Printed Circuit Board(PCB) Assembly Visual Inspection
Testing of the PCBs in design and manufacturing is crucial for quality control. Companies want to avoid realizing the product is faulty when it is already in the production or in the market. There is always chance for defects even after following the proper design and production processes. Identifying the defects before manufacturing the final product is essential for ensuring performance, reliability, and functionality of the products. Errors in PCB assemblies may occur due to human error, wrong production processes, and poor design. Luckily, with the help of proper testing procedures and inspection measures the quality and the reliability of the product can be maintained.
The benefits of a PCB assembly visual inspection include;
- Paying attention to preventative measures instead of addressing the issue after the production.
- Using preventative measures are helpful since fixing the problems on a finished product is costly and time consuming.
- Identifying and addressing errors such as short circuits, and functional issues.
- Reducing the number of waste and cost since PCB assembly testing requires a small-scale assembly and a prototype rather than the complete product.
What to test on PCB
PCBs can be found in different shapes, sizes, and quality requirements. They are also consisted of different components. Each part has an impact on the overall performance of the PCB and the assembly as a whole. Therefore, it is crucial to inspect every part of the PCB assembly such as electrical conductivity, mechanical strength, quality of the hole wall, cleanliness, and component placement.
PCB Testing Methods
PCB assembly visual inspection requires a unique set of inspection and testing methods. The inspection of PCB assembly involves verifying design features in the means of visual, electrical, structural, and functional techniques. There are various ways of testing PCBs, however, the selection of the method depends on board complexity, application, design, etc. The most common methods used are:
This is the most basic form of an inspection. This is basically a tech review checking things like wrong or missing components, solder bridges, missing solder, tomb stoning and different kinds of errors. This method is dependent on the operator therefore it may be time consuming when large amounts of PCBs are needed to check.
2) Automated Optical Inspection(AOI)
AOI uses high resolution cameras and software in order to detect manufacturing errors. The softwares inspects multiple images of the PCB against an image of a golden board stored in its memory and it marks the discrepancies. Another method can also be comparing it with ideal design specifications. AOI can be put through an SMT line. The inspections can detect defects in soldering, inadequate wetting, and tombstoning. After inspecting defects, the system can use the feedback from the machine to make finer adjustments resulting in fewer defects. However, AOI does not work well with hole parts. Even though this technology has come a long way, it experiences difficulties in detecting differences vin height, casted shadows, and hidden parts.
3) X-Ray Inspection
X-ray inspection is needed for hidden leads. This method provides a non-destructive technique with the ability to detect defects that are not visible to the human eye. For instance, ball grid arrays (BGA) have pins arranged under them. After soldering it is impossible to inspect connections optically. As a result, x-ray inspection is needed to ensure leads are properly soldered.
4) In-Circuit Testing
The ICT method consists of an in-circuit tester, a fixture, and a software that can detect most of the defects occurring in the manufacturing process. By utilizing ICT it is possible to check for shorts, opens, resistance, capacitance, and inductance. The components of PCBs are checked according to the model of the design. The benefits of this technique include; simple defect detection, programming, and easily interpreting test reports. Unfortunately, this method has a few setbacks such as costly equipment, difficulties in updating the test equipment systems and inability access to some nodes in complex circuits.
5) Functional Testing
This method is very variable. It is designed to simulate the device in the field. This method of testing is created by OEM and given to the CM to run. Functional testing includes a power source and several inputs that confirms that the board is working as intended.
This method simulates real-life environments. The PCBA will be set to a specific time under elevated temperatures variating from 24 hours onward. After the PCBA cools down it should have no problems. This method is validated through a functional test or an in-circuit testing.
Choosing a PCB Testing Method
The selection of PCB testing solution will differ according to the type of PCB, test performance, application, sensitivity, and tolerance. As the complexity of a PCB increases more advanced techniques will be required.
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