There are a number of inspection tools that were invented for the task of inspecting printed circuit board assembly. On the inner layer of the PCB assembly, the automatic optical inspection is applied just before the printed circuit board will be laminated.
After it is laminated, to ensure that the layers are aligned properly and there are no minor defects, an x-ray monitoring system will be used to scan through the PCB assembly. A laser scan will also be run onto the printed circuit board assembly. These methods and scanning procedures along with a visual inspection are made to ensure the preciseness of the PCB assembly.
However, there are times when even though all the necessary procedures to make a printed circuit board assembly are made, the final inspection of the printed circuit board will still be invaluable. The final inspection is considered as the most critical of all the procedures.
This process is executed in two ways simultaneously:
The manual and automatic methods. In the manual method, an inspector will be checking the completed printed circuit board and will judge whether there is a defect on the printed circuit board or not. For the automatic method, an automatic scanning system will be run onto the printed circuit board to spot any defect.
If a printed circuit board does not conform to the requirements or parameters, then it is considered as a defective one. Defects are classified depending on their degree or their severity and their effects to the performance of the printed circuit board.
One of the most common defects that affect a printed circuit board assembly is the wave soldering defect. Wave soldering is a soldering process where the electronic components are soldered to the board using a tank with molten solder. The electronic components are inserted on the printed circuit board. The loaded printed circuit board will then pass through a waterfall of solder which will moisten the exposed metallic parts of the device.
However, although this process is faster and provides high quality printed circuit boards compared to the manual process of soldering the electronic components, it can result to many different soldering defects such as the ones mentioned below:
• Bulbous joint
• Pin/Blow hole
• Lifted component
• Cracked joint
• Poor hole fill
• Flux residue
• Joint contamination
• Incomplete joint
• Lifted resist
• Lifted pads
• Pad contamination
• Poor solder ability
• Solder ball
• Poor penetration
• Solder flags
• Sunken joint
• Solder skip
• Solder shorts
• Mask discoloration
Another common failure of a printed circuit board is an open circuit, which may be caused by a lot of different factors such as physical stress and poor quality control. A printed circuit board exposed to any vehicle may cause its electronic connection to either wear down or break down entirely. A low quality printed circuit board with a malformed vias or poor soldering work is a result of poor quality control during the processes of manufacturing and assembling.
To prevent these defects from happening, a visual inspection conducted on a regular basis is very important. The inspection should be conducted along with an x-ray imaging system to know where exactly the defective parts of the printed circuit board are. If the location of the defect is hard to detect, then a specialized process such as the Time Domain Reflectometry is used.
In performing a printed circuit board analysis, it is important to have a full understanding of the common printed circuit board defects. For most companies manufacturing printed circuit boards, it is essential to have people with extensive background and practice in the printed circuit board technology to be able to find the errors in a defective PCB assembly.