Manufacturing PCB’s can often be an extremely complex and very costly process, especially when costs associated with faulty products are added to the picture.
Even after following precise design and manufacturing processes, there is always a risk of defects, bugs and human errors during early production stages. Identifying and addressing these issues before the product is complete is critical. This ensures the performance, functionality, and reliability of the product stays consistent.
Therefore, a robust approach to test and inspection is vital to ensure top-quality products and satisfaction for the product end-user.
This article will cover the primary types of PCB testing & inspections that should be undertaken.
Benefits of PCB Testing & Inspection
Identifying and addressing faults and bugs such as short circuits, opens, poor soldering, and functional issues.
Provides an opportunity to address any potential issues early before going into the final stage, this saves time and money as fixing issues on finished products is more difficult, time-consuming, and costly.
Reduces wastage and costs since the testers use the small-scale assemblies instead of complete product builds. This prevents the waste of faulty full-scale assemblies.
Types of PCB Testing & Inspection:
In-Circuit Testing (ICT)
ICT also known as Bed of nails testing covers most of the defects that occur during the manufacturing processes. This test involves fixed probes set out in a way that matches the original design of the PCB that is being tested.
Testers can use ICT to check for the integrity of the solder connection. It has the potential accuracy to detect around 98% of PCB faults.
The benefits of ICT include simple defect detection, programming, and easy to interpret test reports. This test is suitable for bigger “mature” products that expect very few revisions.
Flying Probe Testing
The flying probe test uses an element with a smaller pitch to make contact with test points such as the SMD pins. This type of testing is suitable for smaller-sized contacts down to a 0.2mm test pitch and is less expensive than ICT.
Flying Probe Testing Checks:
- Opens
- Shorts
- Resistance
- Capacitance
- Inductance
- Diode Issues
The test works by using needles attached to a probe on an X-Y gride obtained from basic CAD. The ECM program then coordinates and matches the circuit board design and runs the test.
Automated Optical Inspection (AOI) 
AOI uses multiple 2D or 3D cameras to optically analyse the PCB designs. The program then uses software to compare images from the PCB under test to a detailed schematic. If the board does not match the schematic to a certain degree, it is flagged for inspection by an operator.
This type of inspection can be useful for detecting issues in the early stages. However, it does not power up the board and is mostly limited to surface mount electronic devices as there’s often too much variation in ‘through hole’ device placement. This means that AOI should always be used in conjunction with another test.
Some most common examples are:
- AOI & Flying Probe
- AOI & ICT
- AOI & Functional Testing
Automated X-Ray Inspection (AXI) 
AXI is more of an inspection tool rather than a test. This inspection enables technicians to located defects early during the manufacturing process by looking at solder connections, internal traces, and barrels. This technique is generally suitable for testing invisible areas located in the centre of the board.
This method is ideal for checking the board, its layers, soldering, component orientation alignment and other physical features.
Functional Testing (FCT)
FCT is used as a final step during the PCB process. It provides a pass or fail determination on finished PCB designs before they are shipped.
This type of testing is time-consuming and not ideal if you want to get your product shipped out quickly. However, from a quality and longevity standpoint, functional testing can save face and save money.
Choosing The Right Testing & Inspection Solution
Testing and inspection techniques vary due to the type of PCB, testing to perform, application, sensitivity, and tolerance. For example, medical and military devices will require higher levels of reliability and testing.
Although a combination of all the techniques will provide the most accurate and comprehensive analysis picking up 99% of all the defects, it will not always be possible as it is very time-consuming. Therefore, it is important to look at the most cost-effective testing solution.
By Timmy Bubak | 27/08/21