FQC (Final Quality Control) for PCB bare boards, is the final comprehensive inspection stage before packaging, with the primary objective of preventing to deliver defective PCB boards to the customers.
The scope of FQC typically includes: visual appearance, dimensions, performance, and the verification of reliability for specific processes.
The exact inspect approaches depend on the grade (e.g., standard boards versus high-end boards for AI or automotive applications).
1. Visual and Dimensional Inspection
This is the fundamental operation of FQC, primarily through visual observation, or with the aid of inspection tools, such as magnifier to observe the appearance&outlooks details.
– Visual Inspection:
Conducted under standard lighting, this involves spotting the defects, such as scratches, dents, contamination dots, dusts and fibre, board warpage, solder mask issues (e.g., missing solder mask and un-even drops), blurred&messy silkscreen, burrs and breaks along the PCB edges, as well as wrinkling, blistering, or color inconsistencies on the solder mask.
– Dimensional and Structural Measurement:
This includes measuring the final thickness of PCB, hole diameters, the residual thickness of V-cuts, and overall dimensions to ensure they meet specifications.
Specific requirements may dictate that the finished PCB board thickness be maintained within a precise tolerance range.
2. Performance and Reliability Testing
This stage focuses on verifying electrical, physical, and chemical properties.
Depending on customers’ requirements or the product grade, these tests may performed on a sampling basis or as a 100% inspection.
– Electrical Performance:
Typically includes open/short-circuit testing (to ensure proper connectivity and isolation) and high-potential (Hi-Pot) testing, which verifies insulation reliability and prevents electrical leakage or breakdown.
– Physical/Chemical Properties:
This involves measurements, conducted either via cross-sectioning (micro-sectioning) or non-destructive methods, by parameters such as:
– Copper thickness on hole walls.
– Dielectric layer thickness.
– Solder mask thickness.
Ensuring the PCB boards comply with customers’ specifications.
3. Advanced Specialized Testing (for High-Density/High-Speed Boards)
For high-end electronics (such as PCB for AI servers), FQC may conduct more rigorous testing approaches, including:
– Micro-resistance (4-wire Kelvin) testing to monitor the reliability of copper plating in holes.
– Ionic contamination testing.
– Insertion loss testing (for signal integrity).
– Residual copper filaments or debris resulting from back-drilling processes.
Key Focuses for Defects on PCB
During the Final Quality Control (FQC) stage, QC engineers/inspectors typically pay attention to observe the defects, which more frequently to occur, such as:
– Burrs on PCB edges.
– Blistering or delamination of the solder mask.
– Voids in the walls of plated-through-holes (PTH).
– Solder mask mess into holes.
– Roughness on gold-plated surfaces.
– Clogged or blocked silkscreen markings.
Note:
In standard PCB manufacturing process, FQC generally takes place after electrical testing (ET) and before packaging.
While Automated Optical Inspection (AOI) and flying-probe testing are also essential approaches of quality control, typically categorized as in-process inspections or electrical tests—FQC serves as the final gatekeeper, focusing on the physical appearance and overall performance of the finished PCB.
