One of the more challenging processes of selling a house is having it inspected. Not only can scheduling the inspection cause a lot of anxiety, but replacing and repairing items can throw off your closing schedule and put a dent in your bank account. On the other hand, inspection becomes a lot more appealing when buying a home instead of selling it. The home inspection can potentially protect you from expensive problems or errors that you can’t afford.
Detecting faults to protect the end user from expensive problems is the goal of any type of inspection, including circuit board assemblies hot off the production line. The problem is that circuit boards can have hundreds of parts and thousands of solder joints, all of which require separate inspection. When you multiply those thousands of inspection points by the number of boards built in a production run, it is apparent that standard visual inspection by an operator won’t be enough. Thankfully, help is available for quality control through automated optical inspection systems (AOI). Here are more details on how PCB fault detection using image processing will assist with printed circuit board inspections.
Circuit Board Manufacturing Problems that Require Inspection
With all of the parts, connections, and other critical aspects of a circuit board that must be examined, some complicated PCBs can have up to three or four thousand opportunities for errors. Locating a single problem out of so many possibilities is simply too many for manual inspection methods to reliably find, especially when you consider the volume of boards. Here, automated optical inspection systems detect anomalous conditions and flag those areas for closer scrutiny by human inspectors.
Before we delve into how automated inspection works, let’s first take a moment to look at all the different areas of a circuit board that require examination. Although our focus is chiefly on the assembly side of PCB manufacturing, automated optical inspection systems are also used by fabricators to search for the following:
- Metal to metal shorts
- Metal to metal spacing
- Broken or cut metal
- Improper widths of metal
- Excessive metal on a net
- Drilled holes breaking out of the metal
For circuit board assembly, AOI equipment will verify the following conditions:
- Solder paste application
- Good solder joints
- Targeting fiducial locations
- Component alignment
- Component values
- Polarity indicators
- PCB markings such as labels
As you can see, many items can be automatically inspected using AOI equipment. Next, we’ll see how this is accomplished.
How PCB Fault Detection Using Image Processing Inspects a Circuit Board
Depending on what portion of the circuit board is being inspected, different AOI systems are used. Solder paste inspection equipment, for instance, will use laser scanners with micron resolution to determine the amount of solder on a pad.
The automated optical inspection systems used for PCB assembly verification rely on LED illumination and high-resolution cameras to capture circuit board images. Using a known good, or “golden” first article board, the AOI system will capture images of its part markings and solder joints. These images are clear enough to record polarity indicators, color codes, and other markings and compare subsequent circuit boards. Once recorded, the system can detect incorrectly aligned components, open solder joints, and solder bridges on new boards using the standard.
The image recognition can also be de-tuned to reduce false detections or increase its sensitivity for extra critical areas of the board. AOI systems can also be programmed to accept alternate part numbers to keep acceptable replacement parts from being flagged as errors. This ability to fine-tune the AOI system allows operators to configure it to its most optimum level for fault detection. Now let’s take a look at the actual inspection process used during manufacturing.
The Process of Using AOI Equipment for PCB Inspection
The first step in programming an automated optical inspection system is to create a known golden circuit board as a first article inspection board. This board will require a manual inspection to ensure that all part types and values are correct and that all solder joints are good. Next, the validated golden board is run through the inspection system to teach and tune it for the most optimum level of operation. This will be done in separate passes for assembly verification and solder inspection.
Once the AOI system is fully set up, it can run the production run of boards through it. Production boards are run through only once, and the system will verify the assembly and check the solder joints all in one pass. With the inspection of each board and the new images collected, the AOI system’s algorithms are continually fine-tuned using the additional images. Any anomalies detected by the system are flagged, allowing the operator to zoom into those areas recorded by the high-resolution cameras to confirm whether or not an actual problem exists.
Partnering with a PCB CM that Uses AOI Processes
The use of automated optical inspection systems in the PCB manufacturing industry has taken quality control to the next level. Instead of spending their time looking through thousands of potential problems on a circuit board, the inspectors focus only on those areas flagged by the system. This streamlined process results in less time looking for problems, while more potential problems are found and examined, resulting in higher quality circuit boards.
At VSE, we understand how important this high level of quality is to you and all of our customers. Our staff is well-trained in using our AOI systems so that you don’t have to worry about spending time chasing intermittent problems that shouldn’t be there.
