PCB Assembly Inspection and Testing Options
As technology advances and PCBAs become more complex, the testing and inspection options for these boards must carefully be taken into consideration. PCBs are critical components and are expected to function properly in a wide range of different environments. Proper testing procedures and inspection measures are required to maintain the quality and reliability of product.
Benefits of PCB Inspection and Testing
Having a trusted contract manufacturer is one of the most crucial steps in having a successful circuit board built. Vinatronic prides itself on delivering high-quality products to our customers. This is done through our PCB assembly manufacturing processes that have undergone years of iteration. We pay close attention to preventative measures and pre-build steps, rather than finding an issue later down the line and having to fix defects with rework. The most common types of inspection and testing methods that Vinatronic has experience with are:
- Visual Inspection
- Automated Optical Inspection
- X-Ray Inspection
- First Article Inspection
- In-Circuit Testing
- Functional Testing
- Burn-In Testing
PCBs come in a variety of different shapes, sizes, and quality requirements. They could be rigid or flex, single-sided, double-sided, multi-layered, and others. There are also three “classes” that the industry uses to classify PCB and PCBAs. These are Class 1, Class 2, and Class 3 with Class 3 being of the highest quality and requiring the most attention.
As the Class requirement increases, so does the complexity of inspection and testing methods. PCB fabrication and PCB assembly both require a unique set of inspection and testing methods in order to build a board to spec.
Visual Inspection
The most basic form of inspection is visual inspection. This is done by having a tech review a board with a golden board, BOM, and prints. The person then checks for things like wrong components, missing components, solder bridges, missing solder, tombstoning, and a variety of other errors. Equipment that can be used include magnifying lenses, high powered microscopes, and of course great lighting. Since this method is highly dependent on the operator, it can be time consuming for large quantities and complex boards. This is mainly done at the end but it is important to visually inspect boards throughout the manufacturing process in order to validate programs and procedures. Inspection after SMT placement can catch if the pick-and-place machine has missed or wrong component placement, and problems with solder paste. Vinatronic utilizes high-power, multi-source, glare-free lighting for our operators in order to adequately see PCBA under inspection. Each also has an adjustable high-power lens for viewing to minimize eye strain.
Automated Optical Inspection (AOI)
AOI utilizes high resolution cameras and software in order to catch manufacturing errors. The software essentially checks multiple images of the board under inspection against an image of a “golden” board stored in its memory, and flags discrepancies.
These machines can be put throughout the SMT line. Inspections after the reflow stage can catch defects in soldering, such as dry solder, solder bridging, inadequate wetting, tombstoning, and others. Operators can then use the feedback from machine to make finer adjustments to previous stages to ensure fewer defects.
Although AOI technology has come a long way, it does still have some weaknesses. For one, AOI does not do well with through hole parts. It can catch a lot of through hole errors like wrong or missing parts but sometimes the differences in height, casted shadows, and hidden parts can be limitations of AOI. It also takes a while to program which is additional overhead.
X-ray Inspection
For components with hidden leads, x-ray inspection is required. BGAs have pins arranged under them which makes it impossible to inspect their connections optically after soldering. X-ray is then used to ensure that all the leads are properly soldered.
First Article Inspection
In order to validate the programs and components, often times OEMs will require a first article inspection. Companies FAI programs differ, some require paperwork from the CM validating the completion of a FAI, some require that first article to physically be sent to them for approval. Whatever your company deems necessary, it is important to communicate with the CM in order to check all the boxes.
In-Circuit and Functional Testing
In-Circuit Testing: This form of test requires a customized fixture often known as a bed of nails. It is usually several spring-loaded metal probes assembled in an array on an insulated bed. If ICT testing is seen as the best form of testing, it is usually planned during the design phase because it requires the designer to place test pads at strategic locations on copper traces on the bottom layer of a PCB.
The person doing the testing places the assembled PCB on the probes to connect it electrically to the test pads. This is sometimes by hand or is built into the fixture. The test will then check various parameters such as resistance, capacitance, and inductance between specified probes, and flag discrepancies from an established criteria.
Functional Testing: This method is highly variable. It essentially simulates the device in the field. This form of test is created by the OEM and given to the CM to run. It generally includes a power source and several inputs confirming that the board works as intended.
Burn-in Testing
Burn-in tests simulate real-life environments. The PCB assembly will be set a specified time under elevated temperatures ranging from 24hrs onward and after cooling down, should have no problems performing as intended. This is validated through a functional test or ICT.
Vinatronic Inspection and Testing
We here at Vinatronic cater our inspection and testing methods according to our customers requirements. Whether your board requires every form of testing or very little, our experienced team is here to help.
Please feel free to contact us via phone or email, or visit our website with your query.
