What Are the PCB Inspection StandardsPosted on 2020-07-16
What Are the Aspects of PCB Inspection Standards
PCB can be divided into rigid PCB and flexible PCB, the former can be divided into three types: single-sided PCB, double-sided PCB and multilayer PCB. According to the quality level, PCB can be divided into three quality levels: Class 1, Class 2 and Class 3, of which Class 3 has the highest requirements. Differences in PCB quality levels lead to differences in complexity and testing and inspection methods. So far, rigid double-sided PCBs and multilayer PCBs account for relatively large applications in electronic products, and sometimes flexible PCBs are used in some cases. Therefore, here we will focus on the quality inspection of rigid double-sided and multilayer PCBs. After PCB manufacturing, an inspection must be conducted to determine whether the quality is compatible with the design requirements. It can be considered that quality inspection is an important guarantee for product quality and the smooth implementation of subsequent procedures.
PCB inspection standards mainly include the following aspects:
- Standards set by each country.
- Military standards of each country.
- Industry standards such as SJ/T10309.
- PCB inspection operation instructions formulated by equipment suppliers.
- Technical requirements marked on PCB design drawings.
For PCBs that have been identified as devices, in addition to periodic inspections. It is also necessary to concentrate and check these key characteristic parameters and indicators from the head to the feet.
PCB inspection items
No matter what type of PCB, they must go through similar quality inspection methods and projects. According to the inspection method, quality inspection items usually include visual inspection, general electrical performance inspection, general technical performance inspection and metallization inspection.
With the help of a ruler, vernier caliper or magnifying glass, visual inspection is simple. The inspection content includes:
- Board thickness, surface roughness and warpage.
- Appearance and assembly dimensions, especially those compatible with electrical connectors and rails.
- The integrity and clarity of the conductive pattern and the presence of short circuits, open circuits, burrs or voids in the bridge.
- Surface quality on printed traces or pads, the presence of pits, scratches or pinholes. Location of pad vias and other vias. It should be checked whether the via hole is missed or whether there is incorrect punching, whether the diameter of the through hole meets the design requirements, and whether there are nodules and voids.
- Pad quality and firmness, roughness, brightness and voids for raised defects.
- Coating quality. Whether the coating flux is uniform and firm, whether the position is correct, whether the flux is uniform, and whether the color meets the requirements.
- Character qualities, such as whether they are firm, clean and clean, without scratches, penetrating or breaking.
General electrical performance check
There are two types of tests under this type of inspection:
- Connection performance test. In this test, a multimeter is usually used to check the connectivity of the conductive pattern. Through the focus of double-sided PCB metallized vias and multilayer PCB connection performance. For this test, PCBCart provides a general inspection before each manufactured PCB leaves its warehouse to ensure the realization of its basic functions.
- Insulating performance test. This test is to check the insulation resistance between the same plane or different planes to ensure the insulation performance of the PCB.
General technical inspection
General technical inspections include solderability and plating adhesion inspections. For the former, check the wettability of the solder to the conductive pattern. For the latter, the qualified tip can be used for inspection. These tips are first glued to the plating surface to be inspected, and then quickly pulled out after being evenly pressed. Next, the plating plane should be observed to ensure that shedding has occurred. In addition, you can choose some inspections according to the actual situation, such as copper foil anti-drop strength and metallized tensile strength.
Metallization by inspection
The quality of metallized vias plays an extremely important role on double-sided PCBs and multilayer PCBs. A large number of failures in electrical modules and even the entire device are due to the quality of metallized vias. Therefore, it is very necessary to pay more attention to the inspection of metallized vias. Metallization inspection includes the following aspects：
- The metal plane of the through-hole wall should be complete and smooth, without voids or nodules.
- The electrical performance inspection should be based on the short circuit and open circuit of the pad and through the metallization of the plating plane, the resistance between the through hole and the lead. After the environmental test, the resistance change rate of the via should not exceed 5% to 10%. Mechanical strength refers to the bond strength between the metallized via and the pad. The metallographic analysis test is responsible for checking the quality of the plated plane, the thickness and uniformity of the plated plane, and the adhesion strength between the plated plane and the copper foil.
Metallization inspection usually combines visual inspection and mechanical inspection. Visual inspection is to observe by placing the PCB under light, and the complete and smooth through-hole wall can reflect the light evenly. However, the walls containing nodules or voids are not so bright. For mass production, the inspection should be conducted through online testing equipment such as flying probe testers.
Due to the complex structure of the multilayer PCB, it is difficult to quickly locate the fault once the problem occurs in the subsequent unit module assembly test. Therefore, the quality and reliability of the inspection must be very strict. In addition to the above conventional inspection items, other inspection items include the following parameters: conductor resistance, metallized through-hole resistance, inner layer short circuit and open circuit, insulation resistance between each wire, plating plane bonding strength, adhesion, thermal shock resistance, impact resistance , Mechanical shock, current strength, etc. Each indicator must be obtained through the application of professional equipment and methods.
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