Key Points of Quality Control in the PCB Manufacturing Process

The following is a detailed introduction to the key points of quality control in the PCB (Printed Circuit Board) manufacturing process:

I. Key Points of Quality Control in the Design Stage

Design Rule Check (DRC)
Ensure that the wiring width, spacing, via size, etc. comply with the PCB manufacturing process capabilities and electrical peRFormance requirements. For example, if the line width is too narrow, it may lead to insufficient current-carrying capacity, and if the spacing is too small, it may easily cause short-circuit problems. It is necessary to carefully check according to the design specifications and the process parameter ranges provided by the manufacturer to avoid design violations.
Check the rationality of component layout, taking into account factors such as heat dissipation and signal interference. For example, components with high heat generation should not be placed together, and the wiring of high-speed signals should be kept as far away from interference sources as possible to prevent signal integrity issues that may affect the overall performance of the PCB.

Accuracy Review of Documents
Confirm the consistency between the schematic diagram and the PCB layout, including component connection relationships, pin definitions, etc., to prevent the situation where the manufactuRed Pcb fails to achieve the expected functions due to inconsistencies between the two.
Carefully check the basic parameters such as the number of PCB layers, size, and outline to ensure that these key pieces of information are accurate. Because once there is a deviation, the subsequently manufactured PCB may not be able to be installed in the corresponding equipment.

II. Key Points of Quality Control in the Raw Material Procurement Stage

Selection and Inspection of Substrate Materials
Select appropriate substrate materials, such as FR-4, aluminum substrate, etc., according to the usage environment and electrical performance requirements of the PCB. Different substrates have differences in dielectric constant, thermal expansion coefficient, temperature resistance, etc. It is necessary to ensure that the selected materials can meet the design requirements.
Conduct visual inspections on the purchased substrates to check whether there are scratches, pits, delamination, and other defects on the surface. At the same time, test whether parameters such as thickness and flatness meet the standards. These factors will affect subsequent processing and the quality stability of the PCB.

Quality Control of Copper Foil
The thickness, purity, and adhesion of copper foil are crucial. The thickness should meet the design requirements to ensure the conductive performance and current-carrying capacity of the PCB. High-purity copper foil can reduce resistance and signal transmission loss. Good adhesion can prevent the copper foil from peeling off during subsequent processing and use. Professional testing methods are needed to ensure that these quality indicators are qualified.
Inspect the surface roughness of the copper foil. Appropriate roughness is helpful for the smooth progress of subsequent etching, electroplating, and other processes and for good bonding with other materials, avoiding the impact on processing quality due to overly smooth or rough surfaces.

III. Key Points of Quality Control in the Inner Layer Pattern Fabrication Stage

Quality Inspection of Photoplotting Films
Check the graphic accuracy of the photoplotting films, including the size accuracy of lines, pads, etc. The deviation should be controlled within the allowable range. Otherwise, problems such as uneven line widths after etching and non-compliant pad sizes will occur, affecting the electrical connection and component soldering of the PCB.
Check the clarity of the films to ensure that the graphic edges are sharp and there is no blurring. Clear films are the basis for high-precision inner layer pattern transfer. Blurred films will lead to defects in pattern transfer.

Control of Inner Layer Line Etching
Strictly control parameters such as the concentration, temperature, and etching time of the etching solution. Inappropriate concentration of the etching solution may cause incomplete or excessive etching, affecting the quality of the lines. Improper temperature and time will also lead to similar problems. Therefore, it is necessary to accurately regulate and regularly test and adjust according to the process requirements.
Conduct visual inspections on the etched lines to check whether the lines are complete, whether there are short circuits, open circuits, and whether the line width meets the design standards. Use AOI (Automated Optical Inspection) and other equipment for comprehensive inspections and promptly identify and remove defective inner layer boards.

IV. Key Points of Quality Control in the Lamination Stage

Setting and Monitoring of Lamination Parameters
Set appropriate lamination temperature, pressure, and time parameters according to the number of PCB layers and substrate materials. Excessive temperature or pressure may cause substrate deformation and damage to the inner layer lines. Insufficient time may result in weak interlayer bonding, affecting the mechanical strength and electrical performance of the PCB. It is necessary to monitor and record these parameters in real-time through professional equipment to ensure that they meet the process requirements.
Ensure the cleanliness of the lamination environment to avoid dust, impurities, and other substances from mixing between layers, which may cause interlayer short circuits or voids and other defects, affecting the reliability of the PCB. Measures such as using a clean workshop can be adopted to reduce the adverse effects caused by environmental factors.

Quality Inspection after Lamination
Check whether the thickness of the laminated PCB is uniform by measuring the thickness at different positions. Uneven board thickness may cause problems in subsequent installation and soldering and may also affect the uniformity of signal transmission.
Use ultrasonic flaw detection and other methods to detect whether there are delamination, bubbles, and other defects between layers. These internal defects will seriously reduce the quality and service life of the PCB. Once found, the corresponding PCB boards should be handled or scrapped in a timely manner.

V. Key Points of Quality Control in the Outer Layer Pattern Fabrication Stage

Quality Control of Drilling
Accurately control the hole diameter and position accuracy of drilling. If the hole diameter is too large, it may lead to loose component pin soldering, and if it is too small, the pins may not be able to be inserted. Position deviations will cause incorrect component installation. High-precision drilling equipment and drilling templates can be used, and regular verification through testing tools can be carried out to ensure the quality of drilling.
Check the perpendicularity of the drilled holes to avoid inclined holes. Inclined holes will affect the normal progress of subsequent electroplating, soldering, and other processes and the overall performance of the PCB. Use professional measuring tools for perpendicularity detection and adjust the drilling process parameters in a timely manner.

Similar Points to Inner Layer for Outer Layer Line Fabrication and Etching
Similarly, strict quality inspections should be carried out on the photoplotting films to ensure the accuracy of pattern transfer.
Precisely control the various parameters of outer layer line etching, and carefully check the appearance quality of the etched lines to ensure that the lines are complete, without short circuits or open circuits, and meet the requirements of the designed line width and spacing. Use AOI and other testing equipment for comprehensive screening to ensure the high quality of the outer layer lines.

VI. Key Points of Quality Control in the Electroplating Stage

Control of Electroplating Solution Composition and Parameters
Regularly test the composition of the electroplating solution, including the concentration of metal ions, acidity and alkalinity, and the content of additives, to ensure that they are within the appropriate range. Changes in these components will affect quality indicators such as the thickness, uniformity, and adhesion of the electroplating layer. For example, if the concentration of metal ions is too low, the electroplating layer will be too thin, affecting the conductive performance and anti-corrosion ability.
Control parameters such as current density, time, and temperature of electroplating. Different PCB products have different electroplating process requirements. Reasonable parameters can ensure that the electroplating layer is uniform and dense, avoiding defects such as local thickness variations and burning. Through the precise regulation and real-time monitoring of electroplating equipment, the accuracy of the parameters can be ensured.

Quality Inspection of the Electroplating Layer
Measure the thickness of the electroplating layer. Use professional thickness measuring instruments to conduct multi-point measurements at different positions to ensure that the thickness meets the design requirements and satisfies the electrical and protective performance needs of the PCB.
Check the adhesion of the electroplating layer. Methods such as the cross-cut test can be used for detection. An electroplating layer with poor adhesion is prone to peeling off during subsequent use, affecting the reliability of the PCB.
Check the appearance quality of the electroplating layer. The surface should be flat, smooth, and free of pits, pinholes, and other defects. Use appearance inspection equipment for comprehensive inspections to ensure the quality of electroplating.

VII. Key Points of Quality Control in the Solder Mask and Legend Printing Stage

Quality Control of Solder Mask Ink
Select solder mask inks that meet environmental requirements and have good compatibility with PCB substrate, electroplating layer, and other materials. Verify its performance indicators such as hardness after curing, wear resistance, and chemical corrosion resistance to ensure that it can effectively protect the lines, prevent short circuits during soldering, and resist the erosion of the external environment during subsequent use.
Test the viscosity and other process parameters of the ink. Inappropriate viscosity will affect the uniformity and thickness of printing, resulting in poor solder mask effects. Viscosity can be tested using a viscometer and adjusted as needed.

Control of Printing Process and Quality Inspection

Control parameters such as printing pressure, speed, and squeegee angle to ensure that the solder mask ink and legend ink can be evenly and accurately printed onto the corresponding positions, avoiding problems such as missing prints, ink accumulation, and blurred graphics. Through the precise adjustment of printing equipment and trial printing, optimize the process parameters.
Conduct visual inspections on the printed solder mask layer and legends to check for defects. At the same time, test the thickness and coverage integrity of the solder mask layer to ensure that it can play a good protective and identification role. Use optical inspection equipment to assist in quality judgment.

VIII. Key Points of Quality Control in the Surface Treatment Stage

Selection and Parameter Control of Surface Treatment Processes
Select an appropriate surface treatment process according to the usage requirements of the PCB, such as hot air solder leveling (HASL), electroless nickel/gold plating, OSP (Organic Solderability Preservative), etc. Different processes have different characteristics and application scenarios. It is necessary to ensure that the selected process can meet the requirements of soldering performance, antioxidant performance, etc.
Strictly control the parameters of the surface treatment process. For example, for hot air solder leveling, control the temperature, time, and tin layer thickness. For electroless nickel/gold plating, control the composition of the plating solution and the reaction time to ensure that the surface treatment effect is uniform and stable and meets the quality standards. Use professional process equipment and testing methods for monitoring and adjustment.

Quality Inspection after Surface Treatment
Check the appearance quality of the surface-treated PCB. The surface should be flat, shiny, and free of discoloration, peeling, and other defects. For PCBs with soldering requirements, also test their solderability. Methods such as the solder test can be used to verify that soldering operations can be carried out smoothly during subsequent assembly and soldering processes to ensure the quality and reliability of the product.

IX. Key Points of Quality Control in the Finished Product Inspection Stage

Electrical Performance Testing
Use professional testing equipment to conduct comprehensive tests on electrical performance indicators such as the conductivity, insulation, and impedance of the PCB to ensure that they meet the design requirements. For example, use flying probe testers, network analyzers, and other tools to detect the connection status between lines and the characteristics of signal transmission. Timely identify PCBs with electrical performance defects and conduct repair or scrapping operations.

Appearance and Dimension Inspection
Conduct a detailed visual inspection of the overall appearance of the PCB again to check whether there are scratches, stains, unclear legends, etc. on the surface. At the same time, accurately measure the dimensions of the PCB, including length, width, thickness, and various hole diameters and outlines, to ensure that the dimensional tolerances are within the allowable range and meet the installation and usage requirements. Use measuring tools and optical inspection equipment for comprehensive inspection operations.

Packaging and Protection Inspection
Confirm whether the packaging materials and packaging methods of the PCB are appropriate. The packaging should be able to effectively prevent the PCB from being affected by collisions, moisture, oxidation, etc. during transportation and storage to ensure that its quality is not damaged. For example, use anti-static and moisture-proof packaging materials and conduct sealed packaging. Check the integrity of the packaging and the accuracy of the labels.