welding defects can be identified.
More consistent and accurate than manual visual inspection.
It can be added directly to the production line for early detection of defects.
Cons:
AOI is a passive inspection method – only surface defects can be detected. Line-of-sight control is limited to detect connections that are hidden by BGAs or other types of packages.
It is not possible to cover 100% of all part types.
Template matching is time-consuming to set up and program, and each design change has to be redone.
Database-based matches may not be as accurate and depend on the quality of the database.
3.Testing (ICT).
PCBA ICT is currently the most powerful and popular type of PCBA testing for high-volume and established products, and it is also a popular PCB testing method trusted by many PCB manufacturers and customers. Its fault coverage is more than 95%. During PCBA ICT, an electrical probe in the form of a bed-of-nails sends current through a specific location on the board at a specified test point. These tests are used to verify the correct function, position, orientation, and defects of each electronic component on the PCB. The test includes verification of parameters such as short circuit, open circuit, resistance, capacitance, etc. The bed of the nail tester simply pushes the circuit board over the probe bed to start testing. Access points are pre-designed on the circuit board, allowing ICT test probes to be connected to the circuit.
For large or repetitive batches, test fixtures can be customized for faster and more efficient in-circuit testing. This test method is expensive and will depend on factors such as board and fixture size. Therefore, it is strongly discouraged that you change your mind in the production process and adopt an ICT strategy instead.
This test method uses special PCB test procedures and equipment, including:
In-circuit tester:A tester system consists of a matrix of hundreds or thousands of drives and sensors that perform the measurements of the test.
Fixtures:Connected to the tester, it is a part that directly interacts with the circuit board under test. This fixture looks like a bed of nails and is designed for the corresponding circuit board. each"Nails"or sensor points are connected to relevant points on the test board to feed information back to the tester. Fixtures are often the most expensive part of a system.
Software:The tester's software instructs the system which tests to perform on each type of board under test and indicates the parameters that pass or fail.
Pros:
Fault coverage can be as high as 98%.
Efficient and fast testing methods for mass-produced products.
Cons:
Test fixtures are an additional cost.
Not suitable for low-volume production or prototyping, as any changes to the design require modification of the test fixture.
Only test points can be used, and the designer needs to add test points to the board.
Certain defects, such as too much or too little solder, voids, cannot be evaluated.
4.Flying Probe Test (FPT).
Similar to the nature of traditional ICT work, the flying probe test is often seen as an improved version of the needling ICT bed. In addition to the test point, the flying probe machine can enter the uncovered through hole or the end of the component itself as a test point, and can be programmed to check the value of the passive component, directly check the direction of the diode transistor, and make a voltage measurement . It can be adapted to new boards quickly, easily and cost-effectively with simple programming modifications. This testing method makes it ideal for low-volume production testing and prototype testing, but it is slower and less cost-effective for mass production.
The flying probe test is used to check:
Open-circuit, short-circuit, back-current, capacitance, inductance, diode issues.
Pros:
It is cheaper and faster to implement or modify. No fixtures are required.
Higher Test Coverage - Ability to use vias and component pads as test points.
There is no need to add additional test points. Save board space.
Cons:
Testing is too slow for large-scale testing.
Certain defects, such as too much or too little solder, voids, cannot be evaluated.
5.Automated X-ray Inspection (AXI).
X-ray inspection of PCBs is required when pads with solder joints or lead-free components cannot be seen through a microscope or with the naked eye. X-rays can penetrate the PCB and component body, producing a 2D or even 3D image of the solder joint. This makes it ideal for inspecting hidden solder joints, such as solder joints under chip packages and ball grid array packages. Axi inspection can also detect weld voids, which many other optical inspection methods can't do. While this inspection can be very useful, it requires a trained and experienced operator. With specially trained and experienced staff to perform this operation, you can confidently deliver your PCB project to us.
When used in conjunction with the production process, AXI can be a useful tool for early detection of defects, allowing engineers to make process adjustments to eliminate the source of the problem. In this test, the X-ray technician was able to locate defects early in the manufacturing process by looking at them.
Solder connection. Traces of the interior
Pros:
The highest defect detection rate can be achieved among common inspection methods.
Emphasis is placed on long-term solder joint quality, not just connections.
Cons:
Trained and experienced operators are required.
Very time-consuming and expensive process.
6.Programming (environment) test
Burn-in testing is a more intensive PCB test that can help you check the performance of your board and find hidden defects before it is put into use. During the programming test, the programming test may cause damage to the component under test due to the high test intensity. Boards are subjected to conditions that exceed rated operating conditions to detect early failures and test load capacity to eliminate premature failures during real-world use. The power supply is pushed through other electronic devices, usually through the board at maximum rated current, and operates continuously for 48 to 170 hours. Of course, not every PCB product needs to be burn-in tested, it will only play its role in PCB projects with specific requirements and environments.
The operating conditions tested may include temperature, voltage and current, operating frequency, or any other operating conditions relevant to the design. The data collected through this process can in turn help engineers understand the cause of defects and optimize the design or manufacturing process.
Pros:
Performance is checked under real-world usage conditions (which is not possible with other tests).
Higher product reliability.
Cons:
The testing process may shorten the life of the product.
Reduce overall yield.
A time- and labor-intensive process.
7.Functional Testing (FCT).
Functional testing is the last step in the manufacturing process, and a functional tester is used to check whether the finished PCB is functioning properly. This does not test whether the board is in good condition, whether there is solder, or if the part is tolerant. The circuit is properly powered and energized through the interface connector, verifying that it meets the design specifications.
Depending on the complexity of the design and specific test requirements, the functional test can be a simple switching power supply test or a comprehensive test with strict protocols and test software. Due to its flexibility, functional testing can be used to replace more expensive test procedures. Functional testing simulates the actual operating environment, so it can be simpler and clearer than other testing methods. Full 100% functional testing is increasingly being used in low-volume manufacturing to ensure that every board that comes off the production line functions properly.
Pros:
Discover potential circuit anomalies.
Measure the power absorption at a specific point in a circuit.
Flexible and highly customizable, almost all types of PCBs can be tested.
It is cheaper and more convenient than other test methods that require specialized equipment.
Cons:
The defect discovery rate depends on the inspections covered by the test plan.
A trained technician is required to isolate the cause of the defect.
Under different pressures, the board can fail shortly after passing the functional test. Therefore, complex PCBs are also subject to burn-in tests.
8.Boundary scan test
Boundary scan testing is a technique suitable for testing the interconnects between components on a PCB. In this type of test, the cell is placed on a wire from the silicon wafer to the external pins to test the functionality of the circuit board.
The biggest difference of this type of test is its ability to evaluate the board without reaching all the nodes. This quality is important for evaluating integrated circuits with multiple layers and high density, as these types of PCBs have become more common in recent years.
In fact, this test method is versatile and can be used in a variety of applications, including system-level testing, memory testing, flash programming, and processor (CPU) functions. In field service, it is often used to detect problems with functional systems.
In addition to the common test methods mentioned above, other types of PCB assembly tests include:
Microdissection Analysis:Investigate defects, open circuits, short circuits, and other faults.
Solderability test:Make sure the surface is firm and increase the chances of reliable solder joints.
Peel Test:Find out the strength measurement required to peel the laminate off the board.
PCB Contamination Testing:Detect high concentrations of ions that can contaminate circuit boards, causing corrosion and other problems.
Time Domain Reflectometer (TDR):Look for faults in the high-frequency board.
Solder Float Test:Determine the level of thermal stress that a PCB hole can withstand.
Regardless of the method chosen, PCB testing is a necessary step in the board design and manufacturing process, saving a lot of unnecessary time and cost in identifying defects that may affect the circuit before moving into final production. In general, the right combination of the above inspection and test methods can detect all possible defects, the cost of which depends on the specific application and complexity of the circuit under test.