Manual Inspection of Assembled Circuit Boards
Manual visual inspection is a vital step in the PCB assembly process. It helps ensure that the components and connections are correct and that the finished product functions as it should. It’s also a valuable complement to other testing methods such as AOI and X-ray. However, it can be susceptible to error because of human factors like eye fatigue and inexperience. Therefore, it’s important to make sure that your PCBA company uses trained technicians and high-quality equipment when conducting manual visual inspections.
Printed assembled circuit board are becoming increasingly complex, with more layers and higher component densities. This makes it more challenging to guarantee quality without incorporating multiple testing links into the manufacturing process. In the past, manufacturers mainly relied on MVI to check for major problems like misalignment and shorts in the electrical circuits of a board. Today, a combination of automated inspection techniques (AOI and X-ray) and MVI are the most common PCB inspection methods.
The most basic form of inspection, MVI is a simple lookover of the finished assembly. It’s often performed using a microscope, which provides a higher level of precision than a naked eye can provide. The resulting images are then compared against the original design specifications or a sample of an approved completed unit to spot defects in the board.
What Techniques Are Used For Manual Inspection of Assembled Circuit Boards?
MVI can detect issues such as misalignments, polarity, and orientation of components. It can also identify defects that aren’t always apparent to the naked eye, including solder bridges and voids. It can also pinpoint the location of a specific part on the board by its reference designation (letters and numbers).
The MVI method is effective in detecting most major defects, but it has its limitations. For instance, it cannot detect errors related to the placement of buried or blind vias. It can also miss some defects that occur during the reflow stage, such as tombstoning and inadequate wetting. It can also be difficult to inspect fine-pitch IC packages, since they contain pins that are arranged in an array and cannot be easily viewed by optical inspection.
A more sophisticated type of MVI involves the use of an AOI system to check for different aspects of the board. AOI systems combine LED lighting from various angles and cameras to create a 3D image of the board and compare it against what it should look like. There are both 2-D and 3-D AOI machines available. The latter is more advanced and can verify the coplanarity of different components, a vital aspect of a good PCB.
It can also detect other defects that are difficult or impossible to see with a naked eye, such as solder paste deposition, copper pad thickness, and component height. It’s also capable of detecting reflow-related defects. This includes dry solders, solder bridging, tombstoning, and incomplete wetting. These are all critical errors that can cause a circuit board to fail. Rush PCB conducts both MVI and AOI on every finished product to help our clients ensure the best possible results.