We can divide PCB manufacturing defects into appearance defects and functional defects. Both of these defects are important for ensuring 100% PCB quality.
Appearance defect
Appearance defects are defects that affect the appearance of PCB, such as pinholes, excessive etching, insufficient etching, and damage. Such defects will not directly affect the functionality of the circuit board, but may pose a threat to humans after prolonged use.
Functional defects
Functional defects refer to serious defects that have adverse effects on the operation of PCBs. This type of defect includes short circuits, conductor fractures, or open circuits.
These PCB board manufacturing defects may be caused by contamination, high parameters, plating issues, or incorrect etching processes. PCB can withstand pressure caused by vibration, temperature changes, and other harsh environmental stresses. Therefore, testing is required after PCB board manufacturing.
In order to meet quality assurance, large-scale PCB manufacturing services adopt automatic optical inspection (AOI), online testing (ICT), flying pin testing, and X-ray testing. These commercial tests are used to locate manufacturing defects in printed circuit boards through reliable inspection and testing techniques (using electrical or non electrical, non-contact methods).
AoI
Automatic optical inspection uses image processing software to inspect PCBs through reference comparison method. This software has a defect detection algorithm that can be compared with defect free PCBs. This helps PCB manufacturers detect defects and avoid potential hazards. This is usually accomplished by conducting pixel by pixel analysis and comparison to identify changes and locate defects.
Online testing
Online testing is the best testing method for mass production of PCB boards. This testing method uses fixtures (also known as nail beds) to test the circuitry of PCBs. This type of PCB performance verification method is in automatic mode, involving capacitance and resistance testing. ICT has efficient testing throughput and high diagnostic accuracy, which can provide fast feedback for short circuits and open circuits.
Flying needle test
Flying needle testing is the most suitable testing method for small-scale production and prototype design, as it is slower than ICT. This type of testing uses movable probes to contact PCB test points and circuit pads. The movement of the probe is controlled through programming; Therefore, due to its ability to access any contact point on the circuit board, this test has the advantage of testing high-density and complex circuits. Flying needle testing does not require customized fixtures, making it highly cost-effective for small businesses.
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